[SOLVED] What is the different between a synchroniser and a deglitch-er

[wtr]

Hello all,

Surprisingly the word deglitch doesn't exist in a dictionary. We really should get it added.
de- (to the opposite - latin preposition = from, down, away)
glitch (unexpected spurious signal)

What is the difference between a synchroniser and a deglitcher?

Is it simply that a deglitcher is multiple synchronisers to confirm the stability of a signal?

Regards,
Wes

 

[TrickyDicky]

Sounds like both terms are mostly interchangable in various circumstances. But they both imply getting some ansynchronous signal into a synchronous domain.

 

[asdf44]

A synchronizer just safely moves a signal across a clock domain.

A deglicher might remove spurious pulses from a signal but may have nothing to do with domain crossing.

However it’s easy to combine them because they can both be based on a shift register.

 

[ads-ee]

Think switches....
A de-glitch circuit is required on a mechanical switch. Just using a synchronizer will allow a bunch of synchronous glitches to pass through. You first need to de-glitch the switch signal as it is very slow to transition and can bounce. After some ms of time the switch will stop bouncing and will be steady at whatever level it was switched to.

 

[filip.amator]

Is it simply that a deglitcher is multiple synchronisers to confirm the stability of a signal?

That is right - degitcher is a set of filp-flops in series and multi input NOR gate. Each stage of the synchronizer (ff output) goes into one input of the gate. So 4 stage deglitcher is made of 4 ff-ps and 4 input NOR gate. The output of the systems is taken from gate output.

 

[wtr]

A synchronizer just safely moves a signal across a clock domain.

A deglicher might remove spurious pulses from a signal but may have nothing to do with domain crossing.

However it’s easy to combine them because they can both be based on a shift register.

SOLVED ^^
Except in circumstances when the deglitching happens over an impractically long period for a shift register, like a mechanical switch as #4 touched on. In such cases the user may wish to use https://www.doulos.com/knowhow/fpga/switchcleaner/ solution 2

 

[KlausST]

Hi,

I'm not sure if I use the correct terminology.
I say "deglitcher" for the D-FF that supresses glitches caused by a combinatorial output.

For example: a combinatorial multi-bit comparator that follows a counter causes glitches at the output...
A D-FF, fed with the same clock as the counter, supresses the glitches. Thus I call the D-FF "deglitcher".

Klaus