Varactor Diode Calculator

What is Varactor Diode?

A varactor or variable capacitor diode is a p-n-junction diode in which the junction capacitance of the diode can be easily altered by varying the applied reverse bias voltage. This diode works in the reverse-biased mode. The depletion region of the diode forms the junction capacitance, and the capacitance value is inversely proportional to the width of the depletion region. 

When the applied reverse bias voltage is increased that results in the depletion width getting increased; thus, the junction capacitance will decrease. Similarly, the junction capacitance will increase when the applied reverse bias voltage level is decreased. The varactor diodes are used in TV receivers, FM radio, adjustable bandpass filters, microwave frequency multipliers, and much more applications.

How to calculate Diode Capacitance, Cutt Off Frequency and Q Factor? 

The varactor Diode capacitance, cut off frequency and Q factor can be calculated by using the following formulas.

C_d = Diode Capacitance (at 0V)

k = 1

V_b = Barrier potential/voltage

V = Applied reverse bias potential/voltage

m = constant (i.e. material dependent)

R_s = Series resistance

F =  Cutoff frequency

f = Operating frequency

Q = Quality Factor

Example:

C_d at 0V = 90 pF, V_b  = 0.52V, V = -5V, R_s = 14 Ohm, Operating frequency = 60 MHz, m factor = 0.5

Diode capacitance = 38.30 V, cutoff frequency = 296.92 MHz, Quality factor = 4.94