[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:01.16,0:00:03.36,Default,,0000,0000,0000,,>> Hi. In this next set of videos,
Dialogue: 0,0:00:03.36,0:00:05.58,Default,,0000,0000,0000,,we're going to take a look at little electronic devices known as
Dialogue: 0,0:00:05.58,0:00:07.86,Default,,0000,0000,0000,,operational amplifiers. My name is Lee Brinton.
Dialogue: 0,0:00:07.86,0:00:10.86,Default,,0000,0000,0000,,I'm an Electrical Engineering Instructor at Salt Lake Community College,
Dialogue: 0,0:00:10.86,0:00:14.12,Default,,0000,0000,0000,,and this is an Introduction to Electrical and Computer Engineering.
Dialogue: 0,0:00:14.12,0:00:19.22,Default,,0000,0000,0000,,Operational Amplifiers are little bugs, little silicon devices,
Dialogue: 0,0:00:19.22,0:00:22.05,Default,,0000,0000,0000,,and in these videos,
Dialogue: 0,0:00:22.05,0:00:24.82,Default,,0000,0000,0000,,we are going to be looking at what they are and what are they're good for.
Dialogue: 0,0:00:24.82,0:00:27.81,Default,,0000,0000,0000,,We'll introduce the ideal Op Amp approximations.
Dialogue: 0,0:00:27.81,0:00:31.42,Default,,0000,0000,0000,,We'll then look at a number of common Op Amp configurations,
Dialogue: 0,0:00:31.42,0:00:35.98,Default,,0000,0000,0000,,the applications that op-amps are frequently used in.
Dialogue: 0,0:00:35.98,0:00:37.94,Default,,0000,0000,0000,,So what is an Op Amp?
Dialogue: 0,0:00:37.94,0:00:40.84,Default,,0000,0000,0000,,An operational amplifier is, as I mentioned,
Dialogue: 0,0:00:40.84,0:00:43.61,Default,,0000,0000,0000,,a semiconductor circuit consisting of
Dialogue: 0,0:00:43.61,0:00:46.96,Default,,0000,0000,0000,,a bunch of transistors and some capacitors and resistors.
Dialogue: 0,0:00:46.96,0:00:54.40,Default,,0000,0000,0000,,But the main idea is that they have two input terminals and an output.
Dialogue: 0,0:00:54.40,0:00:58.38,Default,,0000,0000,0000,,The output terminal becomes a scaled version.
Dialogue: 0,0:00:58.38,0:01:03.65,Default,,0000,0000,0000,,By scaled, we mean a version of the input that is in some way changed.
Dialogue: 0,0:01:03.65,0:01:05.62,Default,,0000,0000,0000,,The output is a function of the input.
Dialogue: 0,0:01:05.62,0:01:11.22,Default,,0000,0000,0000,,It's either going to be amplified or have some other linear operation performed upon it.
Dialogue: 0,0:01:11.22,0:01:13.08,Default,,0000,0000,0000,,Now, at our level,
Dialogue: 0,0:01:13.08,0:01:17.54,Default,,0000,0000,0000,,we're not going to be concerned with all of these internal workings.
Dialogue: 0,0:01:17.54,0:01:24.29,Default,,0000,0000,0000,,We're going to be treating these as a black box device that has inputs and an output,
Dialogue: 0,0:01:24.29,0:01:28.76,Default,,0000,0000,0000,,and we'll work with them in an ideal environment.
Dialogue: 0,0:01:28.76,0:01:32.81,Default,,0000,0000,0000,,So, first of all, op-amps are electronic devices.
Dialogue: 0,0:01:32.81,0:01:37.31,Default,,0000,0000,0000,,They come in silicon semiconductor packaging.
Dialogue: 0,0:01:37.31,0:01:40.98,Default,,0000,0000,0000,,Here's a picture of an eight pin chip.
Dialogue: 0,0:01:40.98,0:01:43.94,Default,,0000,0000,0000,,They come in eight-pin, 14-pin.
