Using a MOSFET correctly as a switch in this circuit and how to prevent it from "loading" the circuit?

Question

I have a staircase generator circuit with a MOSFET connected to capacitor 2. The input of the capacitor is connected to a comparator and I wish for the MOSFET to cut off when the output of the comparator is high.

The comparator is connected to a sine wave generator.

The waveform I want to achieve is shown below:

I am having problems achieving this, when the MOSFET is disconnected as above, the wave form I get is this:

So the blue staircase wave is working as intended albeit not resetting. However, the moment I connect the MOSFET the staircase waveform is affected with some weird fluttering at the beginning and it is not resetting the staircase:

.

I have confirmed that with a manual switch the staircase resets as needed, however, I cannot get the transistor to work as intended.

Answer 1

It cannot work like that. The MOSFET discharges the capacitor just down to the value where VStaircase goes a bit lower than Vsine, not down to zero as you wish. It's a negative feedback, that it should do.

To act as you wish you need to trigger a short impulse that fully opens the MOSFET for a short time.