Browse Prior Art Database

CMOS Mixed Voltage Interface between Chips

IP.com Disclosure Number: IPCOM000115151D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Cao, TA: AUTHOR [+4]

Abstract

Sometimes chip-to-chip communication involves chips of different power supplies. In that case a mixed voltage interface is needed. Disclosed is a CMOS mixed voltage interface. The circuit is placed on the CMOS chip of lower power supply to receive the signal from the CMOS chip of higher power supply.

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CMOS Mixed Voltage Interface between Chips

      Sometimes chip-to-chip communication involves chips of
different power supplies.  In that case a mixed voltage interface is
needed.  Disclosed is a CMOS mixed voltage interface.  The circuit is
placed on the CMOS chip of lower power supply to receive the signal
from the CMOS chip of higher power supply.

      Mixed voltage interface is needed in chip-to-chip communication
between chips of different power supplies.  This disclosure proposes
a CMOS mixed voltage interface to be used in Bellatrix Project.  The
circuit is placed in the receiving chip of lower power supply.

      Fig. 1 shows chip-to-chip communication of mixed voltages.
Fig. 2 shows the mixed interface circuit.  It is consisted of a N
device and a pull-up resistor made of BR mask layer.

      Without Buried Resisor (BR) mask resistor, the voltage at node
B in Fig. 2 will be around VDD (of receiving chip) - Vtn, where Vtn
is the threshold of N device.  For example, if the sending chip has
VDD= 3.6 V and the receiving chip has VDD= 2.5 V, the voltage at node
A is around 3.6V but the voltage at node B is only around 1.8 V.
This represents a loss in noise margin of the up level.  The result
is shown in Fig. 3.

      However, with BR mask resistor connected as shown in Fig. 2,
the voltage at node B is restored back to VDD of the receiving chip.
Fig. 4 shows the waveforms at node A and node B with pull-up BR mask
resistor

      The...