Dialogue: 0,0:01:43.94,0:01:47.33,Default,,0000,0000,0000,,Suffice to say that when you're working with operational amplifiers,
Dialogue: 0,0:01:47.33,0:01:49.31,Default,,0000,0000,0000,,you'll be taking a silicon chip and plugging
Dialogue: 0,0:01:49.31,0:01:51.82,Default,,0000,0000,0000,,it into a protoboard and working with it that way.
Dialogue: 0,0:01:51.82,0:01:56.25,Default,,0000,0000,0000,,Internally, functionally, the op-amp,
Dialogue: 0,0:01:56.25,0:01:58.13,Default,,0000,0000,0000,,as I mentioned, has two inputs.
Dialogue: 0,0:01:58.13,0:02:00.40,Default,,0000,0000,0000,,One we're going to designate with a minus sign.
Dialogue: 0,0:02:00.40,0:02:03.39,Default,,0000,0000,0000,,It's known as the inverting terminal.
Dialogue: 0,0:02:08.59,0:02:11.44,Default,,0000,0000,0000,,For the inverting input,
Dialogue: 0,0:02:11.44,0:02:14.83,Default,,0000,0000,0000,,one of them is designated with a positive sign that's known as
Dialogue: 0,0:02:14.83,0:02:22.80,Default,,0000,0000,0000,,the non-inverting terminal or input,
Dialogue: 0,0:02:22.80,0:02:26.60,Default,,0000,0000,0000,,and then there is the output.
Dialogue: 0,0:02:26.60,0:02:28.88,Default,,0000,0000,0000,,But these devices are electrical devices,
Dialogue: 0,0:02:28.88,0:02:30.40,Default,,0000,0000,0000,,and so they also need to be plugged in.
Dialogue: 0,0:02:30.40,0:02:32.22,Default,,0000,0000,0000,,They need to have power supplies.
Dialogue: 0,0:02:32.22,0:02:40.81,Default,,0000,0000,0000,,So, the op-amp will also have a positive voltage source and a negative voltage source.
Dialogue: 0,0:02:40.81,0:02:49.64,Default,,0000,0000,0000,,This little diagram here is meant to show that inside this chip there is one op-amp.
Dialogue: 0,0:02:49.64,0:02:55.90,Default,,0000,0000,0000,,First of all, pin one and pin five are not connected to anything.
Dialogue: 0,0:02:55.90,0:03:01.34,Default,,0000,0000,0000,,This eight-pin chip had two pins that weren't needed and so there just to be ignored.
Dialogue: 0,0:03:01.34,0:03:06.19,Default,,0000,0000,0000,,You'll also notice that on the chip there's a marking.
Dialogue: 0,0:03:06.19,0:03:10.80,Default,,0000,0000,0000,,Usually, there's a little dot closest to the number one pin.
Dialogue: 0,0:03:10.80,0:03:14.22,Default,,0000,0000,0000,,Sometimes you'll see a little notch taken out of the top.
Dialogue: 0,0:03:14.22,0:03:17.42,Default,,0000,0000,0000,,Whatever it is, there'll be something identifying pin one,
Dialogue: 0,0:03:17.42,0:03:19.56,Default,,0000,0000,0000,,and then they number the pins one, two, three,
Dialogue: 0,0:03:19.56,0:03:21.14,Default,,0000,0000,0000,,four coming down one side,
Dialogue: 0,0:03:21.14,0:03:23.34,Default,,0000,0000,0000,,and then going up the other side.
Dialogue: 0,0:03:23.34,0:03:27.62,Default,,0000,0000,0000,,So, what this diagram is telling us is that pin two,
Dialogue: 0,0:03:27.62,0:03:29.39,Default,,0000,0000,0000,,this pin right here,
Dialogue: 0,0:03:29.39,0:03:31.58,Default,,0000,0000,0000,,is connected to the inverting terminal,
Dialogue: 0,0:03:31.58,0:03:34.62,Default,,0000,0000,0000,,pin three is connected to the non-inverting terminal,
Dialogue: 0,0:03:34.62,0:03:39.08,Default,,0000,0000,0000,,pin six is where we'll be looking to get our output voltage,
Dialogue: 0,0:03:39.08,0:03:43.01,Default,,0000,0000,0000,,and pin four and pin seven will be
Dialogue: 0,0:03:43.01,0:03:47.92,Default,,0000,0000,0000,,tied to our negative and positive voltages respectively.
