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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Electronic circuitry contains new operational amplifier which incorporates monolithic super-gain transistors. Electrode does not provide voltage amplification; instead, it acts as current amplifier to make it possible to pick up electrical potentials from surface of highly resistant dry skin.
Circuit switches a plus or minus 2.5 volt peak, dc to 300 kHz input to an operational amplifier. Featured is a bilateral transistor which draws a saturation current of equal amplitude and opposite polarity to the saturation current of the bilateral transistor, cancelling the dc bias effect at the output.
Minimization of common mode effects in differential amplifier arrangement which processes signals from two high impedance photosensors is achieved by connecting one photosensor in feedback loop of amplifier and using field effect transistors in the input circuit.
Shunt regulator circuit for outer-planet-spacecraft radiosotope thermoelectric generator minimizes power-conditioning losses. Unit consists of bank of duplicate regulator control amplifiers and their associated shunt transistors connecter across power supply line. Its high-gain circuitry arranged in redundant configuration in very reliable and is characterized by low standby loss. Circuit can be used on other power-supply applications where size, weight, and reliability are important.
Investigations in critical technology of the solar power satellite (SPS) concept development program are summarized. Studies of the potential application of fiber optics transmission links across the SPS one kilometer antenna and evaluation of gallium arsenide field effect transistors and their associated power amplifier circuitry are discussed in more detail.
The results of preliminary 32 GHz calibrations of the 70 meter antenna at Goldstone are presented. Measurements were done between March and July 1989 using Virgo A and Venus as the primary efficiency calibrators. The flux densites of theses radio sources at 32 GHz are not known with high accuracy, but were extrapolated from calibrated data at lower frequencies. The measured value of efficiency (0.35) agreed closely with the predicted value (0.32), and the results are very repeatable. Flux densities of secondary sources used in the observations were subsequently derived. These measurements were performed using a beamswitching radiometer that employed an uncooled high-electron mobility transistor (HEMT) low-noise amplifier. This system was installed primarily to determine the performance of the antenna in its 1989 configuration, but the experience will also aid in successful future calibration of the Deep Space Network (DSN) at this frequency.
Research accomplished during the third 6-month period is summarized. Research covered the following: dual-horn antenna performance; high electron mobility transistors (HEMT) low-noise amplifiers; downconverters; fast Fourier transform (FFT) array; and backend 'feature recognizer' array.
A cryogenically cooled Ka-band (33.6-GHz), seven-element front-end array for the DSN was built and tested. This system uses seven high electron mobility transistor (HEMT) low-noise amplifiers cooled by a two-stage closed-cycle refrigerator. All system components from the polarizers to the output isolators are cooled to a physical temperature between 18 and 35 K. The noise temperatures of the individual elements range from 64 to 84 K over a 2.75-GHz bandwidth.
Recent tends in the design, fabrication and use of High-Electron-Mobility-Transistors (HEMT) in low noise amplifiers are reviewed. Systems employing these devices have achieved the lowest system noise for wavelengths greater than three millimeters with relatively modest cryogenic cooling requirements in a variety of ground and space based applications. System requirements which arise in employing such devices in imaging applications are contrasted with other leading coherent detector candidates at microwave wavelengths. Fundamental and practical limitations which arise in the context of microwave application of field effect devices at cryogenic temperatures will be discussed from a component and systems point of view.
Recent tends in the design, fabrication and use of High-Electron-Mobility-Transistors (HEMT) in low noise amplifiers are reviewed. Systems employing these devices have achieved the lowest system noise for wavelengths greater than three millimeters with relatively modest cryogenic cooling requirements in a variety of ground and space based applications. System requirements which arise in employing such devices in imaging applications are contrasted with other leading coherent detector candidates at microwave wavelengths. Fundamental and practical limitations which arise in the context of microwave application of field effect devices at cryogenic temperatures will be discussed from a component and systems point of view.
Prototype cooled low-noise microwave amplifiers based on high-electron-mobility transistors (HEMT's) considered as replacements for cooled ruby masers used as low-noise receiver-front-end amplifiers in communications, radio science, radar systems, radio astronomy, and telemetry. HEMT amplifier operates at 12 K, requires less cooling power and operates at lower cost with simpler, more-reliable cooling system.
