Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.electronics.design > #518573

Re: really bad oscillators

Show all headers | View raw

Am 06.10.2018 um 19:33 schrieb John Larkin:
> 
> 
> A timestamper is a circuit that latches the time of arrival of a pulse
> edge. We use a clock and a binary counter as MC, the master counter
> definition of time. We extend those MC bits down into picoseconds with
> a time interpolator, adding 8 to 12 bits below the counter LSB.
> 
> One way to test a time stamper is to stamp pulses that are random in
> time, and then histogram/analyze the codes. That can catch all sorts
> of nasties, like stuck or shorted bits or interpolator problems; we've
> done the math on that. In the test set that I'm designing, I want a
> simple but really bad pulse generator, maybe around 1 MHz with tons of
> period jitter, to get good statistics and never alias against the
> master clock. Aliasing can make really weird histograms.
> 
> https://www.dropbox.com/s/vv6dqeffxrkmca3/Timestamp_Noisy_Osc.jpg?raw=1
> 
> The single inverting schmitt oscillator is probably good enough, but
> it's fun to consider other really nasty oscillators. A bad power
> supply will only help.
> 
> We have an FPGA, so I guess we could build a pseudorandom bit stream,
> filter that a little, and use that to confuse a schmitt oscillator.
> The kids might enjoy programming that.

I do not think that this is a really good idea. If your test signal
is REALLY noisy, it will dither away the contributions of your
interpolator / pulse stretcher. You get nice statistics, but for a
wrong reason.

The standard way to measure linearity of an interpolator is to have
two OCXOs that drift very slowly against each other, maybe 20 nsec
difference per hour. Then you know the value to be expected and you
have enough time to do statistics wrt single vs. 1000 times averaged.
Dynamic nonlinearity (arbitrary pulse width, cycle-to-cycle) can only
be worse than that.

And it is a task for itself to make sure that the 2 VCXOs
do not injection lock, even when they happen to be close.
We used our house reference (hydrogen maser based) and an offset generator.

I also had good results with a switchable Synergy CML delay line and
measured the resulting pulse width in parallel with a Stanford SR-620.
The SR620 is quite old by now (Z80..) but still there are no TICs that
are SIGNIFICANTLY better.

Back then, when men still were men and HP still was HP, they published
a description of the two-stage time stretcher of the HP54570A sampling
scope in HP journal. Still worth reading. All of HP journal.

cheers,
Gerhard

Back to sci.electronics.design | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

really bad oscillators John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-06 10:33 -0700
  Re: really bad oscillators "Tim Williams" <tiwill@seventransistorlabs.com> - 2018-10-06 12:51 -0500
    Re: really bad oscillators whit3rd <whit3rd@gmail.com> - 2018-10-06 15:16 -0700
      Re: really bad oscillators John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-06 15:52 -0700
      Re: really bad oscillators "Tim Williams" <tiwill@seventransistorlabs.com> - 2018-10-06 22:55 -0500
  Re: really bad oscillators George Herold <gherold@teachspin.com> - 2018-10-06 11:33 -0700
  Re: really bad oscillators John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-06 11:35 -0700
  Re: really bad oscillators <698839253X6D445TD@nospam.org> - 2018-10-06 18:49 +0000
  Re: really bad oscillators Steve Wilson <9fe142ac@gmail.com> - 2018-10-06 11:50 -0700
  Re: really bad oscillators bloggs.fredbloggs.fred@gmail.com - 2018-10-06 12:13 -0700
    Re: really bad oscillators John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-06 15:55 -0700
  Re: really bad oscillators Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-06 21:28 +0200
    Re: really bad oscillators Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-06 21:35 +0200
    Re: really bad oscillators John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-06 16:01 -0700
  Re: really bad oscillators bitrex <user@example.net> - 2018-10-06 21:59 -0400
    Re: really bad oscillators John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-07 08:05 -0700
      Re: really bad oscillators bitrex <user@example.net> - 2018-10-07 23:04 -0400
        Re: really bad oscillators John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-07 21:10 -0700
      Re: really bad oscillators bitrex <user@example.net> - 2018-10-07 23:12 -0400

csiph-web