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Why resistors produce so much noise (Read 17533 times)

pancho_hideboo

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Re: Why resistors produce so much noise
Reply #15 - Sep 28^th, 2010, 8:19pm

vp1953 wrote on Sep 28^th, 2010, 5:08pm:

In you analysis, can you take out R2 altogether (and not set it to 0)
- and have a non-zero voltage source connected across a noisy resistor with one end of the resistor and voltage source connected to ground.

Try by yourself.
Then show me your results and netlists.

I showed noise current RMS value evaluated from transient noise analysis when "R2=0" is replaced by "vdc=0".

I think simply you are wrong in obserbing noise current.
Obserbe "Inoise=Itotal-Idc" not "Itotal".

You have to consider difference of magnitude order between Idc and Inoise.
Inoise is very very very very very small comapred to Idc.

Also you have to set "reltol", "vabstol" and "iabstol" appropriately with considering Idc and Inoise magnitudes.

« Last Edit: Sep 29^th, 2010, 4:17pm by pancho_hideboo »

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Andrew Beckett

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Re: Why resistors produce so much noise
Reply #16 - Jan 2^nd, 2011, 3:33am

pancho_hideboo wrote on Sep 27^th, 2010, 4:28am:

But conventional small signal noise analysis of Cadence Spectre results in error when resistor value is zero,
regardless of http://www.designers-guide.org/Forum/YaBB.pl?num=1236837379/10#10. Quote:

******************************************************
Noise Analysis `noise': freq = 1 GHz, r2 = (0 -> 50)
******************************************************

Internal error found in spectre during DC solution estimation, during DC analysis, during Noise analysis `noise'. �Please run `getSpectreFiles' or send the netlist, the spectre log file, the behavioral model files, and any other information that can help identify the problem to support@cadence.com.
� �FATAL (SPECTRE-18): Segmentation fault.

On the other hand, there is no error even for R2=0 in both Agilent GoldenGate and Synopsys HSPICE.
Only Cadence Spectre can not run for R2=0.

I just tested this in MMSIM72, and the simulation runs successfully, even with R2=0. No crash. Possibly a problem caused by some optimization where the zero-value resistor was removed causing a topology change. I did see in IC5141 spectre it gave an error about the conductance form being used for the zero-value resistor (but it didn't crash).

So whatever the problem was, it seems to be resolved now.

Regards,

Andrew.

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