 I am K Radhakshan Rao currently working in Texas Instruments India in Bangalore. I am going to talk about analog circuits and systems a basic course in electronics. An electronic system you can see a large number of these electronic products which are popular today you can easily identify the significance of all these products they are made up of two basic parts these can be classified as analog mostly today analog front end and analog back end and in between we have digital signal processors. So most of the products that are mentioned here are comprising of this kind of architecture out of this we are going to concentrate on depart on analog and the interface. So in order to understand the current role of analog signal processing we are going to first present you the various products okay and the architecture the structure of these various products and even before that we should really know what is signal processing in analog domain what is it in digital domain what portion of signal processing is still done in analog domain in fact earlier all these products used to be totally analog circuit and analog system based today it is so that the digital signal processing has dominated over analog signal processing and most of the signal processing activity is confined to only digital signal processors then we may wonder where analog signal processing comes into picture it is these areas which are going to be touched upon in this course. So what is the influence of current day technology on product design that also we should know and therefore first we will concentrate on why is it that digital signal processors have become popular in signal processing as against analog signal processing and how the product cost has come down because of adoption of DSPs and how the product cost is getting concentrated mostly on analog signal processing parts and how significant it is necessary for us to learn analog signal processing even today. So let us consider these products what do you think is the product that is going to be ah profitable to produce it will be a product which is popular with the masses okay it is important that the demand for the product should be large in order to bring down the cost of the product itself and therefore the technology today technology of fabrication of integrated circuit today has helped us to bring down the cost of most of these electronics that is necessary for these products considerably and just take why the cost of the product has come down and the integrated circuit technology also has facilitated reliability to increase and the signal processing power has been refined to that extent that it can be done mostly by digital signal processing okay very accurately precisely and totally. Now let us consider these some of these products cell phone for example is one of the product that has become most popular today almost everybody would like to possess a cell phone because it is helping the individual in planning his day to day activity regarding his office or home or entertainment anything is possible with the cell phone it is nothing but a transmitter and a receiver facilitating communication with anybody anywhere and it is also a means of gathering information. So all these facilities made available in such small space okay which can be easily carried by an individual that is why this product has become very popular and each individual has nowadays at least one or two cell phones with him. So likewise the other products are also popular but not so popular as that of cell phone computers for example another product that is very popular with the masses is the wrist watch the wrist watch production got revolutionized with the advent of integrated circuit fabrication and digital signal processing activity becoming prominent. So electronic product what do they do they have to send signals will let us see what signals mean send signals and then process signals and preserve signal in some form or other right in memory for example sense process present and display for example audio signal it can be also outputted using oscilloscope okay it can be sort of preserved in the memory it can be displayed okay in a recorder so preserve process storage these are the activities of signal processing you can see an ECG equipment with this indicating the recording okay and this is the sensor okay some of the other electronic products are for storing information these days you can see the memory cards and then USB a drives okay and USB stick DVD etc other electronic products are for entertainment radio and television these have been in existence for long originally these are totally analog these days digital transmissions also will be happening all over the world and most of the signal processing activity of both audio and video these are called base band signals take place okay digitally. We have an important industrial robot robotics where these sensed signals are processed and activate okay for operating machinery okay these are the other electronic products transmission and reception this is a transceiver right primarily for a transmitting your telephone call and receiving your friends message okay as a telephone information or message and further it has also FM receiver in it okay and mp3 player okay and video production and display all these things are made possible within this piece of equipment this is the satellite communication that is prevalent today electronic products these primarily process signals and what are these signals primary function is processing signals and data signals can be identified as that that carry information information can be speech information music information scenery chipping of birds gestures these are all signals chemical signals that control body functions these also are signals electronic products deal with electrical signals which are voltages and currents so these naturally formed signals have to be converted into electrical voltages or currents that is done by what is called a transducer electric signal electrical signals are derived from the real world through trans users which convert a physical or chemical variable into an electrical signal trans users produce electric analog signals which are continuous functions of independent variables independent variables can be just pressure force okay and