Re: Debouncing....at About 1Mhz

On Wed, 07 Nov 2007 09:44:50 -0700, Jim Thompson
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On Wed, 07 Nov 2007 08:32:24 -0800, D from BC
<myrealaddress@xxxxxxxxx> wrote:

On Wed, 07 Nov 2007 07:27:27 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@xxxxxxxxxxxxxxx> wrote:

On Wed, 31 Oct 2007 21:53:15 -0800, D from BC
<myrealaddress@xxxxxxxxx> wrote:

This has got to be a classic signal clean up problem....

I need a circuit that triggers on edge A, then ignores about 0.1uS of
jitter then triggers on edge B and then ignores a following 0.1uS of
jitter.

+-+ +-+ +----------------+ +-+ +-+
In | | | | | | | | | |
A | | | | B | | | |
-------+ +-+ +-+ +-+ +-+ +-----------

|<0.1uS>| |<0.1uS >|
|< 0.5uS >|


Out +------------------------+
| |
A' B'
-------+ +-------------


Edge A to A' is ~ less than 10nS
Edge B to B' is ~ less than 10nS

All values are approximates.
"In" and "Out" are repeating waveforms.

I think I can do it with:

1 flip flop
1 >0.1us delay circuit
Sprinkled with gates..

Or maybe I need 2 flip flops..one for edge A and one for edge B..

I'm not even sure yet which type of FF to get.

If anybody has done this problem before and doesn't mind sharing..let
me know a topology...

In the meantime, I'll be doodling until I get a solution...


D from BC

My thoughts....

http://www.analog-innovations.com/SED/AlternatingEdge.pdf

make a flip-flop that can alternately be positive- or negative-edge
triggered, by adding XOR in front of clock input and tying one XOR
input back to output.

BUT... DELAY switch-over to avoid racing.

My 74HC74 model indicates it can't cope with 20ns/20ns noise, so
faster logic is needed.

Timings, etc., for illustration only... squeeze to fit ;-)

...Jim Thompson

Hey... that looks good. :)
It looks like a hairballized spin off of JFs circuit.
Still with 2 gate tp. Impressive.... :)

One detail I'm wondering about...
You have Pre and Clr connected together for a system reset.
Shouldn't one or the other be used..Not both..


D from BC

Yep, Just spotted that myself ;-)

...Jim Thompson

Actually, just pull them high. There's really no powerup preference
for either state.

John

.

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