WEBVTT 00:00:05.600 --> 00:00:08.650 >> In this video, we'll discuss the basics of 00:00:08.650 --> 00:00:11.605 implementing operational amplifier based circuits. 00:00:11.605 --> 00:00:14.170 Main points to look for are the fact that we have to 00:00:14.170 --> 00:00:16.975 apply power to our Op-Amps to make them work, 00:00:16.975 --> 00:00:21.625 and that the output voltage from the Op-Amp is limited by the power supply voltages. 00:00:21.625 --> 00:00:24.100 These are probably two of the points that get 00:00:24.100 --> 00:00:27.655 overlooked most often when we analyze Op-Amps circuits, 00:00:27.655 --> 00:00:31.865 but they have a huge effect when we build and test a circuit. 00:00:31.865 --> 00:00:34.990 First, let's just briefly go over the rules that we 00:00:34.990 --> 00:00:38.230 use to analyze operational amplifier based circuits. 00:00:38.230 --> 00:00:41.290 The Op-Amp circuit schematic symbol is shown here. 00:00:41.290 --> 00:00:45.125 Op-Amps typically have five or more terminals. 00:00:45.125 --> 00:00:50.360 The operational amplifier has two inputs and one output terminal. 00:00:50.360 --> 00:00:54.860 The ideal operational amplifier rules are that there are no voltage difference 00:00:54.860 --> 00:01:00.700 between the input terminals and no current flowing into the input terminals. 00:01:00.700 --> 00:01:07.460 Two of the terminals V plus and V minus are used to provide power to the operational 00:01:07.460 --> 00:01:08.375 amplifier. 00:01:08.375 --> 00:01:12.685 The Op-Amp will not function if you don't apply power to these terminals. 00:01:12.685 --> 00:01:17.420 To complicate things, these terminals are sometimes not even evident on circuit diagrams. 00:01:17.420 --> 00:01:20.150 We just assume that they're there and let it go with that. 00:01:20.150 --> 00:01:22.549 When we analyze ideal Op-Amps, 00:01:22.549 --> 00:01:26.635 we generally don't assume anything about the voltage and current at the output terminal. 00:01:26.635 --> 00:01:31.160 However, there are some practical limitations associated with these parameters. 00:01:31.160 --> 00:01:36.290 The output voltage is restricted to being between the power supply voltage is 00:01:36.290 --> 00:01:41.870 V+ and V- and the output current is limited by the design of the Op-Amp itself. 00:01:41.870 --> 00:01:44.780 The Op-Amps in Digilent unlike, parts kit are provide 00:01:44.780 --> 00:01:49.450 relatively little current but higher current devices are available. 00:01:49.450 --> 00:01:54.440 Finally, one very important point relative to the voltages on this diagram, 00:01:54.440 --> 00:01:58.070 they should all be relative to the same reference voltage. 00:01:58.070 --> 00:02:01.760 This isn't a big deal if your using only the analog discovery, 00:02:01.760 --> 00:02:06.230 since all of the voltages provided by it are automatically relative to the same voltage. 00:02:06.230 --> 00:02:09.229 But if you're using other sources of power in your circuit, 00:02:09.229 --> 00:02:13.820 you may need to physically interconnect them to ensure a common reference. 00:02:13.820 --> 00:02:16.580 All the labs in this chapter specify use of 00:02:16.580 --> 00:02:20.300 the OP27 Op-Amp from the digital and analog parts kit. 00:02:20.300 --> 00:02:22.790 So, I want to spend a little time talking about 00:02:22.790 --> 00:02:26.270 the physical pin descriptions for that Operational Amplifier. 00:02:26.270 --> 00:02:28.850 The general comments I'll make for this Op-Amp will 00:02:28.850 --> 00:02:31.340 be typical for most operational amplifiers, 00:02:31.340 --> 00:02:35.260 but the specific pin descriptions may vary from Op-Amp to Op-Amp. 00:02:35.260 --> 00:02:38.515 In order to find the pin descriptions for any given Op-Amp, 00:02:38.515 --> 00:02:40.650 simply look up a datasheet online. 