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Programmable Impedance Off-Chip Driver

IP.com Disclosure Number: IPCOM000103001D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 37K

Publishing Venue

IBM

Related People

Adams, RD: AUTHOR [+3]

Abstract

A programmable circuit is added to off-chip drivers (OCDs) allowing end users to match output impedance to their circuitry, e.g., a card or a module network. A conventional multistage circuit is altered to allow electrical selection of the number of stages desired to appropriately match the application.

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Programmable Impedance Off-Chip Driver

      A programmable circuit is added to off-chip drivers (OCDs)
allowing end users to match output impedance to their circuitry,
e.g., a card or a module network.  A conventional multistage circuit
is altered to allow electrical selection of the number of stages
desired to appropriately match the application.

      In the figure, a conventional two-stage complementary metal
oxide silicon (CMOS) circuit is shown which may be programmed so that
one or both stages are used, thus controlling output impedance and
rate of change of current (di/dt) pulses out of an OCD.   Input IN
turns on the first stage, which is comprised of p-type transistor T1
and n-type transistor T2.  After a delay through inverter I1 and NAND
2 and NOR 4, the second stage, which is comprised of transistors T3
and T4, is activated if programming input P is low.  If input P is
high, the second stage is turned off and only the first stage output
is provided at OUT.

      More than two stages may be similarly made programmable, thus
providing a wider range of adjustment of OCD output impedance and
di/dt.  Also, other than CMOS circuitry may be used to provide the
same result.

      Disclosed anonymously.