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How to plot C-V characteristics of varactor diode in LT-Spice?
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kankanas:
Can anyone tell me how to plot C-V characteristics of varactor diode in LTspice?
I made a simple circuit providing reverse bias voltage and swiping the value attached below. I-V plot is observed by this, but how to do C-V plot?
kankanas:
attached schematic.
magic:
Not sure if you can do that with DC sweep.
Try the .step command instead and use AC analysis with the bias voltage source set to 1V AC, measure current through the diode.
Jay_Diddy_B:
Hi,

Do it like this:




There is a special block for measuring capacitance.
The scale is 1V per Farad. pV = pF.

I have attached the LTspice model.

Regards,
Jay_Diddy_B

 capometer.asc (1.01 kB - downloaded 381 times.)
T3sl4co1l:
If your sim doesn't have a C-meter (or it's not general purpose -- IIRC XSPICE introduced such a thing, that really just serves to measure pure capacitances (C's) and digital pin loads, nothing else; YMMV in other tools), you'll have to do it the old fashioned way.  For this, set up for AC steady state analysis, with the expression C = Ic / (2*pi*freq*Vc), where Ic is the capacitor current (magnitude), and Vc is the capacitor voltage (magnitude).  Then sweep DC bias.

Tim
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