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Design >> Analog Design >> noise aliasing
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Message started by raja.cedt on Apr 9^th, 2009, 3:44am

Title: noise aliasing
Post by raja.cedt on Apr 9^th, 2009, 3:44am

hi,
i am new to sample and hold circuits,just i am reading the basics, mean while i got this doubt.When we are sampling with above the Nyquist rate,output noise spectrum will be white and with variance kt/c, because we are sampling uncorrelated noise.If we are sampling below Nyquist rate then probably we will sample correlated noise and we wont get white,my question is what it's shape?even though it is not the general case i feel there are lot of interesting things inside,so can any body please explain this or direct any reference.
Thanks,
Rajasekhar.

Title: Re: noise aliasing
Post by Peruzzi on Apr 9^th, 2009, 7:16am

You can have some fun while getting an intuitive feel for wide-band noise aliasing using Spectre's transient noise simulation, if you have the time and the circuit isn't too big. Or better yest, create analog behavioral models for your system. Also create a transient noise source which you can parameterize and insert where appropriate.

You'll be able to see the noise in the time domain, and with Fourier analysis, see its spectrum too. At different points in the circuit. I've done this before and got results which correlated nicely with lab measurements.

A Google search will turn up several papers, or you may contact me directly for further information.

Bob Peruzzi
www.RPeruzzi.com

Title: Re: noise aliasing
Post by thechopper on Apr 11^th, 2009, 7:36am

Hi Rajasekhar,

You might also want to take a look at:

http://www.designers-guide.org/Analysis/sc-filters.pdf and
"Design-Oriented Estimation of Thermal Noise in Switched-Capacitor Circuits" R. Schreirer, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: REGULAR PAPERS, VOL. 52, NO. 11, NOVEMBER 2005

These two references describe the aliasing processes for white input noise in a basic sample and hold circuit.

Hope this helps
Tosei