On 07/21/2012 03:30 AM, Hal Murray wrote:
albertson.ch...@gmail.com said:
Maybe, but it is absolutely needed if there is any noise on the signal.
A
perfect comparator with zero hysteresis would dither on every zero
crossing.
On 07/21/2012 01:41 AM, Hal Murray wrote:
Hysterssis will eliminate spikes or double pulses that are caused by noise
on a signal with low rise time as long as the noise isn't too big.
mag...@rubidium.dyndns.org said:
... which is what he called dither.
OK, I need a few hints.
What is dither in this context and what does it have to do with hysteresis?
I think of dither as being related to noise at the sampling level. In that
context, hysteresis just shifts the switching point. It doesn't change
anything (much) related to noise. How does that translate into eliminating
spikes or double pulses?
The jump about around the sampling point which non-schmitt triggered
comparators shows results in a signal which is _similar_ to a dithered
signal. It causes multiple spikes. The schmitt trigger will shift it's
trigger level depending on state to avoid this.
Exactly what to call the forrest of spikes for a non-hysteresis trigger
is to the best of my knoweldge not really well established. Dither is
similar enough to "work".
Oh, and the dithering noise does not need to be applied specifically,
you may use the noise that is there. It works for GPS receivers. It's
only when you don't have enough noise that you need to apply it, so the
Wikipedia article is incorrect in that aspect.
But if you object to the term dither to be applied for this jumping
around, then propose a better term.
Cheers,
Magnus
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