Hi At least in my “unconstrained by reality” state, my thought is that the “sync” PPS signal is there all the time. You are as much doing a phase lock as a sync. The “PLL” only has a phase resolution of 100 ns so once it’s running, not much happens. Yes, this might get you into all sorts of issues like some D-FF’s for early / late detection. Things are getting more complex ……
Bob > On Nov 27, 2016, at 7:18 PM, John Ackermann N8UR <j...@febo.com> wrote: > > Hi Bob -- > > It's certainly possible to synchronize the TICC timescale epoch to an > external pulse at startup. The external sync pulse would have to > simultaneously reset (a) the picDIV and (b) the coarse (100us) counter in the > Arduino. The signals to do that are available, so it's a worthwhile > experiment. > > I have to think through whether there are any other gotchas but I'm pretty > sure that you would not get closer than a few hundred nanoseconds given how > closely the picDIV can sync -- I think Tom specifies that it's within 4 > clocks, or 400 ns. > > (Now, syncing two TICCs to each other is a different matter because there we > one unit is master and provides the coarse clock directly to the slave; if > both units are run from the same 10 MHz clock they should align within one 10 > MHz tick.) > > John > ---- > > On 11/27/2016 12:26 PM, Bob Camp wrote: >> Hi >> >> Ok, so the guess was fairly close :) >> >> How about a connector to allow an external PPS to reset the internal 10 MHz >> divider? That way all >> the data is “in sync� with the house standard. If I want to know that my >> GPSDO is +32.751 ns off from >> the house standard, I just look at the data on a terminal program … >> >> Or am I missing something really obvious (again)? >> >> Bob >> >>> On Nov 27, 2016, at 10:04 AM, John Ackermann N8UR <j...@febo.com> wrote: >>> >>> Good guess. The 10 MHz reference drives all the logic on the board, and >>> particularly the counter that maintains a local timescale in 100us >>> increments; the TDC7200 interpolates between the 100us ticks to stamp >>> incoming events on channel A and/or B with picosecond precision. The >>> stamps on both channels are referenced to the same local timescale. >>> >>> Therefore, you can do a measurement of a PPS source against the 10 MHz >>> reference and the resulting timestamp output can be processed by TimeLab or >>> whatever into stability data (the requirement being that the software knows >>> how to deal with timestamps that increment by the nominal measurement rate, >>> e.g., 1 second per measurement for PPS data). >>> >>> So with PPS from GPSDO "A" on channel A the timestamp output after >>> unwrapping will show the phase of A vs. 10 MHz. >>> >>> You can add PPS from GPSDO "B" on channel B and the TICC will also output >>> timestamps of B vs. the 10 MHz source. >>> >>> If you want, you can subtract A from B to get the time interval between the >>> two GPSDO, since both timestamp measurements are against a common >>> timescale. The TICC has a mode to output the (B-A) difference, so it can >>> act as either a traditional time interval counter, or as a two-channel >>> timestamping counter. >>> >>> And as noted in my other message to Luciano, the TICC can also output both >>> timestamp and time interval data simultaneously to allow three-corner-hat >>> measurements of (A-C, B-C, B-A) where C is the 10 MHz reference. >>> >>> John >>> ---- >>> >>> On 11/27/2016 09:24 AM, Bob Camp wrote: >>>> Hi >>>> >>>> Without doing a bunch of actual *work* I’m not sure what is inside >>>> the guts of the board. Being >>>> lazy I’ll just guess …. >>>> >>>> There appears to be a 10 MHz time base input and a pair of measurement >>>> inputs. In a lot us will >>>> be comparing to a “house standardâ€�. That standard has a pps >>>> output that is related directly to >>>> the 10 MHz reference. If I can uniquely identify one edge (out of 10 >>>> million edges) as the right >>>> edge, I can use the 10 MHz as my pps reference. Put another way, I >>>> don’t really need to measure >>>> a pps input from the house standard if I’m already locked up in >>>> phase to the 10 MHz. All I need to >>>> do is to tag an edge / reset a counter. >>>> >>>> The advantage of this is that I may not need another fancy TDC chip to set >>>> up the reference. I can >>>> use *both* inputs for DUT’s rather than using one as a reference. >>>> >>>> Part of the reason I’m guessing this would work is the claim that >>>> boards can be stacked for multiple >>>> input setups …. >>>> >>>> Bob >>>> >>>>> On Nov 27, 2016, at 7:36 AM, timeok <tim...