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?
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.
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