[time-nuts] High rate, high precision/accuracy time interval counter methods

[Magnus Danielson]

I&Q sine sampling works, but a continuous sampling allows for N samples 
to reduce the noise by sqrt(N) rather than 2 samples. The white-noise 
will be the limiting factor for the higher rates.

Least-square estimation provides a 2.5 dB improvement over straight 
sample average.

Cheers,
Magnus

On 05/03/2016 10:33 PM, David wrote:
> Wouldn't this be a natural application of a centroid or transition
> midpoint timing TDC implemented with a pulse shaper, fast ADC, and
> FPGA?
>
> What about sampling inphase and quadrature sine waves?  This should be
> more amendable to a microcontroller only solution and if I had to
> start working on something immediately, this is what I would try
> first.
>
> I assume in the earlier discussion Bruce mentioned these methods since
> they are included on his page of the various ways to implement TDCs:
>
> http://www.ko4bb.com/~bruce/TDC.html
>
> On Tue, 3 May 2016 08:40:53 -0700, you wrote:
>
>> HP/Agilent/Keysight laser interferometers
>> measure at the kind of rates you are talking
>> about and (last time I heard) could divide
>> an interference fringe down to 1/512 of a
>> wavelength.  As you say, they definitely use
>> an ASIC with a ring oscillator.  Perhaps
>> there is some way you could repurpose the
>> interferometer electronics to make your
>> measurement.
>>
>> You also might consider that over 25 years
>> ago, HP developed the 5313X counters with
>> interpolators implemented in FPGA's.  The
>> FPGA's available now are vastly more
>> sophisticated and much faster.  Perhaps there
>> is a way you do your ASIC in an FPGA.
>>
>> If you really do need an ASIC, the best way
>> to get that done is to partner with a university
>> and have some PhD student design it.  Universities
>> often have arrangements to do this.
>>
>> Rick
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