@timeok.it> wrote: >>>>> >>>>> >>>>> Hi John, >>>>> I have planned to buy two TICC. >>>>> An interesting feature would be to be able to do two simultaneous >>>>> acquisitions, >>>>> and Timelab as real time display,using the two indipendent input channels >>>>> and the 10Mhz clock as single reference. >>>>> Luciano >>>>> www.timeok.it >>>>> >>>>> >>>>> From "time-nuts" time-nuts-boun...@febo.com >>>>> To "Discussion of precise time and frequency measurement" >>>>> time-nuts@febo.com >>>>> Cc >>>>> Date Wed, 23 Nov 2016 10:48:57 -0500 >>>>> Subject [time-nuts] New Timestamping / Time Interval Counter: the TICC >>>>> Counters with resolution below 1 nanosecond are difficult. They require >>>>> either outrageous clock speeds, or interpolators that are typically a >>>>> bunch of analog components mixed with black magic and stirred by >>>>> frequent calibration. The very best single-shot resolution that's been >>>>> commercially available is 22 picoseconds in the HP 5370A/B, with jitter >>>>> somewhat more than that. My 5370B has an one-second noise ADEV of about >>>>> 4x10e-11. >>>>> >>>>> With the help of some very talented friends, I've been working on a new >>>>> counter called the "TICC" with <60ps resolution and similar jitter, >>>>> based the Texas Instruments TDC7200 time-to-data-converter chip. The >>>>> noise ADEV is about 7x10e-11, not much worse than the 5370, >>>>> but here's the trick: the TICC is an Arduino shield (mounting a Mega >>>>> 2560 controller) that weighs a couple of ounces, requires *no* >>>>> calibration, and is powered from a USB cable! >>>>> >>>>> The TICC is implemented as a two-channel timestamping counter. That >>>>> means it can measure or two low-frequency (e.g., pulse-per-second) >>>>> inputs against an external 10 MHz reference, or it can do a traditional >>>>> time interval measurement of input against the other. It can also >>>>> measure period, ratio, or any other function of two-channel timestamp >>>>> data. (And by the way -- multiple TICCs can be connected to yield 4, 6, >>>>> 8, or more synchronized channels, though we haven't tested this >>>>> capability yet.) >>>>> >>>>> I've attached a picture of the TICC prototype as well as an ADEV plot of >>>>> a 17+ day run of multiple measurements taken by two TICCs, and also >>>>> showing the TICC noise floor. The good news behind that plot is that >>>>> there are more than 6 million data points behind these results, and >>>>> there was not a single glitch or significant outlier among them. >>>>> >>>>> There's more information available at http://febo.com/pages/TICC >>>>> >>>>> The software is open source (BSD license) and is available at >>>>> https://github.com/TAPR/TICC -- the current version seems be reliable >>>>> but there are still features to add and a *lot* of cleanup to do; it's >>>>> currently ugly and very much a work in process. >>>>> >>>>> As always, I'll be making the TICC available through TAPR. We're still >>>>> finalizing details, but we expect the price to be less than $200 for a >>>>> turn-key system: TICC mounted an Arduino with software loaded and >>>>> tested for basic functionality. We hope to ship the TICC by February. >>>>> >>>>> I'll post a note in a week or two with final price and ordering >>>>> information. As a heads up, we will probably offer a small discount for >>>>> pre-orders. TAPR is a shoestring non-profit group and the up-front cost >>>>> to manufacture this unit will frankly be a challenge for us. Getting >>>>> pre-orders will help our cash flow significantly, so we ask you to keep >>>>> that in mind. >>>>> >>>>> John >>>>> _______________________________________________ >>>>> time-nuts mailing list -- time-nuts@febo.com >>>>> To unsubscribe, go to >>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>>> and follow the instructions there. >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@febo.com >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
