[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
such)
> 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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