[time-nuts] Re: Measurement and correction of non-linearity of a TDC

[Poul-Henning Kamp]

--------
Erik Kaashoek via time-nuts writes:

> Is there someone on this list that has experience with the measurement
> and correction of non-linearity of a TDC?

I used my HP3336:

10 MHz house-standard to HP3336-ref-in and TDC chan A

HP3336 set to 10MHz output, and that output to TDC chan B

TDC triggers on positive zero-crossing on both channels.

Then step the HP3336 through 360 degree of phase, plot set phase vs. TDC reading

Repeat more than once to judge how well it works for you.

If you /really/ want to get into the weeds, you need to feed both
input A & B on the TDC from their own phase-settable sig-gen, and
work your way through all of 360x360 degrees.

If you do that to a HP5370, you can measure that two very specific PCB
traces cross each other inside the 5370 :-)

Note that the HP3336 steps the phase relative to an arbitrary and
unpredictable starting phase, so you have to do all measurements in
one session.

In principle pretty much any sig-gen which can set the phase can
be used, possibly even the $10 "DDS chip on a PCB" from eBay, but
the spectral purity of the sig-gen output, in particular around the
zero-crossing is a very significant source of noise.

I always apply corrections in postprocessing.

-- 
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