[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.
> 

I don't have experience cascading BBDs either but my thought was the 
unfiltered clock noise out of the first BBD would alias in the second.

After your response I rethought and decided the same aliasing must 
happen between each stage within an individual BBD. Does that seem right?

In that case I guess a filter would not be needed between cascaded BBDs. 
But that just wouldn't feel right. :)

Nick.