[time-nuts] TDC-GPX2 TDC chip

Bill Byrom time at radio.sent.com
Wed Mar 15 22:54:49 EDT 2017

"the large print giveth and the small print taketh away"

(Quoted from this great description of modern life:

http://www.tomwaits.com/songs/song/322/Step_Right_Up/ )

I'm not trying to be too critical, but look carefully at the datasheet
for that part:

The "accuracy" can in no way be described as 10 ps. In high
resolution mode:
* Single shot RMS time resolution: 10 ps typical, 15 ps maximum

* Integral non-linearity: 20 ps max

* Differential non-linearity: 5 ps typ

* Channel to channel isolation: 20 ps typ, 100 ps max

* Offset error: 200 ps typ

* Offset error drift vs temperature: 1.5 ps typ, 3 ps max / K

* FWHM (full width half maximum) histogram: 20-25 ps

So if the temperature changes 6 F (3.3 C), the measurement may drift by
10 ps. The single shot absolute uncertainty due to jitter (see the
histogram) could easily be +/- 25 ps. There is no mention of long-term
drift, since that isn't a typical use of this part. It would be
interesting to put one in a simple oven and see how it drifts over a
few months.

Bill Byrom N5BB

----- Original message -----

From: Christopher Hoover <ch at murgatroid.com>

To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Subject: [time-nuts] TDC-GPX2 TDC chip

Date: Wed, 15 Mar 2017 15:28:20 -0700


Claims to have single-shot accuracy of 10 ps.


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