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In Reply to: RE: Thanks for the good wishes. posted by Tony Lauck on January 16, 2011 at 07:12:26:
Howdy
The issue is how do you clock those flip flops without having the signals going into the first flip flop affecting it's clock or power supply ... and hence the clock or power supply of the final flip flop... If you get into it further it's the same problem as using a PLL to attenuate jitter: you are at best are filtering the jitter and that filter isn't as simple as uniform attenuation. TANSTAAFL. Tho I don't have the proof at hand I believe that once again the best you can do is some form of low pass filtering of the jitter. In the limit tho low passed jitter becomes wander and wander slow enough to not affect the bass firmness isn't a problem.
I'm sure that I've posted my implementation of the idea you are talking about elsewhere but here's a synopsis:
I use a FPGA to do the bulk FIFO storage. The FPGA outputs a clock and the data associated with it and these signals go into a high quality flip flop to align the signals with a separate clean power supply. Then the signals go from that flip flop to another with it's own PS which is clocked directly by the master clock (with it's own PS and thru only a few mm of traces.) And when I say "own PS" I'm not just talking about a local ferrite bead and some caps.
The initial mistake I made was to clock the two external flip flops exactly out of phase with each other which is almost the worst timing possible: the only worse timing would be to clock them in phase. The beauty of FPGAs is that I only had to change one parameter to advance the FPGA and it's flip flop 90 degrees and make a significant difference in the audible jitter. Taking this lesson to the limit you can see how there isn't room for an arbitrary number of flip flop stages: you eventually are switching some of the flip flops too close to the switching of other flip flops and increasing the possibility of jitter leakage thru the power supplies or clocks.
I'm not claiming that this proves my case, but just like other "jitter solutions" things aren't as simple as a first level analysis might lead one to believe.
-Ted
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Follow Ups
- RE: Thanks for the good wishes. - Ted Smith 14:06:21 01/16/11 (0)
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