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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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17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A pulsed current-mode class-D low-voltage high-bandwidth power amplifier for portable NMR systems

Low-field NMR has seen growing interest in recent years, especially for portable applications. The lower homogeneity magnets used for portable applications require short RF pulses to ensure enough transmit bandwidth to excite the sample volume and also support short echo periods. Furthermore, the preferred use of a high-Q coil to improve signal-to-noise ratio (SNR) prolongs the pulse transients. Thus, at such low Larmor frequencies, the excitation pulse transients become comparable or longer than the pulse length, such that the transmit bandwidth begins to limit measurement SNR. This paper describes the design of a pulsed current-mode class-D power (PCMCD) transmitter that addresses this issue by generating high power in a tuned sample coil while maintaining short transients, thus resulting in high output bandwidth. The transmitter also uses a charge recycling mechanism to maximize power efficiency for RF train excitation, which also results in faster pulse repetition rate and reduces allowable echo time. In this work, experimental results from a small form-factor PCMCD transmitter are presented. This design generates a peak RF power of 240 W into a 9.16 µH coil at 4 MHz while operating off a single 12 V power supply. NMR measurement results using the transmitter are also described, showing minimum achievable echo time of 70 µs and 25 µs depending on the transmitter mode of operation.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

A Hybrid Transmitter With Voltage-Mode SST Preemphasis and Current-Mode Transmitter Equalization Capable of Operating at 77 K in DUNE

The Deep Underground Neutrino Experiment (DUNE) requires that the front-end transmitters operate at cryogenic temperature and drive 25–35 m long twin-axial (twinax) cables. Here, to compensate the frequency-dependent channel loss over the long cables and alleviate the de-emphasizing of the low-frequency signal magnitude, a hybrid of a current-mode (CM) transmitter equalization (TXEQ) and a voltage-mode (VM) preemphasis is proposed. The TXEQ employs a finite-impulse response (FIR) filter to boost the high-frequency components while de-emphasizing the low-frequency signal magnitude, thereby flattening the overall channel frequency response and reducing the intersymbol interference (ISI). The VM preemphasis is proposed to further mitigate ISI by boosting the high-frequency portion without degrading the signal magnitude, allowing for high signal swing. The main driver utilizes VM source-series-terminated (SST) output stages, which offers higher signal swing and better power efficiency than the conventional CM logic (CML) drivers. To ensure the lifetime and reliability at cryogenic temperature, the transmitter is implemented in a 65-nm CMOS process operating at 1.1 V of supply voltage and employing transistors with larger than minimum lengths. Silicon measurement results at 77 K have validated the proposed approaches.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Synchrotron characterization of high-Z, current-mode x-ray detectors

Fast x-ray detectors are critical tools in pulsed power and fusion applications, where detector impulse response of a nanosecond or better is often required. Semiconductor detectors can create fast, sensitive devices with extensive operational flexibility. There is typically a trade-off between detector sensitivity and speed, but higher atomic number absorbers can increase hard x-ray absorption without increasing the charge collection time, provided carriers achieve high velocity. This paper presents x-ray pulse characterization conducted at the Advanced Photon Source of x-ray absorption efficiency and temporal impulse response of current-mode semiconductor x-ray detectors composed of Si, GaAs, and CdTe.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

Energy response characterization of current-mode MeV Cherenkov aerogel detectors

Current-mode Cherenkov aerogel detectors have been used to measure time resolved spectra of MeV radiographic x-ray sources and have been considered to replace gas Cherenkov systems. The simulations of the Cherenkov response of aerogel detectors have uncertainties in how to model the complex structure of aerogels. Data from three sites—the Idaho electron beam, the Los Alamos Site electron beam and microtron sources at Los Alamos—have been used to calibrate the relative energy response of 15 aerogels, varying in density from 10 to 430 mg/cm 3 , from incident electrons with energies from 1 to 12 MeV. Detector simulations need to introduce density variation in the aerogels to match the collected data.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2000

Fuzzy Current-Mode Control and Stability Analysis

In this paper a current-mode control (CMC) methodology is developed for a buck converter by using a fuzzy logic controller. Conventional CMC methodologies are based on lead-lag compensation with voltage and inductor current feedback. In this paper the converter lead-lag compensation will be substituted with a fuzzy controller. A small-signal model of the fuzzy controller will also be developed in order to examine the stability properties of this buck converter control system. The paper develops an analytical approach, introducing fuzzy control into the area of CMC.

