Taming the Oscillating Op Amp

RE: Taming the Oscillating Op Amp

Giorgio Minai — Tue, 11 Feb 2025 00:10:12 GMT

Hi Bruce, could you please post the link to the post that followed this one?

RE: Taming the Oscillating Op Amp

Bruce Trump — Sun, 24 Jun 2012 23:07:22 GMT

Philip,

Good point. My primary experience is the the <50MHz range but, of course, all op amps need need good bypassing to avoid feedback through the power supplies. The issues are much trickier in your GHz range because good supply bypassing is harder to achieve. Circuit board trace inductance that would be unimportant in the MHz range can create significant impedance at a GHz. And the higher supply currents due to low impedance loads make good layout and bypassing technique crucial. Data sheets for these amplifiers often make recommendations and provide suggested layouts that are helpful.

Thanks for your comments-- Bruce.

RE: Taming the Oscillating Op Amp

Philip Petch — Sun, 24 Jun 2012 21:19:01 GMT

The most interesting oscillating opamp problem I have had involved a 1GHz+ bandwidth current feedback with limited power supply rejection. Four such amplifiers in series formed a bandpass filter up to 160MHz with 120 times gain into a 50 ohm load. In this case the feedback path was via the power supplies and was cured with heavy filtering of the supplies to each amplifier.

Keep up the good work! PeppyKiwi

RE: Taming the Oscillating Op Amp

Bruce Trump — Wed, 20 Jun 2012 14:55:08 GMT

Ramin-- I see that Collin is assisting you on the forum so I'll let him respond. I think it's best to keep all the advice regarding your circuit in your forum thread. Thanks for reading. Bruce

RE: Taming the Oscillating Op Amp

ramin anushiravani — Wed, 20 Jun 2012 13:35:41 GMT

Thanks a lot for posting this awesome information. Quick question, can I apply my microphone to Vin with a lowpass filter on the side to the positive input? The reason I'm asking is because I tried applying to my preamp circuit ( I was getting very high oscillation from OPA2134) and now I'm not getting any signal out and I still have the oscillation :(

RE: Taming the Oscillating Op Amp

Bruce Trump — Fri, 01 Jun 2012 19:19:49 GMT

Thanks, BigDogGuru (I've never addressed anyone that way). I will consider your suggestion. The mechanics would not be difficult as preparation is in MS-Word with the figures dropped it. I would need to go back a capture some minor tweaks. I always seem to find something to change when I see it in the blog format.

Regards, Bruce.

RE: Taming the Oscillating Op Amp

BigDogGuru — Fri, 01 Jun 2012 01:44:35 GMT

"The Signal" is a fantastic blog Bruce and each post a true gem. Keep them coming.

Have you considered publishing your series of posts in PDF format for reference off site?

BigDog