Problem with using imaginary current method

[yushen_yang]

Hi all,

I am using the imaginary current mehtod to test the input capacitance.

Vtest Vnd gnd sin(0.5V 0.5V 100Meg)

.print cap = 'IM(Vtest)/(2*pi*f*Vac)

where f=100Meg and Vac=1v

Is there any thing wrong about this equation, I'm stuck here for a while.

thx

 

[obovolo]

Imaginary current

i suggest u to use s parameter analysis to get the equivalent capacitance.

 

[maxwellequ]

Re: Imaginary current

yushen_yang

Are you making an AC or transient analysis?

 

[gszczesz]

Imaginary current

It looks like you are taking the imaginary of the voltage, not the current...

If Vtest is the current, then you can't take the imaginary of it before dividing it by the voltage. You must take the current and divide it by the voltage waveform first, and then extract the imaginary resistance and real resistance. Taking the imaginary of the current doesn't make any sense since phase is only relevant relative to something (i.e. relative to the voltage applied).

Greg