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Forced Perfect Termination: A Self-Matching Transmission Line

IP.com Disclosure Number: IPCOM000105641D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Le, T: AUTHOR

Abstract

This technique, now in use in SCSI Buses and with potential applications in other signal-transmission applications, formalizes a new way of looking at transmission line termination. The technique was developed to resolve difficulties in exactly matching transmission line impedances to termination impedances. Impedance matching is rendered unnecessary with resultant flexibility and cost advantages for manufacturing. System configuration flexibility is greatly increased, due to increased system tolerance for stubs and reflections. The classical signal line drop problem in long distance transmission has been reduced by orders of magnitude. The regenerative property of this technique allows pulses to be sent long distances without repeaters. Tests were success-ful with pulses sent 100 ft. with zero loss in noise immunity.

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Forced Perfect Termination:  A Self-Matching Transmission Line

      This technique, now in use in SCSI Buses and with potential
applications in other signal-transmission applications, formalizes a
new way of looking at transmission line termination.  The technique
was developed to resolve difficulties in exactly matching
transmission line impedances to termination impedances.  Impedance
matching is rendered unnecessary with resultant flexibility and cost
advantages for manufacturing.  System configuration flexibility is
greatly increased, due to increased system tolerance for stubs and
reflections.  The classical signal line drop problem in long distance
transmission has been reduced by orders of magnitude.  The
regenerative property of this technique allows pulses to be sent long
distances without repeaters.  Tests were success-ful with pulses sent
100 ft.  with zero loss in noise immunity.

     The new technique achieves perfect matching by purposely
mismatch- ing impedances of line and terminators based on the theory
that equality can be achieved by forcing the simultaneous existence
of two inequali- ties.

     The technique works as follows.  Instead of attempting to match
the line in order to minimize reflections, we forced reflections to
occur and then trap and dissipate the excess energy at the
terminator.  A pulse is sent down a line from a to be as shown in
Fig. 1.  The line is matched with an impedance higher than its
characteristic impedan...