1 00:00:05,600 --> 00:00:08,650 >> In this video, we'll discuss the basics of 2 00:00:08,650 --> 00:00:11,605 implementing operational amplifier based circuits. 3 00:00:11,605 --> 00:00:14,170 Main points to look for are the fact that we have to 4 00:00:14,170 --> 00:00:16,975 apply power to our Op-Amps to make them work, 5 00:00:16,975 --> 00:00:21,625 and that the output voltage from the Op-Amp is limited by the power supply voltages. 6 00:00:21,625 --> 00:00:24,100 These are probably two of the points that get 7 00:00:24,100 --> 00:00:27,655 overlooked most often when we analyze Op-Amps circuits, 8 00:00:27,655 --> 00:00:31,865 but they have a huge effect when we build and test a circuit. 9 00:00:31,865 --> 00:00:34,990 First, let's just briefly go over the rules that we 10 00:00:34,990 --> 00:00:38,230 use to analyze operational amplifier based circuits. 11 00:00:38,230 --> 00:00:41,290 The Op-Amp circuit schematic symbol is shown here. 12 00:00:41,290 --> 00:00:45,125 Op-Amps typically have five or more terminals. 13 00:00:45,125 --> 00:00:50,360 The operational amplifier has two inputs and one output terminal. 14 00:00:50,360 --> 00:00:54,860 The ideal operational amplifier rules are that there are no voltage difference 15 00:00:54,860 --> 00:01:00,700 between the input terminals and no current flowing into the input terminals. 16 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 17 00:01:07,460 --> 00:01:08,375 amplifier. 18 00:01:08,375 --> 00:01:12,685 The Op-Amp will not function if you don't apply power to these terminals. 19 00:01:12,685 --> 00:01:17,420 To complicate things, these terminals are sometimes not even evident on circuit diagrams. 20 00:01:17,420 --> 00:01:20,150 We just assume that they're there and let it go with that. 21 00:01:20,150 --> 00:01:22,549 When we analyze ideal Op-Amps, 22 00:01:22,549 --> 00:01:26,635 we generally don't assume anything about the voltage and current at the output terminal. 23 00:01:26,635 --> 00:01:31,160 However, there are some practical limitations associated with these parameters. 24 00:01:31,160 --> 00:01:36,290 The output voltage is restricted to being between the power supply voltage is 25 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. 26 00:01:41,870 --> 00:01:44,780 The Op-Amps in Digilent unlike, parts kit are provide 27 00:01:44,780 --> 00:01:49,450 relatively little current but higher current devices are available. 28 00:01:49,450 --> 00:01:54,440 Finally, one very important point relative to the voltages on this diagram, 29 00:01:54,440 --> 00:01:58,070 they should all be relative to the same reference voltage. 30 00:01:58,070 --> 00:02:01,760 This isn't a big deal if your using only the analog discovery, 31 00:02:01,760 --> 00:02:06,230 since all of the voltages provided by it are automatically relative to the same voltage. 32 00:02:06,230 --> 00:02:09,229 But if you're using other sources of power in your circuit, 33 00:02:09,229 --> 00:02:13,820 you may need to physically interconnect them to ensure a common reference. 34 00:02:13,820 --> 00:02:16,580 All the labs in this chapter specify use of 35 00:02:16,580 --> 00:02:20,300 the OP27 Op-Amp from the digital and analog parts kit. 36 00:02:20,300 --> 00:02:22,790 So, I want to spend a little time talking about 37 00:02:22,790 --> 00:02:26,270 the physical pin descriptions for that Operational Amplifier. 38 00:02:26,270 --> 00:02:28,850 The general comments I'll make for this Op-Amp will 39 00:02:28,850 --> 00:02:31,340 be typical for most operational amplifiers, 40 00:02:31,340 --> 00:02:35,260 but the specific pin descriptions may vary from Op-Amp to Op-Amp. 41 00:02:35,260 --> 00:02:38,515 In order to find the pin descriptions for any given Op-Amp, 42 00:02:38,515 --> 00:02:40,650 simply look up a datasheet online. 