acceleration okay and sound picture so these are converted by transducers to analog signals the real world has only analog signals available as the output of the transducer if tomorrow you can get from the transducer directly digital signal then analog does not have any role in signal processing such a thing is unlikely to happen. So we have here an example of a strain gauge which is primarily used for force acceleration pressure measurement so here what is done is it is having the trans users arranged in the form of a bridge these are all strain gauges with resistance R as nominal values when some force changes the value of the resistance to R – delta R R press delta R depending on where you are placing the strain gauges one can be subject to compression another expansion and therefore we have the change in a resistance happening and that is sensed as a differential signal this is the common practice so here this voltage difference is called the differential signal and it will be V naught plus minus V naught minus these are called the actually node voltages at these points and the variation in the resistance appears as a voltage across this the common node voltage at these two nodes is rejected is supposed to be rejected by the amplifier that is amplifying the differential signal so output difference signal is equal to delta R by R into V excitation so here V excitation by 2 is the common mode signal at both the points so this is one form of transducer giving an output which can be amplified further some of the other transducers are microphone which is converting the audio signal in signal into electrical signal this is the charge couple device which converts the image into electrical signal right camera now talking of nature of signals there are what are called periodic signal this is a periodic signal it repeats itself with a time period of T or a frequency of omega this is the time duration called time period one over time period is the frequency now you can see that this frequency is lower than this this is a higher frequency signal these are sine waves sine wave simply means it is producing a single tone suppose I whistle this whistle appears if you apply to the oscilloscope apply the output of the microphone to the oscilloscope will see it appearing as a sine wave so that is the periodic signal these are these signals are necessary to be generated in electronics in order to test your amplifier okay these are therefore called test signals which are primarily used to understand how linear your amplifier is if the amplifier is not linear this signal apart from getting amplified just gets distorted also which means it produces harmonics so looking at the harmonic content one can say whether it is linear or not how linear it is now this is almost double the frequency of this actually I think for one period here you have almost two such harmonics appearing so if you add these two you will get this kind of periodic signal which is having fundamental which is this and its harmonic now other test signals are which are popular are the triangle as shown here this is called the saw tooth this is called the square these are primarily generated in order to test most of the electronic components if you place your finger at the input terminal of an oscilloscope what do you see you normally pick up the power line frequency signal which is at 50 hertz or 60 hertz depending upon the region where you are living and therefore the signal that you get picked up is of this frequency it is about 20 milliseconds time period 50 hertz corresponds to 20 milliseconds okay and it may have as you see here symmetry around this half the time period indicating predominant occurrence of second harmonic so this mathematical expression that I had put here is 0.1 sign 100 pi t plus 0.05 sign 200 pi t so it has certain amount of harmonic content in it introduced so this is somewhat looking like what gets picked up when you put your finger to the oscilloscope input terminals so you have to understand signals before you start processing them that is why we are going through first understanding what is signal processing what are the signals what is noise okay later on we will see what it is a periodic waveform is shown here estimate the frequency of the waveform and the harmonic content of the waveform now you can just look at this waveform the time period is again 20 milliseconds so immediately you can conclude that the frequency is 50 hertz and you can see that if I draw the waveform here like this right it gives me a third harmonic okay and that harmonic content will get added to the fundamental here and get subtracted from the fundamental here so it gives a dip like this and the dip is symmetric around half time period so this clearly indicates that there is a third harmonic content dominating you had seen earlier how when second harmonic content dominates the waveform as a symmetry around this okay whereas here the symmetry is occurring around this point t by 4 okay so this is the kind of what is that intuitive approach that you should take in understanding what is happening okay without really going into the mathematics of it now the same thing can be mathematically indicated as 0.1 sin 100 pi t plus 0.05 sin 300 pi t so you will see that this is the third harmonic content what is an a periodic signal now when I just ring the bell the bell sound keeps on decaying you can see that this is the process of decay with respect to time the signal strength the decay is okay exponentially with respect to time such a signal is called a periodic signal there is no periodicity associated with it this is a randomly varying signal there is no time period that I can identify okay at any point of time so that is called a periodic signal okay so there is no periodicity associated now this is the mathematical expression a to power minus 1000 t sin 2 pi 1000 t means this is a sort of oscillation sin wave decaying exponentially you can see exponential decay which is the envelope okay so this is a decaying envelope this kind of sound gets produced when bell is rang or when you activate cantilever okay so it resonates and the amplitude of vibration keeps on decreasing exponentially now you have to also learn about spectrum and bandwidth every signal has a certain limited bandwidth spectrum is