Pin Diode Junction Capacitance

March 17, 2017

Any variation of the charge within a p n diode with an applied voltage variation yields a capacitance wich must be added to the circuit model of a p n diode. The low capacitance will not pass much of an rf signal.

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Thus making it a pin diodethe presence of intrinsic region exhibits high resistance property.

Pin diode junction capacitance. Under a forward bias of 1 ma the on state a typical pin diode will have an rf resistance of about 1 ohm making it a good rf conductor. Consequently the pin diode makes a good rf switch. When reverse bias voltage applied to the p n junction diode is increased a large number of holes majority carriers from p side and electrons majority carriers from n side are moved away from the p n junction.

Under zero or reverse bias the off state a pin diode has a low capacitance. A pin diode is an advancement of normal pn junction diode. Although not as widely used as normal pn junction diodes pin diodes are nevertheless used in large quantities.

It will vary with its voltage vc. Pin diodes are particularly used in rf applications where there low levels of capacitance and also their switching and variable resistance properties make them very good in switching and variable attenuator applications. For subsequent analyses the depletion capacitance is not fixed at dc bias.

It is a 3 layer device in which an intrinsic layer ie undoped semiconductor is sandwiched between p and n regions. The capacitance associated with the charge variation in the depletion layer is called the junction capacitance while the capacitance associated with the excess carriers in the quasi. The capacitance at the depletion region changes with the change in applied voltage.

After the dc condition of the diode model has been determined that is under forward or reverse bias condition the pin diode intrinsic resistance r is fixed for all subsequent analyses.