43 00:02:40,650 --> 00:02:43,730 One of the first pieces of information on the sheet will generally be 44 00:02:43,730 --> 00:02:47,870 a picture similar to this one with a description of the pin functions. 45 00:02:47,870 --> 00:02:52,600 First, a couple of comments about Operational Amplifiers in general. 46 00:02:52,600 --> 00:02:56,960 Op-Amps which can be used in a solderless breadboard are generally in what are 47 00:02:56,960 --> 00:03:00,560 called dual in-line packages abbreviated as DIP. 48 00:03:00,560 --> 00:03:05,555 This simply means that the pins are oriented in two rows of pairs. 49 00:03:05,555 --> 00:03:08,810 The spacing of the pins allows the chip to be inserted in 50 00:03:08,810 --> 00:03:13,520 a solderless breadboard with the central channel of the breadboard separating the rows. 51 00:03:13,520 --> 00:03:18,145 This ensures that any pin is electrically isolated from any other pin. 52 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, 53 00:03:23,720 --> 00:03:25,895 or a dot in one corner of the chip. 54 00:03:25,895 --> 00:03:28,100 Many chips have both of these indicators. 55 00:03:28,100 --> 00:03:31,310 If you're looking down at the chips with the notches at the top, 56 00:03:31,310 --> 00:03:34,775 pin one will be in the upper left-hand corner of the chip. 57 00:03:34,775 --> 00:03:39,695 Other pins are numbered successively in a counterclockwise direction. 58 00:03:39,695 --> 00:03:43,430 Alternately, if you use the dot to orient the pins, 59 00:03:43,430 --> 00:03:45,695 the dot is closest to pin one. 60 00:03:45,695 --> 00:03:49,405 Now, let's take a look at some physical Op-Amps themselves. 61 00:03:49,405 --> 00:03:52,050 This is the OP27 Op-Amp. 62 00:03:52,050 --> 00:03:55,700 The Op-Amp type is printed directly on the top of the chip. 63 00:03:55,700 --> 00:03:59,525 It has eight pins in two rows of four each. 64 00:03:59,525 --> 00:04:02,120 It's been inserted into the breadboard correctly with 65 00:04:02,120 --> 00:04:06,040 the central channel of the breadboard between the two rows of pins. 66 00:04:06,040 --> 00:04:11,225 This particular Op-Amp has both a notch and a dot to indicate pin one. 67 00:04:11,225 --> 00:04:13,520 The other pins are numbered counterclockwise, 68 00:04:13,520 --> 00:04:15,035 so this is pin two, 69 00:04:15,035 --> 00:04:18,375 three, four, five and so on. 70 00:04:18,375 --> 00:04:23,245 >> The individual pin descriptions for the OP27 Op-Amp are shown here. 71 00:04:23,245 --> 00:04:27,905 Pins two and three are the inverting and non-inverting inputs. 72 00:04:27,905 --> 00:04:30,595 Pin six is the output terminal. 73 00:04:30,595 --> 00:04:33,500 The positive voltage supply is connected to pin 74 00:04:33,500 --> 00:04:37,375 seven and the negative voltage supply is connected to pin four. 75 00:04:37,375 --> 00:04:42,385 Pins one and eight are offset voltage trim terminals. 76 00:04:42,385 --> 00:04:45,055 These can be used to fine tune the Op-Amp behavior, 77 00:04:45,055 --> 00:04:47,075 but we won't use them in this course. 78 00:04:47,075 --> 00:04:49,705 Pin five doesn't do anything. 79 00:04:49,705 --> 00:04:53,255 It's said to be not connected or NC. 80 00:04:53,255 --> 00:04:56,350 We will always need to provide power to our circuit. 81 00:04:56,350 --> 00:04:58,240 So, I'll go ahead and connect the voltage supplies 82 00:04:58,240 --> 00:05:00,685 now before we wire up our example circuit. 83 00:05:00,685 --> 00:05:03,685 This pin is the positive voltage supply, 84 00:05:03,685 --> 00:05:06,305 this pin is the negative voltage supply. 85 00:05:06,305 --> 00:05:09,270 I'll use V plus on my analog discovery for 86 00:05:09,270 --> 00:05:14,240 the positive voltage supply and V minus for the negative voltage supply. 