simulation varactor

Hi, I am trying to simulate a varactor using cadence . I would like to
know the type of simulation (transient simulation or S-parametres
simulation) and the circuit that I can use to plot the control
voltage vs the capacitance of a varactor using cadence.
Does anyone know how to make this simulation using cadence.
Thanks

 

Hi Maryouma,

I would advice :

1. A simple DC sweep to plot the varactor capacitance vs voltage.
You have to connect a DC voltage source (analogLib/vdc) to your A/K
node (in case of a P/N type diode varactor) or G node (in case of a
MOS varactor).
launch ADE and choose DC and sweep the value of your VDC.

2. If you want to plot the Q factor :

2.1 You can either run an AC simulation and plot the Q-factor as the
ratio of the imaginary part to the real part of Y11 at a given
frequency. You can run mutliple simulations with a set of voltages if
you want to plot the Q-factor vs Voltage at a given frequency.

2.2 Or, Run S-parameter simulation, that's the common way to plot Q
factors.
You need for this to add the input/output ports to your schematic
(analogLib/port). Specify the port numbers in the properties of your
ports: 1 for input, 2 for output.
Specify the port resistance (default is 50 Ohm).
+ Run ADE and choose SP in the Analysis setup.
+ Under the Ports box, select the input and output ports on the
schematic
+ Select Frequency as the Sweep Variable
+ Sweep frequency from min to max with a given step
+ Run the simulation
+ Go to Results -> Direct Plot -> S-Parameter ... and Plot S11 (dB20)
(other if you want) using the S-parameter results window.

Simple as that ;-)

Please give a look to the following readings for more infos.

1. www.designers-guide.org/Modeling/varactors.pdf
2. www.cadence.com/whitepapers/pspapn1.pdf

Any other ideas folks ?

Good luck ;-)

Riad.