[sdiy] Newbie questions about summing buffers

Ian Fritz ijfritz at comcast.net
Fri Feb 24 20:14:25 CET 2012

>Capacitor across Rf forms a low pass filter, helps dampen any high 
>frequency oscillations at the output.

People often write this but it isn't quite true.  The feedback cap 
stabilizes the circuit by compensating for opamp nonidealities, not by 
acting as a LP filter.  IOW you can't clculate the cap size just from the 
frequency of the spurious oscillations.  There is a good TI writeup about 
this online somewhere.


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