**10. Nonlinear capacitance of the OHC**

Between the inner and outer cell membrane of the OHC, there is a linear (static) capacitance and nonlinear capacitance. The linear capacitance has a constant value (∼30 pF), which does not depend on the applied voltage *u*. The nonlinear capacitance *C*(*u* ) depends on the voltage applied between the inner and outer wall of the OHC. The shape of this function resembles a bell curve, with a maximum value of approximately 25 pF. It is assumed that the nonlinear capacitance *C*(*u* ) is produced by the movement of confined charges in walls of the OHC.

This nonlinear capacitance of the OHC *C*(*u* ) will be used as an active element in the pro‐ posed parametric cochlear amplifier based on a single OHC. In classical electronics, nonlin‐ ear voltage‐dependent capacitance is called "varactor." By driving a nonlinear capacitance *C*(*u* ) with a the time‐dependent voltage *u*(*t* ), we obtain the capacitance *C*(*t* ) which is a func‐ tion of time.