Dialogue: 0,0:03:47.92,0:03:55.43,Default,,0000,0000,0000,,Schematically, we have the op-amp showing wires coming to the input terminals,
Dialogue: 0,0:03:55.43,0:03:57.35,Default,,0000,0000,0000,,a wire going from the output terminal.
Dialogue: 0,0:03:57.35,0:04:02.57,Default,,0000,0000,0000,,This also shows the negative terminal reference to zero plus to minus,
Dialogue: 0,0:04:02.57,0:04:06.17,Default,,0000,0000,0000,,so it's dropping down to a negative voltage here for the power supply
Dialogue: 0,0:04:06.17,0:04:10.97,Default,,0000,0000,0000,,and from ground going up to a positive voltage.
Dialogue: 0,0:04:10.97,0:04:15.70,Default,,0000,0000,0000,,So, the op-amp does have both a positive and negative voltage powering it.
Dialogue: 0,0:04:15.70,0:04:19.31,Default,,0000,0000,0000,,Generally speaking, in a circuit schematic,
Dialogue: 0,0:04:19.31,0:04:22.62,Default,,0000,0000,0000,,we won't show the voltage sources,
Dialogue: 0,0:04:22.62,0:04:25.34,Default,,0000,0000,0000,,the pins where the power supplies are connected.
Dialogue: 0,0:04:25.34,0:04:29.93,Default,,0000,0000,0000,,We know that there's got to be a power source to them just like an amplifier in
Dialogue: 0,0:04:29.93,0:04:35.28,Default,,0000,0000,0000,,a guitar you plug it in and that's where it gets the power to do the amplification.
Dialogue: 0,0:04:37.07,0:04:41.22,Default,,0000,0000,0000,,These op-amps, again, let's just draw the symbol
Dialogue: 0,0:04:41.22,0:04:48.30,Default,,0000,0000,0000,,here with it's inverting and it's non-inverting terminal.
Dialogue: 0,0:04:48.30,0:04:51.27,Default,,0000,0000,0000,,The voltage at the non-inverting terminal,
Dialogue: 0,0:04:51.27,0:04:54.54,Default,,0000,0000,0000,,we're going to refer to as V sub n, and this,
Dialogue: 0,0:04:54.54,0:04:57.37,Default,,0000,0000,0000,,of course, will be referenced to a ground,
Dialogue: 0,0:04:57.37,0:04:58.46,Default,,0000,0000,0000,,so it's a node voltage.
Dialogue: 0,0:04:58.46,0:05:03.24,Default,,0000,0000,0000,,The voltage at the inverting terminal relative to ground we're going to call V sub n.
Dialogue: 0,0:05:03.24,0:05:09.02,Default,,0000,0000,0000,,The voltage at the non-inverting terminal we're going to refer to as V sub p.
Dialogue: 0,0:05:09.02,0:05:11.65,Default,,0000,0000,0000,,V sub n, it's not great nomenclature,
Dialogue: 0,0:05:11.65,0:05:13.18,Default,,0000,0000,0000,,but the n refers to the negative sign,
Dialogue: 0,0:05:13.18,0:05:16.02,Default,,0000,0000,0000,,the p refers to the positive sign.
Dialogue: 0,0:05:16.02,0:05:25.84,Default,,0000,0000,0000,,The op-amp is designed to perform the operation so that the output is equal to A,
Dialogue: 0,0:05:25.84,0:05:31.90,Default,,0000,0000,0000,,some constant, times the difference between those two voltages.
Dialogue: 0,0:05:31.90,0:05:37.09,Default,,0000,0000,0000,,So, A known as the open-loop gain of the amplifier times
Dialogue: 0,0:05:37.09,0:05:42.43,Default,,0000,0000,0000,,the voltage at the p or the non-inverting terminal minus
Dialogue: 0,0:05:42.43,0:05:48.22,Default,,0000,0000,0000,,the voltage at the n terminal will give you
Dialogue: 0,0:05:48.22,0:05:55.00,Default,,0000,0000,0000,,the output or the output is then this gain term multiplying that difference.
