[time-nuts] New Timestamping / Time Interval Counter: the TICC
John Ackermann N8UR
jra at febo.com
Wed Nov 23 10:48:57 EST 2016
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 on the Texas Instruments TDC7200 time-to-data-converter chip. The
one-second noise ADEV is about 7x10e-11, not much worse than the 5370,
but here's the trick: the TICC is an Arduino shield (mounting on a Mega
2560 controller) that weighs only 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 one 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 one 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 on 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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