I want to know what the Ctot(v) and dCtot/dv component are.It’s better to have a model of this variable capacitor
The variables are described in the documentation. Ctot is Q/v (charge in coulombs divided by voltage) and dCtot/dv is the derivative of Ctot with respect to voltage.
These parameters aren’t often defined in capacitor data sheets. The approach taken to model a variable capacitor depends on the available data, but often the data can be converted into a differential capacitance, dQ/dv, as described in the component documentation.