Dialogue: 0,0:05:55.00,0:06:03.16,Default,,0000,0000,0000,,This graph here shows the output V out as a function of that difference.
Dialogue: 0,0:06:03.16,0:06:05.77,Default,,0000,0000,0000,,The output is a linear.
Dialogue: 0,0:06:05.77,0:06:10.94,Default,,0000,0000,0000,,It's just a scaled version of that difference over
Dialogue: 0,0:06:10.94,0:06:16.79,Default,,0000,0000,0000,,quite a range of input values or range of Vp minus Vn values.
Dialogue: 0,0:06:16.79,0:06:26.20,Default,,0000,0000,0000,,But when the output gets to the positive source, the positive side,
Dialogue: 0,0:06:26.20,0:06:32.93,Default,,0000,0000,0000,,or when the output would exceed the negative source or power supply,
Dialogue: 0,0:06:32.93,0:06:35.84,Default,,0000,0000,0000,,the amplifier is set to saturate.
Dialogue: 0,0:06:35.84,0:06:38.07,Default,,0000,0000,0000,,It's impossible for, again,
Dialogue: 0,0:06:38.07,0:06:39.21,Default,,0000,0000,0000,,let's just draw those in here.
Dialogue: 0,0:06:39.21,0:06:41.95,Default,,0000,0000,0000,,This is positive Vcc,
Dialogue: 0,0:06:41.95,0:06:46.20,Default,,0000,0000,0000,,the positive power supply, and negative Vcc.
Dialogue: 0,0:06:46.20,0:06:51.44,Default,,0000,0000,0000,,These are the sources of the voltage and the output can't exceed those sources.
Dialogue: 0,0:06:51.44,0:06:56.87,Default,,0000,0000,0000,,So, if Vp minus V sub n were to get large enough that when it was multiplied by
Dialogue: 0,0:06:56.87,0:07:03.93,Default,,0000,0000,0000,,A the output would exceed positive Vcc or be less than negative Vcc,
Dialogue: 0,0:07:03.93,0:07:06.87,Default,,0000,0000,0000,,the amplifier then saturates.
Dialogue: 0,0:07:06.87,0:07:11.32,Default,,0000,0000,0000,,The output becomes simply the source voltage.
Dialogue: 0,0:07:11.32,0:07:14.20,Default,,0000,0000,0000,,It can't go any further than the source voltage.
Dialogue: 0,0:07:14.20,0:07:20.34,Default,,0000,0000,0000,,Sometimes the source voltages are referred to as the rail voltages.
Dialogue: 0,0:07:20.44,0:07:27.72,Default,,0000,0000,0000,,You can think of them as something like two rails between which we must operate.
Dialogue: 0,0:07:27.72,0:07:31.12,Default,,0000,0000,0000,,We can't go beyond the rails.
Dialogue: 0,0:07:32.36,0:07:36.10,Default,,0000,0000,0000,,Operational amplifiers can function either
Dialogue: 0,0:07:36.10,0:07:39.43,Default,,0000,0000,0000,,in the saturation regions or in the linear regions.
Dialogue: 0,0:07:39.43,0:07:40.78,Default,,0000,0000,0000,,When it's in the linear region,
Dialogue: 0,0:07:40.78,0:07:44.94,Default,,0000,0000,0000,,the output again is just a scaled version of the input,
Dialogue: 0,0:07:44.94,0:07:46.66,Default,,0000,0000,0000,,and under those circumstances,
Dialogue: 0,0:07:46.66,0:07:48.76,Default,,0000,0000,0000,,we refer to them as amplifiers.
Dialogue: 0,0:07:48.76,0:07:53.95,Default,,0000,0000,0000,,You can also drive an amplifier into one saturation region or another saturation region,
Dialogue: 0,0:07:53.95,0:07:55.12,Default,,0000,0000,0000,,and under those circumstances,
Dialogue: 0,0:07:55.12,0:07:57.97,Default,,0000,0000,0000,,we sometimes think of them as switches.