Report discusses aspects of effort to develop low-noise, low-gate-leakage gallium arsenide-based junction field-effect transistors (JFETs) for operation at temperature of about 4 K as readout amplifiers and multiplexing devices for infrared-imaging devices. Transistors needed to replace silicon transistors, relatively noisy at 4 K. Report briefly discusses basic physical principles of JFETs and describes continuing process of optimization of designs of GaAs JFETs for cryogenic operation.
Special designs of two types of electronic components transistors and transmission lines have been conceived to optimize the performances of these components as parts of waveguide-embedded differential-amplifier monolithic microwave integrated circuits (MMICs) of the type described in the immediately preceding article. These designs address the following two issues, the combination of which is unique to these particular MMICs: Each MMIC includes a differential double-strip transmission line that typically has an impedance between 60 and 100 W. However, for purposes of matching of impedances, transmission lines having lower impedances are also needed. The transistors in each MMIC are, more specifically, one or more pair(s) of InP-based high-electron-mobility transistors (HEMTs). Heretofore, it has been common practice to fabricate each such pair as a single device configured in the side-to-side electrode sequence source/gate/drain/gate/source. This configuration enables low-inductance source grounding from the sides of the device. However, this configuration is not suitable for differential operation, in which it is necessary to drive the gates differentially and to feed the output from the drain electrodes differentially. The special transmission-line design provides for three conductors, instead of two, in places where lower impedance is needed. The third conductor is a metal strip placed underneath the differential double-strip transmission line. The third conductor increases the capacitance per unit length of the transmission line by such an amount as to reduce the impedance to between 5 and 15 W. In the special HEMT-pair design, the side-to-side electrode sequence is changed to drain/gate/source/gate/ drain. In addition, the size of the source is reduced significantly, relative to corresponding sizes in prior designs. This reduction is justified by the fact that, by virtue of the differential configuration, the device has an internal virtual ground, and therefore there is no need for a low-resistance contact between the source and the radio-frequency circuitry. The source contact is needed only for DC biasing. These designs were implemented in a single-stage-amplifier MMIC. In a test at a frequency of 305 GHz, the amplifier embedded in a waveguide exhibited a gain of 0 dB; after correcting for the loss in the waveguide, the amplifier was found to afford a gain of 0.9 dB. In a test at 220 GHz, the overall gain of the amplifier- and-waveguide assembly was found to be 3.5 dB.
A power-amplifier module that operates in the frequency range of 145 to 165 GHz has been designed and constructed as a combination of (1) a previously developed monolithic microwave integrated circuit (MMIC) power amplifier and (2) a waveguide module. The amplifier chip was needed for driving a high-electron-mobility-transistor (HEMT) frequency doubler. While it was feasible to connect the amplifier and frequency-doubler chips by use of wire bonds, it was found to be much more convenient to test the amplifier and doubler chips separately. To facilitate separate testing, it was decided to package the amplifier and doubler chips in separate waveguide modules. Figure 1 shows the resulting amplifier module. The amplifier chip was described in "MMIC HEMT Power Amplifier for 140 to 170 GHz" (NPO-30127), NASA Tech Briefs, Vol. 27, No. 11, (November 2003), page 49. To recapitulate: This is a three-stage MMIC power amplifier that utilizes HEMTs as gain elements. The amplifier was originally designed to operate in the frequency range of 140 to 170 GHz. The waveguide module is based on a previously developed lower frequency module, redesigned to support operation in the frequency range of 140 to 220 GHz. Figure 2 presents results of one of several tests of the amplifier module - measurements of output power and gain as functions of input power at an output frequency of 150 GHz. Such an amplifier module has many applications to test equipment for power sources above 100 GHz.
Wide range vibrating-reed Mariner II ELECTROMETER, describing components, performance characteristics and results
Miniature amplifier for bioelectronic instrumentation consumes only about 100 mW and has frequency response flat to within 0.5 dB from 0.14 to 450 Hz. Device consists of five thin film substrates, which contain eight operational amplifiers and seven field-effect transistor dice.
Limiting amplifier, using gallium arsenide field effect transistor (FET), delivers constant-amplitude drive signal to KU-band traveling wave tube (TWT) thus preventing distortion in output from TWT.
IC printed-circuit board tester measures resistance as low as 0.1 ohm but uses little power. Two 4.7 kilohm resistors and connected transistors prevent current flow through operational amplifier until probe circuit is complete, eliminating need for on/off switch. Zener diode in series with amplifier output prevents audio oscillator operation until output has sufficient amplitude. Circuit utilizes 741 operational amplifier on 11.2 volt battery or lower voltage amplifiers.