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Defining both current and voltage at output port? (Read 3661 times)
Saran
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Defining both current and voltage at output port?
Jan 15th, 2007, 1:26pm
 
I don't know if I am abusing Verilog-A...but, can't we specify both output voltages and currents in a block. For instance, in this oversimplified and incomplete model of a common source amplifier,

snip..
snip..

ampSig = gain * (V(in) - dcoff);
V(out) <+ ampSig + vds;
I(out) <+ some previously computed value.

snip..
snip..

When I run this sim in spectre, my voltage V(out) is what I am expecting to be..However I(out) returns zero. Is there anything horrible I am doing here? I am playing with Verilog-a modeling. This is a simple module with one input and output port (Common source amp).

Thanks,
Saran

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Ken Kundert
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Re: Defining both current and voltage at output po
Reply #1 - Jan 15th, 2007, 2:48pm
 
Conceptually what you are trying to do does not make sense. If you specify the output voltage, then the output current will be determined by the load. If you specify the output current, then the output voltage will be determined by the load. You cannot specify both.

-Ken
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Saran
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Re: Defining both current and voltage at output po
Reply #2 - Jan 15th, 2007, 3:23pm
 
Oh..I was just trying to write a test module. I had specified the voltage but I also wanted to see the drain current of the output transitor. I guess it was clear abuse of Verilog-a. I know I should have specified an intermediate node for that. Anyways, thanks for the response.
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Geoffrey_Coram
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Re: Defining both current and voltage at output po
Reply #3 - Jan 16th, 2007, 6:27am
 
Saran wrote on Jan 15th, 2007, 3:23pm:
I know I should have specified an intermediate node for that.


I'm not sure that specifying an intermediate node will help.  As Ken said, if you specify the voltage, then the load determines the current, and the most you can do is measure it (not set it).
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