[time-nuts] Centroid pulse timing

Hal Murray hmurray at suespammers.org
Wed Sep 27 04:58:25 EDT 2006

> Another way of determining the the arrival time of a pulse with high
> resolution is to use centroid timing techniques. The input pulse is
> converted to a short pulse using a delay line timed monostable then
> the resultant pulse is low pass filtered by a discrete component RLC
> Gaussian low pass filter.

This sounds like fun.  Thanks.

> A sampling ADC continuously samples the low pass filter output at a
> fixed clock speed. The centroid of the pulse can then be calculated
> from the resultant sequence of ADC samples. Monostable output pulse
> width ~ 2x ADC sample clock period. Low pass filter risetime ~ 2 ADC
> sample clock periods. With a 10MHz sample clock a resolution of
> 100picosec or better can be achieved with a 12 bit ADC. 

The idea seems simple, but I don't see how to write the code.  Is there a 
good URL on that?  Table lookup and average?  (make the table from spice or 

> A delay line timed monostable is required for low output pulse jitter
> and good output pulse width temperature stabilty.

2x 100 ns delay line seems like a pain.

What's the (ballpark) tempco of coax?  What's the ballbark tempco of a normal 
(whatever that means) delay chip?  (Assume I use a chip designed for this 
rather than kludging gate delays.)

Can I correct for the change in pulse width if I have more samples?

How much accuracy do I give up by making the pulse wider so I can get more 
info on the width/height of the pulse in order to correct?

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