Analog Circuits and Systems

Prof. K Radhakrishna Rao

Lecture 3 Role of Analog Signal Processing in

Electronic Products – Part 11

1

Cell Phone

o  The most dominant product of present day world o  Its basic function is to make and receive telephone calls over a radio

link while moving around a wide geographic area. o  It connects to a cellular network provided by a mobile phone

operator, allowing access to the public telephone network.   o  They also support a wide variety of other services such as text

messaging, multimedia messaging, email, Internet access, short-range wireless communications (infrared and Bluetooth), business applications, gaming, and photography.

o  Mobile phones that offer these and more general computing capabilities are referred to as smart phones.

2

Cell Phone Block Diagram

(Md Whaiduzzaman, Abdulla Gani: A Study of Anatomy of Smartphone; Computer Communication and Collaboration, 2013)

3

Radio and Analog Base Band Block Diagram

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RF Front End

o  Typical path consists of, after diplexer, a tunable band pass filter, RF low transmitting power of cell phone is 500mW

o  RF filter in the transmission path is a tunable band pass filter o  Antenna is connected to transmitter and receiver through a

diplexer o  Low noise amplifier (LNA)

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IF Block

o  The output of the LNA goes to a mixer to generate IF signal using the local oscillator that is under the control of digital base band processor to produce a sinusoidal signal at (�IF).

o  The IF signal is amplified by IF amplifier which is a fixed frequency band pass filter

o  The IF amplifier output is demodulated using local oscillator which down converts the signal to analog/digital base band.

6

Analog Back-End and Baseband

o  The output of the demodulator may represent the digitally coded speech, video or data.

o  The video signal and speech signal are reconstructed using D/A converter. The digital data directly goes to the digital base band processor

o  The output from IF amplifier whose input is from the Modulator is up converted to the radio frequency of transmission by a mixer and power amplified before getting connected to the antenna.

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Analog Back-End and Baseband (contd..)

o  Speech and video signals generated by the user are converted into digital data using Analog-to-Digital converter.

o  Digital data goes to the Modulator and to digital base band processor

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Digital Baseband

o  Human interface (keyboard and display), dialing, memory and power management are controlled by digital baseband processor

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Power Management

o  Power management system consists of battery charging, battery monitoring and efficient power distribution

o  Digitally controlled analog sub-systems.

10

Electrocardiogram (ECG)

o  An electrocardiogram (ECG) is a non-invasive procedure for recording of the electrical activity on the body surface generated by the heart.

o  An electrocardiogram (ECG or EKG) shows a series of waves that relate to the electrical impulses of heartbeat.

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Idealized version of ECG Waveform

o  It has features defined as the P, QRS, and T for each heartbeat.

o  The amplitude and relative timing of the various segments (PQRST) are used for diagnosis.

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Important Components of ECG

o  Heart rate: 0.67 – 5 Hz (i.e. 40 – 300 beats per minute) o  P-wave: 0.67 – 5 Hz o  QRS: 10 – 50 Hz o  T-wave: 1 – 7 Hz o  High frequency potentials: 100-500 Hz

13

Artifacts and Noise in ECG

o  Muscle: 5 – 50 Hz o  Respiratory: 0.12 – 0.5 Hz (e.g. 8 – 30 bpm) o  External electrical: 50 or 60 Hz (A/C “mains” or “line” frequency) o  Other electrical: typically >10 Hz (muscle stimulators, strong

magnetic fields, pacemakers with impedance monitoring)

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ECG Recording

o  It uses several electrodes o  The machine detects and

amplifies the electrical impulses picked up by electrodes that occur at each heartbeat and records them on to a paper, computer or any storage device. (google images)

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Positioning of Electrodes

o  A differential recording between two points on the body are made

o  They are defined as VI, VII and VIII

(google images) where RA = right arm, LA = left arm, and LL = left leg

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ECG Signal Characteristics

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ECG Block Diagram

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Analog Front End

◦  The inputs from groups of electrodes are multiplexed and processed for common mode rejection by the instrumentation amplifier (INA) ◦  The output of INA is amplified by the variable gain amplifier ◦  Frequencies lower than 0.05 Hz are eliminated by High Pass Filter ◦  Frequencies above 150 Hz are eliminated by Low Pass Filter ◦  The noise at power supply frequency is eliminated using a Notch

Filter

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Analog Front End (contd..)

o  The output of the notch filter is amplified and coded to digital form using an Analog-to-Digital Converter

o  The digital data is suitable processed by a Digital Signal Processor for recording, display or storage.

