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Circuit Protection Technique for 5V/3V Mixed Signalling

IP.com Disclosure Number: IPCOM000113133D
Original Publication Date: 1994-Jul-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Cases, M: AUTHOR [+4]

Abstract

Described is a hardware circuit implementation that enables 3V BI-CMOS Very Large Scale Integration (VLSI) circuit chips to operate in a 5v/3v signalling environment without requiring power sequencing or special power supply sensing.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Circuit Protection Technique for 5V/3V Mixed Signalling

      Described is a hardware circuit implementation that enables 3V
BI-CMOS Very Large Scale Integration (VLSI) circuit chips to operate
in a 5v/3v signalling environment without requiring power sequencing
or special power supply sensing.

      In three volt integrated BI-CMOS VLSI chips that incorporate
five volt signalling levels, such as 5v rail to rail driver levels,
the VLSI processes have limits of voltage excursions that can exist
at the Input/Output (I/O) pads.  If the limits are exceeded, a
latch-up can occur as well as other undesirable long term reliability
failures.  However, various clamping techniques are used, such as the
use of diode circuits returned to a positive power supply to limit
the transient voltage excursions to values that do not damage the
silicon chip.

      Fig. 1 shows a schematic of a standard clamping technique.  In
this case, the diode clamps used in 3v VCC chips cannot be returned
to 3v if that chip is to co-exist in a 5v signalling arena.  However,
a 5v reference supply may be brought into the I/O cell of a 3v
technology integrated circuit for use with an overshoot clamp.  This
technique is acceptable provided additional I/O signals are available
and that some power sequencing or sensing prevents unwanted forward
biasing of the clamping diode during power up/power down or loss of
the 5v reference voltage.

      In order to eliminate the requirements of power sequencing
protect sensing when using a clamping diode returned to a positi...