 Good morning dear friends and Sachin R. Gengze, Professor and Head, Department of Electronics Engineering at Vulture Institute of Technology, Singapore. In today's short lecture, we are going to have a look at different electrical characteristics of ideal op-ed. The learning outcome of this session will be, after completing this session, the student will be able to explain different important electrical characteristics of ideal op-ed. The content of this session, first we are going to discuss about what is an op-ed and secondly we are going to discuss about what are important electrical characteristics of an ideal op-ed. Let us start with first knowing what is an operational amplifier or which is popularly called as an op-amp. As we already know, op-amp is a directly coupled high gain amplifier. So it has different stages which are directly coupled without any capacitor coupling. Op-amp is available as a single integrated circuit or IC. Different op-amps are available, different ICs are available. And most importantly, op-amp is a very versatile device that can be used to amplify and process DC as well as AC signals. Op-amp can be also used to perform different mathematical operations like addition, subtraction, multiplication, integration on analog signals. Furthermore, we can design different circuits like oscillators or filters, comparators, regulators using op-amp. So as you can see, op-amp can find numerous applications in analog signal processing. Just to have a look how the op-amp has evolved, I think that the first op-amp was introduced in year 1953 and then that op-amp was designed using vacuum tubes. Then the op-amp was designed using solid state discrete component. Then in 1962, it was available as a potted module and then a modern day mini op-amp is available as a DIP IC. Let us have a look at the logical symbol of an op-amp. Op-amp consists of two inputs. One is of course, this is especially this symbol is for op-amp 741, but almost all op-amp will have similar kind of input and output signal. So let us look at the IC 741, what it has. Pin number 2 is an inverting input, pin number 3 is a non-inverting input. So the op-amp has two input, one called as an inverting input and the other one is called as a non-inverting input. Pin number 6 is an output, which is a single ended output. We can take the output with respect to ground and as we know op-amp require two power supply plus VCC and minus VEE. So this is what is a logical symbol or pin diagram for IC 741. So what is an ideal op-amp? An ideal op-amp has a perfect condition to allow it to function as an op-amp with an 100% efficiency. But as we know in real life, no ideal component is available and similarly no ideal op-amp exists. However, if we can get an op-amp, which is performing or showing the characteristic as close as possible to that of an ideal op-amp, then we can use this op-amp to design more efficient circuits for the real world application. So rather we require a practical op-amp, which is as close as an ideal op-amp. So if we want to know what is this ideal op-amp, let us have a look at some of the electrical characteristics of an ideal op-amp. The very first electrical characteristic of an ideal op-amp is that it has infinite input resistance. As we know, the input impedance is the ratio of input voltage to the input current and in case of ideal op-amp, this input impedance is infinite. It means that no current enters into the op-amp and as no current op-amp enters, enters into the op-amp, op-amp do not draw any current and then this avoids the loading effect of the previous stage, that is the stage which is driving an ideal op-amp. So the very first characteristic of ideal op-amp is that its input impedance is infinite. So again, the same thing can be shown like that if the input impedance is infinite, then I1, which is a current entering into the non-inverting terminal, I2, which is current entering into the inverting terminal, both of these terminals, both of these currents are ideally supposed to be zero. Same characteristic of ideal op-amp is that its output resistance is or output impedance is zero. The output impedance is assumed to be zero and then that op-amp is acting as a perfect internal voltage source with no internal resistance so that whatever the output is given by the op-amp, the entire output appears across the load and then in other words, the op-amp can supply as much current necessary into the loop. The another way to look at this characteristic that the output voltage V0 is independent of the current drawn from the output, hence the output can drive infinite other devices. Of course, this is only an ideal characteristic and practically we know that there no device can drive infinite other devices. The third characteristic of an ideal op-amp is that the open loop voltage gain of an ideal op-amp is infinite. As we know, op-amp always try to amplify the differential voltage VD, which is nothing but the voltage difference between inverting and non-inverting input of an op-amp. Now if the voltage, open loop voltage gain of an op-amp is infinite, it simply means that when the output voltage is some finite voltage, the differential voltage input voltage must be 0. So in that case, we can say also that the inverting and non-inverting terminals of op-amp are always at the same voltage. So this is very important electrical characteristic of an ideal op-amp that the open loop voltage gain of an op-amp is infinite. Practically it is not infinite, but it is having very high value. Now we can pause the video for a while and can answer this question. We always think that an amplifier for any amplifier, we should have a very high gain. So now let us assume that I have an amplifier, an ideal op-amp operational amplifier which has an infinite gain. So do you really think, dear student, do you really think that is it useful to have any amplifier like an ideal op-amp which is having an infinite gain? Can we design any circuit or can we find any practical application of an amplifier which is having an infinite gain? So you can pause the video for a while and answer this question. I think you must have found out answer whether if I have an amplifier which is having an infinite gain, can I find any practical application for that? Let us move to the next characteristic of an ideal op-amp and we can say that ideal op-amp has infinite bandwidth and zero phase shift. Now we know that what is a bandwidth is the range of the frequencies for which the amplifier can offer a constant gain. So when I say that an ideal operational amplifier has an infinite bandwidth, it means that an op-amp can amplify any signal with the frequency right from DC to the highest AC with the same gain. So op-amp will offer the same gain for entire spectrum right from DC to the highest AC. So regardless of the frequency of the input signal applied to the op-amp, the gain offered by the op-amp is going to be constant for all these signals. Secondly, the phase shift is zero. It simply means that the input signal and output signal, the input signal applied to the op-amp and output of the op-amp are in phase. The next characteristic of an op-amp is called as a zero offset voltage. Zero offset voltage simply means that when I apply the inverting input and non-inverting input to zero, in other words, if I make the inverting input and non-inverting input to the zero, the output of the op-amp is also zero. So let us come to the end of the session and you can discuss about two questions. Is it possible to have an ideal op-amp? Can we design an ideal op-amp? And if no, why? And even if a real op-amp is available, will it be useful as an amplifier? So in real, if we have an ideal op-amp, can we use it for any of the practical application? So these are the two references which you can refer to and thank you very much.