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Design >> Mixed-Signal Design >> Output of interest of Sigma delta Modulators
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Message started by cdbular on Apr 15^th, 2008, 10:25pm

Title: Output of interest of Sigma delta Modulators
Post by cdbular on Apr 15^th, 2008, 10:25pm

Which signal in sigma delta modulators in general (single bit, mulibit, order N) should be spectrally analyzed (PSD, SNR), the digital output? the integrator output? in order to evaluate converter performance

Title: Re: Output of interest of Sigma delta Modulators
Post by Berti on Apr 15^th, 2008, 10:35pm

Hi,

In general you can analyzed any signal ;) But usualy the wanted spectrum
is found at the modulator output (ADC : digital out; DAC, digital SDM : after
truncation).

Regards

Title: Re: Output of interest of Sigma delta Modulators
Post by cdbular on Apr 16^th, 2008, 7:13am

Thanks for you reply berti.
But in the case of multibit architechures, how can I analyze the output spectrum?

Title: Re: Output of interest of Sigma delta Modulators
Post by Berti on Apr 16^th, 2008, 10:26pm

I assume you are designing an ADC: Take the output of the quantizer, which is usually termomether-decoded and
perform a FFT on that. (Or take the output after the therm. to binary decoder, if there is one).

Example:

Quatizer (therm.) output : 000 -> binary : 00 -> value : -1
Quatizer (therm.) output : 001 -> binary : 01 -> value : -1/3
Quatizer (therm.) output : 010 -> binary : 10 -> value : 1/3
Quatizer (therm.) output : 100 -> binary : 11 -> value : 1