LV instrumentation amp with decent CM input range?

Question

I'm looking for an instrumentation amp to be run on a lithium battery (3V). I need low power consumption and a common-mode input range (CMIR) of as much of the "power supply" as I can get. All of the IAs I've looked at so far

- TI, AD, LT, good grief I've even checked out Maxim's - all are pretty limited on CMIR. Especially towards the positive end. The closest, so far is the AD623, but that's not good enough.

Have I overlooked something? Must I build my own from a RRIO amp + resistors? I need to switch gains, so that's looking kinda klunky!

Any tips appreciated!

-f

Hal Murray · Accepted Answer

You can boost the input range by running the input signal(s) through a resistor divider to ground. Of course, you have to get the resistors ballanced.

Here is another possibly crazy idea to add to your collection...

They make flying-cap boost regulators. The chip and caps might be less-ugly than the do-it-yourself alternatives.

Jamie · Answer

Hmm:   Flying-cap boost regulators? that's a new one on me.do you mean charge pump maybe?-- "I'm never wrong, once i thought i was, but was mistaken"Real Programmers Do things like this.

Frank Miles · Answer

Thanks, but... the differential signal is very low level. Can't attenuate without losing it in the noise. I'm also very space and power limited, so it's hard to come up with a converter - and adequately filter its output to keep supply-coupled noise in check.

I was really hoping someone would know of a device that wouldn't lose half or more of its CMIR when operated at low voltages. If there's no alternative, either the RRIO+resistors or sort of voltage converter may be unavoidable.

Thanks for the thoughts...

-f

Ecnerwal · Answer

In article , Frank Miles  wrote:Two-three lithium batteries might be simpler than a voltage converter.-- Cats, coffee, chocolate...vices to live by

LV instrumentation amp with decent CM input range?

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