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Basic Analog Signal Processing Functions

o  Amplification/Attenuation o  Filtering o  Comparison o  Multiplication o  Digital-to-Analog Conversion o  Analog-to-Digital Conversion

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Amplification/Attenuation

o  Output (voltage or current) = K x Input (voltage or current)+Offset;

where |K| >1 or |K| < 1 = ��ai x �Input i where ai can be positive or negative (addition and/or subtraction

o  If X1 and X2 are two independent variables (inputs)

(X1+X2)/2 is known as common mode signal (X1-X2) is known as differential mode signal

o  Ideal Difference Amplifier: Output=Kd x (X1-X2)

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Amplification/Attenuation (contd..)

o  Non-ideal Difference Amplifier: Output = Kd x (X1-X2) + Kc x (X1+X2)/2 where Kd is known Differential Mode Gain and Kc is Common Mode Gain

o  (Kd/Kc) = � is known as Common Mode Rejection Ratio. It is normally expressed in decibels as 20log �

o  An ideal difference amplifier should have Common Mode Rejection Ratio of ∞.

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Filtering

o  Filtering is rejecting or accepting signals in bands of frequencies o  Filtering can be Low Pass, High Pass, Band Pass and Band Stop

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Low Pass Filtering

o  An ideal low pass filter will pass all frequency components below a specified frequency known as upper cut off frequency

o  A non-deal low pass filter causes varying amplification/ attenuation of frequency components around the upper cut off frequency

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High Pass Filtering

o  An ideal high pass filter will pass all frequency components above a specified frequency known as lower cut off frequency

o  A non-deal high pass filter causes varying amplification/ attenuation of frequency components around the lower cut off frequency

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Band Pass Filtering

o  An ideal band pass filter will pass all frequency components within a upper cut off frequency and lower cut off frequency

o  A non-deal high pass filter causes varying amplification/attenuation of frequency components around the upper and lower cut off frequencies

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Band Stop Filtering

o  An ideal band stop filter will stop all frequency components within a upper cut off frequency and lower cut off frequency

o  A non-deal band stop filter causes varying amplification/attenuation of frequency components around the upper and lower cut off frequencies

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

-0.1

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

x

y

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Comparison

o  When the input is less than a reference value the output has a specified fixed value and when the input is more than the reference value the output has another specified fixed value

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Multiplication

o  The output of a multiplier is the product of two inputs o  An ideal multiplier has a relationship o  where VX and VY are two independent inputs o  A non-ideal multiplier will have relationship

where KXVX and KYVY are feed through components

0 0 X YV K V V=

0 0offset X X Y Y X YV V K V K V K V V= + + +

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Multiplication Applications in Communication

( )( ) ( ) ( )

( )( )

o p1 p2o o p1 1 p2 2 1 2 1 2

1o o p1 1 p2 2 1 o p1

K V Va)V K V sin t V sin t cos t cos t

2DSB, Balance Modulator and Mixer

1 cos 2 tb)V K V sin t V sin t sin t K V

⎡ ⎤= ω ω = ω −ω − ω +ω⎣ ⎦

− ω= ω ω ω =

( )

( ) ( )( ) ( )

p2 2

o p1 p2o o p1 p2

V sin t2

DSB DemodulationK V V

c)V K V sin t V sin t cos cos 2 t2

Phase detector, frequency doubler

ω

⎡ ⎤= ω ω + φ = φ− ω + φ⎣ ⎦

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Digital to Analog Conversion

o  The input is n-bit digital data and the output is analog signal o  Output = o  It can also be called a multiplier with Vref as analog input

and is the digital signal

1,

12

0n

i ref ii na V wherea−

=

=∑

{ }1 2 ... na a a

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Analog to Digital Conversion

o  The output is n-bit digital data and the input is analog signal o  A comparator is a one-bit A/D converter

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Analog Systems require

o  Signal Generation

o  Power Supplies

( )

2

2

p

v Kv 0tv V sin Kt

K

∂ + =∂= + φ

ω =

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