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single input on in-amp or op-amp

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throbscottle

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I want to create a single-sided input amplifier with very high input impedance (it is fed off a 10M divider), precise gain, low noise and low drift. Bandwidth up to 1MHz would be nice, but 100's of KHz will do. I started off looking at the CA3160, but got onto looking at instrumentation amps, since this is for a voltmeter which should be able to resolve 3mV.

Comparing data sheets, for my purposes there doesn't seem to be much to choose between the op-amp and any of the in-amps I can afford.

So I was wondering, with the inverting input grounded in both cases, is there any advantage in using an in-amp, or had I better stick with using an op-amp, and if this is the case, is there anything more suitable than the CA3160?

TIA :)
 

MikeMl

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Most Helpful Member
You have both pos and neg supplies?
What are your power supplies?
What Common-mode input range?
Can you use a voltage follower config, and get the gain in a second stage?
How much gain?
What offset can you tolerate?
 
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crutschow

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Most Helpful Member
The main reason to use an instrumentation amp is for its differential inputs with controlled gain. If you don't need to amplify differential signals then a standard op amp will be cheaper and likely work just as well or better than an instrumentation amp.
 

Roff

Well-Known Member
I want to create a single-sided input amplifier with very high input impedance (it is fed off a 10M divider), precise gain, low noise and low drift. Bandwidth up to 1MHz would be nice, but 100's of KHz will do. I started off looking at the CA3160, but got onto looking at instrumentation amps, since this is for a voltmeter which should be able to resolve 3mV.

Comparing data sheets, for my purposes there doesn't seem to be much to choose between the op-amp and any of the in-amps I can afford.

So I was wondering, with the inverting input grounded in both cases, is there any advantage in using an in-amp, or had I better stick with using an op-amp, and if this is the case, is there anything more suitable than the CA3160?

TIA :)
You don't want to ground the inverting input if you use an op amp.
 

throbscottle

Well-Known Member
MikeMl:
Supply voltage somewhat moot at the moment, but it is + and -
Input range realistically +/- 0.25v, though it could go momentarily rail to rail, at which point ovp kicks in until the autoranging catches up. I'm still going round in circles on this one.
This was originally going to be a voltage follower with gain in the next stage, but it's possible that could change
Total gain including the next stage will only be 10 in either case, or possibly some other number to get more desirable scaling
I put "resolve 3mV" in my original post - I actually meant "resolve 3μV". The total offset for combined stages needs to be less than 1μV, really, to prevent screwy readings at the very lowest end of the scale.

Roff:
Thanks for pointing that out. Duh. My excuse is my head is full of cold and aches and stupid.

crutschow:
After several hours of poring over datasheets and theory, that is what I was starting to think, but I had to ask people who actually know :)

Thanks everyone
 
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