Engineering topics

Fossum, Eric R.

Publications and source records attributed to Fossum, Eric R..

68 records · Page 4

NASA NTRS1993

Active Pixel Sensors: Are CCD's Dinosaurs?

Charge-coupled devices (CCD's) are presently the technology of choice for most imaging applications. In the 23 years since their invention in 1970, they have evolved to a sophisticated level of performance. However, as with all technologies, we can be certain that they will be supplanted someday. In this paper, the Active Pixel Sensor (APS) technology is explored as a possible successor to the CCD. An active pixel is defined as a detector array technology that has at least one active transistor within the pixel unit cell. The APS eliminates the need for nearly perfect charge transfer -- the Achilles' heel of CCDs. This perfect charge transfer makes CCD's radiation 'soft,' difficult to use under low light conditions, difficult to manufacture in large array sizes, difficult to integrate with on-chip electronics, difficult to use at low temperatures, difficult to use at high frame rates, and difficult to manufacture in non-silicon materials that extend wavelength response.

Fossum, Eric R.↗

NASA NTRS1993

Design of a Low-Light-Level Image Sensor with On-Chip Sigma-Delta Analog-to- Digital Conversion

The design and projected performance of a low-light-level active-pixel-sensor (APS) chip with semi-parallel analog-to-digital (A/D) conversion is presented. The individual elements have been fabricated and tested using MOSIS* 2 micrometer CMOS technology, although the integrated system has not yet been fabricated. The imager consists of a 128 x 128 array of active pixels at a 50 micrometer pitch. Each column of pixels shares a 10-bit A/D converter based on first-order oversampled sigma-delta (Sigma-Delta) modulation. The 10-bit outputs of each converter are multiplexed and read out through a single set of outputs. A semi-parallel architecture is chosen to achieve 30 frames/second operation even at low light levels. The sensor is designed for less than 12 e^- rms noise performance.

Mendis, Sunetra K.↗

NASA NTRS1992

Delta-Doped Buried Channels In Charge-Coupled Device

Buried-channel charge-couple devices (CCD's) of proposed new type contain multiple thin, highly-doped channel layers instead of single relatively thick channel layers. Benefits: better performance at low temperature and less sensitivity to damage by radiation.

Fossum, Eric R.↗

NASA NTRS1992

An analysis of the temperature dependence of the gate current in complementary heterojunction field-effect transistors

The temperature dependence of the gate current versus the gate voltage in complementary heterojunction field-effect transistors (CHFET's) is examined. An analysis indicates that the gate conduction is due to a combination of thermionic emission, thermionic-field emission, and conduction through a temperature-activated resistance. The thermionic-field emission is consistent with tunneling through the AlGaAs insulator. The activation energy of the resistance is consistent with the ionization energy associated with the DX center in the AlGaAs. Methods reducing the gate current are discussed.

Cunningham, Thomas J.↗

NASA NTRS1992

Optical Link For Readout From Focal-Plane Array

Outputs of photodetectors modulate beam of light. Proposed optical link carries analog readout signals from photodetectors in focal-plane array to external signal-processing circuitry. Insensitive to electromagnetic interference at suboptical frequencies, and imposes smaller heat load on cryogenic apparatus because it does not include high-power electronic amplifier or laser transmitter within cold chamber.

Fossum, Eric R.↗

NASA NTRS1992

CCD With Back-Side Illumination And Charge Steering

Proposed charge-coupled device (CCD) imaging array of photodetectors has features of back-side-illuminated CCD and interline-transfer CCD. Photoelectrons generated near back surface and swept by electric fields toward front into collecting potential wells, not directly opposite that location. By suitable timing of control signals, charges from multiple image frames stored in rapid succession. Useful in imaging rapid transient phenomena as chemically reacting flows, with interframe intervals of microseconds.

Fossum, Eric R.↗

NASA NTRS1992

Infrared readout electronics; Proceedings of the Meeting, Orlando, FL, Apr. 21, 22, 1992

The present volume on IR readout electronics discusses cryogenic readout using silicon devices, cryogenic readout using III-V and LTS devices, multiplexers for higher temperatures, and focal-plane signal processing electronics. Attention is given to the optimization of cryogenic CMOS processes for sub-10-K applications, cryogenic measurements of aerojet GaAs n-JFETs, inP-based heterostructure device technology for ultracold readout applications, and a three-terminal semiconductor-superconductor transimpedance amplifier. Topics addressed include unfulfilled needs in IR astronomy focal-plane readout electronics, IR readout integrated circuit technology for tactical missile systems, and radiation-hardened 10-bit A/D for FPA signal processing. Also discussed are the implementation of a noise reduction circuit for spaceflight IR spectrometers, a real-time processor for staring receivers, and a fiber-optic link design for INMOS transputers.

