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At least 883 records · Page 49

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NASA NTRS1981

Transfer-matrices for series-type microwave antenna circuits

Transfer matrices are developed which permit analysis and computer evaluation of certain series type microwave antenna circuits associated with an L-Band microwave radiometer (LBMR) under investigation at Goddard Space Flight Center. This radiometer is one of several diverse instrument designs to be used for the determination of soil moisture, sea state, salinity, and temperature data. Four port matrix notation is used throughout for the evaluation of LBMR circuits with mismatched couplers and lossy transmission lines. Matrix parameters in examples are predicted on an impedance analysis and an assumption of an array aperture distribution. The notation presented is easily adapted to longer and more varied chains of matrices, and to matrices of larger dimension.

Schmidt, R. F.↗

NASA NTRS1980

Silicon solar cells with high open-circuit voltage

Open-circuit voltages as high as 0.645 V (AM0-25 C) have been obtained by a new process developed for low-resistivity silicon. The method utilizes high-dose phosphorus implantation, followed by furnace annealing and simultaneous oxide growth to form high-efficiency, shallow junctions. The effect of the thermally grown oxide is a reduction of surface recombination velocity; the oxide also acts as a moderately efficient AR coating. Boron doped silicon with resistivities from 0.1 to 0.3 ohm-cm has been processed according to this sequence; results show highest open-circuit voltage is attained with 0.1-ohm-cm starting material. The effects of bandgap narrowing, caused by high doping concentrations in the junction, were also investigated by implanting phosphorus over a wide range of dose levels.

Minnucci, J. A.↗

NASA NTRS1983

Solid State Circuits for Cryogenic Operation

Tests confirm operation of five commercial semiconductor devices at cryogenic temperatures. The five devices - one tunnel diode, one field-effect transistor, and three CMOS integrated circuits - all perform well in circuits immersed in liquid-helium bath. For some tests, bath temperature was reduced to 1,25K by pumping.

Petrac, D.↗

NASA NTRS1983

Terminal Strip Facilitates Printed-Circuit Board Changes

Laminanted copper and polyimide terminal strip makes it easy to modify printed-circuit (PC) board, after board has been fabricated. When epoxied over conductors or insulating portion of PC board, strip provides series of solder-coated copper conductor pads to which integrated-circuit leads are soldered for functional changes. Terminal strips accommodate leads on dual inline IC package or as staggered single or multiple leads on planar mounted flatpacks.

Pinto, E. A.↗

NASA NTRS1981

Development of integrated thermionic circuits for high-temperature applications

Integrated thermionic circuits (ITC) capable of extended operation in ambient temperatures up to 500 C are studied. A set of practical design and performance equations is demonstrated. Experimental results are discussed in which both devices and simple circuits were successfully operated in 5000 C environments for extended periods. It is suggested that ITC's may become an important technology for high temperature instrumentation and control systems in geothermal and other high temperature environments.

Mccormick, J. B.↗

NASA NTRS1981

State-variable analysis of non-linear circuits with a desk computer

State variable analysis was used to analyze the transient performance of non-linear circuits on a desk top computer. The non-linearities considered were not restricted to any circuit element. All that is required for analysis is the relationship defining each non-linearity be known in terms of points on a curve.

Cohen, E.↗

NASA NTRS1981

Computer circuit card puller

The invention generally relates to hand tools, and more particularly to an improved device for facilitating removal of printed circuit cards from a card rack characterized by longitudinal side rails arranged in a mutually spaced parallelism and a plurality of printed circuit cards extended between the rails of the rack.

Sawyer, R. V.↗

NASA NTRS1982

Harmonic analysis approach to the 'TunneLadder' - A modified Karp circuit for millimeter-wave TWTA's

A field approach to the summed harmonic analysis of the TunneLadder structure, or modified forward-wave Karp circuit, is developed by combining TM(01) and TE(11) modes. Results suggest the suitability of this structure as a high-impedance, about 1-% bandwidth circuit, millimeter-wave forward-wave-type amplifier that is voltage tunable over about a 5-% frequency range and has excellent power handling ability. Theory gives good agreement with experimental results obtained by Karp in omega-beta dispersion and predicts qualitatively the appearances of the antisymmetric mode discussed and of the so called Hightron mode that was discussed earlier in White, Enderby and Birdsall (1964), and Enderby (1964), in addition to the desired symmetric mode.

