analysis of internal rf interferences in mobile phones9977/fulltext01.pdf · analysis of internal...

Analysis of Internal RF Interferencesin Mobile Phones

SEVAG BALKORKIAN & HAO ZHANG

Master of Science Thesis in Radio Electronics Stockholm, Sweden 2005

IMIT/LECS-2005-101

2

Abstract

Nowadays, mobile phones have greater functionality; a camera, color LCD screen, wireless LAN, Bluetooth, IrDA and others. In the near future wider variety of new functionalities will be added, from high quality voice, high definition video to high data rate wireless channels. As consumer electronics integrate greater functionality and high operating frequencies, their emissions will exceed the specified limits, most of these emissions will be a result of the internal interferences in the mobile phone. Moreover higher operating frequencies will be required to improve the quality of these functionalities, something that will make it more difficult to control these interferences. Internal or external sources of electromagnetic interference can degrade the performance of sensitive analog/digital circuits inside the mobile phone. Moreover the electronic device must satisfy a host of global regulations that limit it’s susceptibility to these interferences, as well as the interference emitted by the device itself. Therefore designing a new electronic device to perform new and exciting functions will not be a pleasant task if it can not meet certain specifications and function as required to adhere to certain global regulations. This thesis project investigates the sources of interference inside a mobile phone; mainly the electromagnetic interferences and its effect on the radio transceiver focusing on the GSM receiver sensitivity. This report is a result of intensive research, an investigation of possible sources of interference, also actual measurements were performed; RSSI, OTA and sniffing measurements; to identify the physical sources of interferences, and their effect on the receiver sensitivity. Finally solutions were recommended and implemented to suppress the interferences due to different sources, mainly through filtering, shielding or proper grounding of signals and components/subsystems in the mobile phone.

3

Acknowledgments

We would like to express our gratitude to the following people: Zareh Mahdessian, our advisor at Sony Ericsson Mobile Communications AB for proposing the project and for the guidance. Professor Håkan Olsson, our examiner at KTH, for motivation and advice. We would like to thank the staff at Sony Ericsson Kista that helped us make this project successful, thank you all for the support. Finally we would like to thank Sören Karlsson at Sony Ericsson Mobile Communication s AB for his continuous support for our project.

4

Abbreviations 3GPP 3rd Generation Partnership Project ARFCN Absolute Radio Frequency Channel Number ASIC Application Specific Integrated Circuit BER Bit Error Rate CISPR Comite International Special des Perturbations Radioelectriques CTIA Cellular Telecommunications and Internet Association DUT Device under Test EGSM Extended GSM EMC Electromagnetic Compatibility EMI Electromagnetic Interference ESD Electrostatic Discharge ETSI European Telecommunications Standards Institute FCC Federal Communications Commission GSM Global System for Mobile Communications IC Integrated Circuit IRDA Infrared Data Association LAN Local Area Network LCD Liquid Crystal Display MS Mobile Station OTA Over the air PCB Printed Circuit Board PDA Personal Digital Assistant RFI Radio Frequency Interference RSSI Received Signal Strength Indicator SAM Standard Anthropomorphic Model WLAN Wireless Local Area Network

5

Table of Contents ABSTRACT............................................................................................................................................................................2 ACKNOWLEDGMENTS .....................................................................................................................................................3 ABBREVIATIONS ................................................................................................................................................................4 TABLE OF CONTENTS.......................................................................................................................................................5 1 INTRODUCTION ........................................................................................................................................................7 2 RELATED WORK.......................................................................................................................................................7 3 TRANSCEIVER STANDARDS..................................................................................................................................8

3.1 GSM STANDARD ...................................................................................................................................................8 3.1.1 GSM 900 / EGSM.............................................................................................................................................8 3.1.2 GSM 1800 / DCS ..............................................................................................................................................8 3.1.3 GSM 1900 / PCS ..............................................................................................................................................8

4 SOURCES OF RF INTERFERENCE........................................................................................................................9 4.1 THERMAL NOISE ....................................................................................................................................................9 4.2 ELECTROMAGNETIC INTERFERENCE ....................................................................................................................10 4.3 POWER SUPPLY INTERFERENCE ...........................................................................................................................10 4.4 IC / PACKAGE DESIGN .........................................................................................................................................11 4.5 PCB AND COMPONENT PLACEMENT....................................................................................................................11 4.6 CLOCK AND DATA ...............................................................................................................................................12 4.7 GROUNDING DESIGN............................................................................................................................................12

4.7.1 Single Point Ground System...........................................................................................................................12 4.7.2 Multipoint Ground System..............................................................................................................................13

4.8 INTERFERENCE DETECTION PROCEDURES............................................................................................................14 5 POSSIBLE SOLUTIONS ..........................................................................................................................................15

5.1 LAYOUT & PLACEMENT OF COMPONENTS ...........................................................................................................15 5.2 GROUNDING SOLUTIONS......................................................................................................................................16 5.3 EMI SUPPRESSION BY FILTERING ........................................................................................................................17

5.3.1 Noise Suppression using Higher Order Filters ..............................................................................................18 5.3.2 Distortion suppression using filters................................................................................................................19

5.4 SHIELDING SOLUTIONS ........................................................................................................................................20 6 RSSI MEASUREMENTS ..........................................................................................................................................21

6.1 MEASUREMENT SCENARIOS.................................................................................................................................21 6.2 MEASUREMENTS WHERE CAMERAS ACTIVE/INACTIVE & ANALYSIS...................................................................22 6.3 MEASUREMENTS IN PRESENCE OF WLAN & ANALYSIS.......................................................................................23

7 OTA SENSITIVITY MEASUREMENTS................................................................................................................24 7.1 MEASUREMENT PROCEDURE ...............................................................................................................................25 7.2 MEASUREMENT RESULTS AND ANALYSIS............................................................................................................26

8 SNIFFING MEASUREMENTS ................................................................................................................................28 8.1 MEASUREMENT PROCEDURE ...............................................................................................................................29 8.2 MEASUREMENT CASES ........................................................................................................................................29 8.3 MEASUREMENT RESULTS AND ANALYSIS............................................................................................................30 8.4 SOURCES OF UNCERTAINTY .................................................................................................................................31

9 RECOMMENDED SOLUTIONS.............................................................................................................................32 9.1 LCD DISPLAY DATA/CONTROL LINES .................................................................................................................32 9.2 RADIATED EMISSIONS FROM FLEX CABLES .........................................................................................................32 9.3 IMPROPER GROUNDING OF SHIELD BOXES...........................................................................................................33 9.4 2MPX CAM SUBSYSTEM INTERFERENCES ..........................................................................................................34

6

9.4.1 Simulations .....................................................................................................................................................35 9.4.2 Oscilloscope Measurements ...........................................................................................................................36 9.4.3 RSSI Results & Analysis .................................................................................................................................37

9.5 VGA CAM SUBSYSTEM INTERFERENCES............................................................................................................39 9.5.1 Simulations .....................................................................................................................................................40 9.5.2 Oscilloscope Measurements ...........................................................................................................................41 9.5.3 RSSI Results & Analysis .................................................................................................................................43

9.6 RADIATED EMISSIONS FROM DIODES...................................................................................................................44 9.6.1 Audio subsystem interferences .......................................................................................................................44 9.6.2 Power subsystem interferences.......................................................................................................................45

CONCLUSION.....................................................................................................................................................................47 FUTURE WORK .................................................................................................................................................................47 APPENDIX A .......................................................................................................................................................................48 APPENDIX B .......................................................................................................................................................................49 REFERENCES.....................................................................................................................................................................59

7

1 Introduction Nowadays, mobile phones have greater functionality; a camera, color LCD screen, wireless LAN, Bluetooth, IrDA and others. In the near future wider variety of new functionalities will be added, from high quality voice, high definition video to high data rate wireless channels. As consumer electronics integrate greater functionality and high operating frequencies, their emissions will exceed the specified limits, most of these emissions will be a result of the internal interferences in the mobile phone. Moreover higher operating frequencies will be required to improve the quality of these functionalities which will make it more difficult to control these interferences. Internal/external sources of electromagnetic interference can degrade the performance of sensitive analog/digital circuits inside the mobile phone. Moreover the electronic device must satisfy a host of global regulations that limit its susceptibility to these interferences, as well as the interference emitted by the device itself. Therefore designing a new electronic device to perform new and exciting functions will not be a pleasant task if it can not meet certain specifications and function as required to adhere to certain global regulations (3GPP, FCC, ETSI, and CISPR). This thesis report is roughly divided into the following parts: An introduction in chapter 1, related work or background information about the project described in chapters 2, 3, 4 and 5. Measurement setups and results analysis described in chapters 6, 7 and 8. Solutions to internal interferences described in chapter 9. Later in the report there is a conclusion and future work proposed, commonly used terminologies in Appendix A, higher order filter simulations in Appendix B, and finally the references.

