Output to an op-amp differentiator circuit
I suppose your circuit is an &quot;ideal&quot; differentiator? A feedback path with just one capacitor and one resistor ?
This circuit will always be unstable because the opamp behaves (nearly) like a 2nd-order lowpass. Together with the feedback network (1st-order lowpass) the loop gain will violate the stability criterion (loop gain magnitude still larger than 0dB for 360deg loop phase shift).
You should use a resistor in series with the capacitor. The price for the stabilization is a reduced range of frequencies where the circuit can differentiate.
EDIT:  Here are some hints for finding an appropriate value for the additional (compensating) resistor Rs:
When wo=1/RfCs (Feedback resistor Rf, Series capactor Cs) and wt is the transit frequency for the opamp (first-order model), then the resistor Rs can be calculated (for a phase margin of app. 45 deg) as
Rs=Rf/SQRT(wt/wo)