Experimenting with Op Amps: Input Offset Voltage

RE: Experimenting with Op Amps: Input Offset Voltage

kkazem — Sun, 05 Dec 2021 21:21:52 GMT

Excellent op-amp blog.

RE: Experimenting with Op Amps: Input Offset Voltage

DAB — Fri, 29 May 2020 18:13:45 GMT

Yes, there are many aspects about opamps that every engineer should know and explore, but usually do not.

Thanks for taking a look into one of them.

DAB

RE: Experimenting with Op Amps: Input Offset Voltage

fmilburn — Fri, 29 May 2020 15:42:55 GMT

Hi Jon,

Great post. By coincidence I have been playing with an op-amp I built from discrete parts a week or two back and experimenting with it. It was to be a 1day experiment but due to unexpected complexity and personal situation it has turned into weeks. Anyway, it has been very illuminating and I hope to incorporate the techniques you have demonstrated and publish soon.

RE: Experimenting with Op Amps: Input Offset Voltage

ralphjy — Fri, 29 May 2020 12:27:29 GMT

Wow, brings back a lot of memories. I just realized that the 741 passed its 50th anniversary. I think I first used one back in 1971. I remember the TI versions had better offset than the Fairchild ones but the were prone to latch up. We were just really happy to have a compensated 709.

RE: Experimenting with Op Amps: Input Offset Voltage

jw0752 — Fri, 29 May 2020 02:38:34 GMT

Hi Jon,

Tonight I ran your offset experiment with various stock numbers and a quantity of each. I had quite a time as I initially set the experiment up on a single supply. Things didn't go well and I was about to ask you some questions when I realized my mistake by looking at your circuit board. Once the experiment was set up properly things went a little smoother. With the exception of one stock number (LT1006) I was amazed at how the off sets varied from one chip of the same stock number to the next. I even ran tests on a set of TL2142 Dual Op Amps. Along with the offsets I also noted the quiescent current of the chips. Here is my Data:

LT1006 Quiescent Current .35 to .43 mA Offsets noted: -57uV 57uV 59uV 10uV -43uV This was the most consistent of the stock numbers tested

LM741 Quiescent Current 1mA +- .2mA Offsets noted 544uV 330uV -1190uV -292uV

LF411 Quiescent Current 2mA Offsets noted 69uV 151uV -422uV 581uV

LF351 Quiescent Current 2mA Offsets noted -3179uV 2950uV -540uV

TL2142 Dual OP Amp Quiescent Current 7mA Offsets noted: 100uV -54uV -300uV -110uV -36uV -185uV -69uV -126uV 2.1uV 336uV 107uV 277uV

I have learned a lot tonight about op amps. I like your technique for measuring the offset and it should come in useful for selecting chips for important and critical circuits in the future. Fortunately I do not have these applications very often. Your technique has also given me a crude way to measure micro volts, a capacity that my lab has not had before.

John

RE: Experimenting with Op Amps: Input Offset Voltage

Andrew J — Thu, 28 May 2020 21:25:56 GMT

Very interesting Jon.

I’m creating a prototype PCB at the moment with an Opx192. Actually, two of them and they both have a spare unit. What I could do is wire these up to run a similar test, in two different ways if you want? Let me know and I’ll add it in - I think I will have space. I can provide it with a +5v, -5v, +12v or +15v and, if you want to be fancy, I could jumper those rails and provide variation.

RE: Experimenting with Op Amps: Input Offset Voltage

genebren — Wed, 27 May 2020 22:18:50 GMT

Very interesting blog. You have a knack for taking on some interesting topics and bringing a lot of interesting lessons to the readers.

Thanks!

RE: Experimenting with Op Amps: Input Offset Voltage

jw0752 — Wed, 27 May 2020 14:34:02 GMT

Hi Jon,

Thanks for another interesting area of exploration. I will have to set up and run some tests. Since I salvage lots of components from boards I have several types where there are quantities. Please keep the ideas coming.

John