Fossum, Eric R.↗

NASA NTRS1992

Noise and current-voltage characterization of complementary heterojunction field-effect transistor (CHFET) structures below 8 K

Noise and current-voltage characterization of complementary heterojunction field-effect transistor (CHFET) structures below 8 K are presented. It is shown that the CHFET exhibits normal transistor operation down to 6 K. Some of the details of the transistor operation, such as the gate-voltage dependence of the channel potential, are analyzed. The gate current is examined and is shown to be due to several mechanisms acting in parallel. These include field-emission and thermionic-field-emission, conduction through a temperature-activated resistance, and thermionic emission. The input referred noise for n-channel CHFETs is presented and discussed. The noise has the spectral dependence of 1/f noise, but does not exhibit the usual area dependence.

Cunningham, Thomas J.↗

NASA NTRS1992

Smart Focal-Plane Technology for Micro-Instruments and Micro-Rovers

It is inevitable that micro-instruments and micro-rovers for space exploration will contain one or more focal-plane arrays for imaging spectroscopy or navigation. In this paper, we explore the state-if-the-art in focal-plane technology for visible sensors. Also discussed is present research activity in advanced focal-plane technology with particular emphasis on the development of smart sensors. The paper concludes with a discussion of possible future directions for the advancement of the technology.

Fossum, Eric R.↗

NASA NTRS1991

A resistive-gate In(0.53)Ga(0.47)As/InP heterostructure CCD

The first InGaAs/InP charge-coupled device is demonstrated, exhibiting a charge transfer efficiency (CTE) of 0.98 at 13 MHz and 1 GHz. Cooling the device improves the CTE to greater than 0.99 at 13-MHz clock frequency. The 0.76-eV In(0.53)Ga(0.47)As bandgap makes this structure applicable to direct-detection short-wavelength infrared imagers.

Rossi, D. V.↗

NASA NTRS1991

Report of the sensor readout electronics panel

The findings of the Sensor Readout Electronics Panel are summarized in regard to technology assessment and recommended development plans. In addition to two specific readout issues, cryogenic readouts and sub-electron noise, the panel considered three advanced technology areas that impact the ability to achieve large format sensor arrays. These are mega-pixel focal plane packaging issues, focal plane to data processing module interfaces, and event driven readout architectures. Development in each of these five areas was judged to have significant impact in enabling the sensor performance desired for the Astrotech 21 mission set. Other readout issues, such as focal plane signal processing or other high volume data acquisition applications important for Eos-type mapping, were determined not to be relevant for astrophysics science goals.

Fossum, Eric R.↗

NASA NTRS1991

Wire transfer of charge packets using a CCD-BBD structure for charge-domain signal processing

A structure for the virtual transfer of charge packets across metal wires is described theoretically and is experimentally verified. The structure is a hybrid of charge-coupled device (CCD) and bucket-brigade device (BBD) elements and permits the topological crossing of charge-domain signals in low power signal processing circuits. A test vehicle consisting of 8-, 32-, and 96-stage delay lines of various geometries implemented in a double-poly, double-metal foundry process is used to characterize the wire-transfer operation. Transfer efficiency ranging between 0.998 and 0.999 is obtained for surface n-channel devices with clock cycle times in the range from 40 ns to 0.3 ms. Transfer efficiency as high as 0.9999 is obtained for buried n-channel devices. Good agreement is found between experiment and simulation.

Fossum, Eric R.↗

NASA NTRS1991

Future directions in focal-plane signal processing for space-borne scientific imagers

The potential of focal-plane signal processing for space-borne scientific imagers is discussed. Significant improvement in image quality and consequent scientific return may be enabled through the utilization of focal-plane signal processing techniques. The possible application of focal-plane signal processing to readout noise reduction, cosmic ray circumvention, non-uniformity correction, and throughput enhancement is described. On-focal-plane analog-to-digital (A/D) conversion and micromotion stabilization are also discussed. It is the intention of this paper to stimulate further thought and efforts in this field.

Fossum, Eric R.↗

NASA NTRS1990

Issues and directions in IR detector readout electronics

An introduction to the major issues encountered in the readout of imaging detector arrays in the infrared are presented. These include circuit issues such as multiplexing, buffering, and noise, as well as materials issues. Future directions in infrared readout electronics will also be discussed. These include on-chip signal processing and advanced hybridization schemes. Finally, recent work at Columbia on 2DEG-charge coupled devices for IR detector multiplexing are described.

Fossum, Eric R.↗