Varactor Model
A diode in reverse is often used as a voltage controlled variable capacitor, or varactor,
in high-frequency applications.
The parameters cj and phi
are temperature dependent, where again the temperature coefficients depend on material constants.
The grading parameter m
and the parasitic parallel capacitance cp only depend on the data,
and are independent of all other material constants.
The parameters cj, the capacitance at zero volts,
and phi, the build-in voltage,
represent the values at the nominal temperature Tnom.
The BB909 is a Silicon varactor with a hyper-abrupt junction: