Op Amp Decoupling

Discussion in 'General Electronics Chat' started by liquidair, Sep 23, 2012.

  1. liquidair

    Thread Starter Active Member

    Oct 1, 2009
    Here's a simple question that maybe people can learn from.

    I understand why we use decoupling on every chip and active device and why it is beneficial. The common practice seems to be to place the cap directly to the + pin and gnd as close as possible, but this isn't always the best way to do it.

    From what I gather, the best way in opamps is to ground the cap(s) at the ground end of the load as this minimizes the loop area and keeps currents flowing optimally. Correct?

    This is simple 9 times out of ten as the load ground point is very close. But what if it's not as in a relay based attenuator where there is a string of L pads in a row. Here, even using very small relays, I have a 4 inch long circuit. The ideal in this case would be to have the cap right at the + pin but a 4" long ground path. If the cap was grounded right at the most convenient place, you have the supply current flowing against the signal current. What is optimal in this situation?