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Design Languages >> Verilog-AMS >> Separating real from imaginary
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Message started by jefkat on Aug 5^th, 2005, 6:49am

Title: Separating real from imaginary
Post by jefkat on Aug 5^th, 2005, 6:49am

Hello everyone,
I'm trying to make a complex impedance meter. Well to begin with I can connect an external voltage source to an external impedance, sense the current inside the module and then find the impedance ...
How about real en imag. parts? any idea?
Thanks for your comments
bye
shafkat

Title: Re: Separating real from imaginary
Post by Eugene on Aug 5^th, 2005, 10:45am

Since your post is in the VerilogAMS section I assume you are asking a modeling question, not a circuit design question.

How would you connect the meter to the device under test? Are you trying to find the impedance looking into a pair of nodes? A transimpedance? Are you trying to measure a small signal impedance or a large signal impedance?

Title: Re: Separating real from imaginary
Post by jefkat on Aug 8^th, 2005, 12:08am

well yes, it's the same as measuring the impedance bw two nodes. I connect the meter to two nodes. Internally short them by making their volt. difference equal to 0 (in the module). The voltage at the terminal is known so I need to sense the current to find the impedance Z= V/I.

Now an AC analysis quits at this statement saying it is a divide by zero. This is driving me nuts ,,any help !!!

Thanks anyway.
shafkat

Title: Re: Separating real from imaginary
Post by Ken Kundert on Aug 8^th, 2005, 1:22am

You cannot measure impedance in Verilog-A/MS because it is a time-domain language and impedance is a frequency-domain concept.

You are no doubt getting the divide by zero because the DC current I is zero. Remember that AC analysis linearizes about the DC operating point.

-Ken

Title: Re: Separating real from imaginary
Post by Eugene on Aug 8^th, 2005, 8:11am

If you are trying to measure an AC impedance (which involves small signals), why wouldn't you simply drive the pair of nodes with an AC current source (0 amps DC, ACmagnitude=1A) and observe the AC voltage? Why do it through AMS?

Title: Re: Separating real from imaginary
Post by jefkat on Aug 8^th, 2005, 8:33am

Thanks for your time guys..
Well I wanted to characterize different technology caps..
I am not using simply AC analysis to avoid using calculator.
Besides I need some other parameters as well like
Q. And it is important for me to be able to separate real and imaginary parts (parasitics determination).

Alright thanks again..
have a nice day
shaf.