2 Related Work Throughout the years electronics manufacturers have put serious effort to identify possible causes of internal interference in mobile phones and other consumer electronic devices, and ways to solve these issues. The big part of this work was related to electromagnetic interference caused by the PCB, high rate clocks and other internal components of devices like oscillators on the analog/digital circuitry. The authors of [1] discuss radio frequency effects on electronics systems integrated with high performance chips. Unwanted interferences when superimposed on the system signals that cause spurious state changes on logic devices and system level breakdown. The authors of [2] discuss the test requirements that cover OTA performance of mobile phone antennas; they describe a typical OTA test system and key parameters extracted from such a test.

8

3 Transceiver Standards

3.1 GSM Standard The Global System for Mobile communications is a second generation cellular telecommunication system which was first planned in the early 1980s. Unlike first generation systems operating at the time, GSM was digital and thus introduced greater enhancements such as security, capacity, quality and the ability to support integrated services. [11] Compared with the existing analog systems, the new system was required to have a higher capacity, comparable or lower operating costs and comparable or better speech quality.

Standard Lower Band Frequency RFCN Upper Band Frequency Fl(n) = 890 + 0.2*n 0 ≤ n ≤ 124 Fu(n) = Fl(n) + 45 E-GSM 900 Fl(n) = 890 + 0.2*(n-1024) 975 ≤ n ≤ 1023 Fu(n) = Fl(n) + 45

DCS 1800 Fl(n) = 1710.2 + 0.2*(n-512) 512 ≤ n ≤ 885 Fu(n) = Fl(n) + 95 PCS 1900 FI(n) = 1850.2 + .2*(n-512) 512 ≤ n ≤ 810 Fu(n) = FI(n) + 80

Table 1: ARFCN and Corresponding Frequency Range of Channels [3] The carrier spacing is 200 KHz and frequency is designated by the absolute radio frequency channel number is ARFCN. If we call Fl(n) the frequency value of the carrier ARFCN n in the lower band, and Fu(n) the corresponding frequency value in the upper band. Note that all frequencies in the table above are in MHz. [3]

3.1.1 GSM 900 / EGSM The spectrum range for the GSM 900 operation is between 890 MHz and 915 MHz for uplink operation and 935 MHz and 960 MHz for downlink operation. EGSM is an extension to the GSM 900 spectrum, it has additional 10 MHz that provides an additional 50 channels. Thus the spectrum range for EGSM operation is between 880 MHz and 915 MHz for uplink operation and 925 MHz and 960 MHz for downlink operation.

3.1.2 GSM 1800 / DCS GSM 1800 also known as DCS1800 or DCS is a digital network working on a frequency of 1800 MHz. The spectrum range for the GSM 1800 operation is between 1710 MHz and 1785 MHz for uplink operation and 1805 MHz and 1880 MHz for downlink operation.

3.1.3 GSM 1900 / PCS The spectrum range for the GSM 1900 operation is between 1850 MHz and 1910 MHz for uplink operation and 1930 MHz and 1990 MHz for downlink operation.

9

4 Sources of RF Interference In a mobile phone there are many sources of interference which can be in the form of radiated or conducted electromagnetic interferences and could affect the quality of signal perceived at the transceiver. These interferences cause signal integrity issues and improper functionality of sensitive analog/digital circuits inside the mobile phone. Thermal noise, from power supply or IC packaging, PCB traces, grounding and crosstalk should be considered as sources of interference inside a mobile phone. In this section we will discuss the different sources of interference independently; in later chapters we will propose solutions for these disturbances.

4.1 Thermal Noise Generally, noise is considered to be an electromagnetic interference. Unwanted voltages and currents induced by external magnetic fields, electric fields and ground currents fall into the category of noise and often cause serious errors in low power circuits. Usually conducting media generates internal noise without current flow. [4] One common noise category is resistor thermal noise, which is the noise developed in a resistor in the absence of current flow, often referred to as Johnson noise. This noise is generated in a resistor independent of any current flow and has a mean-square voltage value of ( )BWKTR4 . In this expression k is Boltzman’s constant, T is temperature in degrees Kelvin, R is resistance in Ω, and BW is bandwidth, in Hz. In practice, there is always some parasitic capacitance across the leads of a resistor due to the printed circuit board or lead wire connections. For this situation, when the thermal noise in a resistor is shunted by a non-zero capacitance, the mean-square voltage value is given by C

KT .

Temperature and resistor values can not always be minimized; however, using signal conditioning modules with small bandwidth multi-pole low-pass filters will ensure that external thermal resistor is essentially eliminated. [4]

10

4.2 Electromagnetic Interference RFI is an electromagnetic radiation or interference which is emitted by electrical circuits carrying rapidly changing signals as a by-product of their normal operation. It causes unwanted signals in the form of interference or noise which in turn is to be induced in other circuits. This interrupts, obstructs degrades or limits the effective performance of those other circuits inside the system. EMI can be induced intentionally, or unintentionally, as a result of spurious emissions and responses, inter-modulation products, and the like.

Figure 1: EMI Propagation Model: (1) Conduction mode, (2) Radiation mode, (3) Conduction mode – Radiation mode and (4) Radiation mode – Conduction mode

The efficiency of the radiation is dependant on the height above the ground or power plane; at RF one is as good as the other, and the length of the conductor in relationship to the wavelength of the signal components either the fundamental, harmonic or transient (overshoot, undershoot or ringing). At lower frequencies, such as 133 MHz, radiation is almost exclusively via I/O cables; RF noise gets onto the power planes and is coupled to the line drivers via the VCC and ground pins. The RF is then coupled to the cable through the line driver as common mode noise. Since the noise is common mode, shielding has very little effect, even with differential pairs. The RF energy is capacitively coupled from the signal pair to the shield and the shield itself does the radiating. At higher frequencies, usually above 500 MHz, traces get electrically longer and higher above the plane. Two techniques are used at these frequencies: wave shaping with series resistors and embedding the traces between the two planes. If all these measures still leave too much RFI, shielding such as RF gaskets and copper tape can be used.

4.3 Power Supply Interference Switching power supplies can be a source of RFI, but have become less of a problem as design techniques have improved. Noise which is conducted or radiated should be prevented from returning to the input source, where it can potentially cause havoc on other devices operating from the same input power. Here EMI filters are utilized to block this noise and provide a low-impedance path back to the noise source. The larger the noise interference; the greater is the size, expense, and difficulty of the filter to be designed. Power supplies that operate at a fixed frequency have their largest EMI emission at this fundamental, fixed frequency. Emissions also occur at multiples of the switching frequency but at diminished amplitudes.

11

4.4 IC / Package Design The IC packaging of a component or an ASIC could cause certain amounts of thermal noise. The IC package design affects the equivalent thermal resistance generated noise. Below is a table that shows different packaging designs and a comparison between different thermal resistances.

Table 2: IC Packaging and Thermal Resistances [5]

4.5 PCB and Component Placement The PCB connects electronic passive/active components such as transistors, diodes, capacitors resistors, oscillators and ICs. The routing of the traces on the PCB largely affects the electromagnetic compatibility performance of the PCB with respect to both electromagnetic radiations and susceptibility to electromagnetic fields. In order to get a PCB on which the circuits function properly, the trace routing, the placement of components/connectors and the decoupling used with certain ICs will have to be optimized. Electromagnetic interference can be transferred by electromagnetic waves, conduction, and inductive/capacitive coupling. This interference must reach the conductors in order to disturb the components. This means that the loops, long length and large surface of the conductors are vulnerable to EMI, making the PCB the principle subject of EMC improvements. The following equation shows the relationship of current, its loop area, and the frequency to electric field which is in (V/m):

θsin12 ⎟⎠⎞

⎜⎝⎛=

rkIAfE

Where k is the constant of proportionality, I is the current in amperes, A is the loop area in m2, f is frequency in MHz, r is the distance and θ is the angle. And since the distance to the ground plane is usually fixed due to board stackup requirements, minimizing trace length on the board layout is crucial to decreasing emissions. [6]

Package RthJC (K/W)

RthJC Still Air (K/W)

RthJC 0.5 m/s (K/W)

RthJC 2.0 m/s (K/W)

DIP16 19 48 SOIC24 17 77 PLCC44 10 33 31 27 QFP44 15 48 46 42 BGA256 13 40 38 33

12

4.6 Clock and Data Controlling clock and data EMI issues has remained a challenge for the electronics designer, a look at the origin of this noise shows that the digital system clock is the largest contributor. This is understandable both because the frequency of the system clock is often the highest of all the signals in the system, and because it is usually a periodic square wave. The frequency spectrum of such a signal consists of a fundamental tone of higher amplitude than the harmonic tones, whose amplitudes diminish as frequency increases. Other signals within the system (e.g., those on the data and address buses) are updated at the same frequency as the clock, but occur at irregular intervals and are uncorrelated. This results in a broadband noise spectrum of much lower amplitude than the clock. Although the total energy in this spectrum is much larger than the clock energy, it has little effect on the EMI tests. In these tests, the highest spectral amplitude is what is looked at and not the total radiated energy. The clock or data signal may cause an electromagnetic interference, transition time of the pulse from off to on and vise versa is the most important factor in determining the spectral content of the pulse. Fast transition times generate wider range of frequencies than do slower transition times. The spectral content of digital devices generally occupies a wide range of frequencies and can also cause interference in electrical and electronic devices. [7]

4.7 Grounding Design It is important to realize that there are several purposes of a ground system. The concept of a ground as being a zero-potential surface may be appropriate at dc or low frequencies, but it is never in higher frequencies, since conductors have significant impedance (inductance) and high frequency currents flow through these impedances, resulting in points on the ground having different high frequency potentials. There are basically two major philosophies regarding signal ground schemes: single point ground systems and multi-point ground systems, there are other types of ground systems that are used less frequently and in special cases. These are referred to as hybrid ground systems, and are a combination of the previous two systems over different frequency ranges.