the distribution of power as a function of frequency power of the signal components okay as a function of frequency analog signals are characterized by their spectrum the frequency range over which most of the signal power is concentrated is called the bandwidth of the signal it is an important thing in practice that you should know about if you just take a sine wave this is a sine wave it has a sort of spectrum uniquely defined at a specific frequency that is 100 for example this is 100 hertz okay sine wave so it has a power only at 100 hertz these are called tones right this is the double the frequency 100 200 so it has a spectrum here right this one is I think triple the frequency no 4 times the frequency we have spectrum at 400 hertz so a combination of all these 3 is the composite time signal as indicated here and it has spectrum at all these points add addition of all these powers so this is the way you will be able to identify the various types of signals that you will encounter in fact this is a problem here so here you can see that this is the spectrum of some general signal what can you say about this corresponds to the spectrum of what is called white noise it is going to be uniformly distributed all over the frequency range this is what is available as white noise and over that normally you have this which is called narrow band noise that is it is having power mostly concentrated around this single frequency distributed on either side of that particular center frequency so it is spread over a band so this is called narrow band signal most of the machine vibrations for example air conditioner vibration etc produce this kind of narrow band noise now let us consider a voltage which is 5000T into sign 10000T that is a multiplication of two frequencies 1000 and 10000 what happens to the spectrum of the signal you can just see that sign A sign B is cos A – B – cos A plus B by 2 that means this kind of multiplication of two frequencies produces A – B okay component frequency component and A plus B component so here is it is indicated this 1000 multiplied by 10000 has produced 1.1 which is A plus B and 1 – 0.1 which is 0.9 K these are called side bands this is what is produced by double side band kind of modulation double side band carrier is absent in AM for example this carrier is going to be present okay predominantly to facilitate detection and these two side bands also get transmitted by the signal speech signal characteristics of some signal speech signal which is important not music this is confined to 300 hertz to 3 kilo hertz where you are able to identify the individuals voice okay and identify the message exactly the quality of the speech may not be all that good okay but it is decipherable as the correct message video signal has a bandwidth on the other hand starting from very low frequency 25 hertz up to about 5 to 5 mega hertz till 100 mega hertz for high definition images high free music on the other hand has bandwidth from 20 hertz to 30 kilo hertz these are the range of frequencies that earlier with okay before starting signal processing activity you should be able to identify what is quality music what is speech what is video easy the signals have very low frequency 0.04 hertz to 150 hertz the message is contained in that the rest of the band contains noise okay and that noise has to be removed when you are processing these signals some base band signals of interest are biomedical ECG is what we have shown audio and video signal these are called base band signals base band signals are pretty normally wide band and therefore cannot be transmitted directly over long distances output from transducer is used to modulate a carrier for transmission over long distances this technique of giving the message on to a carrier so that that can be carried for a large distance is called a coding technique that you are transferring the message from one frequency domain to another frequency domain by shifting it using a carrier so output from transducer is used to modulate you consider so in order to get back the information you have to demodulate okay which is again shifting it from the carrier to the base band let us try to understand what noise is 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 hertz 50 or 60 hertz when the ambient audience creates created noise picked up by the microphone okay in a music performance music is the information that we want to listen to however the ambient audience also create some kind of noise which gets picked up by the same microphone that is amplifying the musicians music so that is noise similarly in the case of ECG signal when the electrodes pick up the ECG waveform we will see later on when we are discussing the transducer arrangement in a ECG it also picks up the 50 hertz power line frequency which is a close to it internal noise generated by electronic components of the electronic circuit also add to the noise this can occur as a white band noise all over the frequency range white noise it is called let us look at this this is the typical ECG signal which most of you would have seen in your ECG recording okay and this is of great help for the doctor to diagnose some problem with your heart now this signal gets mixed up with these 50 hertz power line pickup and you can see that the signal strand may be of the order of hundreds of micro volts is sitting on the power line pickup which may be of the order of tens of millivolts so the power line frequency is 50 hertz therefore it is a narrow band noise within the bandwidth of the ECG signal so this is pretty troublesome to remove we will see how to remove it using a filter later on. So in that case before amplifying it is better to get rid of these predominant noise for example 50 hertz signal in our this thing it is better to sort of get rid of this even before amplification of the wanted signal is done otherwise the amplifier itself may go to saturation because of the noise so this is the important aspect this has to be done using analog filters only okay we cannot postpone this to digital filtering etc. Signal with noise but noise is not so dominant this is the noise this is not so dominant compared to the signal you see this may be the predominant signal that we want to amplify in this case you can actually effort to amplify straight away