Re: Missing Schmitt Gates??
- From: John Larkin <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Thu, 29 Nov 2007 17:34:44 -0800
On Thu, 29 Nov 2007 21:49:20 +0100, Frank Buss <fb@xxxxxxxxxxxxx>
wrote:
D from BC wrote:
On Digik*y it looks like one can get a:
schmitt inverter
schmitt NAND
schmitt OR
... and that's it?
You can build your own Schmitt trigger with two resistors:
http://www.edn.com/index.asp?layout=article&articleid=CA6262539
You need a positive feedback for it, so maybe this is possible for
converting an OR gate to one with a Schmitt trigger input, but for NAND
you'll need an additional buffer, which can be converted to a Schmitt
trigger buffer with two resistors per input.
Adding external resistors to a gate (or a comparator) has problems.
The positive feedback is delayed, so fast noise can sneak through
before the feedback arrives. If you add an extra gate to adjust the
polarity, that's even more delay so the problem gets worse.
If you just want hysteresis so that you can make an rc oscillator,
it's OK, because the input is slow and controlled.
John
.
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