4.7.1 Single Point Ground System A single point ground system is one in which subsystem ground returns are tied to a single point within the subsystem. The intent in using a single point ground system is to prevent currents of two different subsystems from sharing the same return path and producing common-impedance coupling. [7] Typically, single point ground systems are used in analog sub-systems, where low-level signals are involved. In these cases, milli-volt and microvolt ground drops create significant common-impedance coupling interference problems for those circuits. Digital

13

sub-systems on the other hand are inherently “immune” to noise from external sources; however they are susceptible to internal noise. In order to minimize this common-impedance coupling, the ground system in digital sub-systems tends to be multi-point, using a large ground plane such as in inner plane such as in inner plane board or placing numerous alternate ground paths in parallel such as with a ground grid, thus reducing the impedance of the return path. It is also important to route the signal conductors in close proximity to the ground returns, since this will also reduce the impedance of the return.

Figure 2: Single-point ground system: Common Impedance Coupling in daisy

chain connection

Figure 3: Single-point ground system: Unintentional coupling between ground

wires

4.7.2 Multipoint Ground System The other type of ground system philosophy is the multipoint ground system. Typically a large conductor, often the ground plane, serves as the return in a multipoint ground system. In such a system the individual grounds of the sub-systems are connected at different points to the ground conductor. In using a multipoint ground system it is assumed that the ground return to which the individual grounds are terminated have a very low impedance between any two points at the frequency of interest. [7]

Figure 4: Multipoint ground system: Ideal case

14

4.8 Interference Detection Procedures There are several methods used to determine radiated EMI in a system. Some common methods employed in industry are OTA measurements, EMI screening, probing or sniffing and actual software tests performed by the mobile phone. Below is a tabulated summary of the possible measurement and investigation scenarios proposed for this project. On the right side of each measurement or investigation scenario is the reason why it should be performed.

Measurements and Investigations Reasons

Screening for EMI

To locate possible sources of electromagnetic radiation and regions of high EMI. A method used to determine which components contribute to EMI in different modes.

Examining CLK/Data signals on PCB

To determine possible loops, sources of crosstalk, signal coupling components and oscillator/clock signal harmonic interferences.

Spectral analysis of interferences in different modes

To find out radiated frequencies and physically locate components; the sources of interferences. This method is also called sniffing.

OTA Measurements (BER RX / Sensitivity)

To find the effect of interference on RX sensitivity / BER in real life scenarios where the phone is connected to a network.

Table 3: Different Measurement and Investigation Scenarios

15

5 Possible Solutions This chapter describes guidelines on how to tackle the problem of EMI internal to the system. EMC describes the ability of electronic and electrical systems or components to function correctly when they are close together. In practice this means that the electromagnetic interference from each device must be limited and also that each device must have an adequate level of immunity to the interference in its environment the same holds in micro-level where components inside the device itself interfere with each other. There are some emitters whose emissions can serve unintentional radiation; these emitted signals are regarded as interference signals or EMI. In general there are three main methods to prevent this interference; other methods are described in the following sections and in more detail:

• Suppress the emission • Make coupling path as efficient as possible. • Make the receptor less susceptible to the emission.

The most important concept is to suppress the emission as much as possible at the source. For example, we can determine that fast rise/fall times are primary contributors to the high-frequency spectral content of these signals. In general higher the frequency of the signal to be passed through the coupling path the more efficient the coupling path. So we should slow the rise/fall times of the digital signals to improve the efficiency of the coupling path thus reduce EMI. One can not slow the rise/fall times without considering the normal operation signaling conditions required by various devices dependant on those signals. By reducing the high-frequency spectral content of an emission tends to inherently reduce the efficiency of the coupling path and hence reduces the signal level at the receptor. Other brute force methods are viable, but the cost-effectiveness is questionable. For example, placing the receptor in a metal enclosure or a shield will serve to reduce the efficiency of the coupling path. But shielded enclosures are more expensive than reducing the rise/fall time of the emitter, and sometimes the resulting performance is far less than the ideal. [7]

5.1 Layout & Placement of Components During the PCB design phase, the layout designer should foresee the need of suppression for some clock harmonics in the future when the product is eventually tested for compliance. If the PCB designer places pads at the output of the clock on the PCB, a capacitor can be easily inserted, across the clock terminals, thus reducing the emissions of the clock. Also pads may be placed in series with the trace of a clock output to provide for later insertion of a series resistor to additionally reduce the clock

16

rise/fall times and further reduce the high frequency emissions of the clock signal. In the initial design the capacitor pads can be left vacant and the series resistor pads can be wired across with a 0 Ω resistor. If problems with the clock emissions occur during testing, a capacitor can be inserted and only the PCB artwork and the product parts list needs to be changed. If this is not done, the entire PCB would need to be re-laid out, thus by adhering to certain design principles and maintaining the necessary EMC insight throughout the design will tend to make the necessary suppression easy to apply and at minimal expense. For technical reasons, it is best to use a multi-layer printed circuit board with a separate layer dedicated to the ground and another one to the VDD supply, which results in good decoupling, as well as good shielding effect. For many applications, economical requirements prohibit the use of this type of board. In this case, the most important feature is to ensure good structure for the ground and power supply. [7] The layout of a digital logic board can have a significant effect on its performance. The edges of the waveforms being very fast, the frequencies that are contained within waveforms are particularly high. Accordingly leads should be kept as short as possible if the circuit is to be able to perform correctly. A preliminary layout of the PCB must separated the different circuits according to their EMI contribution in order to reduce cross coupling on the PCB, i.e. noisy, high-current circuits, low voltage circuits and digital components. There are also some general guidelines to minimize EMI with a good component placement, like:

• Place all components associated with one clock trace closely together to reduce the trace length and reduce radiation. • Keep oscillators, and clock generators away from I/O ports and board edges, EMI from these devices can be coupled onto the I/O ports. • Place high-current devices as closely as possible to the power sources. [6]

5.2 Grounding Solutions For circuit board grounds, it is almost impossible to get good low-impedance grounds on two-sided circuit boards, so it is critical to keep ESD currents and high-level radio-frequency interference off such boards. On the other hand, it is easy to achieve low impedances with the ground plane underneath the traces on multilayer boards. Circuits built immediately above the ground plane are well protected, regardless of the threat. EMI problems are frequently the result of high-impedance interconnects. Again, designers need to keep the ground impedance low; either by connecting the circuit boards or modules to a common ground plane or by providing a very-low-impedance ground interconnects, usually by allocating as many connector pins to grounds as possible. Although the connector space is an important concern, so is functionality. [8]

17

5.3 EMI Suppression by Filtering The most important means of reducing electromagnetic interference are: the use of bypass or decoupling capacitors on each active device connected across the power supply, as close to the device as possible, or control the rise time of high speed signals using series resistors and VCC filtering. Shielding is usually a last resort after other techniques have failed because of the added expense of RF gaskets and the like. EMI suppression filters are used to suppress noise produced by conductors. Noise radiation can be suppressed, if it is eliminated with a filter in advance. Generally, such noise suppression is achieved with DC EMI suppression filters, according to the capacitive and inductive frequency characteristics of the respective conductors in the circuit. Filters of this kind can be roughly divided into those; employing a capacitor, an inductor or a capacitor and inductor combination. When a decoupling capacitor is connected from a noisy signal line or power line to ground; the circuit impedance decreases as the frequency increases. Since noise is a high frequency phenomenon, it flows to ground if a capacitor has been connected to ground, thereby making it possible to eliminate noise, see figure below. EMI suppression filters employing a capacitor in this way are used to eliminate this type of noise (See Figure 6).

