AVR-Chat

Robert Wrote
>That's a caution that the s/h cannot track a rapidly changing signal.  It,
>after all, forms a low pass filter as well.  Also the cap will form a low
>pass filter with the divider with quite a low frequency given the resistor
>values.  The signal simply will not change quickly enough to effect the low
>pass filter.  

Well, that was unclear.  I meant something more like

The signal on the external cap will not change quickly enough to effect the
s/h circuit in the A/D circuitry.

>And the cap is large enough the voltage it won't be disturbed
>by the delta Q from the sample and hold cap.


>>Have you used such a circuit successfully before?
>
>Many times.  I use a simple RC to provide Nyquist filtering quite
>frequently, even or maybe especially on bandwidth limited signals.

I even had a case where I left it out since the sensor was bandwidth
limited to the frequency I wanted to sample and its impedance was low
enough to feed the A/D input directly.  After some hair tearing
troubleshooting I ended up putting it back in.

Robert



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