00:02:40.650 --> 00:02:43.730 One of the first pieces of information on the sheet will generally be 00:02:43.730 --> 00:02:47.870 a picture similar to this one with a description of the pin functions. 00:02:47.870 --> 00:02:52.600 First, a couple of comments about Operational Amplifiers in general. 00:02:52.600 --> 00:02:56.960 Op-Amps which can be used in a solderless breadboard are generally in what are 00:02:56.960 --> 00:03:00.560 called dual in-line packages abbreviated as DIP. 00:03:00.560 --> 00:03:05.555 This simply means that the pins are oriented in two rows of pairs. 00:03:05.555 --> 00:03:08.810 The spacing of the pins allows the chip to be inserted in 00:03:08.810 --> 00:03:13.520 a solderless breadboard with the central channel of the breadboard separating the rows. 00:03:13.520 --> 00:03:18.145 This ensures that any pin is electrically isolated from any other pin. 00:03:18.145 --> 00:03:23.720 Second, the orientation of the pins is specified by a notch at one end of the chip, 00:03:23.720 --> 00:03:25.895 or a dot in one corner of the chip. 00:03:25.895 --> 00:03:28.100 Many chips have both of these indicators. 00:03:28.100 --> 00:03:31.310 If you're looking down at the chips with the notches at the top, 00:03:31.310 --> 00:03:34.775 pin one will be in the upper left-hand corner of the chip. 00:03:34.775 --> 00:03:39.695 Other pins are numbered successively in a counterclockwise direction. 00:03:39.695 --> 00:03:43.430 Alternately, if you use the dot to orient the pins, 00:03:43.430 --> 00:03:45.695 the dot is closest to pin one. 00:03:45.695 --> 00:03:49.405 Now, let's take a look at some physical Op-Amps themselves. 00:03:49.405 --> 00:03:52.050 This is the OP27 Op-Amp. 00:03:52.050 --> 00:03:55.700 The Op-Amp type is printed directly on the top of the chip. 00:03:55.700 --> 00:03:59.525 It has eight pins in two rows of four each. 00:03:59.525 --> 00:04:02.120 It's been inserted into the breadboard correctly with 00:04:02.120 --> 00:04:06.040 the central channel of the breadboard between the two rows of pins. 00:04:06.040 --> 00:04:11.225 This particular Op-Amp has both a notch and a dot to indicate pin one. 00:04:11.225 --> 00:04:13.520 The other pins are numbered counterclockwise, 00:04:13.520 --> 00:04:15.035 so this is pin two, 00:04:15.035 --> 00:04:18.375 three, four, five and so on. 00:04:18.375 --> 00:04:23.245 >> The individual pin descriptions for the OP27 Op-Amp are shown here. 00:04:23.245 --> 00:04:27.905 Pins two and three are the inverting and non-inverting inputs. 00:04:27.905 --> 00:04:30.595 Pin six is the output terminal. 00:04:30.595 --> 00:04:33.500 The positive voltage supply is connected to pin 00:04:33.500 --> 00:04:37.375 seven and the negative voltage supply is connected to pin four. 00:04:37.375 --> 00:04:42.385 Pins one and eight are offset voltage trim terminals. 00:04:42.385 --> 00:04:45.055 These can be used to fine tune the Op-Amp behavior, 00:04:45.055 --> 00:04:47.075 but we won't use them in this course. 00:04:47.075 --> 00:04:49.705 Pin five doesn't do anything. 00:04:49.705 --> 00:04:53.255 It's said to be not connected or NC. 00:04:53.255 --> 00:04:56.350 We will always need to provide power to our circuit. 00:04:56.350 --> 00:04:58.240 So, I'll go ahead and connect the voltage supplies 00:04:58.240 --> 00:05:00.685 now before we wire up our example circuit. 00:05:00.685 --> 00:05:03.685 This pin is the positive voltage supply, 00:05:03.685 --> 00:05:06.305 this pin is the negative voltage supply. 00:05:06.305 --> 00:05:09.270 I'll use V plus on my analog discovery for 00:05:09.270 --> 00:05:14.240 the positive voltage supply and V minus for the negative voltage supply. 