. Varactor . Construction P N

. Theory . For testing purposes, a front to back ratio of 10:1 is considered normal. . The size of the depletion region in a varactor diode is directly proportional to the amount of bias applied. . As forward bias increases, capacitance (Depletion region) decreases. . As reverse bias increases, capacitance (Depletion region) increases. . In the capacitance equation below, it is shown that only the distance between plates can be changed. Where: A = Plate Area C = Ak k = Constant d d = Distance between plates

. An increase in reverse bias increases the width of the gap (d) which reduces the capacitance of the PN junction and vice versa. . Advantage: Allows DC voltage to be used to tune a circuit for simple remote control or automatic tuning function. . Operation . used to replace old style variable capacitor tuning circuits. . They are used in tuning circuits of more sophisticated communications equipment and in other circuits where variable capacitance is required.

3V 6V 20F 5F P N Depletion Region