[sdiy] Newbie questions about summing buffers

[Neil Johnson]

Hi,

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

Ian Fritz wrote:
>> 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.

David G Dixon wrote:
> I've been reading up on this stuff myself -- break points and loop gain and
> all the rest of it -- but I must confess that when I've got spurious
> oscillations in a circuit, I use good old trial and error to find the cap
> value which eliminates them.

Walt Jung has a nice little write-up about this in his "IC Op-Amp 
Handbook", section 3.3.1.

Cheers,
Neil
-- 
Modules and more :: www.cesyg.com
Homepage :: www.njohnson.co.uk ::