[sdiy] BBD question

[Nicholas Gregorich]

Ingo Debus wrote:
> 
> Am 30.08.2008 um 23:36 schrieb Nicholas Gregorich:
> 
>> I guess this is the part I'm having a hard time with here, why is 
>> there not aliasing between every single stage in a BBD?
> 
> Sampling creates copies of the baseband spectrum (you mentioned it 
> yourself in anther posting), centered around multiples of the sampling 
> frequency. If the anti-aliasing filter before the first stage does its 
> job properly, there are no frequencies above half the sampling frequency 
> present in the signal, so the sprectra do not overlap.
> 
> If this sampled signal is re-sampled (by the second and all following 
> stages) with the same clock the copies of the baseband spectrum don't 
> cause aliasing because they are folded back exactly into the baseband 
> position (and into positions where already copies of the spectrum were).
> 
> Makes sense?
> 
> A different issue is, perhaps BBDs create other noises, not only the 
> copies of the baseband spectrum. If these contain frequencies above half 
> the sampling frequency then it would indeed make sense to place 
> anti-aliasing filters between cascaded BBDs.
> 

I think I go wrapped up somewhere in between over complicating BBDs into 
an A/D/A system and confusion over re-sampling with the same clock.

Sorry if I misled anyone and thanks for the explanation.

Nick.