rf fundamentals development2

7/28/2019 Rf Fundamentals Development2

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RF TOPICS

ontentsFUNDAMENTAL DEFINITIONS ......................................................................................................... 2

Smith Chart ..................................................................................................................................... 3

POWER ............................................................................................................................................ 5

Real/Imaginary ............................................................................................................................ 5

Decibels ....................................................................................................................................... 5

VSWR ............................................................................................................................................... 6

BJT ................................................................................................................................................... 7

Modes of Operation .................................................................................................................... 7

Current Mirror/ Widlar Current Source ...................................................................................... 8

Bipolar Mirror with Base-Current Compensation....................................................................... 9

AMPILFIERS ..................................................................................................................................... 9

Single Stage ................................................................................................................................. 9

Cascaded Amplifiers .................................................................................................................. 10

Amplifier Classes ....................................................................................................................... 12

Amplifier Design ........................................................................................................................ 13

Maximum gain design ........................................................................................................... 13

Noise ......................................................................................................................................... 13

SILICON/CMOS .............................................................................................................................. 15

ATTENUATORS/FILTERS ................................................................................................................ 16

DuFIS Attenuator ...................................................................................................................... 16Cellular Overview & 3G UMTS HSPA High Speed Packet Access Tutorial. ................................ 17

Terms ................................................................................................Error! Bookmark not defined.

APPENDIX ..........................................................................................Error! Bookmark not defined.

Reflection Coefficient ...............................................................Error! Bookmark not defined.


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UNDAMENTAL DEFINITIONSParameters

parameters, or scattering parameters, are elements of an n-port network that defines a circuits input and output

orts. They are power measurements that describe output powers for various input powers by using matched load

sertion Loss: IL = -20log10|S21|[dB]

sertion loss is the dB expression of the transmission coefficient |S21|

ot that this loss can be intrinsic loss in the DUT and/or mismatch loss (imperfect |S11|)

put Return Loss: RLout=|20log10|S11||[dB]

y definition, return loss is a positive quantity but is commonly referred to as a negative value.

is a scalar measure of how close the input impedance of the network is to the nominal system impedance.

utput Return Loss: RLout=|20log10|S22||[dB]

milar to RL just on the output.

everse gain & Reverse Isolation: grev=20log10|S12|[dB] . . &. . Irev=|grev|=|20log10|S12||[dB]


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mith Chart

Smith chart is a mapping (bilinear transformation) of the impedance plane onto the reflection coefficient plan usin

e below formula. (Weber pg 27)

= Z-Zo / Z+Zo

uestion: Why use this equation?

oints: Outside the smith chart assume negative impedances

SWR is defined as the maximum voltage on the line divided by the minimum voltage on the line.

otate Locus

ockwise is toward the generator

= 3x108

m/s = f

wavelength = 180 degrees on Smith Chart

mpedance repeats itself every half wavelength along uniform transmission line

oving x degrees along the line moves a point on the locus 2x


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tp://www.microwaves101.com/encyclopedia/smithchart.cfm


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OWERower is the amount of work that is done over a period of time. Watt [J/s]

eal/Imaginary

ecibels

0log()

0log()

dB point


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SWRoltage Standing Wave Ratio at a port is the ration of the standing wave maximum voltage to the standing wave

inimum voltage. It therefore relates to the magnitude of the voltage reflection coefficient and hence to the magn

either S11 for the input port or S22 for the output port.

=||

||sout =

||

||

eflection Coefficient


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JThile the BJT is biased to operate in the active mode, it is at heart, a transconductance amplifier represented by a f

aracteristic parameters. (Sedra/Smith -- pg29)

= input resistance between B and E

m = a short-circuit transconducatnace

= output resistance

Modes of Operation

ctive Mode, also called forward active mode,

nly base-emitter junction is forward biased

sed if the transistor is to operate as an amplifier.

utoff Mode, is used for switching applications.

turation Mode,

ollector-base junction is forward biased.

so used for switching applications.

everse Active Mode, or inverse active, mode is rarely used but important.

ode EBJ CBJ

toff Reverse Reversetive Forward Reverse

verse Active Reverse Forward

turation Forward Forward

orward Active

everse Biased

mitter-Follower

ommon Base/ Common Emitter


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urrent Mirror/ Widlar Current Source

ob Widlar patent in 1967)

he Widlar Current Source is a variant of a current mirror with an emitter resister on Q2 allowing very low currents e realizable with very small resistor values.


