Browse Prior Art Database

Clamping Circuitry for Off-Chip Push-Pull Drivers

IP.com Disclosure Number: IPCOM000100979D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Beranger, H: AUTHOR [+3]

Abstract

A clamping circuitry for up levels in push-pull drivers is disclosed which has the following characteristics: - It allows to clamp reflected waves of the transmission line with the same elements that define the up level. - It allows to define the up level through a regulator that has a low output impedance and is less sensitive to loading currents. - It is compatible with a simple disabling control, and with severe constraints on the maximum allowable reverse Vbe's across transistors.

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Clamping Circuitry for Off-Chip Push-Pull Drivers

       A clamping circuitry for up levels in push-pull drivers
is disclosed which has the following characteristics:
   - It allows to clamp reflected waves of the transmission line with
the same elements that define the up level.
   - It allows to define the up level through a regulator that has a
low output impedance and is less sensitive to loading currents.
   - It is compatible with a simple disabling control, and with
severe constraints on the maximum allowable reverse Vbe's across
transistors.

      In the figure, T1 is the pull-up transistor and T2 is the pull-
down transistor. Among the up level clamping elements RX, RY, TC, TD,
TB are the elements delivering a kVBE + VCE up-level voltage at the
output. The current in TB is copied from the current in a transistor
TA mounted as a current mirror, with its collector connected to the
base of T1. Thus TA and TB current are both determined by the R2
resistor value. If the output tends to increase above the defined up
level, TB current increases, which increases TA current, lowers T1
base, and thus stabilizes the up level.

      This regulator action enables a low output impedance at the up
level. The DC variations of the up level due to various terminations
or to the number of receivers connected on the net, are reduced.

      If a reflected positive the wave comes back on the output, the
TB current is suddenly increased and the T1 base is lowere...