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Virtual Ground Active Terminator

IP.com Disclosure Number: IPCOM000099728D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Banker, DC: AUTHOR [+3]

Abstract

An active terminator is proposed which enables matching the characteristic impedance of a transmission line over a signal swing range of between 400 mv to 700 mv.

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Virtual Ground Active Terminator

       An active terminator is proposed which enables matching
the characteristic impedance of a transmission line over a signal
swing range of between 400 mv to 700 mv.

      The active terminator is shown in Fig. 1, with a similar
terminator which functions the same way, but using lateral PNPs shown
in Fig. 2.  The terminator initially provides an under termination
during the initial start of the signal transition.  This produces a
negative reflection coefficient which reduces the total amount of
energy of the positive reflection.  During the middle part of the
transition the impedance of the termination produces a reflection
coefficient approximately equal to '1', thus providing voltage
doubling at the end of the transmission line. During the end of the
transition the active terminator again becomes under terminated with
a reflection coefficient approximately equal to minus '1'.  Thus, the
terminator provides identical terminations for either positive or
negative-going transitions and reduces the total amount of unwanted
reflections on the transmission line.