[SI-LIST] Re: Hysteresis in SI (Signal Integrity)??
- From: Chris Cheng <Chris.Cheng@xxxxxxxxxxxx>
- To: "'dimiter.popoff@xxxxxxxxxxx'" <dimiter.popoff@xxxxxxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Tue, 10 Feb 2004 16:12:33 -0800
Good point, I believe LTL actually latch/drive the receiver at the previous
state rather than just the threshold change. That's the difference between
Schmitt trigger and LTL.
-----Original Message-----
From: Dimiter Popoff [mailto:dimiter.popoff@xxxxxxxxxxx]
Sent: Tuesday, February 10, 2004 3:11 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Hysteresis in SI (Signal Integrity)??
Chris,
> ...
> Back in the days when Bill Gunning and I were working on GTL. ...
> ...
> ... The idea was to increase the noise margin by forcing the
> threshold to change based on the previous level.
>
When was that? The Schmitt trigger has been done on discrete parts
prior to TI 74XX series, which includes 7413, 7414, 74132 (these are
just the oldest I know of), all with an input hysteresis (and
available today in various CMOS processes). Most if not all buffer
parts (this was already mentioned, I just lost the message so cannot
quote it) originating from the 74LS244, 245 etc. have Schmitt-trigger
like inputs (i.e. with hysteresis).
Another very popular hysteresis circuit used in the analog world
is the one of an analog comparator (or perhaps an opamp used as such,
i.e. with no negative feedback) with some positive feedback.
To answer the initial question, the input hysteresis of a voltage
sensitive buffer is the difference between the voltage necessary
to turn the output from 0 to 1 and the voltage which will turn it
from 1 to 0, where the former > latter.
As it was already mentioned, this is a basic kind of knowledge,
but then the thread length made me think that perhaps in todays
world of narrowly profiled education the answer may be less clear
than I believed.
Dimiter
--------------------------------------------------------------------
Dimiter Popoff
Transgalactic Instruments, Gourko Str. 25 b, 1000 Sofia, Bulgaria
http://transgalactic.freeyellow.com
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