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Diode Junction Capacitance With Diffusion: PNDCAP



PNDCAP models a PN junction depletion and diffusion capacitance. It is identical to the model used in SPICE for diodes and the capacitance components of BJTs.


Name Description Unit Type Default
ID Device ID Text PD1
*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
*TT Storage time Time 0 ns
*IS Reverse saturation current Current 1e-11 mA
*N Ideality factor   1
*T Temperature Temperature 27 DegC
AFAC Area scaling factor   1

* indicates a secondary parameter

NOTE: Although junction current parameters must be entered to calculate diffusion capacitance, this model does not include junction current.

Implementation Details

The depletion charge expression is identical to that of PNCAP. Additionally, PNDCAP includes a diffusion charge component, given by the following:


In the above equations, q is electron charge, K is Boltzmann's constant, and T is temperature in Kelvins. The total charge is the sum of the depletion and diffusion components.


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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