Analog Circuits and Systems
Prof. K Radhakrishna Rao
Lecture 1
Introduction to Sensors, Signals and Systems
1
Some present day popular electronic products
o
Cell phone
o
Camera
o
Television
o
Medical instruments
o
Music system
o
Printer
o
Radio
o
ATM
o
Computers
o
Home appliances
o
Watches and clocks
o
Lighting
o
Security systems
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Electronic products: Sense and process signals (ECG)
o Sense, process, present
o display audio output record oscilloscope and
o preserve processed signals
o Storage in memory
3
Electronic products: Store information
4
Electronics Products: Output processed information in
audio and or video form
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Electronics Products: Activate/control devices using
processed information
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Electronics Products: Transmit and receive information
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Electronic products
Primary function is processing
signals/data
Signals
o  Anything that carries
information is a signal
◦  Speech
◦  music
◦  scenery
◦  chirping of birds
◦  gestures
—
o
o
chemical signals that control
body functions
Electronic products deal with
electrical signals which are
voltages and currents
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Electronic products
Signals from real world
o  Electrical signals are derived from the real world through
transducers which convert a physical or chemical variable into an
electrical signal
o  Transducers produce analog signals which are continuous functions
of independent variables
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Strain Gage Bridge
¢  Vo+
= ((R+DR)/ 2R)Vexc
¢  Vo-
= ((R-DR)/ 2R)Vexc
¢  Output Difference Signal =
(DR/R)Vexc, Output Common
Mode Signal = Vexc/2
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Some Transducers
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Nature of Signals: Periodic Analog Signals
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Problem
o
o
Place your finger at the input terminal of an oscilloscope. What do
you see?
Ans: 50Hz/60Hz power line frequency signal.
13
Problem
o
o
A periodic waveform is shown
Estimate the frequency and the harmonic content of the waveform.
14
Solution
0.1sin100π t + 0.05sin 300π t
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Aperiodic Signals
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Problem
o
What can you say about the nature of the signal shown:
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Spectrum and Bandwidth
o
o
o
Spectrum is the distribution power as a function of frequency
Analog signals are characterized by their spectra.
The frequency range over which most of the signal power is
concentrated is called the bandwidth of the signal.
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Spectra
19
Spectra
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Problem
o
Draw the spectrum of the following signal
v = 5 (sin1000t )(sin10000t )
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Solution
sin A sin B
=
cos ( A − B ) − cos ( A + B )
2
Spectrum
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Characteristics of some signals
o
o
o
o
Speech signal has a band width of 300 Hz – 3 kHz
Video signal has a bandwidth of 25 Hz - 5 MHz to 100 MHz
HiFi music has a bandwidth of 20 – 30 kHz
ECG 0.04 to 150 Hz
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Baseband Signal
o
o
o
Some baseband signals of interest are biomedical, audio and video
signals
Baseband signals cannot be transmitted directly over long distances
Output from a transducer is used to modulate a carrier for
transmission over long distances
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Noise
o
o
o
o
Noise is unwanted electrical or electromagnetic energy that
interferes with wanted signal When we measure ECG signal using electrodes, they also pick up
the noise at 50/60 Hz
When the ambient audience created noise is picked up by the
microphone in a music performance
Internal noise generated by the electronic components of the
electronic circuit performing signal processing function
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ECG Signal and 50/60Hz Noise
Noise dominating the signal
Narrow Band
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Signal with Noise
Signal dominating the Noise
Narrow Band
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Signal and Noise
o
o
o
o
A signal is always contaminated by noise
The unwanted noise will have to be suppressed (filtering) or
reduced (cancellation)
Wanted signal may be strengthened with respect to noise
(amplification)
Improvement of signal-to-noise (S/N) ratio (SNR) is one of the
purposes of signal processing
SNR = 10 log (signal power/noise power) decibels
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Signal Processing
o
o
o
o
o
Using a megaphone to communicate with a crowd (amplification)
Eliminating or reducing the ambient noise (filtering, and noise
cancellation and subtraction)
Selecting a radio station (selection) filtering (bandpass)
Smoke signal, Morse code, drum beats (coding/modulation, A/D
conversion/ multiplication)
Reading smoke signals and message sent by Morse Code
(Demodulation/Digital to Analog Conversion/ multiplication)
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Analog signal processing
o
o
o
o
Amplification of microphone output
Filtering 50 Hz interference from power line in ECG signal
Modulating a carrier with an audio signal (multiplication)
Storing music on a magnetic tape – as against this in digital it is
stored in memory
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Why digital signal processing?
o
o
o
o
Complexity and accuracy can be greatly improved if signals are
processed in their digital coded form
DSP leads to great reduction in cost, size, reliability and efficiency
Analog signals are encoded into digital form using analog-to-digital
converter
Powerful digital signal processing (DSP) devices are currently
available
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Analog Circuits and Systems
Design of analog circuits and systems requires performing:
o  signal processing functions including, amplification, addition,
subtraction, integration, comparison, filtering and multiplication
o  signal generation
o  interfacing including sample and hold, A/D conversion and D/A
conversion
o  power supply management
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Aim of the Course
The aim of the course ‘Analog Circuits and Systems’ is to design
analog circuits and systems that perform signal processing functions,
and signal generation using the devices including Op-Amps,
amplifiers, multipliers and comparators.
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Course Outcomes
CO1 Understand the characteristics of linear one-port and two-port
signal processing networks
CO2 Model one-port devices including R, L, C and diodes, two-port
networks, and active devices including amplifiers, Op Amps,
comparators, multipliers, BJTs and FETs
CO3 Understand how negative and positive feedback influence the
behaviour of analog circuits
CO4 Design VCVS, CCVS,VCCS, CCCS, and DC and SMPS voltage
regulators
CO5 Design analog filters
CO6 Design waveform generators, phase followers and frequency
followers
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References
1.
2.
3.
Applications of Operational Amplifiers: Third Generation
Techniques (The BB electronics series); Jerald G.
Graeme (Author); Mcgraw-Hill (Tx); First Edition 1973 https://
archive.org/details/
ApplicationsOfOperationalAmplifiers-3rdGenerationTechniques
Operational Amplifiers: Theory and Practice; James J Roberge; John
Wiley & Sons; 1st Edition http://ocw.mit.edu/resources/res-6-010electronic-feedback-systems-spring-2013/textbook/
Function circuits: design and applications;Yu Jen Wong, William E.
Ott; McGraw-Hill, 1976
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