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Simulators >> Circuit Simulators >> How to plot capacitor value in Spectre?
https://designers-guide.org/forum/YaBB.pl?num=1208773083

Message started by shuguang on Apr 21^st, 2008, 3:18am

Title: How to plot capacitor value in Spectre?
Post by shuguang on Apr 21^st, 2008, 3:18am

I want to simulate the varactor in Spectre and plot the capacitor value vs. voltage.
How to do it?
Thanks.

Title: Re: How to plot capacitor value in Spectre?
Post by pancho_hideboo on Apr 21^st, 2008, 4:19am

shuguanguy wrote on Apr 21^st, 2008, 3:18am:

I want to simulate the varactor in Spectre and plot the capacitor value vs. voltage.
How to do it?
Thanks.

It depends on what domain you use in evaluation of capacitor, AC or Transient.

(1) AC
Drive DUT by voltage source, then get impedance.

(2) Transient
Drive DUT by ramp voltage signal, then get current.

Title: Re: How to plot capacitor value in Spectre?
Post by achim.graupner on Apr 21^st, 2008, 4:23am

Dear shuguang,

Description:
Set up a schematic with a voltage source connected to the varactor. Set AC Magnitude to "1".
Set up an AC-Simulation, sweep DC Voltage of the voltage source. Use 1/2Pi=0.159 as frequency.
Plot the current (AC current) of the voltage source = capacitance value. When using any other frequency than above, divide the current by 2Pi and the frequency.

Explanation:
AC computes small signal values, i.e. derivatives of the plotted signal vs. the AC sources. If plot the varactor's current IF("/V1/PLUS") the AC Analysis yields dIC/dVC.
dIC/dVC = j*ω*C * vc = j*2πf*C * vc
where vc is the small signal voltage (AC Magnitude), vc=1.
Thus:
C = dIC/dVC / 2πf / vc = IF("/V1/PLUS") / VF("/V1") / 2πf

Understandable? If not - please ask.
Regards,
Achim

Title: Re: How to plot capacitor value in Spectre?
Post by shuguanguy on Apr 21^st, 2008, 8:29pm

Good idea.
Thanks.