the signal because the noise is not going to drive it to saturation in this particular case. So however if you have noise dominating over signal it is important that you have to somehow get rid of this noise either by filtering or cancellation okay before you amplify a signal is most of the time contaminated by noise the unwanted noise will have to be suppressed that suppressing the noise is done by filtering or reduced that is by cancellation right wanted signal may be strengthened with respect to noise okay that is called amplification. Improvement to signal to noise ratio SNR is one of the purposes of signal processing SNR improvement 10 log signal power a noise power in decimal right. So this is always expressed in terms of decibels of power ratio of signal and noise now what is signal processing using a megaphone to communicate with crowd that is a non electronic way of straight away amplifying a megaphone but we like to use electronic means of doing this eliminating or reducing the ambient noise filtering this is called filtering and noise cancellation and subtraction that is if it is possible to cancel this without using electronic means that has to be done first we will see how this can be done selecting a radio station that is if you want to particularly receive a specific station that is selection that is done by filtering again band pass filter. So you will see that filtering is a major function of a front end that is to improve signal to noise ratio. Smoke signal this is a way of encoding most code was the first one to almost deploy a digital communication okay for most of the time communicating telegraphically drum beats that is again coding the information in some form and transmitting over distance as sound okay. Smoke signal is a video or picture signal right. Now similarly a to D conversion okay or multiplication is a means of coding okay analog to digital conversion is a technique for coding analog information in digital form and that is normally adopted in present day signal processing. Reading smoke signals and message sent by most code is equivalent to demodulation digital to analog conversion again it is involving mathematical process which is multiplication. So multiplication is a technique of coding basically the mathematical aspect of modulation demodulation mixing all these things mean the same thing multiplication that is why it is imperative that we should learn about how signal processing involves multiplication most of the time. Amplification of microphone output that is analog signal processing filtering 50 hertz interference from power line in ECG signal this also is signal processing modulating a carrier with an audio signal or multiplication storing music on a magnetic tape as against this in digital it is stored in memory after getting it converted to digital form. So the analog form of storage has almost vanish okay and we have digital storage media DVDs CDs and other things that are becoming important today. Now why would one go for digital signal processing predominantly complexity in accuracy can be greatly improved in if signals are processed in their digital coded form. So DSPs today have advanced so much that most of the accurate precise signal processing activity can be carried out in DSPs. Analog signals are encoded therefore to digital form using A to D converters powerful digital signal processing devices are currently available and after conversion the digital form of storage okay is most reliable because it is amenable to error correction and then ahh resurrection okay of the original signal. So these are all possible in the case of DSPs and therefore DSPs are doing now 99.99% of the signal processing activity that is required in any system it is that 0.01% of the activity which is carried out that is carried out by analog signal processing but it is still important because it is different than and the back end design of analog circuits and systems require performing of these following functions signal processing functions including amplification addition subtraction integration comparison filtering multiplication and these are the signal processing activity I have already pointed out how ahh filtering comes into picture how multiplication is nothing but modulation demodulation mixing frequency transition frequency multiplication and all these things mean the same thing multiplication signal generation is important for test purposes generating sinusoidal signals clock signal is an important aspect of signal processing in DSPs. Now it is almost imitating signal processing activity in the human body that even the human body has a clock so there is nothing but the heartbeat okay which makes most of the ahh other parts function in synchronism with the heartbeat okay. Similarly the DSPs also work with predominantly ahh important clock okay and this clock is to be generated at signal generation then sign waves required for testing amplifiers etc A to D converters D to A converters all these things are to be tested out and signal generation is an important activity of signal processing interfacing including sample hold A to D conversion D to A conversion ahh the so called mixed mode activities which are important power supply management this is something that has been ahh mostly ignored but this is the predominant the electronic ahh part that is important in almost every electronic equipment okay and these are the analog circuits and system that we have to understand the aim of the course analog circuits and systems part 1 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. So ahh you might be seeing that ahh mention of transistor is not there but it is included in what is called amplifiers transistors and that is both bipolar and MOSFETs form part of our active devices which are amplifiers okay. Course outcomes is important to know beforehand what are the ahh outcomes of the course okay as we go through the entire course understand the characteristics of linear one port okay one port means two terminal and two port that is four terminal signal processing networks. So we are starting with a generalized ahh sort of network theory approach towards understanding signal processing activity. So we are starting with one port and two port signal processing networks model one port devices including RLC