ADA4637 OP Oscillate


Have the below circuit with ADA4637, without or with input, have the below interesting issue.

       ----30M oscillation when C34 is 220pf, Oscillation disappear when C34 is 12pf. Why? Change R35 can't help.

      --I select other FET OP, there is similar oscillation as ADA4637 when C34 220pf. I change OP into no FET OP, there is no oscillation even C34 220pf.  Why?

Best Regards,


  • 0
    •  Analog Employees 
    on Oct 20, 2020 6:50 AM 1 month ago

    Hi Kent,

    According to the datasheet, the ADA4637 is a decompensated amplifier. This means that you must set the noise gain of the op amp equal to or greater than 5 to achieve stability. Upon checking your schematic, I can't verify the gain that you've set for the ADA4637.

    If you can't change the noise gain of your circuit to 5 or more, then you could also look into the ADA4627. The difference between the ADA4627 and ADA4637 is that the ADA4627 has lesser GBW and slew rate, but it is stable at a gain of 1.