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.
