Some more questions.
What this circuit actually wants to do is to test the AC impedance of the power supply source.
Assume that the V_source is the DUT , with the R1 and L1 being its AC impedance.
For a giving frequency of the control signal(V_ctl), the MOSFET(Q1A) will draw a current from the V_source,
then the AC impedance of the V_source at this frequency is obtained by FFT(V_Q1A_D)/ FFT(I_Q1A_D)。
The simulation result at 50Hz and 100Hz seems normal, as there is a slight phase difference between V_Q1A_D with I_Q1A_D, as shown in the picture.
But when the frequency of control signal increased to 150Hz, the result seems terrible.
The sweep frequency required should increase at least to 1K Hz.
My questions are:
1. Is it feasible to test the AC impedance in this way?
2. If yes, which changes should I do to the circuit to improve the response under high frequency?