A Question About Delta-Sigma Modulators

[naalald]

Hi,
In the Shcreier book (2004), page 6, it's said that in delta-sigma converters since the signal is unchanged, i.e. there is only a delay for the signal, in the receiver no demodulation is needed and this is a great advantage of delta-sigma modulators comparing with delta modulators. Therefore, when defining the filter coefficients we usually try to set the Signal Transfer Function to (1/Z).
Now if we use delta-sigma modulators as ADCs there would be no receiver. Can we choose the filter coefficients so that the STF is not only a delay (1/z)?

 

[jiangxb]

hi naalald,

we can select STF a complex function not only 1/z.
for signal we only need to ensure the frequency response is flat within signal band.

 

[s0g0]

how to achieve a delay (1/z) in hardware? Flip-Flop can do?

 

[naalald]

hi naalald,

we can select STF a complex function not only 1/z.
for signal we only need to ensure the frequency response is flat within signal band.

Hi jiangxb,
Thanks for your reply. But here is a question;
If we have a sinusoidal input, its power spectral density function is a delta,

and the modulator output signal power would be,

Therefore whatever the STF is, the output signal power would be the input signal power multiplied by the value of STF at f=fB and it need not to be flat necessarily.
Is this correct?

 

[safwatonline]

usually the input signal is with a certain BW, and usually the relative magnitude and phase information between different components are important and this set the spec on the STF, so SDADC are just like filters u should set the Transfer function between input and output according to ur application

 

[jiangxb]

it depends on the spec..
in general the signal within signal bandwidth is digitized with the same gain.