Browse Prior Art Database

Off-Chip Driver for Small Computer System Interface

IP.com Disclosure Number: IPCOM000112436D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Masenas Jr, CJ: AUTHOR [+2]

Abstract

Controlled switching of large currents when driving off chip requires tightly controlled transition rates across a wide range of load conditions. If switching is too slow, delays will be excessive, and if too fast, overshoots and subsequent false switching will occur. Moreover, switching transitions must be controlled both during turn-on and turn-off of the driver. A circuit is described which provides the required controlled transitions of an open drain output driver.

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This is the abbreviated version, containing approximately 68% of the total text.

Off-Chip Driver for Small Computer System Interface

      Controlled switching of large currents when driving off chip
requires tightly controlled transition rates across a wide range of
load conditions.  If switching is too slow, delays will be excessive,
and if too fast, overshoots and subsequent false switching will
occur.  Moreover, switching transitions must be controlled both
during turn-on and turn-off of the driver.  A circuit is described
which provides the required controlled transitions of an open drain
output driver.

      A circuit showing a voltage reference circuit A, a controlled
transition switching circuit B, and an open drain off chip driver C,
loaded with the elements Rload and Cload connected to a 3.0V power
supply.  Transistor e represents the output device of the open drain
off chip driver.  Transistors a and d are switching devices to
control the switching of the gate of transistor e.  Transistors b and
c are series discharge devices used to control the transition rate of
the switching of the gate of transistor e.

      The negative going transition of the output driver is
controlled by the charging of node 1.  This charging is controlled by
series device transistor b.  The DC voltage of the gate of transistor
b is regulated at approximately 2 times the device threshold voltage
below the supply voltage V dd by a reference circuit comprised of
transistors f, g, h, and i. The operation of this circuit is
described in previous art....