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ipolar Mirror with Base-Current Compensation

edra/Smith pg 650) Matt Raygors assignment

hy do we need Base-Current compensation?

MPILFIERSicrowave Engineering 3

rdEdition - David M. Pozar

ower Amplifiers Chapter 11.5 pg 570

ingle Stage

ase-to-Emitter/Collector Phase Shift

ommon Emitter (output from the collector) --- 180 degree phase shift

ommon Collector (output from the emitter) --- 0 degree phase shift

Single Stage Transistor Phase Splitter

http://electriciantraining.tpub.com/14180/css/14180_40.htm

he phase shift occurs when a voltage is applied to the base of the BJT. This voltage causes the current ic to increas

erefore increasing the emitter voltage. Since VE + VCE must equal Vcc, and VBE is theoretically constant, VCE will

erefore decrease with an increase in VB.
http://electriciantraining.tpub.com/14180/css/14180_40.htmhttp://electriciantraining.tpub.com/14180/css/14180_40.htmhttp://electriciantraining.tpub.com/14180/css/14180_40.htm


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to VCE Phase Shift

he reason IC and VCE waveforms are out of phase is because of the load line. As the base voltage increases, IC incre

s IC increases, Vout increase but VCE decreases.

and VCE AC waveforms are offset by 180.

his is important because power, and therefore efficiency, is calculated using IC and VCE waveforms.

ascaded Amplifiers

Microelectronics Circuits 5th

Edition (Sedra/Smith) Pg. 25)

ost amplifier designs utilize multiple stages. For example, a typical GSM power amplifier is usually composed of a

scade of three stages. The amplifier is fed by a signal source, with a corresponding impedance, and drives the first

age which then drives the second stage which then drives the third stage ultimately bringing power to the load. Th

ason for using multiple stages is because it allows for a design realizing a voltage gain and power gain that would

herwise not be realizable with a single stage amplifier.

ch stage in the below figure plays a different role in the overall amplifier design.


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age 1) In order to avoid losing signal strength at the input where the signal is usually very small, the first stage has

latively high input resistance with only a modest gain factor of 10.

age 2) The second stage is used to realize the bulk of the voltage gain and therefore has a higher gain factor of 10

ower input resistance.

age 3) The third and final stage acts as a bugger amplifier and is not asked to provide any voltage gain. This last st

as unity gain but a low output resistance, much lower than RL allowing for all of the signal to be transferred to the

ad.


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mplifier Classes

ass A

Conduct over entire range of the input signal cycle

Theoretical maximum efficiency 50%

Inherently linear circuits - Most small-signal and low-noise amplifiers operate as class A circuits

ass B

Conducts over the input signal cycle

Theoretical maximum efficiency 78%

Usually two complimentary transistors operate in a push-pull configuration

ere, the bias is arranged to shut of the output device every half cycle.

ass C

Conducts over very small amount of input signal cycle

Theoretical maximum efficiency of 100%

Generally uses a resonant circuit on output stage to recover fundamental - Can only be used with constant

envelope modulations

ass D, E, F (Switching Amplifiers) Conducts over small amount of input signal cycle

May achieve very high efficiencies

Uses transistor as a switch to pump a highly resonant tank circuit

witching amplifiers ideally operate on the two axis of the IC-VCE curve.


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mplifier Design

aximum gain design

11.3 Single-Stage Transistor Amplifier Design

ter stability is checked, maximum gain (maximum power transfer) can be realized by conjugately matching the inp

nd output. This occurs because GO of a transistor is fixed. Therefore overall gain is controlled by maximizing GS an

=*S

ut=*

L

oise

NR

Signal to noise ration. Ratio of single power to the noise power.

oise power

oise power (Pnoise) can be equated to an equivalent noise temperature.

