[time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking
csteinmetz at yandex.com
Sat Jan 28 16:49:49 EST 2017
> Parasitic capacitance on the inverting terminal from routing and the
> input capacitance of the opamp itself, adds another pole to your opamp's
> loopgain, burning phase margin.
> A small compensation cap across the top leg of your feedback divider, would
> boost your phase margin.
Also, block out the ground plane on all layers under the inverting input
and the traces leading to the feedback resistors, to minimize stray
The OP mentioned that the peaking was greater at the outputs farther
away from the input opamp (i.e., those with longer feed trace). The
trace inductance resonates with any stray capacitance. Block out the
ground planes under and adjacent to the feed trace. It may also help to
terminate the far end (not the near end) of the feed trace with 50-100
ohms, and increase R109 to ~50 ohms.
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