three op amp instrumentation amp

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Your comments and opinions are sought on gain distribution within the classic three op amp instrumentation amplifier.

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I suppose my first question is why not just use one of the many InAmp ICs that exist on the market? That is, why the need for a 3 Op-Amp solution?

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For low-gain (1 to 10) instrumentation amplifier I use TL084 or one from the more modern TLC-series. First job is to match 4 resistors. I usually make more sets at the same matching-job.

For higher gain (10 to 1000) I select a better OpAmp, LT1014 or so. Matching resistors is not good enough in a 1000x IA, so a trimpot is added in the leg to ground.

Frequency response is another thing to consider: higher gain means lower frequncy.

Nard

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The LT1167 is terribly expensive in single quantities, but beats any discrete three opamp solution and you won't need any precision resistors; only one to set the gain.

Of course, you might not need all that performance in your app.