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question about the instrumentation amplifier for biomedical

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Newbie level 5
Sep 24, 2007
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instrumentational amplifier objective questions

I'm currently surveying the related papers about instrumentation amplifier for biomedical signal. Some papers say they have very low power consumption(below 1 uW), but not enough good CMRR(about 80dB) and gain is 40dB.

My first question is, because the power line interference is the largest disturance, does the amplifier with low CMRR work? or not? How much large is the power line interference amplitude if I use AC coupled input ( 1M ohm equivalent assumed). Someone says 1Vp-p, but the output wave may be cut due to the input transistors cut off in low supply voltage environment, right?

My second question is, Could the power line interference be the design issue about the input common-mode range of the instrumentation amplifier? Sufficient large input common-mode range prevents the input transistors from being cut off, but how much large? I am not sure the correction of my words...

Please share the knowledge with me, if u know.
thanks a lot.

instrument amplifier for biomedical

In both your two questions, I think the key point is to make the instrumentation amplifier input range rail to rail.


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I found some papars make an quantitive analysis about the power line interference. It is 1mv p-p at most. Thus, the input common-mode range is mainly limited to the electrode offset +-50mv. And this could be cancelled by the proper feedback. However, some papers don't have feedback network to cancel the electrode offset. They use the rail-to-rail IA in order to endure the offset and the amplified offset at the output, rail-to-rail IA is adapted. But, low CMRR is the drawback.
Anyway, thanks for ur reply and advice.

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