WEBVTT

00:00:00.000 --> 00:00:04.590
>> Now, let's talk about how a differencing or subtracting amplifier works.

00:00:04.590 --> 00:00:06.280
I've drawn the whole amplifier here,

00:00:06.280 --> 00:00:09.510
it's a combination of a inverting and

00:00:09.510 --> 00:00:14.490
a non-inverting amplifier with the two separate voltages Vs1 and Vs2.

00:00:14.490 --> 00:00:18.195
You can see that what happens right here is you have your feedback loop.

00:00:18.195 --> 00:00:21.630
Right here, I'm not going to scribble in the feedback loop.

00:00:21.630 --> 00:00:27.270
There's the feedback loop going to the negative connection and that's the feedback,

00:00:27.270 --> 00:00:30.870
we have one voltage right here connected onto the negative feedback.

00:00:30.870 --> 00:00:35.570
So, Vs1 right here is going to be the negative part of our equation.

00:00:35.570 --> 00:00:42.275
We can see that because the gain on the negative feedback is minus R2 over R1.

00:00:42.275 --> 00:00:46.130
This other term is going to be the positive part or Vs2.

00:00:46.130 --> 00:00:49.115
We can see that we only have positives right here.

00:00:49.115 --> 00:00:51.850
So, that's the gain that we're going to have on Vs2.

00:00:51.850 --> 00:00:57.260
We could basically look at that like bringing in Vs1 and multiplying it

00:00:57.260 --> 00:01:03.785
by the first gain, bringing in Vs2 and multiplying it by the second gain,

00:01:03.785 --> 00:01:06.575
and then adding them up.

00:01:06.575 --> 00:01:13.190
The only cool thing is that gain one is negative and gain two is positive,

00:01:13.190 --> 00:01:16.025
so we end up essentially subtracting off,

00:01:16.025 --> 00:01:18.605
part of Vs1 from Vs2.

00:01:18.605 --> 00:01:20.735
That gives us our output voltage.

00:01:20.735 --> 00:01:23.385
As with all of our op-amps.

00:01:23.385 --> 00:01:28.895
The V0 is limited between the two power supply voltages,

00:01:28.895 --> 00:01:32.130
Vcc and minus Vcc.