87 00:05:14,240 --> 00:05:18,280 I generally connect my power supplies first. Since my experience has been that 88 00:05:18,280 --> 00:05:23,030 forgetting to connect these as my number one silly mistake when wiring circuits. 89 00:05:23,030 --> 00:05:24,820 For this video, we'll create 90 00:05:24,820 --> 00:05:28,840 this inverting voltage amplifier circuit and investigate it's response. 91 00:05:28,840 --> 00:05:30,245 If we analyze this circuit, 92 00:05:30,245 --> 00:05:31,770 we'll find that the output voltage, 93 00:05:31,770 --> 00:05:36,500 V-out, should be negative two times the input voltage, V-in. 94 00:05:36,500 --> 00:05:41,015 We've already connected V plus and V minus to the positive and negative voltage supplies. 95 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. 96 00:05:47,135 --> 00:05:49,090 We'll use channel one of 97 00:05:49,090 --> 00:05:52,990 our waveform generator to apply the input voltage to this circuit. 98 00:05:52,990 --> 00:05:55,160 According to our circuit schematic, 99 00:05:55,160 --> 00:06:00,680 we have a 20 kilo ohm resistor connecting the output terminal to the inverting input, 100 00:06:00,680 --> 00:06:03,510 a 10 kilo ohm resistor connecting 101 00:06:03,510 --> 00:06:07,940 our inverting input to the arbitrary waveform generators channel one, 102 00:06:07,940 --> 00:06:10,450 which is this yellow wire, 103 00:06:12,000 --> 00:06:18,140 and we need to ground the non-inverting input terminal. 104 00:06:18,140 --> 00:06:22,279 We'll use channel one of our voltmeter to measure our output voltage. 105 00:06:22,279 --> 00:06:26,630 We'll measure that between this terminal and ground. 106 00:06:27,560 --> 00:06:29,705 To demonstrate our circuit, 107 00:06:29,705 --> 00:06:32,550 first we'll have to apply power to the power supplies. 108 00:06:32,550 --> 00:06:35,840 I'm going to turn on the voltage instrument. 109 00:06:35,840 --> 00:06:40,795 Now, let's start by applying a relatively small voltage to the input, 110 00:06:40,795 --> 00:06:42,560 say half a volt. 111 00:06:42,560 --> 00:06:45,040 Turning on the waveform generator, 112 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. 113 00:06:50,165 --> 00:06:52,510 Increasing this to one volt, 114 00:06:52,510 --> 00:06:55,085 the output is about negative two volts. 115 00:06:55,085 --> 00:06:57,610 It's negative two times the input. 116 00:06:57,610 --> 00:06:59,855 To emphasize the inversion property, 117 00:06:59,855 --> 00:07:01,540 if I input negative one volt, 118 00:07:01,540 --> 00:07:04,090 I should get positive two volts out. 119 00:07:04,090 --> 00:07:07,400 Now, let's take a look at the saturation of the amplifier. 120 00:07:07,400 --> 00:07:09,495 If we go up to two volts, 121 00:07:09,495 --> 00:07:13,345 we get about negative four volts out which is what we would expect. 122 00:07:13,345 --> 00:07:16,555 Increasing this to three volts, however, 123 00:07:16,555 --> 00:07:21,910 just brings the output up to a little bit over four volts. We've saturated. 124 00:07:21,910 --> 00:07:25,210 We've gotten as close to the voltage supplies as we can. 125 00:07:25,210 --> 00:07:30,980 Increasing the input even more will not change our output. 126 00:07:34,380 --> 00:07:37,515 That's really all there is to Op-Amps for now. 127 00:07:37,515 --> 00:07:39,740 All of the lab assignments in this chapter you use 128 00:07:39,740 --> 00:07:43,060 these basic tools, but apply them to different Op-Amp circuits. 129 00:07:43,060 --> 00:07:45,810 Makes sure that you apply voltage to your Op-Amps for 130 00:07:45,810 --> 00:07:48,805 all your circuits and the lab should be pretty straightforward. 131 00:07:48,805 --> 00:07:52,205 The only thing to look for is that the ideal Op-Amp behavior breaks 132 00:07:52,205 --> 00:07:56,780 down if the output gets too close to the supply voltage rails.