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 2
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 5
Electronics Products: Activate/control devices using processed information 6
Electronics Products: Transmit and receive information 7
Electronic products Primary function is processing signals/data Signals o Anything that carries information is a signal o chemical signals that control body functions o Electronic products deal with electrical signals which are voltages and currents Speech music scenery chirping of birds gestures 8
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 9
Strain Gage Bridge Vo+ = ((R+DR)/ 2R)V exc Vo- = ((R-DR)/ 2R)V exc Output Difference Signal = (DR/R)V exc, Output Common Mode Signal = V exc /2 10
Some Transducers 11
Nature of Signals: Periodic Analog Signals 12
Problem o Place your finger at the input terminal of an oscilloscope. What do you see? o Ans: 50Hz/60Hz power line frequency signal. 13
Problem o A periodic waveform is shown o Estimate the frequency and the harmonic content of the waveform. 14
Solution 0.1sin100πt+ 0.05sin 300 π t 15
Aperiodic Signals 16
Problem o What can you say about the nature of the signal shown: 17
Spectrum and Bandwidth o Spectrum is the distribution power as a function of frequency o Analog signals are characterized by their spectra. o The frequency range over which most of the signal power is concentrated is called the bandwidth of the signal. 18
Spectra 19
Spectra 20
Problem o Draw the spectrum of the following signal ( )( sin10000) v= 5sin1000t t 21
Solution sin Asin B = cos ( A B) cos( A+ B) 2 Spectrum 22
Characteristics of some signals o Speech signal has a band width of 300 Hz 3 khz o Video signal has a bandwidth of 25 Hz - 5 MHz to 100 MHz o HiFi music has a bandwidth of 20 30 khz o ECG 0.04 to 150 Hz 23
Baseband Signal o Some baseband signals of interest are biomedical, audio and video signals o Baseband signals cannot be transmitted directly over long distances o Output from a transducer is used to modulate a carrier for transmission over long distances 24
Noise o Noise is unwanted electrical or electromagnetic energy that interferes with wanted signal o When we measure ECG signal using electrodes, they also pick up the noise at 50/60 Hz o When the ambient audience created noise is picked up by the microphone in a music performance o Internal noise generated by the electronic components of the electronic circuit performing signal processing function 25
ECG Signal and 50/60Hz Noise Noise dominating the signal Narrow Band 26
Signal with Noise Signal dominating the Noise Narrow Band 27
Signal and Noise o A signal is always contaminated by noise o The unwanted noise will have to be suppressed (filtering) or reduced (cancellation) o Wanted signal may be strengthened with respect to noise (amplification) o 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 28
Signal Processing o Using a megaphone to communicate with a crowd (amplification) o Eliminating or reducing the ambient noise (filtering, and noise cancellation and subtraction) o Selecting a radio station (selection) filtering (bandpass) o Smoke signal, Morse code, drum beats (coding/modulation, A/D conversion/ multiplication) o Reading smoke signals and message sent by Morse Code (Demodulation/Digital to Analog Conversion/ multiplication) 29
Analog signal processing o Amplification of microphone output o Filtering 50 Hz interference from power line in ECG signal o Modulating a carrier with an audio signal (multiplication) o Storing music on a magnetic tape as against this in digital it is stored in memory 30
Why digital signal processing? o Complexity and accuracy can be greatly improved if signals are processed in their digital coded form o DSP leads to great reduction in cost, size, reliability and efficiency o Analog signals are encoded into digital form using analog-to-digital converter o Powerful digital signal processing (DSP) devices are currently available 31
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 32
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. 33
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 34
References 1. 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 2. Operational Amplifiers: Theory and Practice; James J Roberge; John Wiley & Sons; 1st Edition http://ocw.mit.edu/resources/res-6-010- electronic-feedback-systems-spring-2013/textbook/ 3. Function circuits: design and applications; Yu Jen Wong, William E. Ott; McGraw-Hill, 1976 35