[time-nuts] Fw: Sawtooth correction with a slower TIC

Richard H McCorkle mccorkle at ptialaska.net
Fri Jul 20 22:52:42 EDT 2007

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.


----- Original Message -----
From: "Tom Van Baak" <tvb at LeapSecond.com>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Friday, July 20, 2007 5:51 PM
Subject: Re: [time-nuts] Sawtooth correction with a slower TIC

> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+mccorkle=ptialaska.net+mccorkle=ptialaska.net at febo.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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