ADC output (Delta Sigma ADC)

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Hello Everyone

I am working on Delta Sigma ADCs in MATLAB, to equalize the amplitude of input and output I have to multiply the output by a scaling factor, anyone who has experience of ADC (using or working on ADCs) share the reason for this scaling ? and Secondly the SNR after Delta Sigma Modulator ~66 dB and after Decimation it drops to ~50dB (using a very high order approx. 3k taps FIR LPF), Reason for this too much decrease in SNR ?

Thanks in advance.
 

 

One reason could be that your signal transfer function has a gain different from 1, due to scaling in the modulator.

BR Jerry
 
helpmejerry said:
One reason could be that your signal transfer function has a gain different from 1, due to scaling in the modulator.

BR Jerry
Click to expand...
Thanks helpmejerry; Yes the signal transfer function in modulator has the gain<1; also I want to ask you that when I captured the output of my 8-bit ADC it does not digitized from 0-255 and it only digitized from e.g [30, 237] at fin=20 hz; and [10, 196] at fin=10khz ...in output frequency range.
does this related to the gain scaling in modulator?
 

I am not sure what you mean by
when I captured the output of my 8-bit ADC it does not digitized from 0-255 and it only digitized from e.g [30, 237] at fin=20 hz; and [10, 196] at fin=10khz ...in output frequency range.
Click to expand...
It could be that the SNR/dynamic ranges are different over the BW or anything else, relay without knowing the STF and NTF it is impossible to say anything concrete.

BR Jerry
 

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