Figure 5: Capacitive Noise Suppression

fCZ

π21

= where f is the frequency and C is the value of the capacitance.

When an inductor is inserted in series in a noise producing circuit, see figure below, its impedance increases with frequency. In this configuration it is possible to attenuate and eliminate noise components which are the high frequency components found in the signal. (See Figure 7)

Figure 6: Inductive Noise Suppression

fLZ π2= where f is the frequency and L is the value of the inductance. If capacitive and inductive suppression characteristics are combined, it is possible to configure a much higher performance filter. In signal circuit applications where this

18

combination is applied, noise suppression effects which have little influence on the signal wave form become possible. This type of filter is also effective in the suppression of high-speed signal circuit noise. When used in DC power circuits, capacitive-inductive filters prevent resonance from occurring in peripheral circuits, thus making it possible to achieve significant noise suppression under normal service conditions.

5.3.1 Noise Suppression using Higher Order Filters The order of the filter determines the sharpness of the rising edge of the processed signal, according to the simulations performed it turned out that the higher the filter order, the slower is the rising edge, thus higher order filters might cause input/ouput driver not meet specifications and have signal integrity problems. Also in higher order filter simulations the best rising time in a certain order of filter is different for different models of the same filter type (e.g. for 3rd order filters: the rising time was the best for the Butterworth Pi-model filter, while for the T-model filter the Chebyshev I filter was the best.) To have an idea about different filtering topologies, signal waveforms and EMI Suppression effect. [See Appendix B] The table below describes different filtering solutions on a transmission line having a specific length and driver technology driving the input/output of the transmission line:

Type of Filter Signal Waveform EMI Suppression Effect

Signal Rising/Falling Edge & Noise

Spectrum before/after filter Mounting

1st Order Chebyshev I PB Ripple = 1dB

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA



3rd Order Chebyshev I PB Ripple = 1dB

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA



5th Order Chebyshev I PB Ripple = 1dB

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

Probe Probe

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

Table 4: Different Chebyshev Filtering Solutions

19

5.3.2 Distortion suppression using filters There are many methods that can be used to reduce distortion in a signal. The table below describes basic methods for distortion suppression: series resistive termination and RC filtering solutions that reduce the ringing effect and distortion of a clock signal improving its signal integrity.

Type of Signal EMI Suppression Effect

Initial waveform

-3.000

-2.000

-1.000

0.000

1.000

2.000

3.000

4.000

5.000

6.000

7.000

0.000 10.000 20.000 30.000 40.000 50.00Time (ns)

Voltage -V-

PP

Series resistor termination applied / waveform ringing effect reduced.

-3.000

-2.000

-1.000

0.000

1.000

2.000

3.000

4.000

5.000

6.000

7.000

0.000 10.000 20.000 30.000 40.000 50.00Time (ns)

Voltage -V-

RC filtering solution applied / waveform distortion is suppressed

-3.000

-2.000

-1.000

0.000

1.000

2.000

3.000

4.000

5.000

6.000

7.000

0.000 10.000 20.000 30.000 40.000 50.00Time (ns)

Voltage -V-

Table 5: Different Distortion Suppressing Solutions

20

5.4 Shielding Solutions It is a form of containment used to preventing RF energy from exiting an enclosure, generally by shielding a product within a metal enclosure or by using a plastic housing with RF conductive paint. By reciprocity, we can also speak of containment as preventing RF energy from entering the enclosure. Therefore a shield is, conceptually, a barrier to transmission of electromagnetic fields, see figures below.

Figure 7: Shield that Contains Radiated Emission

Figure 8: Shield that Excludes Radiated Emission

In order to realize an effective shielding, the shield must enclose the electronics, and must have no penetrations such as holes, seams or slots. [7]

21

6 RSSI Measurements In this chapter we examine the critical interference scenarios in different operation modes; measurement results are presented in the noise spectrum plots. Various possible scenario combinations were enumerated; a total of 52 cases were investigated; and only the critical scenarios are presented in noise spectrum plots.

6.1 Measurement Scenarios Different measurements scenarios were investigated; some cases were discarded since they do not occur in real life. So after filtering out all the non-occurring scenarios and the ones that can not be measured OTA, only three cases remained having critical levels of interference in the GSM band in addition to the reference scenarios.

22

6.2 Measurements where Cameras Active/Inactive & Analysis

925 930 935 940 945 950 955 960-120

-115

-112.7874

-110

-105

-100

-95

-90

Channel Frequency in MHz

RS

SI o

f cha

nnel

EGSM 900 Spectrum

X: 936Y: -110

Figure 9: Noise Spectrum

(Cameras Inactive – Backlight ON – Flash OFF)

925 930 935 940 945 950 955 960-120

-115-114.1149

-110

-105

-100

-95

-90

X: 936Y: -111


RS

SI o

f cha

nnel

EGSM 900 Spectrum


(Cameras Inactive – Backlight OFF – Flash OFF)

925 930 935 940 945 950 955 960-120

-115

-112.954

-110

-105

-100

-95

-90

X: 936Y: -101

X: 949Y: -107


RS

SI o

f cha

nnel

EGSM 900 Spectrum


(VGA CAM Active - Backlight OFF - Flash OFF)

925 930 935 940 945 950 955 960-120

-115

-112.0575

-110

-105

-100

-95

-90

X: 936Y: -100

X: 949Y: -105 X: 955.8

Y: -106


RS

SI o

f cha

nnel

EGSM 900 Spectrum


(2MPx CAM Active – Backlight Off – Flash OFF)

925 930 935 940 945 950 955 960-120

-115

-112.7759

-110

-105

-100

-95

-90

X: 936Y: -101

X: 949Y: -103


RS

SI o

f cha

nnel

EGSM 900 Spectrum

X: 955.6Y: -107

Figure 13: Noise Spectrum (2MPx CAM Active – Backlight On – Flash Off)

In the first two cases there were no high levels of interference, only a single 13MHz harmonic appeared at 936MHz but it had negligible interference strength. From several scenarios only these three cases were chosen to perform further investigations on. (See figures 12, 13 and 14)

23

6.3 Measurements in presence of WLAN & Analysis

In presence of WLAN transmissions an interference was noticed in the DCS band at lower WLAN transmission channels (channels 1 to 7), this interference level diminished in strength as transmission was at higher channels. The levels of interference are much below the threshold level.

925 930 935 940 945 950 955 960-120

-115-113.4598

-110

-105

-100

-95

-90


RS

SI o

f cha

nnel

EGSM 900 Spectrum

Figure 14: Noise Spectrum (WLAN TX1 - Backlight OFF - Flash OFF in EGSM900)

1810 1820 1830 1840 1850 1860 1870 1880

-130

-120

-112.7914-110

-100

-90

-80

X: 1872Y: -104


RS

SI o

f cha

nnel

in d

Bm

DCS 1800 Spectrum

Figure 15: Noise Spectrum (WLAN TX1 - Backlight OFF - Flash OFF in DCS1800)

925 930 935 940 945 950 955 960-120

-115-114.0805

-110

-105

-100

-95

-90

X: 936Y: -111


RS

SI o

f cha

nnel

EGSM 900 Spectrum

Figure 16: Noise Spectrum (WLAN TX7 - Backlight OFF- Flash OFF in EGSM900)

1810 1820 1830 1840 1850 1860 1870 1880

-135

-130

-125

-120

-115-112.8048

-110

-105

-100

-95

-90

-85

X: 1872Y: -105


RS

SI o

f cha

nnel

in d

Bm

DCS 1800 Spectrum

Figure 17: Noise Spectrum (WLAN TX7 - Backlight OFF - Flash OFF in DCS1800)

925 930 935 940 945 950 955 960-120

-115-113.954

-110

-105

-100

-95

-90

X: 936Y: -109


RS

SI o

f cha

nnel

EGSM 900 Spectrum

Figure 18: Noise Spectrum (WLAN TX13 - Backlight OFF - Flash OFF in EGSM900)

1810 1820 1830 1840 1850 1860 1870 1880-140

-130

-120

-112.615-110

-100

-90


RS

SI o

f cha

nnel

in d

Bm

DCS 1800 Spectrum

X: 1872Y: -107

Figure 19: Noise Spectrum (WLAN TX13

- Backlight OFF - Flash OFF in DCS1800)

24

7 OTA Sensitivity Measurements In this chapter we investigate the sensitivity of the receiver in the three different scenarios as selected in the previous chapter where high levels of interference exist. Over-the-air tests determine how a specific network will influence the connectivity performance of a mobile handset. It can yield data that can be used to demonstrate that a product meets performance criteria. Over-the-air performance tests measure the magnitude and direction of transmitted/received energy, sensitivity and BER to determine the performance of the wireless device. A typical polar pattern configuration is obtained with the measurement antenna(s) fixed the antenna under test is rotated through 360°. [9] In OTA tests it is important to determine the influence of the user’s body on the transceiver properties and performance and the differences between free-space and the standard anthropomorphic model. SAM phantom tests determine the blocking effect of the human head on the antenna pattern, but do not address radiation absorption, hazard or health and safety issues [9]. Below is typical OTA test system.

