[sdiy] BBD question

[Nicholas Gregorich]

Ingo Debus wrote:
> 
> Am 30.08.2008 um 05:05 schrieb Nicholas Gregorich:
> 
>> Ian Smith wrote:
>>> I've got the old Panasonic BBD manual and it shows one with a 20 kHz 
>>> 12dB lowpass filter at both the input and output... I'm guessing 
>>> that's to reduce clock noise. So I'm thinking have a filter at the 
>>> beginning of the chain and between each BBD and one at the end.
>>
>> The one at the input is probably considered an anti-aliasing filter, 
>> and at the output a reconstruction filter (reduces clock noise). In 
>> that case a filter between BBD stages is probably a good idea to 
>> prevent aliasing in the second BBD.
>>
> 
> I've got no experience cascading BBDs, but I can't see a reason why an 
> anti-alias or reconstruction filter would be required between the BBDs 
> as long as they are driven from the same clock.
> It's a whole different story if different clocks are used. Then sure 
> filters are required.
> 

In addition I think aliasing would occur from the copies of the sampled
spectrum outside of the baseband. Again this is a problem I would think
would exist between each stage in a BBD so there must not be a problem
cascading BBDs.

Nick.