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Noise analysis of single transistor (Read 150 times)
kabir_fakir
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Noise analysis of single transistor
Jul 11th, 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).
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noise_tb.PNG

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kabir_fakir
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Re: Noise analysis of single transistor
Reply #1 - Jul 11th, 2017, 6:13am
 
Here is the graph of the input and output noise. Its vsd (voltage spectral density)
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Geoffrey_Coram
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Re: Noise analysis of single transistor
Reply #2 - Jul 14th, 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.
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kabir_fakir
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Re: Noise analysis of single transistor
Reply #3 - Jul 17th, 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! Smiley
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Ken Kundert
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Re: Noise analysis of single transistor
Reply #4 - Jul 17th, 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
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kabir_fakir
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Re: Noise analysis of single transistor
Reply #5 - Jul 18th, 2017, 3:23am
 
Ken Kundert wrote on Jul 17th, 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.
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