The questions about the feedback of mu-circuit by capacity


Please look at the following schematic diagram of circuit,I added a resistance of 1M in the first positive input of amplifier.When the capacity of inputted port is 2pF,the outputted wave is as the following picture. As the picture shows,the wave isn’t quite true to the original.In the another situation,while I change the inputted capacity to be 3pF,the negative half wave lacks fidelity.My thought:

1).the range of outputted wave can be adjusted two variable resistances.

2).The phenomenon still exists even I change the amplitude of inputted signal.

3).The capacitors belongs to a kind of common ceramic capacitor so that the precision should be high.

4).I would like to adjust the amplitude by changing C1.

How can I realize that? What’s the reason that appearing such a phenomenon? How to revise it?

Oh,yes,the amplifier I used is OP37. This is the OP37’s datasheet. Do the troubles has any relations with it?

Thank you in advance!

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