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Active Filter using OPA37

Active Filter using OPA37

This question is not answered
Albert Byun
Posted by Albert Byun
on Apr 30 2012 18:49 PM
Prodigy10 points

Hello,

I have designed an active filter using a OPA37 as shown below, but it causes oscillation at the output near 400Mhz frequency. I have tried increasing the feedback resistance t further increase the closed loop gain above 5, but that did not help. Does anyone have an idea what is causing the oscillation?


Thanks,

Albert

 

OPA37 Active Filter
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  • Bruce Trump
    Posted by Bruce Trump
    on Apr 30 2012 21:37 PM
    Mastermind20880 points

    Albert,

    The OPA37 is a so-called decompensated op amp, intended for operation in gains of 5 or greater. It may appear that the resistor ratios put the op amp in sufficient gain for stable operation, but his is not the case. The feedback capacitor, C2, effectively places the op amp in unity gain at high frequency.

    The unity-gain stable version, OPA27, should be used for this type of circuit. You should also consider using the OPA227, an improved generation of the OPA27. It is is a better op amp in every respect.

    Regards, Bruce.

    filter G=1 OPA37 unstable unity gain
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