[time-nuts] Sawtooth correction with a slower TIC

Richard H McCorkle mccorkle at ptialaska.net
Sat Jul 21 13:46:06 EDT 2007

That version was done a few years back when I was big on recycling
parts, so let me dig through my junkbox and see if I still have one

> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+mccorkle=ptialaska.net+mccorkle=ptialaska.net at febo.com
> I am very happy to hear you did this already. Impressive.
> Is there a prototype I could test here in my lab? I'd be very
> interested in measuring it. I hope to finish testing a dozen
> or more GPSDO this year; would like to have something
> this simple in the mix.
> /tvb
> ----- Original Message -----
> From: "Richard H McCorkle" <mccorkle at ptialaska.net>
>> Tom,
>> I did most of the software development work using just the
>> uncorrected 1PPS into TMR0 and two scaled and summed PWM
>> outputs instead of a DAC, and the results were surprizingly
>> good. It made a very low cost, small footprint design without
>> the external counters and DAC. All the added extras since are
>> just part of my continuing education.
>> Richard
>> ----- Original Message -----
>> From: "Tom Van Baak" <tvb at LeapSecond.com>
>>> > My original design used a 50 MHz TIC clock and the TMR0
>>> > prescaler as the phase counter giving 20ns single sample resolution
>>> > in the prototype system.
>>> In this case how about making a super-simple GPSDO
>>> and just put the uncorrected 1pps directly into TMRO.
>>> The sawtooth jitter of an M12+ is 9 ns rms, which is just
>>> the magnitude you need to improve on the 20 ns single
>>> shot PIC-based TIC resolution. If you average long enough
>>> even hanging bridges will not be a concern.
>>> You'd have to do some work to get fancier, but it's hard to
>>> imagine a PIC-only GPSDO that would be simpler.
>>> /tvb
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