[time-nuts] DIY GPS-DO

Azelio Boriani azelio.boriani at screen.it
Sat Mar 10 13:40:07 UTC 2012


Yes, the use of the PPS as a disciplining reference was discussed weeks
ago. It was debated whether an analog filtering/interpolation would do or a
digital one is mandatory. The question is, in my opinion, still open and,
in my opinion again, it can be done in the analog domain if a high
precision/low leakage circuit is designed. I have designed 4 types of
digital GPSDOs in 12 years, 3 using the digital approach
time_interval_measure->DAC and one using the right/left_of_reference->DAC
approach. One of them is implemented in a Xilinx Spartan3 small FPGA
(50Kgates) without a microprocessor. The Spartan3 based design is the last
one. I recommend the digital approach because it can be changed (time
constants, holdover strategy, ...) just writing software.

On Sat, Mar 10, 2012 at 2:14 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> Which module do you have?
>
> Bob
>
>
>
> On Mar 10, 2012, at 8:07 AM, Filip Ozimek <me_super at o2.pl> wrote:
>
> > Hello,
> >
> >
> > could you recommend me a good project of GPS-DO? I've got a GPS module
> with 1PPS output and a 20 MHz VCXO.
> > As I understand to do a phaselock to 1 PPS signal one must build some
> kind of digital PLL. But I'm not sure
> > how to calculate a correction signal to the VCXO and how to test such a
> disciplined oscillator.
> >
> > Filip.
> >
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