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Simulators >> RF Simulators >> about spectre Pnoise nalysis~
https://designers-guide.org/forum/YaBB.pl?num=1145676768

Message started by chungmnig on Apr 21^st, 2006, 8:32pm

Title: about spectre Pnoise nalysis~
Post by chungmnig on Apr 21^st, 2006, 8:32pm

Hi~
I simulate noise of a fully differential OPA switch cap structure using spectre Pnoise .
I have some problems
First i use PSS and Pnoise analysis , then i want to see input referred noise , and it is impractical small , just about 20nV/Hz (better than IEEE papers so imust some where wrong.......)
my clock 2MHz so i set PSS maxacfreq=240M and Pnoise max sideband =100 , i think it is enough.
i had read Simulating switched-capacitor filters with SpectreRF , so i think other settlings is correct.
input reffered noise = (output noise)/(Transfer function) is right? i see output noise , input noise,transfer function of Pnoise i think the former statement is right.
and transfer fuction of Pnoise is the same as PAC analysis.
So where i get wrong? How to measure right input referred noise?

Second i also using chopper to eliminate 1/f noise(chopper clock is 1MHz).
The same simulation step like above.
But the ttransfer function is wrong , it very small (minus dB)
So the input refered noise is larger than output noise.
My circuit is correct.
could some body give me some suggestions about it ~~~
thanks~~

Title: Re: about spectre Pnoise nalysis~
Post by Ken Kundert on Apr 23^rd, 2006, 9:35am

What sideband are you observing. For a chopper it should be sideband 0.

-Ken

Title: Re: about spectre Pnoise nalysis~
Post by Count on Apr 15^th, 2008, 2:45am

Dear Ken, could you please explain why for a chopper, we should observe sideband 0? Thanks!

Title: Re: about spectre Pnoise nalysis~
Post by Ken Kundert on Apr 15^th, 2008, 5:59pm

There is no frequency translation. The input and output are at the same frequency.

-Ken

Title: Re: about spectre Pnoise nalysis~
Post by thechopper on Apr 15^th, 2008, 7:06pm

Hi,

20nV/sqrt(Hz) does not sound to me like ridicously small. State of the art chopper amplifiers show about 8nv/sqrt(Hz).
The relationship between input and ouput noise is (for a linear system)
So(f)=|H(f)|^2*Si(f)

where Si and So are the power spectral densities for both input and output noise respectively.

Tosei.