Kopasakis, George↗
NASA NTRS1994

From neural-based object recognition toward microelectronic eyes

Engineering neural network systems are best known for their abilities to adapt to the changing characteristics of the surrounding environment by adjusting system parameter values during the learning process. Rapid advances in analog current-mode design techniques have made possible the implementation of major neural network functions in custom VLSI chips. An electrically programmable analog synapse cell with large dynamic range can be realized in a compact silicon area. New designs of the synapse cells, neurons, and analog processor are presented. A synapse cell based on Gilbert multiplier structure can perform the linear multiplication for back-propagation networks. A double differential-pair synapse cell can perform the Gaussian function for radial-basis network. The synapse cells can be biased in the strong inversion region for high-speed operation or biased in the subthreshold region for low-power operation. The voltage gain of the sigmoid-function neurons is externally adjustable which greatly facilitates the search of optimal solutions in certain networks. Various building blocks can be intelligently connected to form useful industrial applications. Efficient data communication is a key system-level design issue for large-scale networks. We also present analog neural processors based on perceptron architecture and Hopfield network for communication applications. Biologically inspired neural networks have played an important role towards the creation of powerful intelligent machines. Accuracy, limitations, and prospects of analog current-mode design of the biologically inspired vision processing chips and cellular neural network chips are key design issues.

Sheu, Bing J.↗
DOE OSTI2026

Nanoscale Compositional and Strain Gradients Enable High‐Speed and Amplitude‐Resolved Pyroelectric Sensing

The frequency response of pyroelectric sensors is fundamentally governed by thermal time constant (τth, determined by thermal mass and thermal conductance) and electrical impedance arising from film capacitance and readout circuit. Conventional bulk LiTaO3 detectors are optimized for high responsivity at low modulation frequencies (0.1-10 Hz), possessing a large τth that thermally averages rapid temperature oscillations at elevated modulation frequencies, limiting fidelity in resolving dynamic varying thermal signals. Here, compositional and strain gradients are introduced into 100-nm-thick relaxor-ferroelectric films reducing τth to ≈2 µs and producing built-in potentials (≈1.45 V or 145 kV cm-1) that enhance the pyroelectric coefficient and suppress the dielectric constant. This enables complementary dual-mode operation by enhancing current-mode electrical responsivity and improving the voltage-mode figure of merit - advantageous for superior temperature resolution (ΔTmin ≈ 30 µK). The responsivity peak shifts to near 1 kHz (>2500-times higher than conventional bulk sensors), with measurable responsivity extending to a carrier frequency of 100 kHz and amplitude-resolved detection at modulation frequencies up to 15 kHz. These results establish nanoscale internal-field engineering can reshape electro-thermal trade-off in pyroelectric thin films toward zero-bias, high-thermal-sensitivity, and amplitude-resolved thermal sensing across a wide frequency bandwidth.

Lin, Ching‐Che↗
DOE OSTI2023

Perovskite CsPbBr 3 Single-Crystal Detector Operating at 10 10 Photons s -1 mm -2 for Ultra-High Flux X-ray Detection

Semiconductors for detecting hard radiation are confronted with considerable problems when operating at high photon fluxes. A perovskite CsPbBr 3 single-crystal detector capable of operating at X-ray fluxes of up to 10 10 photons s -1 mm -2 with beam area ≤ 0.25 mm 2 at 58.61 keV for current-mode X-ray detection is reported. The spectrometer-grade melt-grown CsPbBr 3 detectors show a gamma-ray energy resolution of ~7.5% at 122 keV for 57 Co and dark current as low as 4.3 nA (0.5 nA mm -2 ) at a reverse bias voltage of 200 V (118 V mm -1 ). The detector is tested at X-ray energies of 8.2, 10, and 58.61 keV at a synchrotron light source under a reverse bias voltage of up to 1000 V (588 V mm -1 ). Under a sufficiently high bias voltage and within several hundreds of seconds X-ray exposure, good photocurrent linearity (goodness of fit R 2 > 0.99) and reproducibility are obtained up to a flux of ≈10 10 photons s -1 mm -2 at beam area 0.25 mm 2 with Lower Limit of Detection of ≈10 5 photons s -1 mm -2 and Charge Collection Efficiency of ≈100% for 58.61 keV X-rays. Therefore, wide application of CsPbBr 3 detectors in high-flux X-ray detection is anticipated.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Flashlamp Driver for Quasi-CW Laser Pumping

Circuit maintains constant high-current level through lamp while lighted and a low simmer current through lamp while not lighted. Lamp current is switched between these two modes by transistor; transistor is therefore called current-mode switch. Stable light pulses are emitted from flashlamp when monostable multivibrator goes high, in part because unsaturated transistor switch has negative feedback control that keeps lamp current constant.

