7 Apr
2019
7 Apr
'19
2:48 p.m.
On Sat, Apr 06, 2019 at 12:32:29PM -0400, Tim wrote:
So the software would be able to deal with sines
better,
and measure phase differences rather than a pulse edge.
Sure, the pulse will be 'smeared out' a bit, and its actual
position may seem to be ambiguous. But that's no problem.
What you get in the sample stream is the impulse response
of the A/D converter. Assuming that this is a linear and
time-invariant system, the IR contains all information.
If the pulse is smeared out, one way to find the delay is
1. Compute the FFT of the part of the sample stream that
contains the smeared-out pulse.
2. Compute the phase of each frequency bin. If the delay
is independent of frequency (it should be if the A/D
is any good), then the phase will be a linear function
of frequency. The slope of that function indicates
the delay (relative to the start of the FFT input).
The only advantage of using sine waves is that your test
signal has much higher energy than a single short pulse,
so you get a better S/N ratio. But for this test, the
S/N will be very good anyway.
Ciao,
--
FA