[time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking

[Charles Steinmetz]

Scott wrote:

> 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 
capacitance.

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.

Best regards,

Charles