and diodes and amplifiers op amps comparators multipliers BJTs and FETs how to model this we are dealing with millions billions of these active devices in most of the electronic systems today. So how simply understand these models in order to understand the complex behavior of our electronic systems today that is the important part understand how negative and positive feedback influence the behavior of analog circuits and systems. Negative feedback and positive feedback are the concepts which have to be totally understood in electronics okay in order to understand most of the system design that we are confronted with right almost every system today has feedback okay both negative and positive we have to understand where these concepts are important. Design voltage amplifiers called voltage control voltage sources current amplifiers called current control current sources trans resistance amplifiers and trans conductance amplifiers these are called current control voltage sources and voltage control current sources these are the basic amplifiers that we have to understand how to design using available ahh components like transistors. Design analog filters we have already seen how to design a band pass filter tunable band pass filter or tunable band stop filter to select certain band of frequencies or reject certain band of frequencies design waveform generators like sine wave generator square wave generator triangular wave generator etc for testing purposes and ahh the competencies what are the things that you should understand in the course at the end of the course the students should be able to understand the structure of present day electronic products you should know what is the architecture of any particular product identify analog signal conditioning and processing functions in instrumentation control and communication these are the three things instrumentation control and communication right ahh activities that go on in electronic systems today model 1 port devices these resistors inductors and capacitors and diodes characterized linear 2 port networks by YZGH parameters and this is called immittance parameter which is also a common parameter which is used by micro engineers macro model amplifiers op amps comparators and multipliers we are going to use transistors to devise these amplifiers op amps and comparators and multipliers before even we understand what transistor is we should know how to use these blocks these are the sub blocks which make up most of the in fact 100% of analog signal processing activity can be carried out just by using these blocks and one should be able to understand how these can be used macro model BJT and FET in a very simple manner so that we can handle millions of these devices and still become comfortable understand how negative and positive feedback influence the behavior of circuits using op amps comparators and multipliers design VCVS VCCS using op amps VCVS means voltage amplifier VCCS is a transconductance amplifier the CCVS is the dual of VCCS VCVS dual of that is CCVS how to design these current amplifiers and trans resistance amplifiers using any device active device today it is MOSFET tomorrow it may be some nano device it does not matter once we know how these are designed we can actually use these devices in most of the electronic applications and therefore these are technology independent definitions of active devices understand the concept of ideal filters and approximate mathematical representation of filters design first order and second order passive filters design active filters also understand why active filters are important today design active filters using bike quads we will come to know what these bike quads are using switched capacity techniques how to design IC filters understand how frequency stable sinusoidal oscillations can be generated how amplitude stable and frequency stable tunable sinusoidal oscillators which are I mean basically VCOs okay which are nothing but FN generators can be obtained understand the role of regenerative feedback in comparators positive feedback how it can be used to obtain an important block called speed trigger design amplitude stable frequency stable tunable non-sinusoidal oscillators like square wave triangular wave etc. Now these are the references the references deal with primarily okay op amp application this is a multiplier application all integrated circuit applications are done well in this book analog integrated circuit another book by Jacob this is an Indian book on application of linear integration so it is application of integrated circuit which is first to be thought in understanding analog systems op amp circuit design right so application of op amp is primarily dealt with very well in this book and another good book on application of op amp is by Robert this is to deal with function circuits mostly multiplier applications done very well this is a companion value this along with this deal with most of the system applications analog system applications done well we have to understand that in this lecture we have learnt it is important to know what portion of analog signal processing is still important like the front end filtering then noise cancellation and also back end filtering and distortion reduction in power amplifiers is still done in analog and communication users multipliers or mixers or modulators as different and signal processing activity to bring down the information in the carrier down to the base band and that is an important activity that is still done by analog circuits and we have also seen something about signals that are important signals like biomedical signals audio signals video signals what are the bandwidths for these signals the rest of the region we will eliminate the noise that is occurring in the rest of the outside the band thereby improve signal to noise ratio we also know now something about the sensors like the bridge sensor strain gauge sensor how instrumentation amplifier becomes necessary to be designed for rejecting the common mode signal and amplifying only the differential signal so these are the various activities that become necessary and the need for understanding signals and noise is imperative okay before we start anything on active devices understanding active devices that do signal processing.