I have designed a charge amplifier to convert the charge from the force sensor into voltage. The force of the sensor is dynamic from 0 to 100N which is modelled as a voltage source V3 with a sine wave oscillating from 0 to 1KHz. C2 is the sensor static capacitance. The current source B1 is differentiating the voltage from V3. The system need to be able to respond between 0.1 to 1KHz. The problem is as shown in the AC simulation result the circuit on the right hand side does not give a low pass filtered response with a cut off frequency of 1KHz. I have made the circuit on the left hand side with a current source just to confirm that the charge amplifier is designed properly and the response is is as expected so the problem seem to be coming from the charge source. What could be the problem?