Hughes Aircraft Company

Other

Robert N Sato

Cheng P Wen

Chan-Shin Wu

Eugene Robert Worley

Paul R Prince

O Glenn Ramer

David H Alexander

Kachu Ishizuka

An improved multiquantum well superlattice photodetector (10) for detecting long wavelength infrared radiation. Electron transport in a first excited energy state is enhanced in barrier layers (20) of the superlattice (16) by lowering the potential energy barriers of the barrier layers (20) to a predetermined level below the first excited energy state. The tunneling component of the dark current in a multiquantum well photodetector (10) may be substantially eliminated by placing a blocking layer (22) at one end of the superlattice (16). The thickness of the blocking layer (22) is also substantially greater than that of the barrier layers (20) of the superlattice (16) to prevent charge carriers which tunnel through the superlattice (16) from reaching the collector contact. The blocking layer (22) also has a potential energy barrier having a height at a level higher than that of the barrier layers (20) of the superlattice (16).

Dark current-free multiquantum well superlattice infrared detector

A multiquantum well superlattice photodetector for detecting long wavelength infrared radiation in which dark current is reduced by a blocking layer. The tunneling component of the dark current in a multiquantum well photodetector is substantially eliminated by placing a blocking layer at one end of the superlattice. The blocking layer has a potential energy barrier having a height at the same level of the barrier layers of the superlattice. The thickness of the blocking layer is substantially greater than the barrier layers of the superlattice to prevent charge carriers which tunnel through the superlattice from reaching the ohmic contact.

A multiple quantum well photodetector structure has superlattice which absorbs radiation polarized non-parallel to the superlattice during a first pass. Non-absorbed radiation polarized parallel to the superlattice is reflected back into the superlattice at a cross-angle to its incident angle, with its polarization shifted to a substantially non-parallel angle to the superlattice. At least part of this radiation is absorbed during its second pass through the superlattice, thereby increasing the efficiency of the device. An optical back grating is used to perform the cross-angle reflection, and a front grating may also be used to shift an incoming beam which is initially normal to the superlattice to an angle at which part of the beam is absorbed. The front grating is at a cross-angle to the back grating to enable a cross-angular shift by the back grating.

High efficiency multiple quantum well structure and operating method

A capacitive feedback transimpedance amplifier 10 comprises a differential amplifier constructed of GaAs transistor Q.sub.1 and Q.sub.2 and has an input coupled to the output of an infrared detector 12 and an output expressive of the detector signal integrated over a predetermined interval of time. The amplifier has a transistor Q.sub.0 coupled to the input for coupling the input periodically to a predetermined voltage potential and a transistor Q.sub.9 coupled to the output of the amplifier for simultaneously periodically coupling the output to a predetermined voltage reference, thereby initializing the amplifier at the beginning of an integration period. A load is coupled between an amplifier output terminal a source of amplifier power. The load includes a resistor having a first terminal coupled to the amplifier output terminal and a second terminal coupled to a first GaAs load transistor. The first load transistor is serially coupled to a second load transistor. A gate terminal of each of the first and the second load transistors is coupled to the amplifier output terminal.

GaAs focal plane array readout

An integrating transimpedance amplifier 10 comprises a differential amplifier constructed of GaAs, MESFET, HEMT, SDHT or MODFET transistors has an input coupled to the output of a radiation detector 12 and an output expressive of the detector signal integrated over a predetermined interval of time. The amplifier has a transistor Q0 coupled to the input for coupling the input periodically to a predetermined voltage potential and a transistor Q.sub.9 coupled to the output of the amplifier for simultaneously periodically coupling the output to a predetermined voltage reference, thereby initializing the amplifier at the beginning of an integration period. A buffer transistor Q.sub.4 couples the output of the amplifier to a GaAs MISFET switch Q.sub.8 which is periodically activated to couple the buffered amplifier output to a storage capacitor Csmp. The buffer transistor also couples the output of the amplifier to a feedback capacitor Cf which is connected between the output of the buffer amplifier and the input of the amplifier for minimizing an effect associated with the radiation detector parasitic capacitance. The magnitude of the buffered amplifier output is stored on the capacitor at the beginning and end of the integration period. The sample signal is read out by a multiplexer twice during the integration period, the difference between the initial and final value of the buffer amplifier output being indicative of the radiation impinging on the detector minus one or more noise components.

GaAs capacitive feedback transimpedance amplifier

The invention concerns an optical detection matrix (9) contained within a cryogenic chamber (3). Electrical image signals produced by the matrix (9) are converted into optical signals and transmitted out of the chamber (3) on lines 42A-42T. The optical signals on lines 42A-42T are converted into electrical signals carried on line 56.

Optical data link

An improved driver circuit for an integrated gate circuit using Gallium Arsenide direct coupled FET logic. The push-pull driver circuit generally comprises an enhancement mode voltage follower transistor for driving a load during a first logic transition, and an enhancement mode pull-down transistor for driving this load during a second logic transition. Since only one of these transistors are conductive during these logic transitions (i.e., LO to HI, and HI to LO), little or no static current flows through these transistor means during steady state conditions. Thus, particularly for large capacitive loads, the driver circuit will be considerably faster than conventional DCFL technology, while not causing a significant increase in the power consumed by the push-pull driver circuit.

Push-pull DCFL driver circuit

A device and method for accurately sensing the direction and magnitude of small displacements between two objects, independent of the distance between the objects, utilizing a monochromatic light source and a reflector to produce a light standing wave pattern and a transparent photosensitive detector to detect the number of crests and/or nodes of the light standing wave pattern intercepted.

Optical displacement sensor

A scanning mirror position sensor operable from the back side of a scanning mirror which utilizes the front side of the mirror for scanning a scene to be interrogated or displayed. A rectangular uniformly distributed light source is reflected from the back surface of the scanning mirror across a plurality of parallel photo voltaic diode structure bars which may have a gray coded aluminum mask thereon. The outputs of the diode structure bars energized through openings in the aluminum mask may energize sense amplifiers and output logic to provide a continual and accurate mirror position value.

Scan mirror position determining system

A charge coupled device to provide a multi-channel selective transversal filter in which a plurality (N) of channels are sequentially processed in a common transversal filter unit to provide a desired transfer function such as a high pass filter. The analog signals from a plurality of sources or channels are fed into the selective transversal filter in serial fashion with the signal from each channel being nondestructively sampled and multiplied by appropriate weighting coefficients as provided by split electrodes separated by (N-1) charge coupled device storage bits. By having storage electrodes between the split electrodes equal to the number of input channels, the split electrodes, which provide the output signals, operate upon signal information from one channel at a time. The displacement current differences between the two halves of all of the split electrodes provide output signals having the desired filter characteristics. The transversal filter devices in accordance with the invention may be operated in a single phase clock mode or in other clock modes. The filter may have a tuning capability to modify the filter response by providing a variation of the clock frequency applied to the electrodes.

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Palos Verdes Estates, CA, United States of America

Robert N Sato