From: jvincent@bnr.ca (John Vincent)
Subject: The howto of FPT
Organization: Bell-Northern Research, Ottawa, Canada
Date: Wed, 16 Dec 1992 14:36:22 GMT

FPT is actually really simple, I wish I had thought of it. What it does 
is use diode clamps to eliminate over and undershoot. The "trick" is
that instead of clamping to +5 and GND they clamp to the output of two 
regulated voltages. This allows the clamping diodes to turn on earlier
and is therefore better at eliminating overshoot and undershoot. The block
diagram for a FPTed signal is below. The resistor value is probably in the 
120 to 130 ohm range. The actual output voltages of the regulators may not
be exaclty as I have shown them but ideally they are matched to the diode 
characteristics so that conduction occurs when the signal voltage is 
greater than 3.0 V or less than 0.5 V. 

Hope this helps.


          +--------------- TERMPWR 
          |
      ____|____
     |        |
     | Vreg 1 |-------*-------------------------*--------------- 3.? V
     |________|       |                         |
                      |                         |
                      |                         |
                      |                         \
         +------------*                         /    pullup resistor
         |            |                         \
         |            |                         /
         |        ____|___                      |
         |       |        |                     |
         |       | Vreg 2 |----------*----------|--------------- 3.0 V
         |       |________|          |          |
         |                         --+--        |
         |                          / \         |
         +-----------+             /___\        |
                     |               |          |
                     |               |          |              terminated
                     |               *----------*------------- signal
                     |               |
                     |               |
                     |             --+-- 
                     |              / \
                     |             /___\
                     |               |
                  ___|____           |
                 |        |          |                 
                 | Vreg 3 |----------*-------------------------  1.0 V (?)
                 |________|


-- 
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ John Vincent              $  My opinions are my own, until they're worth  $
$ Bell- Northern Research   $  something, at which point they become the    $
$ P.O. Box 3511, Station C. $  property of my employers.                    $
$ Ottawa, Ont , K1Y 4H7     $                                               $
$ (613) 763-8446            $  Better to be dead and cool than alive and    $
$                           $  not cool.                                    $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ INTERNET : jvincent@bnr.ca                                                $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
Newsgroups: comp.periphs.scsi