00:05:14.240 --> 00:05:18.280 I generally connect my power supplies first. Since my experience has been that 00:05:18.280 --> 00:05:23.030 forgetting to connect these as my number one silly mistake when wiring circuits. 00:05:23.030 --> 00:05:24.820 For this video, we'll create 00:05:24.820 --> 00:05:28.840 this inverting voltage amplifier circuit and investigate it's response. 00:05:28.840 --> 00:05:30.245 If we analyze this circuit, 00:05:30.245 --> 00:05:31.770 we'll find that the output voltage, 00:05:31.770 --> 00:05:36.500 V-out, should be negative two times the input voltage, V-in. 00:05:36.500 --> 00:05:41.015 We've already connected V plus and V minus to the positive and negative voltage supplies. 00:05:41.015 --> 00:05:47.135 So, all that remains is to add the resistors in the circuit and apply an input voltage. 00:05:47.135 --> 00:05:49.090 We'll use channel one of 00:05:49.090 --> 00:05:52.990 our waveform generator to apply the input voltage to this circuit. 00:05:52.990 --> 00:05:55.160 According to our circuit schematic, 00:05:55.160 --> 00:06:00.680 we have a 20 kilo ohm resistor connecting the output terminal to the inverting input, 00:06:00.680 --> 00:06:03.510 a 10 kilo ohm resistor connecting 00:06:03.510 --> 00:06:07.940 our inverting input to the arbitrary waveform generators channel one, 00:06:07.940 --> 00:06:10.450 which is this yellow wire, 00:06:12.000 --> 00:06:18.140 and we need to ground the non-inverting input terminal. 00:06:18.140 --> 00:06:22.279 We'll use channel one of our voltmeter to measure our output voltage. 00:06:22.279 --> 00:06:26.630 We'll measure that between this terminal and ground. 00:06:27.560 --> 00:06:29.705 To demonstrate our circuit, 00:06:29.705 --> 00:06:32.550 first we'll have to apply power to the power supplies. 00:06:32.550 --> 00:06:35.840 I'm going to turn on the voltage instrument. 00:06:35.840 --> 00:06:40.795 Now, let's start by applying a relatively small voltage to the input, 00:06:40.795 --> 00:06:42.560 say half a volt. 00:06:42.560 --> 00:06:45.040 Turning on the waveform generator, 00:06:45.040 --> 00:06:50.165 we see that our output is about negative one volts which is exactly what we would expect. 00:06:50.165 --> 00:06:52.510 Increasing this to one volt, 00:06:52.510 --> 00:06:55.085 the output is about negative two volts. 00:06:55.085 --> 00:06:57.610 It's negative two times the input. 00:06:57.610 --> 00:06:59.855 To emphasize the inversion property, 00:06:59.855 --> 00:07:01.540 if I input negative one volt, 00:07:01.540 --> 00:07:04.090 I should get positive two volts out. 00:07:04.090 --> 00:07:07.400 Now, let's take a look at the saturation of the amplifier. 00:07:07.400 --> 00:07:09.495 If we go up to two volts, 00:07:09.495 --> 00:07:13.345 we get about negative four volts out which is what we would expect. 00:07:13.345 --> 00:07:16.555 Increasing this to three volts, however, 00:07:16.555 --> 00:07:21.910 just brings the output up to a little bit over four volts. We've saturated. 00:07:21.910 --> 00:07:25.210 We've gotten as close to the voltage supplies as we can. 00:07:25.210 --> 00:07:30.980 Increasing the input even more will not change our output. 00:07:34.380 --> 00:07:37.515 That's really all there is to Op-Amps for now. 00:07:37.515 --> 00:07:39.740 All of the lab assignments in this chapter you use 00:07:39.740 --> 00:07:43.060 these basic tools, but apply them to different Op-Amp circuits. 00:07:43.060 --> 00:07:45.810 Makes sure that you apply voltage to your Op-Amps for 00:07:45.810 --> 00:07:48.805 all your circuits and the lab should be pretty straightforward. 00:07:48.805 --> 00:07:52.205 The only thing to look for is that the ideal Op-Amp behavior breaks 00:07:52.205 --> 00:07:56.780 down if the output gets too close to the supply voltage rails.