reposting



(kbc) wrote in message
. com...
nobody reading this ??


(kbc) wrote in message . com...
Hi,

I posted this sometime back in comp.dsp.

http://groups.google.com/groups?dq=&...p%26start%3D25

Dont think got the answer there.

Consider a sigma delta adc which first oversamples, does
noise-shaping and then filters and decimates to give final output
at Nyquist rate and with 16 bits per sample.

For this final output, note that quantisation stepsize is uniform.

Now, is it possible to get this same output using a normal adc
for some sampling phase and uniform sampling of the analog signal ?

Or will it be correct to say that the final output is a
non-uniformly sampled version of the original analog signal ?

( I understood the functionality in freq domain, and am trying
to figure out in time domain . )


I guess effectively, sigma-delta adc is equivalent to adding dither to
analog signal and then using a normal adc.

shankar

"kbc" wrote in message
om

Consider a sigma delta adc which first oversamples, does
noise-shaping and then filters and decimates to give final output
at Nyquist rate and with 16 bits per sample.

For this final output, note that quantisation stepsize is uniform.

Only for *perfect* sigma-delta ADCs. Sigma-delta ADCs tend to be more
perfectable at a relatively low cost than other kinds, but they aren't
totally perfect.

Now, is it possible to get this same output using a normal adc
for some sampling phase and uniform sampling of the analog signal ?

Just find a *normal* ADC that is perfect. ;-)

This is going to be harder, but you'll never find that perfect sigma-delta
ADC to compare it to, so where's the beef?

Or will it be correct to say that the final output is a
non-uniformly sampled version of the original analog signal ?

That's always true. It's just a matter of degree.

( I understood the functionality in freq domain, and am trying
to figure out in time domain . )

I guess effectively, sigma-delta adc is equivalent to adding dither
to analog signal and then using a normal adc.

More or less. Sigma-Delta ADCs have artifacts of their own. I seem to recall
something about limit cycles, etc.

How does this question differ philosophically from debating the number of
angels dancing modern ballet on the head of an antique dressmaker's pin?

(kbc) writes:

reposting



(kbc) wrote in message
. com...
nobody reading this ??


(kbc) wrote in message . com...
Hi,

I posted this sometime back in comp.dsp.

http://groups.google.com/groups?dq=&...p%26start%3D25

Dont think got the answer there.

You mean you didn't get the answer you were looking for. I answered you
at least twice on this.
--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
, 919-472-1124