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# hspice warning: Pd =0 is less than W?

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#### vhdl00

##### Junior Member level 2
warning: pd = 0 is less than w.

it is said that hspice will calculate the junction capcitance automatically with w, L only. for the warning, seems it won't calculate the Cj correctly assuming Pd=0?
or my hspice is outdated?

thanks

#### chunlee

the Pd is depend the layout u draw. Pd will always greater than W. so hspice will generate a warning message if Pd < W

#### vhdl00

##### Junior Member level 2
hspice pd

thanks chunlee, you mean it is normal to get the warning like this? i was trying to extract a hspice netlist from cadence tool, it did have ps pd value. Compare the capacitance, there are some differences. I just thought the hspice should generate some pd value, which should depend on the mosfet size(w,L).---it is just the drain perimeter.
thanks again

#### chunlee

pd is less than w.

hspice has default value for pd ps ad as. if i don't forgot, the default value is 0. I don't use cadence before. so i don't know cadence will generate pd and ps automatically or not. But again, pd ps ad as is depend the layout u draw.

But u can use following formula to estimate the value of pd ps ad as. formula was given by somebody in this forum.

PD = PS = 5*Lmin + W or 5*Lmin

#### sunking

ps is less than w

require the foundry for the PDK. then the software will generate the PD PS and so on, Or you have to caculate by yourself.

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