[time-nuts] Zero-Crossing Detector Design?

[Hal Murray]

> albertson.chris at 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.

magnus at 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?

---------

Wikipedia says:
> Dither is an intentionally applied form of noise used to randomize
> quantization error, preventing large-scale patterns such as color banding in
> images. Dither is routinely used in processing of both digital audio and
> digital video data, and is often one of the last stages of audio production
> to compact disc.

http://en.wikipedia.org/wiki/Dither

Their story about WW II mechanical computers working better on airplanes 
(vibration) than in the lab is neat.

I remember my boss one summer telling me a similar story.  The meters he was 
testing didn't work in his lab.  They worked fine in the manufacturer's lab 
which was located above a bunch of punch presses.



-- 
These are my opinions.  I hate spam.