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Diode Junction Capacitance: PNCAP



PNCAP is a PN or Schottky junction depletion capacitance. It is identical to the model used in SPICE for diodes and the depletion components of BJT capacitance.


Name Description Unit Type Default
ID Device ID Text PC1
*CJ0 Zero-voltage junction capacitance Capacitance 0 pF
*VJ Junction potential Voltage 1 V
M Grading parameter   0.5
*FC Depletion capacitance linearization parameter   0.5
AFAC Area scaling factor   1

* indicates a secondary parameter

Implementation Details

The charge-voltage characteristic Q(Vj), where Vj is junction voltage, is identical to that used in SPICE to model depletion capacitances. It is given by the following equations, which result in a linearly with junction voltage when Vj > FC VJ. This prevents the problem of


The capacitance-voltage characteristic C(Vj) is found by differentiating the above equations:


When 0.999 < M < 1.001, it is offset to the closest end of this range.


This element does not have an assigned layout cell. You can assign artwork cells to any element. See “Assigning Artwork Cells to Layout of Schematic Elements” for details.


[1] P. Antognetti and G. Massobrio, Semiconductor Device Modeling with SPICE, New York: McGraw-Hill, 1988.

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