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Old 10-31-2007, 08:22 PM
Peter Alfke
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Default Re: Ping Jim: The PFD is dead!

Hi, John
I suppose you know about the old Xilinx app note:
http://direct.xilinx.com/bvdocs/appnotes/xapp028.pdf
which would benefit from your diode trick.
Cheers
Peter Alfke, Xilinx Applications

On Oct 31, 10:32 am, John Larkin
<[email protected]> wrote:
> On Wed, 31 Oct 2007 09:38:41 -0700, [email protected] wrote:
> >> I "invented" this last week. FPGAs aren't very good at implementing
> >> the classic charge pump.

>
> >>http://s2.supload.com/free/PFD.jpg/view/

>
> >> The outputs here are just hard (not tri-state) logic outputs, driven
> >> directly by the up/down flipflops in the pfd circuit. It's nicely
> >> symmetric.

>
> >> John- Zitierten Text ausblenden -

>
> >> - Zitierten Text anzeigen -

>
> >But the Inventor mentioned the additional jitter due to uncorrelated
> >noise of the 2 PFD outputs and their summation in your example, and
> >the evil glitches due to unmatched symmetry and parasitic coupling of
> >the digital to the analog !
> >This must be worth a patent.

>
> >Having read

>
> >http://www.keystonesemiconductor.com..._releases.html

>
> >i now fear the evil glitch and deadtime jitter to corrupt my computer
> >before global warming blasts icebergs and blazes glaciers.

>
> Oh, the guy is clearly a lunatic, and an amateur lunatic to boot. His
> writing is hilarious.
>
> But the dual-diode thing solves a couple of problems using an FPGA as
> a phase-frequency detector.
>
> John



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