The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Mixed-Signal Design >> excess loop delay compensation in CT sigma-delta modulator
https://designers-guide.org/forum/YaBB.pl?num=1223953611

Message started by baohulu on Oct 13^th, 2008, 8:06pm

Title: excess loop delay compensation in CT sigma-delta modulator
Post by baohulu on Oct 13^th, 2008, 8:06pm

hi, all
I have a question to ask you.
in CT sigma-delta modulator, excess loop delay is from to sources: one is DAC input delay, the other is DAC clock to Q delay in DAC itself.
in most books, there is a diagram which has two rectangles and the x-axis is time, one is rising at "0" point (the original), the other at a delayed time, "td", and then the books give method to compensate the delay time "td".
I want to ask what is the y-axis, is it a DAC input or a DAC output? if it is a DAC output, then it means, both DAC input delay and DAC clock to Q delay can be compensated; if it is just the input of the DAC, then does it mean only DAC input delay (which is caused by quantizater ) can be compensated?
in the book " Continuous time Delta-Sigma AD conversion" written by M.Ortmanns & F. Gerfers, it doesn't tell the difference of the two delay reasons, and it seems the compensation methods can compensate both the two delay, right?

Title: Re: excess loop delay compensation in CT sigma-delta modulator
Post by vrl on Oct 21^st, 2008, 9:26am

Yes, both the quantizer delay and the DAC delay can be compensated through the excess delay compensation schemes..

Vijay

Title: Re: excess loop delay compensation in CT sigma-delta modulator
Post by Berti on Oct 22^nd, 2008, 12:09am

Hi,

I think that the phase-shift of the amplifiers will also contribute to excess loop delay.

Cheers

Title: Re: excess loop delay compensation in CT sigma-delta modulator
Post by Friedel on Dec 11^th, 2008, 9:55am

In a CT SDM the total delay (meaning from the sampling edge of the ADC to the beginning final DAC output) has to be compensated. Thus, the graphs typically show the ideal normalized DAC output.

Cheers