Active-pixel-sensor (APS) circuits and perhaps other dense complementary metal oxide/semiconductor (CMOS) very-large-scale integrated (VLSI) circuits would be powered by infrared beams transmitted by laser diodes and received by photodetectors, according to a proposal. Clock signals for synchronizing the operations of such a circuit would be transmitted as modulation on the infrared power-supply beam. Command data signals could be received via other, low-power infrared beams. Digital APS output signals would likewise be sent to external circuits via modulation of infrared beams transmitted by low-power laser diodes incorporated into the VLSI APS chips.

The power-supply part of the proposal has been made feasible by advances that have reduced the power demands of CMOS VLSI circuits. The power demand of a typical CMOS VLSI APS chip is now low enough that a single, sufficiently illuminated infrared photodetector could serve as the source of a galvanically isolated power supply on the chip. With a sufficiently high duty factor, the clock modulation on the infrared power-supply beam should exert little effect on power-coupling efficiency.

The data-communication part of the proposal has been made feasible by the evolution of sensitive infrared detectors and low-power, frequency-tunable laser diodes. The infrared beams for input and output of data would have wavelengths different from that of the power-input beam. By use of tuned laser diodes in the transmitters and narrow-band dielectric filters in the receivers, it would be possible to communicate simultaneously over multiple infrared bands; thus, it would be possible to use a wavelength-multiplexing scheme to achieve a high data rate.

Multiple CMOS VLSI APS chips could be operated under common control and readout by use of a combination of wavelength and time multiplexing. The multiplexing scheme could be simplified, at the cost of some increase in structural complexity, by using a dedicated optical fiber for data communication between each APS and the common readout and control circuitry.

As APS and other VLSI circuits become denser and more complex, design problems pertaining to reliability of, and power dissipation in, electrical interconnections, become increasingly difficult. The problems are further intensified in cases in which VLSI circuits are required to be connected together in many-to-one networks. In general, the complexity of, and power dissipation in, electrical interconnections increase approximately exponentially with the number of nodes, while reliability decreases approximately exponentially with the number of nodes. The use of all-optical input and output connections according to the proposal described above could reduce overall complexity and increase reliability. In particular, if full-duplex communication with frequency multiplexing of data signals were used, then the complexity of a network with all optical interconnections would increase only linearly with the number of nodes.

This work was done by Frank Hartley and Bedabrata Pain of Caltech for NASA's Jet Propulsion Laboratory. NPO-20438

This Brief includes a Technical Support Package (TSP).
Optical power supply and data communication for APS circuits

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This article first appeared in the February, 1999 issue of Electronics Tech Briefs Magazine.

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