Logan, K. E.↗
NASA NTRS1988

The design of radiation-hardened ICs for space - A compendium of approaches

Several technologies, including bulk and epi CMOS, CMOS/SOI-SOS (silicon-on-insulator-silicon-on-sapphire), CML (current-mode logic), ECL (emitter-coupled logic), analog bipolar (JI, single-poly DI, and SOI) and GaAs E/D (enhancement/depletion) heterojunction MESFET, are discussed. The discussion includes the direct effects of space radiation on microelectronic materials and devices, how these effects are evidenced in circuit and device design parameter variations, the particular effects of most significance to each functional class of circuit, specific techniques for hardening high-speed circuits, design examples for integrated systems, including operational amplifiers and A/D (analog/digital) converters, and the computer simulation of radiation effects on microelectronic ISs.

Kerns, Sherra E.↗
NASA NTRS1991

Power electronics for low power arcjets

In anticipation of the needs of future light-weight low-power spacecraft, arcjet power electronics in the 100- to 400-W operating range were developed. Power topologies similar to those in the higher 2-kW and 5- to 30-kW power range were implemented, including a four-transistor bridge-switching circuit, current-mode pulse-width modulated control, and an output current averaging inductor with an integral pulse generation winding. Reduction of switching transients was accomplished using a low inductance power distribution network, and no passive snubber circuits were necessary for power switch protection. Phase shift control of the power bridge was accomplished using an improved pulse width modulation to phase shift converter circuit. These features, along with conservative magnetics designs, allowed power conversion efficiencies of greater than 92.5 percent to be achieved into resistive loads over the entire operating range of the converter.

Hamley, John A.↗
NASA NTRS1991

Design of a battery charger for the NASA EOS space platform

A battery charger design for the NASA Earth Observing System (EOS) space platform has been developed and tested. The authors discuss the design of the battery charger power state and its current and voltage control loops. In addition to restoring energy to the batteries, this charger regulates the spacecraft bus voltage during the posteclipse transition period. The battery charger design and analysis were facilitated by use of the pulse-width-modulated (PWM) switch model and the new continuous-time model for current-mode control. Analyses of the battery charger small-signal behavior are compared to hardware measurements to verify modeling accuracy.

Sizemore, Tom↗
NASA NTRS1997

Development of Power Electronics for a 0.2kW-Class Ion Thruster

Applications that might benefit from low power ion propulsion systems include Earth-orbit magnetospheric mapping satellite constellations, low Earth-orbit satellites, geosynchronous Earth-orbit satellite north-south stationkeeping, and asteroid orbiters. These spacecraft are likely to have masses on the order of 50 to 500 kg with up to 0.5 kW of electrical power available. A power processing unit for a 0.2 kW-class ion thruster is currently under development for these applications. The first step in this effort is the development and testing of a 0.24 kW beam power supply. The design incorporates a 20 kHz full bridge topology with multiple secondaries connected in series to obtain outputs of up to 1200 V(sub DC). A current-mode control pulse width modulation circuit built using discrete components was selected for this application. An input voltage of 28 +/- 4 V(sub DC) was assumed, since the small spacecraft for which this system is targeted are anticipated to have unregulated low voltage busses. Efficiencies in excess of 91 percent were obtained at maximum output power. The total mass of the breadboard was less than 1.0 kg and the component mass was 0.53 kg. It is anticipated that a complete flight power processor could weigh about 2.0 kg.

Pinero, Luis R.↗
NASA NTRS1999

Fuzzy Control Hardware for Segmented Mirror Phasing Algorithm

This paper presents a possible implementation of a control model developed to phase a system of segmented mirrors, with a PAMELA configuration, using analog fuzzy hardware. Presently, the model is designed for piston control only, but with the foresight that the parameters of tip and tilt will be integrated eventually. The proposed controller uses analog circuits to exhibit a voltage-mode singleton fuzzifier, a mixed-mode inference engine, and a current-mode defuzzifier. The inference engine exhibits multiplication circuits that perform the algebraic product composition through the use of operational transconductance amplifiers rather than the typical min-max circuits. Additionally, the knowledge base, containing exemplar data gained a priori through simulation, interacts via a digital interface.

Roth, Elizabeth↗
NASA NTRS2002

Focal plane infrared readout circuit with automatic background suppression

A circuit for reading out a signal from an infrared detector includes a current-mode background-signal subtracting circuit having a current memory which can be enabled to sample and store a dark level signal from the infrared detector during a calibration phase. The signal stored by the current memory is subtracted from a signal received from the infrared detector during an imaging phase. The circuit also includes a buffered direct injection input circuit and a differential voltage readout section. By performing most of the background signal estimation and subtraction in a current mode, a low gain can be provided by the buffered direct injection input circuit to keep the gain of the background signal relatively small, while a higher gain is provided by the differential voltage readout circuit. An array of such readout circuits can be used in an imager having an array of infrared detectors. The readout circuits can provide a high effective handling capacity.

Pain, Bedabrata↗