about C-V curve......

Ding Yan said:

Hi guys. Can anybody give me some hints on how to plot the C-V curve of a PMOS varactor. I am using cadence ADE and I am trying to find out the linear tuning region. Thanks

Yan

Click to expand...

Ding Yan said:

Hi guys. Can anybody give me some hints on how to plot the C-V curve of a PMOS varactor. I am using cadence ADE and I am trying to find out the linear tuning region. Thanks

Yan

Click to expand...

flatulent said:

The I V curve will look like an ordinary diode. I suspect what you want is a graph of the small signal capacitance verses reverse bias.

One of the problems of using an ordinary capacitance meter is the large signal used for the measurements.

I suggest that you make an LC oscillator and measure the frequency vs. bias and back out the capactiance from a calculation knowing the L.

Even better would be using the data sheet data.

Click to expand...

timof said:

Ding Yan said:

Hi guys. Can anybody give me some hints on how to plot the C-V curve of a PMOS varactor. I am using cadence ADE and I am trying to find out the linear tuning region. Thanks

Yan

Click to expand...

You can simply run Spice (Spectre) AC simulation using PMOS varactor model and by sweeping its voltage, then plot capacitance (equal to imaginary part of the current divided by angular frequency [omega]) versus applied voltage.

Click to expand...

wpchan05 said:

Ding Yan said:

Hi guys. Can anybody give me some hints on how to plot the C-V curve of a PMOS varactor. I am using cadence ADE and I am trying to find out the linear tuning region. Thanks

Yan

Click to expand...

place an ac voltage source with dc voltage as vin, ac_mag=1/(2*pi*1) to the positive node of your varactor, while ground the negative node with 0V. Run an ac analysis using design variable as a sweep and set the frequency as 1. Also, pick up vin and choose the sweep range in the form. Measure the ac current goes into the positive node of your varactor.

i = (2*pi*1 )*C*ac_mag

the measure current will be equal to C

Click to expand...