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Simulators >> Circuit Simulators >> Simulation for Ferroelectric Varactor
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Message started by aguntuk on Nov 29^th, 2018, 2:24am

Title: Simulation for Ferroelectric Varactor
Post by aguntuk on Nov 29^th, 2018, 2:24am

Hi,
I have created a Ferroelectric Varactor model using VerilogA. Now, I wan to simulate the C-V curve. I have added a voltage source with the varactor. Can anyone help to setup in ADE to simulate C-V curve?

I am using Cadence Virtuoso with spectre simulator.
Version: ICADV12.3-64b.500.21

I have attached my ADE and testbench screenshot.

Title: Re: Simulation for Ferroelectric Varactor
Post by Ken Kundert on Dec 2^nd, 2018, 5:07am

Run an AC analysis.
Configure the AC analysis so that it sweeps DC voltage rather than frequency.
Plot the current through the capacitor.

You are left with two free variables: AC magnitude of the source and the analysis frequency. Set one to 1, set the other so that the output current is scaled so that you are plotting in Farads directly.

-Ken

Title: Re: Simulation for Ferroelectric Varactor
Post by Ken Kundert on Dec 2^nd, 2018, 5:10am

That procedure is described in Modeling Varactors.

There is a trick to modeling varactors. You should read and follow the guidance of that paper carefully.

-Ken

Title: Re: Simulation for Ferroelectric Varactor
Post by aguntuk on Dec 14^th, 2018, 2:22am

Ken Kundert wrote on Dec 2^nd, 2018, 5:07am:

Run an AC analysis.
Configure the AC analysis so that it sweeps DC voltage rather than frequency.
Plot the current through the capacitor.

thanks for your answer. I like this manual idea. I am confused about the analysis frequency. I put the ac magnitude to 1 Now in ac analysis, what should be the analysis frequency so that I can make it to farad? I didn't get the conversion here. Can you help me with this?

Title: Re: Simulation for Ferroelectric Varactor
Post by Geoffrey_Coram on Dec 14^th, 2018, 5:55am

If I analyze this circuit

v1 1 0 1 ac 1
c1 1 0 1p

at 1 Hz, then the ac current in the voltage source is 6.28e-12, that is, 2*pi*the capacitance in Farads. So, you could change either the ac magnitude or the frequency to scale out that 2*pi.

Title: Re: Simulation for Ferroelectric Varactor
Post by aguntuk on Dec 14^th, 2018, 7:42am

V=I*Z=I/(jwc) , so |C|=|I/(w*V)| if V=1,w=1 then C=I. w=2×Π×f, if I wanna have w=1 I have to setup f=0.159 Hz

Now I put this frequency in the analysis... but the current which gives me actually the impedance is not the capacitance that should be for a varactor. My verilogA model contains leakage current also which also counts. This curve is ok for the current curve but with the frequency and ac magnitude of 1V the conversion to capacitance is opposite.

Title: Re: Simulation for Ferroelectric Varactor
Post by Ken Kundert on Dec 14^th, 2018, 12:05pm

If the drive voltage is 1, then plotting the current is the same as plotting admittance (not impedance). And if the admittance is purely imaginary and the frequency is 1/2π, then plotting the admittance is the same as plotting the capacitance in Farads.

How are you passing an amp through your capacitor. Is C₀ on the order of a Farad?

-Ken

Title: Re: Simulation for Ferroelectric Varactor
Post by aguntuk on Dec 17^th, 2018, 2:37am

I have applied equation of charge and current from a paper where they implemented the ferroelectric capacitor using the charge and considering the leakage current:

The equations have been provided in the screenshot. I used their equation and the curve that they have generated is not matching maybe my conversion is not right.

I have used the below code before ending module as in the paper described:
I(in,out) <+ itemp + ddt(qq);
V(in,vr) <+ ddt(L*1e-12*I(in,out));
V(vr,vc) <+ R*I(in,out);

Title: Re: Simulation for Ferroelectric Varactor
Post by Ken Kundert on Dec 17^th, 2018, 12:13pm

Please give the whole model. It is hard to make sense of what little you have provided.

-Ken

Title: Re: Simulation for Ferroelectric Varactor
Post by aguntuk on Dec 20^th, 2018, 12:33am

There was a mistake in conversion of units in the model. Now it works Thanks a lot.