Ni = kT0B

k= 1.380x10-23J/K is Boltzmanns constantT is temperature in degrees kelvin (K)

B is the bandwidth of the system in Hz

oise Factor (F)

oise factor is an alternative characterization of noise used to measure the degradation of the signal-to-noise ratio

etween the input and output of the component

he noise factor of a device is related to its noise temperature Te
http://en.wikipedia.org/wiki/Noise_temperaturehttp://en.wikipedia.org/wiki/Noise_temperature


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oise Figure (NF)

oise Figure is just Fdb.


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ILICON/CMOSTs are more reliable, and can realize larger currents and powers. But while BJTs are the component choice for RF

ngineers, Silicon designers weapon of mass destruction is the MOSFET.

andgap Voltage

andgap References


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TTENUATORS/FILTERS

uFIS Attenuator


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ellular Overview & 3G UMTS HSPA High Speed Packet Access Tutorial.tp://www.radio-electronics.com/info/cellulartelecomms/cellular_concepts/mobile-basics-concepts.php

tp://www.radio-electronics.com/info/cellulartelecomms/3g-hspa/umts-high-speed-packet-access-tutorial.php

ell system for frequency re-use

eas are broken up into regions (or cells) allowing different transmitter/receiver communication links to use the sa

equency.

ell Clusters

cluster is a group of adjacent cells, each having a different frequency band, ensuring that no interference will occu

etween cells even if some spectral overlap occurs.

ften these clusters contain 7 cells.

ell Size

y making the cells smaller, a greater capacity is obtained, however, more base stations are required.

Macro cells: Large, remotely populated areas. 10km in diameter

Micro cells: Densely populated areas. 1km in diameter

Pico cells: Very small areas of buildins, tunnels

Selective cells: When 360 coverage is not required. Entrance to tunnel for example.Umbrella cells:Covering many microcells allow for fewer handovers.

ultiple Access Schemes

hese multiple access schemes have allowed multiple users to access the cellular system simultaneous.

DMA Frequency Division Multiple Access

sed by all analogue systems, this scheme divides the spectrum up by frequencies and assigns a channel to each us

e system.

DMA Time Division Multiple Access

sed when cellular systems were transitioning to digital schemes, TDMA sent data in bursts. Each user would not o

et a frequency assigned, similar to the FDMA scheme, but would also get a time allocated allowing multiple users t

e the same frequency by simply sharing the time needed to send short data bursts .

DMA Code Division Multiple Access

hen generating a direct sequence spread spectrum, the data to be transmitted is multiple with a spreading or chi

de. This widens the spectrum of the signal, but it can only be decided in the receiver if it is again multiple with th

me spreading code. All other signals are not seen.

this way, the base station allocates different codes to different users and when it receives the signal it will use on

de to receive the signal from one mobile, and another spreading code to receive the signal from another mobile.

nalogy: Many people in a room talking different languages. Even though noise is high, you can hear and understanour own language over everyone elses conversation.

FDMA Orthogonal Frequency Division Multiple Access

FDMA is the form of multiple access scheme being considered for 4G. (LTE for UMTS/W-CDMA & UMB for CDMA2
http://www.radio-electronics.com/info/cellulartelecomms/cellular_concepts/mobile-basics-concepts.phphttp://www.radio-electronics.com/info/cellulartelecomms/cellular_concepts/mobile-basics-concepts.phphttp://www.radio-electronics.com/info/cellulartelecomms/3g-hspa/umts-high-speed-packet-access-tutorial.phphttp://www.radio-electronics.com/info/cellulartelecomms/3g-hspa/umts-high-speed-packet-access-tutorial.phphttp://www.radio-electronics.com/info/cellulartelecomms/3g-hspa/umts-high-speed-packet-access-tutorial.phphttp://www.radio-electronics.com/info/cellulartelecomms/cellular_concepts/mobile-basics-concepts.php


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ir-Interface Modulations & Waveforms

CPR/ACLR

CPR used for CDMA and

CLR used for WCDMA

TE - 4G

ses OFDMA for downlink

ses SC-FDMA for uplink because it has lower PAPR (Peak to Average Power Ratio)

UTRA is evolution from UMTS

rf fundamentals development2

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