[sdiy] BBD question

[Sean Ellis]

I didnt give this much thought but if both BBDs were running from the same 
clock what would happen if you inverted the signal from the first stage 
before the second stage? Could you cancel some of the clock noise out? I 
guess the delay could render this useless though....

----- Original Message ----- 
From: "Nicholas Gregorich" <nicksdsu at mac.com>
To: "Ingo Debus" <igg.debus at t-online.de>
Cc: "sdi >> synth diy" <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, August 30, 2008 5:18 PM
Subject: Re: [sdiy] BBD question


> 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.
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