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In Reply to: Re: I don't think any USB audio devices have a master clock posted by BFitz on September 8, 2005 at 09:10:31:
Yeah, the old two stage PLL idea is pretty old. I used to do it back in the old days with a two stage loop filter on the CS8412 and I think others did something similar. I migrated to a design where the digital section is completely isolated with the only timing out a 1Hz difference strobe through ISO150 digital couplers used to run the clock regeneration section using an open collector PLL feeding a quality VCXO. So once a second the difference signal provides clock frequency correction that is spread over the next few seconds via passive integration in the very low frequency PLL loop filter. So the high impedance VCXO control pin only sees the voltage stored in a very high quality film and foil 1.5uF cap which sits there almost like a battery nearly all the time. Over 1000X less (my measurement limit) audio correlated jitter @ 1000Hz on the DAC clock than on the clock coming out of the CS8414, and pretty much the same to below 1Hz.BTW, I haven't had the pleasure of talking to you in a long while. Guess we've both been off doing some other things. Nice to see you around again. Coincidentally, I was also just recently talking to Walt Jung again after a few years and it sounds like he's going to be getting back more heavily into audio projects again now that he's retired. Also said he had some capacitor findings he wanted to pass on that seem to agree with the things you and I talked about a long time ago back here (and in some further exchanges with Walt).
Dave
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Follow Ups
- Two stage PLL - Monkey Bones 09/8/0509:45:09 09/8/05 (1)
- Re: Two stage PLL - BFitz 14:12:21 09/8/05 (0)
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