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. Varactor . Construction

. 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.

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. Varactor . Construction

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  1. . Varactor • . Construction P N

  2. . 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

  3. . 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.

  4. Depletion Region 20F 5F P N P N 3V 6V

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