Browse Prior Art Database

Self-Enabling Output Driver

IP.com Disclosure Number: IPCOM000117172D
Original Publication Date: 1996-Jan-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Baumgartner, SJ: AUTHOR [+2]

Abstract

Output drivers using an off-chip enable require two module pins. One pin is used for the output signal, and the other pin is used for the enable signal. This self-enabling low-voltage swing output driver eliminates the need for the external enable signal.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 94% of the total text.

Self-Enabling Output Driver

      Output drivers using an off-chip enable require two module
pins.  One pin is used for the output signal, and the other pin is
used for the enable signal.  This self-enabling low-voltage swing
output driver eliminates the need for the external enable signal.

      The block diagram for the solution is shown in the Figure.  It
consists of core logic which contains a signal that is to be driven
off chip by a source follower through an enable circuit.  A 50 Ohm
load to ground would be typical.  Instead of providing an off-chip
enable signal, the signal can be supplied to the enable logic circuit
by inverting the output with M1 and M2 and connecting it to the
enable input.  This assumes the enable input is active high.  If the
enable input is active low, then another inverter can be put in
series with the one shown.  The maximum output voltage must not
exceed the threshold of the Complementary Metal Oxide Semiconductor
(CMOS) inverter.  The threshold is set to the average of power supply
voltage (VDD) and the maximum output voltage by selecting the proper
ratio of the P Channel Field Effect Transistor (PFET) (M2)
Width-to-Length ratio (W/L) to the N Channel Field Effect Transistor
(NFET) (M3) W/L.

      A PFET pull up resistor (M4) is connected to the inverter input
to disable the enable logic when the output pin is not connected to a
load.  Conceptually, this invention can be implemented using bipolar
transistors as long...