Dialogue: 0,0:07:57.97,0:08:04.36,Default,,0000,0000,0000,,So, operational amplifier circuits or circuits containing op-amps will be designed
Dialogue: 0,0:08:04.36,0:08:07.28,Default,,0000,0000,0000,,to operate either within the linear region or designed
Dialogue: 0,0:08:07.28,0:08:10.75,Default,,0000,0000,0000,,to operate in the saturation regions.
Dialogue: 0,0:08:10.75,0:08:14.26,Default,,0000,0000,0000,,So, generally speaking, in a block diagram perspective,
Dialogue: 0,0:08:14.26,0:08:16.06,Default,,0000,0000,0000,,we're going to have some source.
Dialogue: 0,0:08:16.06,0:08:20.86,Default,,0000,0000,0000,,We're going to run it through our amplifier that has some gain term,
Dialogue: 0,0:08:20.86,0:08:24.83,Default,,0000,0000,0000,,and then the output voltage or the voltage delivered to
Dialogue: 0,0:08:24.83,0:08:29.21,Default,,0000,0000,0000,,the load will be some gain times the source.
Dialogue: 0,0:08:29.21,0:08:32.09,Default,,0000,0000,0000,,So, our gain might be 10 and if our gain was 10,
Dialogue: 0,0:08:32.09,0:08:36.44,Default,,0000,0000,0000,,then the output voltage would be 10 times what the input voltage would be.
Dialogue: 0,0:08:36.44,0:08:39.82,Default,,0000,0000,0000,,From a graphical perspective,
Dialogue: 0,0:08:39.82,0:08:46.04,Default,,0000,0000,0000,,that means that if we were putting a sign wave in that had a one volt peak,
Dialogue: 0,0:08:46.04,0:08:48.88,Default,,0000,0000,0000,,if V sub s had one volt peak,
Dialogue: 0,0:08:48.88,0:08:52.82,Default,,0000,0000,0000,,sinusoidal variation, the output then,
Dialogue: 0,0:08:52.82,0:08:56.07,Default,,0000,0000,0000,,let's see if we can draw this a little bit than I've started,
Dialogue: 0,0:08:58.99,0:09:03.00,Default,,0000,0000,0000,,would have the same form,
Dialogue: 0,0:09:05.65,0:09:08.36,Default,,0000,0000,0000,,but would be 10 times as big.
Dialogue: 0,0:09:08.36,0:09:13.27,Default,,0000,0000,0000,,The oscillations in the output would be 10 times as wide or it'd
Dialogue: 0,0:09:13.27,0:09:19.22,Default,,0000,0000,0000,,oscillate 10 times as great as the input did.
Dialogue: 0,0:09:19.22,0:09:22.65,Default,,0000,0000,0000,,All right. Because we're not interested,
Dialogue: 0,0:09:22.65,0:09:25.75,Default,,0000,0000,0000,,at least at this level, we're not concerned about what's going on inside,
Dialogue: 0,0:09:25.75,0:09:28.57,Default,,0000,0000,0000,,we're going to make some approximations that under
Dialogue: 0,0:09:28.57,0:09:32.39,Default,,0000,0000,0000,,normal circumstances are very, very good approximations.
Dialogue: 0,0:09:32.39,0:09:34.72,Default,,0000,0000,0000,,If these approximations are true,
Dialogue: 0,0:09:34.72,0:09:40.48,Default,,0000,0000,0000,,we'll find that the operational amplifier is operating within it's linear region.
Dialogue: 0,0:09:40.48,0:09:46.54,Default,,0000,0000,0000,,First of all, we're going to make the approximation that i sub p,
Dialogue: 0,0:09:46.54,0:09:48.38,Default,,0000,0000,0000,,the current going into
Dialogue: 0,0:09:48.38,0:09:50.96,Default,,0000,0000,0000,,the non-inverting terminal and the current
Dialogue: 0,0:09:50.96,0:09:53.82,Default,,0000,0000,0000,,going into the inverting terminal is very, very small.
Dialogue: 0,0:09:53.82,0:09:56.63,Default,,0000,0000,0000,,In fact, so small that under ideal circumstances,
Dialogue: 0,0:09:56.63,0:09:59.41,Default,,0000,0000,0000,,we're going to say that there is no current going in.
