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 standard�. 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
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