(2) dirty/clean ground again [sdiy]

jhaible jhaible at debitel.net
Sun Aug 18 21:10:52 CEST 2002


> Is it correct that both this Mhz noise and these oscillations can be
> prevented by placing a small cap in parallel with the feedback resistor??

Usually you're compensating the effect of the opamps input capacitance
with a cap across the feedback resistor. If you don't, and if your feedback
resistor is a rather high value, it will form a significant pole in the
feedback
loop in combination with th einput capacitance. Another pole comes from
the opamp's phase compensation, and together these two poles can form
a self-oscillating 2-pole filter.  You can compensate that pole from the
input
capacitance with a cap across the feedback resistor.

JH.





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