as a DC voltage source on the non-inverting input of your op-amp. So this is inside the op-amp and there's nothing you can do about it other than select an op-amp that has a better input offset voltage. And basically, this is the non-inverting configuration we looked at earlier. The input signal in this case just adds directly to the offset. So if you look at the expected ideal output, it would be the input signal times the gain and the gain is Rf divided by R1 + 1, or 100 in this case. So 30 millivolts times

00:21:24 100 gives us 3 volts out. That's what we're expecting. But because we have this offset voltage, that basically just adds to our input signal, and we end up with no longer, you know, 3.01 volts. So we have an error. And you could calculate the error as a percentage, if you like, and just subtract the ideal from the measure, and then you end up with about 0.3% of error and of course, it could be much larger. The offset in this case is a millivolt or 0.1 millivolt. Offsets can range from 5 microvolts to tens of millivolts.

00:22:07 So, this is actually a pretty good offset. It's not a bad one, but it still introduced some error. And of course, the impact of this offset is much greater in high gain circuits, where the input signal is very small. Is this offset going to stay constant or it will be changing with temperature or current or I don't know? That's a great question. The offset changes with temperature. That's the first thing you think about happening with offset is how it drifts over temperature. And that's specified in the datasheet

00:22:46 as a maximum in microvolts per degree C, but it also changes with power supply, and I talked a little bit about that during a different video where we looked at power supply rejection. It changes with the common mode or input signal and it changes with even things like electromagnetic interference. So there's a lot of factors that cause the offset to shift, but temperature is probably the first one think about. So you can't just simply use calculations and, you know, like, correct the offset in your microcontroller or something?

00:23:28 Can you? No. You can. You can. And people do that. That's called a calibration. So you might have multiple amplifiers and the analog to digital converter itself will have an offset. The amplifiers will have an offset. We'll see that bias current can generate an offset and all those errors will lump together and your microcontroller. What you can do is you can apply a test signal of zero volts in and then maybe your full scale signal in and then you would go through a calibration where you would mathematically correct for that.

00:24:07 So that's a common thing to do but you you can't easily calibrate out things like temperature drift or power supply impact on offset. So, some of these secondary kind of things that cause offset to shift are more difficult to calibrate out. So, you could maybe calibrate it for some kind of average offset, but the temperature influence or something, it still will be okay. Yeah. Exactly. Well, I mean, the other downside, of course, to calibration is it's costly, you know, because oftentimes people don't want to do calibration, because

00:24:54 to calibrate, you have to actually apply a test signal and apply a different test signal, and then you have to make measurements and then you have to store things in an EEPROM or in your microcontroller, basically. You know, so it takes extra effort and it adds cost so sometimes people will just try and pick the optimal signal chain, make sure the offset is as small as possible, and then in other cases they will optimize by using calibration. Okay. What is the next parameter? This is still about offset, okay. Let's actually do a demo.

00:25:35 I think we should just do these demos as we go through the... Okay, okay. ...presentation. So, here is the hardware, and we're going to use two op amps. I'm putting in the OPA211 into this test circuit, which has a cascaded amplifier. Earlier, I mentioned that sometimes you have two amplifiers in series to get a higher gain and this is an example where the gain is quite high. And so I just installed these DIP adapter cards with SOIC versions of the amplifiers and I'm putting jumpers to connect the amplifiers to the test equipment.

00:26:32 So you created two different circuits? One is with the 188 and the other one is 211? That's correct. Okay. And so here we are. We're all connected up. There's no input signal in this case. The signal is really just the output that we're looking at. And you can see in the schematic here that we're grounding the input, so the input's basically zero volts. And what we're really just looking at is the input offset voltage multiplied by a gain of 101 because it's a non-inverting amplifier. And then that gain gets multiplied by 21

00:27:14 and so that's what this is showing, 101 and 21. And then the output offset measured at the output pin here would be the input offset multiplied by the gain in and the gain out. And so we have about 30 microvolts of offset for the OPA or the typical and this op-amp here and 125 microvolts for the maximum and it's getting multiplied by the gain. So these are numbers from datasheet or these are measured... Yeah. Datasheet. This is a, over here these tables are just how it would be displayed in the datasheet. burada iki farklı kişi konuşuoyr birisi bir şey anlatıyhor birisi de dinliyor ve sorular soruyor. buna göre bana bu metni açıkla,