[time-nuts] TDC-GPX2 TDC chip

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Mar 15 23:36:43 EDT 2017


The apparent drift will be determined largely by that of the reference oscillator due to the embedded continuous interpolator calibration. Placing it in an oven will probably degrade the resolution due to the bin size tempco.

All time interval instruments have an offset between channels, This is easily measured and corrected for. 

The performance as stated in the datasheet appears comparable if not better than a typical 5370A/B when one takes the various sources of nonlinearity and crosstalk in a 5370A/B into account. It certainly consumes less power even after the power consumption of a good ocxo is added.  Its also somewhat cheaper.

However a comprehensive evaluation of its performance beyond that given in the datasheet is required.

A comprehensive test of the performance of a n actual 5370A/B would also be useful.

Bruce

> 
>     On 16 March 2017 at 15:54 Bill Byrom <time at radio.sent.com> wrote:
> 
>     "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:
>     http://ams.com/eng/content/download/951531/2270299/381482
> 
>     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
> 
>     http://ams.com/eng/Products/Precision-Time-Measurement/Time-to-Digital-Converters/TDC-GPX2
> 
>     Claims to have single-shot accuracy of 10 ps.
> 
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