plotting SNR

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cjupiter

Joined: 10 May 2004
Posts: 45

27 Oct 2004 20:11 plotting SNR

Does anybody know how I could plot the SNR or SNDR of a sigma delta converter using spice. Im using B2 Spice A/D Pro.

I am also open to any suggestions of how to plot useful results for a sigma delta modulator.

Thanks for any help! Very Happy

borodenkov

Joined: 02 Mar 2004
Posts: 129
Helped: 11

28 Oct 2004 0:27 plotting SNR

Well, personally I used Matlab for it. It should be possible to do it with SPICE signal postproscessing as well, but for me Matlab is more convenient..

The idea is - you make transient simulations in SPICE, then sample the output voltage(s) during the correct clock phase and print them to file then load the data in Matlab. After that round voltages to be exactly 0 or 1 since it's a digital signal now, window it (I used Hanning window), make fft and and calculate PSD. To calculate SNR find the noise signal (substract the input signal from the output) and get the ratio. You can look in some available Matlab files (e.g. Schreier's package) for math..

Last edited by borodenkov on 28 Oct 2004 3:42; edited 1 time in total

andy2000a

Joined: 18 Jul 2001
Posts: 767
Helped: 7

28 Oct 2004 3:41 Re: plotting SNR

in A/D convert design need know ENOB for bit resolution , we use .fft
(not .four)

but you need ideal D/A

your A/D -> digital code -> ideal D/A -> ( option) Low pass filer

and you .fft analysis D/A out put signal
if input is 100kHz then you can get 100KHz signal from D/A

ideal D/A you can use hspice behavior element make it ..