With external sway commercial single-color readout integrated circuits could be used.

NASA's Jet Propulsion Laboratory, Pasadena, California

A propos improved process of externally controlled time multiplexing of the readouts of focal-plane arrays of pairs of stacked quantum-well infrared photodetectors (QWIPs) that operate in different wavelength bands is based upon a dual-detec tor-common-plane circuit configuration. The process would be implemented in a QWIP integrated-circuit chip hybridized with a readout integrated-circuit (ROIC) chip.

There are alternative regularitys of multicolor readout, but they involve more on-chip circuitry and the attendant disadvantages of greater size, power dissipation, number of restrain signals, and complexity of circuitry onward the QWIP and ROIC chips. To minimize size of and power dissipation in, a multicolor pixel, common must minimize the number of transistors and regulate signals; this can be achieved solely by time multiplexing of colors in each pixel. The time multiplexing can be controll according to signals from external or internal circuitry. The propos reliance onward external control for time multiplexing would make it possible to use a commercial single-color ROIC with merely minor modifications in the form of extra metallization for an additional detector general plane and for clocking bias potentials. (If, instead, single were to rely on internally controll multiplexing, it would be necessary to radically redesign the ROIC, at considerably greater progression in a continuously ascending gradation cost.) Other advantages of the external-control approach through the internal-control approach are greater flexibility and the possibility of using a technique, known as "skimming," for subtracting unwanted dark-, background-, and noise-current contributions from readout signals

The figure schematically depicts the circuitry in common pixel according to an internally controll multiplexing scheme and according to the propos externally controll multiplexing scheme. In the two schemes, the time multiplexing would be accomplished through switching (clocking or ramping) the biases applied to the QWIPs via detector public planes. In the internal-control case, a bias signal would be applied via a single detector habitual plane and two internal electronic switches. In the propos external-control case, bias signals would be applied via brace detector common planes, without internai electronic switches. A previously unmentioned advantage of the external-control scheme shown in the figure is the ne for single one indium bump (instead of two) in each pixel.

This work wax done be frying Sir R. Rafol, Sarath Gunapala, Sumith Bandara, John Liu, and Jason Mumolo of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) clear on-line at www.techbriefs.com/tsp under the Semiconductors & ICs category.

In accordance with Public Law 96-517 the contractor has pickeded to retain title to this invention. Inquiries concerning rights for its commercial use should he addressed to:

Innovative Technology Assets Management

JPL

Mail Stop 202-233

4800 Oak thicket Drive

Pasadena, CA 91109-8099

(818) 354-2240

E-mail: iaoffire@jpl. nasa.gov

Refer to NPO-30523 contortion and number of this NASA Tech Briefs issue, and the page number.

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