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Simulators >> Circuit Simulators >> Noise analysis of single transistor
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Message started by kabir_fakir on Jul 11^th, 2017, 6:08am

Title: Noise analysis of single transistor
Post by kabir_fakir on Jul 11^th, 2017, 6:08am

It might be very simple question. But I am trying to simulate a single trasistor output and input noise PSD in spectre. Here is the testbench. Can anyone tell me what is wrong in the testbench because I am getting zero output noise (PSD) with this testbench.I can not understand it.

The output node is drain terminal(net04).

Title: Re: Noise analysis of single transistor
Post by kabir_fakir on Jul 11^th, 2017, 6:13am

Here is the graph of the input and output noise. Its vsd (voltage spectral density)

Title: Re: Noise analysis of single transistor
Post by Geoffrey_Coram on Jul 14^th, 2017, 12:47pm

It looks to me that the drain terminal is vdd!, not "net04", in the schematic you posted.

Obviously, if your drain terminal is connected to a voltage source, then there will be no output noise voltage. Some simulators allow you to get an output noise current directly; others, you'll need a ccvs to convert the current (in the voltage source providing the drain bias voltage) into a voltage.

Title: Re: Noise analysis of single transistor
Post by kabir_fakir on Jul 17^th, 2017, 5:40am

Thanks for your reply. You are right that its drain terminal is connected to the vdd. But I was not aware of the fact that spectre need ccvs.
Now I have modified my testbench and put a resistor at the drain terminal and I can see the output noise PSD! :)

Title: Re: Noise analysis of single transistor
Post by Ken Kundert on Jul 17^th, 2017, 7:16pm

Spectre does not require a CCVS in this situation. You only need to tell the noise analysis that you want the noise in a branch or terminal current rather than a node voltage.

-Ken

Title: Re: Noise analysis of single transistor
Post by kabir_fakir on Jul 18^th, 2017, 3:23am

Ken Kundert wrote on Jul 17^th, 2017, 7:16pm:

Spectre does not require a CCVS in this situation. You only need to tell the noise analysis that you want the noise in a branch or terminal current rather than a node voltage.

-Ken

Thanks for the clarification.