[time-nuts] Time interval interpolation by sampling a pair of sinewaves in quadrature.

Tim Shoppa shoppa at trailing-edge.com
Tue Sep 26 08:27:26 EDT 2006

Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
> Yet another high resolution time interval interpolation technique is to 
> sample a pair of quadrature sinewaves at the leading edge of the pulse 
> to be time stamped.

These are all variants of what I (because of my high-energy physics
background!) call "Time to amplitude converters".

The traditional concept is to just generate a ramp (with RC or
a little better constant current source + capacitor) and stop charging
and then (at your leisure...) sample where it stopped.

But Bruce's suggestions are substantially more advanced in that they
do not suffer from "dead time" to reset the integrator (and we
all know how hard it is to surely reset a capacitor quickly! this
is where I learned all about capacitor "soak") and some of
them (like the quadrature sinewaves) allow you to do "end-to-end"
corrections for even the slightest amplitude offsets/miscalibrations.

I guess technology has advanced since I did this stuff in the 70's 
with NIM bins and early CAMAC crates :-).
(Next thing you know, Bruce will tell us how he was doing this in
the 60's! and in fact the quadrature sinewave thing was in fact in use
as far back as the 50's for RADAR, but not with DAC's and computers...)


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