NetworkAnalyzer

SpectrumAnalyzer

Universal RadioCommunication

Tester

Relay Switch Unit

MAPS Controller

`

walkway

Fibre Optics MAPS system

Device Under Test (DUT)

Diagonal dual polarized horn

Figure 20: DUT in a Typical OTA Test System

To have a reliable channel sensitivity scan, we acquired the average of 5000 samples of data; a threshold BER of 2.439 percent in order for the call not to be disconnected. Transmission from the MS was performed at minimal power to reduce battery consumption for longer hours of measurement. The start level of scanning was -100 dBm for the software to be able to locate interference peaks below this level in a faster seek time.

25

The DUT was positioned in “talk position” so as to emulate actual situation where there are reflections from the human head, although we could not perform measurements considering the human “hand effect”. We can assume that the obtained results in “talk position” will be the worst case, since reflections will be directly heading towards the antenna, so no need to consider the other case.

Figure 21: DUT in Talk Position

7.1 Measurement Procedure Initially we started with a basic scan of every tenth channel of the EGSM band, after obtaining the results of the first pass we made a second pass taking more samples adjacent to the interference channels. Finally we scanned extra channels as a result of the sniffing results discussed in the following chapter. We obtained about 42 channels out of 174 channels which constitutes 24 percent of the total channels for the first case. We had 27 channels which constitute 16 percent of the channels in the band and for the second case, but for the last case only 17 channels which constitute about 10 percent of the channels were required since this case is a reference. These percentages were fair enough to cover all the possible interference frequencies. The first and second cases had the 2MPx camera active, and the backlight on or off respectively. The third was a reference case used to determine the average sensitivity of the band when the cameras and backlight are off.

26

7.2 Measurement Results and Analysis For different DUTs we obtained different interference levels at 955.4 MHz frequency on the EGSM900 band (Figures 24 & 25). This was due to the loose shield of the 2MPx camera, which was not containing radiated emissions of the camera MCLK_2M and its internal oscillator. Resistance measurements were performed between the shielded boxes and the interference at 955.6 MHz disappeared when more pressure was applied or 2MPx shield box changed. This interference and the other 13MHz harmonic frequency interferences were blocked and suppressed in the solutions chapter.

925 930 935 940 945 950 955-120

-115

-110-109.2088

-105

-100

-95

-90

X: 943.4Y : -109

X: 936.6Y: -107.1

X: 936Y: -102.5


Sen

sitiv

ity o

f cha

nnel

EGSM 900 Spectrum

X: 949Y: -105.8

Figure 22: Noise Spectrum with Good Shield

(2MPx CAM Active – Backlight ON – Flash OFF)

925 930 935 940 945 950 955-120

-115

-110

-108.3219

-105

-100

-95

-90

X: 955.4Y: -97.94

X: 936Y: -102.5

X: 936.6Y: -107.1


Sen

sitiv

ity o

f cha

nnel

EGSM 900 Spectrum

X: 949Y: -105.8

Figure 23: Noise Spectrum with Loose Shield

(2MPx CAM Active – Backlight ON – Flash OFF)

925 930 935 940 945 950 955 960-120

-115

-110.0085-110

-105

-100

-95

-90

X: 936Y: -104.5

X: 948Y: -108.5


Sen

sitiv

ity o

f cha

nnel

EGSM 900 Spectrum

X: 943.4Y: -110.3


(Cameras Inactive – Backlight ON – Flash OFF)

In the measurement results above high levels of interference were noticed at 936 MHz and 949 MHz; the backlight had some contribution in the interference at these frequencies.

27

925 930 935 940 945 950 955 960-120

-115

-110-109.4071

-105

-100

-95

-90

X: 936Y: -106.7

Channel Frequency in MHzR

SS

I of c

hann

el

EGSM 900 Spectrum


(Cameras Inactive – Backlight OFF – Flash OFF) This case is a reference used to determine the average sensitivity levels at the receiver when the cameras, backlight and flash are off.

28

8 Sniffing Measurements In an electronic system, the primary emission sources are currents flowing in circuits like clocks, data drivers, oscillators and other components that are mounted on printed circuit boards. Although the radiated measurements in the laboratory environment can not be accurate enough, it is possible to establish a minimum set-up in the lab at which one can perform emissions diagnosis and carry out comparative tests. Analyzing the data obtained from the sniffing measurements, we noticed that several components emitting interference signals above a certain threshold level. In this chapter we try to highlight these components and describe the key interferences. Probing or “sniffing” is a measurement methodology used to physically locate the source of emissions from a product. After detaching external mechanics of the DUT, and scanning its internal components using a probe or sniffer loop antenna.

The emission spectrum can be observed through the spectrum analyzer, and relative emission strength can be concluded. The advantage of sniffing is that the source of interference can be directly located on the PCB, the disadvantage is that the interference amplitude is dependant on the distance between the probe and the component, so any variation in the distance causes an uncertainty in the amplitude of the actual interference, causing the peak value of the interfering signal vary.

Figure 26: Spectrum Analyzer

A near-field or “sniffer” probe was used to physically locate the source of emissions from the product, since we only want to detect the field strengths in the near field. The probe is connected to the spectrum analyzer for frequency domain display. Probe design is a trade-off between sensitivity and special accuracy. The smaller the probe, the more accurately it can locate signals but the less sensitive it will be. The sensitivity can be increased with a preamplifier if working with low power circuits. The sum of radiating sources will differ between near and far fields and the probe will itself distort the field it is measuring. Perhaps one might mistake a particular hot spot

29

found on the circuit board for the actual radiating point, whereas the radiation is in fact coming from cables or other structures that are coupled to this point via an often complex path. Thus probes are best used for tracing and for comparative rather than absolute measurements [10].

8.1 Measurement Procedure Sniffing measurements are performed in a shielded chamber to avoid external interferences. The device has its external mechanics detached to expose the primary and secondary layers. Before the detailed sniffing measurements, a fast pre-scan through is performed to locate major peaks or interference frequencies. This enormously speeds up the sweep rate for a whole frequency scan.

8.2 Measurement Cases Based on the RSSI measurement results of the previous phases of the project, and after dropping the unnecessary cases, we were left with three cases for the secondary layer and two cases for the primary layer as shown in the table below.

Device sides 2MPx Camera Backlight Flash

Inactive ON OFF Inactive OFF OFF Secondary Active ON OFF

Inactive ON OFF Primary Active ON OFF Table 6: Sniffing Measurements on Primary and Secondary Sides

30

8.3 Measurement Results and Analysis On the primary side of the PCB a new frequency of interference at 943.6MHz was found that did not appear in the previous measurement results, this frequency appeared after the pre-scan performed on different components of this side of the PCB. Thus the new sniffing spectral scans were based on four frequencies, 936MHz, 943.6 MHz, 949MHz and 955.6MHz. On this side most of components were covered with shielding boxes which were quite effective to block emissions of internal components to the exterior and vice versa. So the measurements were mainly done on the uncovered components located on the PCB and the flex cables. Many adjacent peaks appear around the center frequency, especially 936MHz and 955.4MHz in (2MPx Cam active – Backlight On – Flash OFF) case. But those adjacent peaks disappeared when cameras and backlight were off. Also on this layer, a new peak frequency was also found at 943.6MHz. This interference was mainly contributed by a capacitor, an inductor and the flex cable between PCB /LCD and the capacitors that are placed on the flex cable. The two mega pixel camera’s shielding box was loose, so while sniffing high levels of emission were observed. While on the secondary side and after examining the obtained results we noticed that the 2 mega-pixel camera when active will cause more interference; not only on the key interference channels, but also its adjacent channels. Similarly the backlight will contribute in raising the interference to higher levels, but will not introduce other interference frequencies in the spectrum. On the secondary side there are two key components that contribute to high levels of interference, these components are diodes. The first one causes very high peak at 936 MHz (-88.56dBm ~ -95.03dBm) for all three cases, a high peak (-93.29dBm ~ -98.3dBm) at 949 MHz and also high peak (-95.73dBm) at 955.4 MHz. The second one causes very high peak and noise floor in certain cases. Only when camera, backlight and flash are all off, the noise floor falls back to normal value (around -110dBm). Note that the noise floor can not be measured from the spectrum analyzer directly, so this average values are only estimates.

31

8.4 Sources of Uncertainty Radiated interference, whether intentional or not, decreases in strength with distance from the source. For radiated fields in free space, the decrease is inversely proportional

to the distance provided that the measurement is made in the near field πλ

2tan <cedis.

