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Design >> Mixed-Signal Design >> SQNR of delta sigma
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Message started by min on Aug 14^th, 2007, 2:07am

Title: SQNR of delta sigma
Post by min on Aug 14^th, 2007, 2:07am

Hi all :

I am studing of delta sigma . and I have a question about the SQNR as function of input amplitude.

My question is " Can SQNR remain high when the input signal above 0dBFS ( such as 0.5dBFS) ?" I usually think that

that when the input signal approach the full scale, the modulator will unstable and the SQNR will decrease sharply,

but recently I see an article , its SQNR remain high as the input signal at 0.5dBFS, the result confuss me. Can

anybody tell me why . and I want to know that the input full scale indicate what ? Is full scale mean reference

voltage?

thanks!

Title: Re: SQNR of delta sigma
Post by ywguo on Aug 14^th, 2007, 9:14pm

Hi,

What do you mean? "SQNR remain high above 0 dBFS", is that mean SQNR value greater than 0 dBFS? That is impossible theoretically.

Title: Re: SQNR of delta sigma
Post by tosei on Aug 15^th, 2007, 2:13pm

min wrote on Aug 14^th, 2007, 2:07am:

Hi all :

and I want to know that the input full scale indicate what ? Is full scale mean reference

voltage?

thanks!

Full scale usually refers to the dynamic range of the modulator. If your are talking about voltage then FS must be smaller than the system's supply voltage and therefore your signal could be larger than you FS if you do not clamp it at the input somehow. In this case I guess you are refering to the reference voltage as the one setting the dynamic range. If that is the case then FS=voltage reference. For a signal larger than the FS I guess you could get lots of quantization noise since the modulator dynamics for the desired noise shaping are not valid any more.

Tosei