[sdiy] Clock-controlled filters?

[rburnett at richieburnett.co.uk]

> It's supposed to be an imaging (reconstruction) filter for a
> variable-rate DAC...

Switched-capacitor filters are commonly used for anti-imaging filters.  
Particularly as the last filtering stage in oversampling DACs, because 
there is a master clock already available at some multiple of the 
sampling rate.  This is exactly what the switched-capacitor filter needs 
to clock its analogue switches.

Which begs the question:  Why can't you use a modern delta-sigma audio 
DAC (like the "Crystal" CS43xx parts from Cirrus Logic) and get the 
tracking anti-imaging filter done for you in the DAC?

-Richie,