Dialogue: 0,0:09:59.41,0:10:02.45,Default,,0000,0000,0000,,Our output, as we've pointed out,
Dialogue: 0,0:10:02.45,0:10:05.58,Default,,0000,0000,0000,,is some gain term times the difference in voltages.
Dialogue: 0,0:10:05.58,0:10:06.86,Default,,0000,0000,0000,,Basically, we're saying, yes,
Dialogue: 0,0:10:06.86,0:10:09.44,Default,,0000,0000,0000,,there will be a small voltage,
Dialogue: 0,0:10:09.44,0:10:12.12,Default,,0000,0000,0000,,it turns out it's going to be a small voltage across here,
Dialogue: 0,0:10:12.12,0:10:16.03,Default,,0000,0000,0000,,but negligible current going in.
Dialogue: 0,0:10:16.30,0:10:23.04,Default,,0000,0000,0000,,The second approximation is that the voltage across here is going to be very small.
Dialogue: 0,0:10:23.04,0:10:24.97,Default,,0000,0000,0000,,It's not going to be exactly zero,
Dialogue: 0,0:10:24.97,0:10:26.92,Default,,0000,0000,0000,,and it's important to notice that because, again,
Dialogue: 0,0:10:26.92,0:10:31.04,Default,,0000,0000,0000,,the output is some gain term times the difference.
Dialogue: 0,0:10:31.04,0:10:32.90,Default,,0000,0000,0000,,But it's going to be so small.
Dialogue: 0,0:10:32.90,0:10:37.03,Default,,0000,0000,0000,,In fact, it might be on the order of millivolts or tens of millivolts while all of
Dialogue: 0,0:10:37.03,0:10:41.74,Default,,0000,0000,0000,,the voltages in the circuit around it will be on the order of perhaps volts.
Dialogue: 0,0:10:41.74,0:10:43.97,Default,,0000,0000,0000,,So, if we're able to keep,
Dialogue: 0,0:10:43.97,0:10:46.81,Default,,0000,0000,0000,,and part of our circuitry will force
Dialogue: 0,0:10:46.81,0:10:51.88,Default,,0000,0000,0000,,the amplifier to operate in this range where Vp minus
Dialogue: 0,0:10:51.88,0:10:54.10,Default,,0000,0000,0000,,V sub n is approximately zero,
Dialogue: 0,0:10:54.10,0:11:00.85,Default,,0000,0000,0000,,or that Vp and V sub n are approximately equal to each other.
Dialogue: 0,0:11:00.85,0:11:04.45,Default,,0000,0000,0000,,We're going to design a circuitry to make that true so that in
Dialogue: 0,0:11:04.45,0:11:09.39,Default,,0000,0000,0000,,our analysis Vp minus V sub n is zero.
Dialogue: 0,0:11:09.39,0:11:12.47,Default,,0000,0000,0000,,The way we're going to work with that is that we're going to say that the voltage at
Dialogue: 0,0:11:12.47,0:11:14.90,Default,,0000,0000,0000,,the inverting terminal is
Dialogue: 0,0:11:14.90,0:11:18.59,Default,,0000,0000,0000,,approximately equal to the voltage at the non-inverting terminal.
Dialogue: 0,0:11:18.59,0:11:22.85,Default,,0000,0000,0000,,The next approximation is that this open-loop gain term,
Dialogue: 0,0:11:22.85,0:11:25.79,Default,,0000,0000,0000,,A, is really big.
Dialogue: 0,0:11:25.79,0:11:28.48,Default,,0000,0000,0000,,In fact, it approaches infinity.
Dialogue: 0,0:11:28.48,0:11:30.62,Default,,0000,0000,0000,,Now, it's not going to be infinite,
Dialogue: 0,0:11:30.62,0:11:36.84,Default,,0000,0000,0000,,but it's going to be on the order of maybe 50,000, 100,000, 200,000,
Dialogue: 0,0:11:36.84,0:11:39.92,Default,,0000,0000,0000,,big enough that for the calculations that we'll be doing,
Dialogue: 0,0:11:39.92,0:11:49.20,Default,,0000,0000,0000,,we can consider it to be infinite which then makes for an interesting mathematical,
Dialogue: 0,0:11:49.20,0:11:52.07,Default,,0000,0000,0000,,not inconsistency, what's the word I'm talking about?
