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Browse Prior Art Database

Integrated Optical Bus System for VLSI Chip Interconnects

IP.com Disclosure Number: IPCOM000108917D
Original Publication Date: 1992-Jul-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 3 page(s) / 105K

Publishing Venue

IBM

Related People

Gfeller, F: AUTHOR

Abstract

Disclosed is an optical bus system for distributing data and clocksignals between CMOS VLSI chips on a common circuit board. The optical interconnect network consists of laser diodes, photo diodes, and waveguides integrated on a GaAs substrate. The network is arranged in a folded-bus topology allowing data paths without physical cross-overs to eliminate optical cross-talk problems. Laser diodes with sub-mA threshold current require smaller drive currents than electrical 50-ohm transmission lines, thus reducing heat dissipation. CMOS driver circuits claim a large chip area which may be substantially reduced with lower drive currents. Furthermore, large di/dt current spikes due to capacitive loading, as well as ground loop problems are avoided with optical networks.

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Integrated Optical Bus System for VLSI Chip Interconnects

       Disclosed is an optical bus system for distributing data
and clocksignals between CMOS VLSI chips on a common circuit board.
The optical interconnect network consists of laser diodes, photo
diodes, and waveguides integrated on a GaAs substrate.  The network
is arranged in a folded-bus topology allowing data paths without
physical cross-overs to eliminate optical cross-talk problems.  Laser
diodes with sub-mA threshold current require smaller drive currents
than electrical 50-ohm transmission lines, thus reducing heat
dissipation.  CMOS driver circuits claim a large chip area which may
be substantially reduced with lower drive currents.  Furthermore,
large di/dt current spikes due to capacitive loading, as well as
ground loop problems are avoided with optical networks.

      Fig. 1 shows the optical bus network integrated on a GaAs
substrate 1 which is embedded in a circuit board 2 with electrical
connector 9.  VLSI chips 3 are bonded with solder balls 4 (C4
technology) to both the circuit boards 2 (power and low speed
electrical signals), and to the GaAs substrate 1 for connecting the
lasers 5 and photodiodes 6 (high-speed optical signals).  An optical
signal, generated by a laser diode 5, is collected on the downstream
optical bus line 7 and guided to a Y-junction waveguide distributor
8, dividing the incoming signal into 2 branches with equal power.
The individual branches (upstream bus line) are connected to
receiving photodiodes, thus interconnecting each output port with
each input port.  This configuration is repeated to form a bus with
the required number of bus lines....