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Bi-CMOS TTL Tri-State Off-Chip Driver Without Schottky Diode

IP.com Disclosure Number: IPCOM000099683D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

Boudon, G: AUTHOR [+6]

Abstract

To improve the performance of a heavily loaded CMOS circuit, the bipolar transistor has been associated with CMOS structure.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 68% of the total text.

Bi-CMOS TTL Tri-State Off-Chip Driver Without Schottky Diode

       To improve the performance of a heavily loaded CMOS
circuit, the bipolar transistor has been associated with CMOS
structure.

      The traditional BI-CMOS circuit used for on-chip drivers is
efficient to drive capacitance load, but when a DC current has to be
driven, the output down level is greater than a Vbe, which does not
match TTL specifications. Continued

      This article describes a tri-state TTL BI-CMOS off-chip driver
(OCD). This driver does not need Schottky barrier diode, usually
required to prevent the pull-down NPN device from saturation.

      The schematic of the OCD is shown in the figure.  The data
input pin is A0, the output is enabled by the control lines DI and
B0. DI and B0 must be set to up level to have output equal to
input. If either of them is down, the OCD is in high impedance mode.

      The OCD can interface the TTL level circuits with a down level
below 0.5 volt MPDL (maximum positive down level). The principle of
operation is based on the fact that the collector-base voltage of the
pull-down device T1 is equal to the voltage drop across the FET T4,
the latter is defined in the 0.2 volt to 0.4 volt range and allows T1
not to be saturated.  To avoid the 5 volt reverse voltage between the
base and the emitter of T3, the transistor T6 has been used. T6 is
turned off when the output is pulled up by T2 and T12, avoiding the
T3 emitter-base junction of T3...