Kosmahl, H. G.↗

NASA NTRS1982

Microwave integrated circuit radiometer front-ends for the Push Broom Microwave Radiometer

Microwave integrated circuit front-ends for the L-band, S-band and C-band stepped frequency null-balanced noise-injection Dicke-switched radiometer to be installed in the NASA Langley airborne prototype Push Broom Microwave Radiometer (PBMR) are described. These front-ends were developed for the fixed frequency of 1.413 GHz and the variable frequencies of 1.8-2.8 GHz and 3.8-5.8 GHz. Measurements of the noise temperature of these units were made at 55.8 C, and the results of these tests are given. While the overall performance was reasonable, improvements need to be made in circuit losses and noise temperatures, which in the case of the C-band were from 1000 to 1850 K instead of the 500 K specified. Further development of the prototypes is underway to improve performance and extend the frequency range.

Harrington, R. F.↗

NASA NTRS1984

Improved High-Current Drive Circuit

Uses VMOS field-effect power transistor. High-current drive circuit employs n-channel enhancement-mode VMOS field-effect power transistor to eliminate problem of oscillation at high power encountered in conventional circuits with bipolar transistors. Drive voltage required is typically 1 to 3 V for load current of 10 A.

Cole, S. W.↗

NASA NTRS1984

Finding Open Faults In CMOS Circuits

Algorithm specifies sequence of input test signals and interpretation of resulting output signals for identifying stuck-open faults in complementary metal-oxide semiconductor (CMOS) integrated logic circuits. Incorporated in software for online production testing of CMOS circuits.

Chandramouli, R.↗

NASA NTRS1983

Active lamp pulse driver circuit

A flashlamp drive circuit is described which uses an unsaturated transistor as a current mode switch to periodically subject a partially ionized gaseous laser excitation flashlamp to a stable, rectangular pulse of current from an incomplete discharge of an energy storage capacitor. A monostable multivibrator sets the pulse interval, initiating the pulse in response to a flash command by providing a reference voltage to a non-inverting terminal of a base drive amplifier; a tap on an emitter resistor provides a feedback signal sensitive to the current amplitude to an inverting terminal of amplifier, thereby controlling the pulse amplitude. The circuit drives the flashlamp to provide a squarewave current flashlamp discharge.

Logan, K. E.↗

NASA NTRS1983

Automatic level control circuit

An automatic level control circuit for an operational amplifier for minimizing spikes or instantaneous gain of the amplifier at a low period wherein no signal is received on the input is provided. The apparatus includes a multibranch circuit which is connected between an output terminal and a feedback terminal. A pair of zener diodes are connected back to back in series with a capacitor provided in one of the branches. A pair of voltage dividing resistors are connected in another of the branches and a second capacitor is provided in the remaining branch of controlling the high frequency oscillations of the operational amplifier.

Toole, P. C.↗

NASA NTRS1983

GaAs microwave devices and circuits with submicron electron-beam defined features

This paper describes the fabrication and application of GaAs FET's, both as discrete microwave devices and as the key active components in monolithic microwave integrated circuits. The performance of these devices and circuits is discussed for frequencies ranging from 3 to 25 GHz. The crucial fabrication step is the formation of the submicron gate by electron-beam lithography.

Wisseman, W. R.↗

NASA NTRS1983

Equivalent-circuit consideration of dual-gate MESFETs at high frequency

The simplified high-frequency equivalent circuit of a dual-gate FET is described. It is shown that the input impedance is similar to that of a single-gate FET but the output resistance and capacitance (parallel equivalent circuit) are higher. The output resistance and the transconductance decrease as frequency increases. The unilateral gain of a dual-gate FET rolls off 12 dB/octave.

Kim, B.↗

NASA NTRS1985

Circuit for Monitoring Cell Voltages

Circuit monitors voltage of each cell in electrical battery within few millivolts. Circuit includes two bipolar analog multiplexers: repeatedly sample outputs of 12 1.5 volt cells. Terminals of multiplexer 1 connected to positive sides of cells and terminals of multiplexer 2 connected to negative sides. Outputs of multiplexers connected to differential operational amplifier: provides signals for recording and display.

Lepisto, J. W.↗

NASA NTRS1982

Flexible composite film for printed circuit board

A flexible printed circuit for a printed circuit board in which layers of reaction product composed of a combination of phenoxy resin - polyisocyanate - brominated epoxy resin, and in which the equivalent ratio of those functional groups is hydroxyl group: isocyanate group: epoxy group - 1 : 0.2 to 2 : 0.5 to 3 are laminated on at least one side of saturated polyester film is discussed.

Yabe, K.↗

NASA NTRS1984

Pulsed thyristor trigger control circuit

A trigger control circuit is provided for producing firing pulses for the thyristor of a thyristor control system such as a power factor controller. The control circuit overcomes thyristor triggering problems involved with the current lag associated with controlling inductive loads and utilizes a phase difference signal, already present in the power factor controller, in deriving a signal for inhibiting generation of a firing pulse until no load current is flowing from the preceding half cycle and thereby ensuring that the thyristor is triggered on during each half cycle.

Nola, F. J.↗