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  1. #1
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    chopper stabilized opamp

    Hello,
    I am working on read out circuits. I am using chopper stabilized folded cascode amplifier. The problem in the chopper stabilized circuit is when using chopper in the input stage drastically reduces the gain of the amplifier from KV to mV.can anybody help with this??

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  2. #2
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    Re: chopper stabilized opamp

    This sounds like a problem with your circuit, not with
    the chopper concept. I've seen recently a CSOA with
    >100dB gain and <100uV Vio at test (not my design,
    and not mine to divulge).

    Chopper should operate out-of-band and moderate gain
    and its per-cycle authority pretty small. Chopper only
    works well when the input spends most of its time at
    null, works poorly when forced to slew hard (fights itself
    and accumulates bogus error-signal).

    If by "readout circuits" you mean high pixel count ROICs
    I think the chopper is a bad idea, video is not like the
    usual DC/LV CSOA application (or if it was, why take a
    picture at high frame rate?). You might want to take a
    step back and consider other "autozero" techniques for
    the front end pixel amplifier if that's what this is about.



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  3. #3
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    Re: chopper stabilized opamp

    Thank you for the reply. I am designing low noise readout IC. For that I need chopper stabilization to get rid of 1/f noise. After doing some modification the input stage of the two stage folded cascode, chopper works fine. But the problem arises when the chopper is introduced between the first stage and second stage. It reduces the gain of the first stage because of the formation of SC resistance due to the parasitic capacitance present in it. For that i reduce the size of the cascoded stage also...but it does not show any improvement..
    previously the gain was 95 db, now it is 65 db..



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