Dialogue: 0,0:11:52.07,0:11:55.16,Default,,0000,0000,0000,,Indeterminate form. If we have A,
Dialogue: 0,0:11:55.16,0:11:58.37,Default,,0000,0000,0000,,which is approximately infinite, multiplying a really,
Dialogue: 0,0:11:58.37,0:12:02.15,Default,,0000,0000,0000,,really small number, which is approximately zero, it is indeterminate,
Dialogue: 0,0:12:02.15,0:12:07.40,Default,,0000,0000,0000,,and what we'll find is that we'll be able to determine the gain of the amplifier or
Dialogue: 0,0:12:07.40,0:12:14.22,Default,,0000,0000,0000,,specify the gain of the amplifier via the circuitry that we wrap around the amplifier.
Dialogue: 0,0:12:14.22,0:12:18.86,Default,,0000,0000,0000,,Finally, the output resistance,
Dialogue: 0,0:12:18.86,0:12:25.16,Default,,0000,0000,0000,,the resistance seen driving at the output is very small.
Dialogue: 0,0:12:25.16,0:12:28.01,Default,,0000,0000,0000,,In fact, we're going to assume that it is zero so that
Dialogue: 0,0:12:28.01,0:12:32.39,Default,,0000,0000,0000,,our output voltage will not experience a drop across
Dialogue: 0,0:12:32.39,0:12:36.05,Default,,0000,0000,0000,,this resistance which means that we can think about the
Dialogue: 0,0:12:36.05,0:12:40.18,Default,,0000,0000,0000,,current here available within limits.
Dialogue: 0,0:12:40.18,0:12:43.31,Default,,0000,0000,0000,,We can get whatever current out of here we need without
Dialogue: 0,0:12:43.31,0:12:46.37,Default,,0000,0000,0000,,seeing appreciable voltage drop across here.
Dialogue: 0,0:12:46.37,0:12:48.77,Default,,0000,0000,0000,,So, for a reasonable range of currents,
Dialogue: 0,0:12:48.77,0:12:50.94,Default,,0000,0000,0000,,the output voltage will be unchanged.
Dialogue: 0,0:12:50.94,0:12:54.85,Default,,0000,0000,0000,,In that sense, it's something like an ideal current source.
Dialogue: 0,0:12:54.85,0:13:00.94,Default,,0000,0000,0000,,At the input, the input resistance R sub i we're going to assume to be infinite.
Dialogue: 0,0:13:00.94,0:13:04.42,Default,,0000,0000,0000,,That ties back into the input currents being zero.
Dialogue: 0,0:13:04.42,0:13:07.44,Default,,0000,0000,0000,,If you're driving a current into an infinite resistance,
Dialogue: 0,0:13:07.44,0:13:09.07,Default,,0000,0000,0000,,effectively an open circuit,
Dialogue: 0,0:13:09.07,0:13:11.98,Default,,0000,0000,0000,,the input currents are going to be zero.
Dialogue: 0,0:13:12.59,0:13:17.98,Default,,0000,0000,0000,,So, recapping, we had these little silicon devices called operational amplifiers.
Dialogue: 0,0:13:17.98,0:13:20.38,Default,,0000,0000,0000,,They draw almost no current at the inputs.
Dialogue: 0,0:13:20.38,0:13:25.12,Default,,0000,0000,0000,,The output is a scaled version of the input and we can use them.
Dialogue: 0,0:13:25.12,0:13:29.78,Default,,0000,0000,0000,,They're very utilitarian devices used in control systems,
Dialogue: 0,0:13:29.78,0:13:31.52,Default,,0000,0000,0000,,used in the circuit in the lab,
Dialogue: 0,0:13:31.52,0:13:35.07,Default,,0000,0000,0000,,and we'll get a lot of experience using these operational amplifiers.