measurement of output impedance

[akhilrathore]

measurement of output impedance of circuit

hi i need to measure output impedance of a circuit as a function of frquency,
in spectre....
can anybody tell me just how to do it.... or can i get some good user guide of
spectre...

thanx in advance...

 

[transbrother]

If you think of the circuit as a blackbox, take the node you want to get the output impedeance of. instantiate a capacitor of a very high value in spectre (>1MegaF). Connect one terminal of the capacitor to the node you want ot measure the output impedance of, and connect the other terminal to an AC voltage source and have the AC magnitude as 1. Run an AC sim.

Use the calculator funciton and plot the AC signal 1/Icap Vs frequency where Icap is the AC current coming out of the capacitor. This ratio (1/Icap) is your impedance of the node you are measuring.

Make sure you dont have any other AC sources.