EMC measurements are inherently less accurate than most other types of measurements. It is always wise to allow a margin of about 10dB between measurements and the specification limits, not only to cover measurement uncertainty but also tolerances arising in production. These uncertainties could arise from different factors such as: instrument and cable errors, mismatch errors in cable impedance, antenna calibration issues, reflections not only from DUT but also from the ground plane and antenna cable. Thus we can say that the radiated measurements in the laboratory environment can not be accurate enough, but it is possible to perform emissions diagnosis and carry out comparative tests based on the results obtained through these measurements. Performing sniffing measurements on the product helps to physically locate the sources of emission. Although the radiated measurements can not be accurate enough, one can carry out comparative tests and observe the key interference components. [10]

32

9 Recommended Solutions

9.1 LCD Display Data/Control lines A cause of EMI could be the CLK signal going in/out of connector from PCB to flex cable. For this case we tried to put decoupling capacitors on the data lines, but the EMI contribution of this section seemed to be quite negligible on the GSM receiver due to the distance from the receiver antenna. Thus this solution did not solve the interference problem. Also we tried to use a copper tape to shield the flex cable, but no improvement in the sensitivity of the receiver was noticed.

Figure 27: A solution for Data/Control lines between PCB and LCD display

9.2 Radiated Emissions from Flex Cables While sniffing the LCD, VGA CAM and 2MPx CAM flex cable, high levels of interference was found on 936 MHz frequency. The interference contribution of the flex cables was noticeable in OTA sensitivity measurements also. The solutions provided could not be implemented on the flex cables, only solutions were done on the PCB.

33

9.3 Improper Grounding of Shield Boxes For the measurements performed in the table below we used a digital multi-meter, two probes and the DUT. We had the external mechanical cover of the device removed in order to access the internal shield boxes and perform detailed measurements. Compared to the older DUTs the new shields required more pressure to be applied in order to get better contact with ground, thus for any reason lesser pressure resulted in higher interference levels at certain frequencies.

DUT 1 High resistance between the two points: 22.5 Ω (2 MPx Camera Shield box – RF Shield box)

DUT 2 High resistance between the two points: 46 ~ 68 Ω (2 MPx Camera Shield box – RF Shield box)

DUT 3 Lower resistance between the two points:2 ~ 3 Ω (2 MPx Camera Shield box – RF Shield box)

Table 7: Improper Grounding of 2MPx CAM Shield Box The problem of interference at 955.6 MHz was solved by changing the shield box in later stages.

34

9.4 2MPx CAM Subsystem Interferences

This section includes simulation results using Mentor Graphics Hyperlynx software, possible solutions to the MCLK_2M trace line were proposed and these solutions were implemented and verified to be consistent with the simulation results. Meeting the specifications of the two mega pixel camera (rising time/slew rate limitations) was the challenge. In this case the specifications were not met after applying solutions, but the camera was functional.

n

MCLK_2MPIX_CLK

CAM_DAT[i]CAM_DAT[i]CAM_DAT[i]CAM_DAT[i]CAM_DAT[i]CAM_DAT[i]CAM_DAT[i]CAM_DAT[i]

Other_CLK

Figure 28: Data/CLK lines between PCB and 2MPx CAM

We tried to apply different filtering solutions to the MCLK_2M in order to reduce the EMI resulting from the clock line and its harmonics. The appendix includes different filtering types (Butterworth, Chebyshev, Bessel and Legendre filters), topologies (t-model and pi-model) and orders (1st, 3rd and 5th). These results were compared and a conclusion was made in section 5.3.1.

35

9.4.1 Simulations

Type of Filter Signal Waveform EMI Suppression Effect

MCLK_2M with decoupling capacitor of

33pF

-40.0

160.0

360.0

560.0

760.0

960.0

1160.0

1360.0

1560.0

1760.0

1960.0

0.000 4.000 8.000 12.000 16.000 20.0Time (ns)

Voltage -mV-

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

MCLK_2M with a series

termination of 22 Ω and

decoupling capacitor of

22pF. -40.0

160.0

360.0

560.0

760.0

960.0

1160.0

1360.0

1560.0

1760.0

1960.0

0.000 4.000 8.000 12.000 16.000 20.00Time (ns)

Voltage -mV-

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

MCLK_2M with a resistive

termination of 220 Ω

-40.0

160.0

360.0

560.0

760.0

960.0

1160.0

1360.0

1560.0

1760.0

1960.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

PrPr

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

Table 8: Solutions Verification for MCLK_2M

36

9.4.2 Oscilloscope Measurements The oscilloscope measurements results were similar to the simulation results, only the falling edge had a 1ns delay. In the figure below the fastest rising edge resembles the original MCLK_2M signal; the other two are the rising edges after applying the 33 pF capacitor and the one with the 22 Ω and 22 pF RC filtering solutions.

Figure 29: Oscilloscope Measurements of MCLK_2M Rise Times

37

9.4.3 RSSI Results & Analysis

Original MCLK_2M Signal

925 930 935 940 945 950 955 960-120

-115

-111.6724

-110

-105

-100

-95

-90

X: 936Y: -98

X: 955.6Y: -101


RS

SI o

f cha

nnel

EGSM 900 Spectrum

X: 948.8Y: -104

Figure 30: Noise Spectrum (2MPx CAM

Active – Backlight Off – Flash OFF)

925 930 935 940 945 950 955 960-120

-115

-112.5977

-110

-105

-100

-95

-90

X: 936Y: -99

X: 948.8Y: -106


RS

SI o

f cha

nnel

EGSM 900 Spectrum

X: 955.6Y: -106


Active – Backlight ON – Flash OFF) For both cases the interference level at 936MHz was -98 ~ -99 dBm and at 949 MHz was -104 ~ -106 dBm, the interference at 955.6 Mhz was excluded since the shield box covering the 2MPx camera totally discards it when properly grounded.

MCLK_2M with Decoupling Capacitor

925 930 935 940 945 950 955 960-120

-115

-112.3391

-110

-105

-100

-95

-90

X: 936Y : -106

X: 949Y : -110


RS

SI o

f cha

nnel

EGSM 900 Spectrum

X: 957Y: -111



925 930 935 940 945 950 955 960-120

-115

-113.1724

-110

-105

-100

-95

-90

X: 936Y: -107

X: 949Y: -110


RS

SI o

f cha

nnel

EGSM 900 Spectrum

X: 951.4Y: -111


Active – Backlight On – Flash OFF) For both cases the interference level at 936 MHz was -106 ~ -107 dBm and at 949 MHz was -110 dBm, thus resulting in interference reduction of 8dB at 936 MHz and 4 ~ 6 dB at 949 MHz.

38

MCLK_2M with series Resistive Termination and Decoupling Capacitor

925 930 935 940 945 950 955 960-120

-115

-112.9655

-110

-105

-100

-95

-90

X: 936Y: -106

X: 949Y : -108


RS

SI o

f cha

nnel

EGSM 900 Spectrum



925 930 935 940 945 950 955 960-120

-115

-112.3966

-110

-105

-100

-95

-90

X: 936Y: -107

X: 949Y: -109


RS

SI o

f cha

nnel

EGSM 900 Spectrum


Active – Backlight On – Flash OFF) For both cases the interference level at 936 MHz was -106 ~ -107 dBm and at 949 MHz was -108 ~ -109 dBm, thus resulting in interference reduction of 6dB at 936 MHz and 3 ~ 6 dB at 949 MHz.

MCLK_2M with series termination

925 930 935 940 945 950 955 960-120

-115

-112.4253

-110

-105

-100

-95

-90

X: 936Y: -104

X: 949Y : -108


RS

SI o

f cha

nnel

EGSM 900 Spectrum



925 930 935 940 945 950 955 960-120

-115

-112.4713

-110

-105

-100

-95

-90

X: 936Y: -103

X: 949Y: -108


RS

SI o

f cha

nnel

EGSM 900 Spectrum


Active – Backlight On – Flash OFF) For both cases the interference level at 936 MHz was -103 ~ -104 dBm and at 949 MHz was -108 dBm, thus resulting in interference reduction of 3 dB at 936 MHz and 3 ~ 5 dB at 949 MHz. According to the experimental results obtained, the solution of having a decoupling capacitor of 33pF was found to be the best. Note that the relative measurements were performed on two different devices.

39

9.5 VGA CAM Subsystem Interferences

A cause of EMI could be the CLK signals going in/out of connector from PCB to flex cable.

Figure 38: Data/CLK lines between PCB and VGA CAM

Filtering is an efficient way to decrease clock rising edge, since longer the rising time, lesser the interference at higher frequencies above 500 MHz. It is important to choose suitable values for the resistor and capacitor, since there is a trade-off between rising time and noise spectrum of the signal. Below is the schematic of the VGA CAM connector, and the proposed solution to suppress the EMI.

