singh wrote on Sep 12th, 2011, 4:35am:Thanks vivek for your valuable suggestions
i referred on document
http://www.patentgenius.com/patent/6909388.htmlthis is the reference paper for the one u provided me for fractal sequencing.here they say that the approach is used to separate offset from the input signal (page 7)
before this sigma delta ADC, I am using an integrator which is setting an offset to my input signal to SD ADC.This offset is mainly due to feedback capacitor KT/C noise.
I was also thinking to give a shot applying fractal sequencing to this integrator block.
the offset due to KT/C is around 20 mV. Is it not possible to use the first stage of DS ADC integrator to nullify the offset. But point is like how the circuit will distinguish input offset value from Input signal as both (input+inp offset) will be stored in capacitor cin (fig 5 of paper ) and will be supplied as combined input to integrator phase of ADC?
regards
manjeet
Manjeet,
There are several points to be made here:
1. As you correctly noticed, it is not possible to separate signal from offset once this "offset" is embedded into the signal, atleast not without removing the low-frequency part of the signal itself, which you don't want to do I suppose. But what you are talking about is anyway not offset. See point 2.
2. kT/C noise is not an offset. It is caused by sampling of wideband thermal noise. Also, you need to use metrics such as standard deviation to specify this noise. On a side note, I do hope that you do not have a standard deviation of 20 mV (given as sqrt(kT/C)), as that would be highly unlikely for most realistic values of C.
It seems to me that you are not yet familiar with concepts related to noise at the moment, which is understandable if you still an undergrad. But perhaps you want to talk to your professor and get his advice on how best to approach the problem at hand.
Vivek