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Need Low Freq. CGD from CDGBO, CGDBO, or simulation

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cl254

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Dear All,

I use HSPICE and in its MOSFET Output Templates, there are parameters with names reversed like CDGBO (LX32, intrinsic drain-to-gate capacitance, =-dQd/dVg) and CGDBO (LX19, intrinsic gate-to-drain capacitance, =-dQg/dVd), looks like they are transcapacitances. My circuit is not high frequency and I only need the low frequency CGD value. How to compute my CGD out of the transcapacitances or get from HSPICE simulation?

Thank you very much!
 

Set up a simple simulation, G=B=S=gnd! and D with
a high value resistor to gnd! and a pulse current
source. Pick a current source pulsed value that
causes drain to jump by maybe 100mV (enough of
a "signal" to trust that tolerances are not affecting
data, not enough to get into C-V curve to the point
that you are no longer like the Cdg0 condition).
Integrate current pulse for Q (cccs onto a fixed cap,
or do the FWHM arithmetic), Cdg=Qpulse/Vd(final).
 

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