Calculate a node's capacitance in Cadence

[milvapp]

Hi all,

I have designed a Cherry Hooper amplifier in Cadence using Spectre-Bsim4 for simulation and i want to find-calculate the total load capacitance at the output node (Vout1 as shown in the image).

Do you have any suggestions or good ideas on how to do that?

Best regards,
Bill

 

[amwygah]

This is a good question, I would like to know the answer. Hope someone can answer.

 

[erikl]

i want to find-calculate the total load capacitance at the output node (Vout1 as shown in the image).

Connect a unit current source (analogLib/idc or analogLib/isin) with AC magnitude=1 and any Frequency between Vout1 and gnd. Then run an ac analysis, sweeping the frequency between your points of interest. The voltage at Vout1 (i.e. over the isin source) is your frequency-dependent impedance: z = v/i . With i=1 , e.g. kVolts ≙ kOhms. From the low frequency part of the magnitude curve you can deduct the resistive part of the impedance, from the high frequency part you can get the reactive, i.e. the capacitive part.

Don't forget to bias the circuit to a reasonable operating point!

 

[milvapp]

Thank you for your help

 

[LvW]

Here is an alternative to the proposed method:

Resulting from the mentioned ac analysis, take the admittance (inverse of impedance) and let display only the imaginary part which is jwC.
This approach assumes that the output admittance consists of a real conductance in parallel with a capacitice conductance (which normally is the case).