Didn't mean to cause a firestorm. Just used the term simple to describe a Lead/Lag D FF phase comparator. I view it as simple compared to a high speed counter. My GPSDO will have just such a FF whose state will be read by the micro which will implement a PI filter in software and drive a 20bit TI sigma delta DAC to apply corrections to the OCXO. Micro and all other clocks on the design are driven from the OCXO. I may switch the GPS module at a later date to one which provides sawtooth info if I really feel the need and add a delay line. Frankly I think I'll never get around to it.
I'll publish a schematic, code and test results once I have something working. Thanks Jim ab3cv Date: Fri, 7 Mar 2014 09:23:54 -0800 From: Chris Albertson <[email protected]> To: Discussion of precise time and frequency measurement <[email protected]> Subject: Re: [time-nuts] Another "atomic" clock question Message-ID: <CABbxVHuc41UQMhgWNyCXdW=ichdg6taxeoka+zdv0hrrmo1...@mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1 On Fri, Mar 7, 2014 at 5:25 AM, Jim Miller <[email protected]> wrote: > I think the hardware delay line approach is the only solution for a simple > D FF lead/lag phase comparator. It would be placed ahead of the FF. Simple? You are going to need a micro controller and software to (1) tall the GPS to output the sawtooth function, they don't typically output it untell you tell it to. then (2) recover the sawtooth function from the serial data. Then(3) convert it to the "counts" that units used in the delay line. Finally (4) you need to interface the delay line to the processor and send the current sawtooth function value over that interface once per second. Also when I do stuff like this I always want some kind of LCD display or at least blink LEDS so I know what's going on inside and then it is at least running. Your simple analog devices no longer a simple analog device. Do a full up parts count for both designes. I think the digital correction comes in lower. Both solutions need the same micro controller and it's support circuitry. As to which GPSes send sawtooth. It's a common feature but typically you need to enable it, the same way you'd enable a self-survey or set a minimum elevation angle or whatever. Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