Figure 39: A Solution for Data/CLK lines between PCB and VGA CAM

40

9.5.1 Simulations Figures 41, 42, 43 and 44 present a comparison of the noise spectrum before and after adding RC filtering solutions to the trace involved.

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

Figure 40: Noise Spectrum before adding

RC filter

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

Figure 41: Noise Spectrum after adding RC filter (R=33Ω, C=22pf)

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

Figure 42: Noise Spectrum after adding RC filter (R=220Ω, C=22pf)

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

Figure 43: Noise Spectrum after adding

RC filter (R=0Ω, C=33pf)

41

9.5.2 Oscilloscope Measurements

Figures 45, 46, 47 and 48 present the results of the oscilloscope measurement of MCLK / PCLK, it is evident how the resistor and capacitor values effect the rising time of both clocks. Note that the rising time is read from 10% ~ 90% rising time of the signal.

Figure 44: VGA_MCLK on test point ¾

(R = 0Ω, C = 33pf)

Figure 45: VGA_MCLK on test point 4

(R = 33Ω, C = 22pf)

Figure 46: VGA_MCLK on test point 4

(R = 220Ω, C = 22pf)

Figure 47: VGA_MCLK on test point ¾

(R = 0Ω, C = 22pf)

Test point

Rising time(ns) R = 0Ω, C = 33pf




3 ------- ------- 4 5.347 9.739 11.13 8.464

Table 9: Rising Time Summary of MCLK_VGA

42

Figure 48: VGA_PCLK on test point ½

(Initially R = 0Ω, no capacitor)

Figure 49: VGA_PCLK on test point 2

(R = 33 Ω, no capacitor)


(R = 220 Ω, no capacitor)

Figure 51: VGA_PCLK on test point ½

(R = 0Ω, C = 22 pf)


(R = 220Ω, C = 22pf)

Test point

Rising Time(ns) R = 0Ω, C = 0pf




Rising time(ns)R = 220Ω, C = 22pf

1 ------- ------- ------- 2 6.291 6.599 9.621 8.709 11.4

Table 10: Rising Time Summary of PCLK_VGA

43

9.5.3 RSSI Results & Analysis

925 930 935 940 945 950 955 960-120

-115-113.6149

-110

-105

-100

-95

-90

X: 936Y: -99


RS

SI o

f cha

nnel

EGSM 900 Spectrum

X: 949Y: -107

Figure 53: Noise Spectrum of Reference

925 930 935 940 945 950 955 960-120

-115

-112.2989

-110

-105

-100

-95

-90

X: 936Y: -104


RS

SI o

f cha

nnel

EGSM 900 Spectrum

X: 949Y: -108

Figure 54: Noise Spectrum after adding RC filter_1 (MCLK-R 33Ω & C 22pf, PCLK-R 33Ω & C 22pf)

925 930 935 940 945 950 955 960-120

-115

-112.8851

-110

-105

-100

-95

-90

X: 936Y: -105


RS

SI o

f cha

nnel

EGSM 900 Spectrum

X: 949Y: -105

Figure 55: Noise Spectrum after adding RC filter on PCLK (MCLK-R 0Ω&C 33pf, PCLK-R

220Ω&C 22pf)

925 930 935 940 945 950 955 960-120

-115-113.1379

-110

-105

-100

-95

-90

X: 936Y: -103

X: 949Y: -105


RS

SI o

f cha

nnel

EGSM 900 Spectrum

Figure 56: Noise Spectrum (2M pixel camera inactive

– VGA camera ON – Backlight OFF)

Peak/channel Peak(dBm)/channel Reference -99dBm / 5 -107dBm / 70 After decoupling R = 33Ω&C = 22pf -104dBm / 5 -108dBm / 70

After decoupling R = 220Ω&C = 22pf -105dBm / 5 -105dBm / 70

After decoupling on PCLK Rpclk = 220Ω&Cpclk = 22pf -103dBm / 5 -105dBm / 70

Table 11: Summary of MCLK_VGA & PCLK_VGA Solutions

Larger resistor values can make more effective EMI suppression, by further damping the rising edge of the signal to reduce higher frequency interference. Though, the timing requirements for the clock rising edge should be acceptable. According to the oscilloscope plots, almost no timing margin was left for both clocks with 220 Ω resistor that will lead to the difficulty to meet hold / setup time requirements for the sensor.

44

From the noise spectrum measurement plots we can deduce that, lower resistor values will be a better choice, the 33Ω for resistor and 22pf for capacitor is a feasible choice. This RC filter can cause reduction of 5dB at 936 MHz.

9.6 Radiated Emissions from Diodes While sniffing the PCB for radiated emissions, two diodes near the RF antenna were suspected to be possible sources of interference. By performing over the air measurements of the receiver sensitivity, the radiation frequencies from the device were detected, and by sniffing the approximate location of the emitting components were verified.

9.6.1 Audio subsystem interferences As a result of the sniffing measurements, two other sources of interference were located which indicated the presence of a RF radiation problem on the audio circuitry which connects the back speakers to the audio power amplifier. (Figure 59)

Figure 57: A Solution for the Audio Subsystem Interference

These two diodes are used for avoiding ESD. A proposed solution was to add four capacitors C1, C2, C3 and C4 of 33 pf on the diodes in parallel. These four capacitors are supposed to work to keep the frequency as original because high frequency signal will go through capacitor instead of diode. That will be helpful to decrease interference on high frequency.

45

925 930 935 940 945 950 955 960-120

-115

-113.0287

-110

-105

-100

-95

-90

X: 936Y: -104

X: 949Y: -102


RS

SI o

f cha

nnel

EGSM 900 Spectrum


925 930 935 940 945 950 955 960-120

-115-114.6552

-110

-105

-100

-95

-90

X: 936Y: -106

X: 949Y: -105


RS

SI o

f cha

nnel

EGSM 900 Spectrum

Figure 59: Noise Spectrum after decoupling

Peak/channel Peak(dBm)/channel

Reference -104dBm / 5 -102dBm / 70 After decoupling -106dBm / 5 -105dBm / 70

Table 12: Summary of Audio Diode Solution Before adding these capacitors, most of the peak levels of interference were below -102 dBm. After adding capacitors, both the noise floor and peak value decreased by 2~3 dB.

9.6.2 Power subsystem interferences A proposed solution was to add one decoupling capacitor C5 of 33 pF and later to put a series resistor 33 Ω.

Figure 60: A Solution for Backlight DC-DC Converter Interference

46

925 930 935 940 945 950 955 960-120

-115-113.2931

-110

-105

-100

-95

-90

X: 936Y: -102

X: 949Y: -105


RS

SI o

f cha

nnel

EGSM 900 Spectrum

X: 955.6Y: -107


925 930 935 940 945 950 955 960-120

-115

-111.7011-110

-105

-100

-95

-90

X: 936Y: -102


RS

SI o

f cha

nnel

EGSM 900 Spectrum

X: 949Y: -103

Figure 62: Noise Spectrum after Solution



Table 13: Summary of Power Diode Solution (2MPx CAM Active – VGA CAM OFF – Backlight OFF)

925 930 935 940 945 950 955 960-120

-115-113.5057

-110

-105

-100

-95

-90

X: 936Y: -104

X: 949Y: -108


RS

SI o

f cha

nnel

EGSM 900 Spectrum


925 930 935 940 945 950 955 960-120

-115-113.1034

-110

-105

-100

-95

-90

X: 936Y: -106

X: 949Y: -108


RS

SI o

f cha

nnel

EGSM 900 Spectrum

Figure 64: Noise Spectrum after Decoupling



Table 14: Summary of Power Diode Solution (2MPx CAM Inactive – VGA CAM OFF – Backlight ON)

For this particular solution, no obvious improvement was noticed by adding a decoupling capacitor.

47

Conclusion Detecting and solving internal interference issues in a mobile phone is a formidable and interesting task. It is formidable since it involves an overhead of measurements and physical implementation of solutions. It is also interesting since the approach of detecting and suppressing these interferences requires understanding of the overall receiver functionality and requirements. This report is a result of intensive research, theoretical background of possible sources of interference. Actual measurements were preformed; RSSI measurements were used to quickly determine the key interference frequencies, OTA measurements uses a more complex setup to determine the receiver sensitivity through BER evaluation of the received signal and sniffing measurements to physically locate the sources of interference; to identify the physical sources of interferences, their effect on the receiver sensitivity and overall receiver performance. Finally solutions were recommended and implemented to suppress these interferences. Some of the solutions resulted in good interference suppression, while others had no obvious improvement in the sensitivity of the receiver. Lower order filters were preferred since they had better EMI suppression results, with less EMI at the resonance frequencies. There is always a tradeoff between the signal integrity and EMI suppression, one should keep in mind to meet the overall system requirements and provide solutions accordingly. Special attention should be given to layout, the layout engineer has to adhere to certain design guidelines, and be able to foresee futuristic EMI suppression needs. Shield boxes should be verified to be well grounded so as not to act as antennas.

