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ADC output (Delta Sigma ADC)

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Eminent.Engineer

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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.
 

Eminent.Engineer said:
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 ?

Dear eminent hello;
Actually I have the same question that why the output of SD ADC is smaller than it's analog input signal?
if you have got answer would you please share it here.
and how you scaled it?
thank you
Click to expand...
 

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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