Capacitance multiplier circuit using variable resistor to change capacity

OP amplifier Ai is a buffer amplifier, which means that although 0- is connected between A, the output
and m positive-phase input, it is connected
to the capacitor between the output and input of the inverting amplifier circuit. ． The circuit is waiting for help. Ai uses a TFET input OP amplifier, so
it can obtain an equivalent capacitance with high impedance and low leakage current.
  The capacitance varies with four. The ratio of wind to wind changes with each other. If the sliding contact of r is
moved, C1 is increased 11 times on one side and 1 time on the other (the same as R). The variable resistor
is used to change the electrostatic capacity, so it can also be called large-capacity fine-tuning. Capacitor circuit, because this circuit uses the feedback circuit formed by the OP amplifier. The maximum frequency depends on the OP amplifier