Future Work In the future investigations, simulations and experimentation on newer technologies with faster and more aggressive driver inputs/outputs should be performed to determine signal integrity, coupling and EMI issues arising due to advances in technology. Also other functionalities of the mobile phone should be investigated, like the IrDA, Bluetooth, USB interface and others.

48

Appendix A Conducted susceptibility – The relative inability of a product to withstand electromagnetic energy that reaches it through external cables, power cords, and other I/O interconnects. Containment – Preventing RF energy from exiting an enclosure, generally by shielding a product within a metal enclosure (faraday cage) or by using a plastic housing with RF conductive paint. By reciprocity, we can also speak of containment as preventing RF energy from entering the enclosure. Electromagnetic compatibility (EMC) – The ability of a product to coexist in its intended electromagnetic environment without causing or suffering functional degradation or damage. Electromagnetic interference (EMI) – A process by which disruptive electromagnetic energy is transmitted from one electronic device to another via radiated or conducted paths or both. In common usage, the term refers particularly to RF signals, but EMI can occur in the frequency range from “DC to daylight.” Immunity – A relative measure of device or system’s ability to withstand EMI exposure. Radiated susceptibility – The relative inability of a product to withstand EMI that arrives via free space propagation. Radio frequency (RF) – The frequency range within which coherent electromagnetic radiation is useful for communication purposes: roughly from 10 KHz to 100GHz. This energy may be generated intentionally, as by a radio transmitter, or unintentionally as a byproduct of an electronic device’s operation. RSSI – Received Signal Strength Indication is a measurement of the strength; not necessarily the quality; of the received signal strength in a wireless environment; it is represented in arbitrary units. Suppression – Designing a product to reduce or eliminate RF energy at the source without relying on a secondary method such as a metal housing or chassis. Susceptibility – A relative measure of device or system’s propensity to be disrupted or damaged by EMI exposure.

49

Appendix B

PI - Model Filter T - Model Filter 1st Order Butterworth Cutoff Frequency = 245 MHz

3rd Order Butterworth Cutoff Frequency = 245 MHz

But

terw

orth

Filt

er P

aram

eter

s

5th Order Butterworth Cutoff Frequency = 245 MHz 1st Order Butterworth Cutoff Frequency = 245 MHz


But

terw

orth

Filt

er P

aram

eter

s in

Hyp

erly

nx

5th Order Butterworth Cutoff Frequency = 245 MHz

50

PI - Model Filter T - Model Filter

1st Order Chebyshev I Cutoff Frequency = 245 MHz Pass band Ripple = 1 dB 3rd Order Chebyshev I Cutoff Frequency = 245 MHz Pass band Ripple = 1 dB

Che

bysh

ev I

Filte

r Par

amet

ers

5th Order Chebyshev I Cutoff Frequency = 245 MHz Pass band Ripple = 1 dB

1st Order Chebyshev I Cutoff Frequency = 245 MHz Pass band Ripple = 1 dB

Rg

RL

11.2 pH

3rd Order Chebyshev I Cutoff Frequency = 245 MHz Pass band Ripple = 1 dB

Che

bysh

ev I

Filte

r Par

amet

ers

in H

yper

lynx

5th Order Chebyshev I Cutoff Frequency = 245 MHz Pass band Ripple = 1 dB

51


1st Order Bessel Cutoff Frequency = 245 MHz 3rd Order Bessel Cutoff Frequency = 245 MHz

Bes

sel F

ilter

Par

amet

ers

5th Order Bessel Cutoff Frequency = 245 MHz

1st Order Bessel Cutoff Frequency = 245 MHz

3rd Order Bessel Cutoff Frequency = 245 MHz

Bes

sel F

ilter

Par

amet

ers

in H

yper

lynx


52


1st Order Bessel Legendre Frequency = 245 MHz 3rd Order Legendre Cutoff Frequency = 245 MHz

Lege

ndre

Filt

er P

aram

eter

s

5th Order Legendre Cutoff Frequency = 245 MHz

1st Order Legendre Cutoff Frequency = 245 MHz 3rd Order Bessel Cutoff Frequency = 245 MHz

Lege

ndre

Filt

er P

aram

eter

s in

Hyp

erly

nx


53


1st Order Butterworth Cutoff Frequency = 245 MHz

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe


-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

Probe Probe

But

terw

orth

Filt

er S

igna

l (R

isin

g Ti

me

of 4

0MH

z C

LK)


-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

Probe Probe

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

54


1st Order Chebyshev I Cutoff Frequency = 245 MHz

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

Probe Probe

3rd Order Chebyshev I Cutoff Frequency = 245 MHz

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

Probe Probe

Che

bysh

ev I

Filte

r Sig

nal (

Ris

ing

Tim

e of

40M

Hz

CLK

)

5th Order Chebyshev I Cutoff Frequency = 245 MHz

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

Probe Probe

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

Probe Probe

55



-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe


-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

Bes

sel F

ilter

Sig

nal (

Ris

ing

Tim

e of

40M

Hz

CLK

)


-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

Probe Probe

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

Probe Probe

56


1st Order Legendre Cutoff Frequency = 245 MHz

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

3rd Order Legendre Cutoff Frequency = 245 MHz

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

ProbeProbe

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

Probe Probe

Lege

ndre

Filt

er S

igna

l (R

isin

g Ti

me

of 4

0MH

z C

LK)


-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

Probe Probe

-80.0

120.0

320.0

520.0

720.0

920.0

1120.0

1320.0

1520.0

1720.0

1920.0

0.000 4.000 8.000 12.000 16.000 20.000Time (ns)

Voltage -mV-

Probe Probe

57


1st Order Butterworth Cutoff Frequency = 245 MHz

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

0 500.000 MHz 1.000 G Hz

1mA

100uA

10uA


0 500.000 MHz 1.000 GHz

1mA

100uA

10uA 0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

But

terw

orth

Filt

er (E

MI L

evel

s)


0 500.000 MHz 1.000 GHz

1mA

100uA

10uA 0 500.000 MHz 1.000 G Hz

1mA

100uA

10uA


1st Order Chebyshev I Cutoff Frequency = 245 MHz

0 500.000 MHz 1.000 G Hz

1mA

100uA

10uA

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

3rd Order Chebyshev I Cutoff Frequency = 245 MHz

0 500.000 MHz 1.000 G Hz

1mA

100uA

10uA

0 ns 75 ns

0 500.000 MHz 1.000 G Hz

1mA

100uA

10uA

Che

bysh

ev I

Filte

r (E

MI L

evel

s)

5th Order Chebyshev I Cutoff Frequency = 245 MHz

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA 0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

58



0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA


0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

0 ns 75 ns

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA B

esse

l Filt

er (E

MI L

evel

s)


0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

0 ns 75 ns

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA


1st Order Legendre Cutoff Frequency = 245 MHz

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

3rd Order Legendre Cutoff Frequency = 245 MHz

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

0 ns 75 ns

0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

Lege

ndre

Filt

er (E

MI L

evel

s)


0 500.000 MHz 1.000 G Hz

1mA

100uA

10uA 0 500.000 MHz 1.000 GHz

1mA

100uA

10uA

59

References

[1] Hongxia Wang et Al., Radio Frequency Effects on the Clock Networks of Digital Circuits, IEEE 2004 [2] Matin Wiles, CTIA test requirements cover over the air performance, Wireless Europe, October – November 2004 [3] 3rd Generation Partnership Project; Technical Specification Group GSM/EDGE V8.17.0, 2004-11 [4] William J. Dally & John W. Poulton, Digital System Engineering, Cambridge University Press 1998 [5] Karl Rinne, Dept. Electronics and Computer Engineering, University of Limerick, http://www.ul.ie, August 2005 [6] Intel, Design for EMI Application Note AP-589, February, 1999. [7] Clayton R. Paul, Introduction to Electromagnetic Compatibility, Wiley-Interscience Publication, 1992 [8] William D. Kimmel and Daryl D. Gerke are principals in the EMI consulting firm Kimmel Gerke Associates, Ltd., based in St. Paul, MN. [9] Martin Wiles, CTIA test requirements cover over-the-air performance, Institute of Physics and Institute of Physics Publishing Ltd. 2005 [10] Tim Williams, EMC for Product Designers, Third Edition, Newnes, 2001 [11] Siegmund M. Redl et Al, GSM and Personal Communications Handbook, Artech House, 1998

analysis of internal rf interferences in mobile phones9977/fulltext01.pdf · analysis of internal...

Documents