If linearity of a semiconductor photodetector is a critical issue in an application like in radiometry, spectrophotometry, etc. the detectors are used in the so called current measurement mode. In this mode the detector is directly connected to a current-to-voltage converter, consequently in an ideal situation all the photogenerated charge carriers appear on the feedback resistor of the converter and produce a voltage drop. Photovoltaic detectors are short circuited by the converter, the built in electric field of the detector transfers the generated carriers to the converter. On the other hand photoconductive detectors should be biased externally by a constant voltage to produce an internal field for the transport of the charge carriers. Some applications need great area detectors, that especially in the IR wavelength region show low shunt resistance values. Ge, InAs, InSb, PbS, PbSe, HgCdTe, etc., have many decades lower shunt resistance values than that of a Si or InGaAs detector operating in the visible or near infrared region. If high sensitivity is needed than a high value of the feedback resistor is required that decreases the closed loop gain, consequently the settling accuracy. Bootstrapping of the detectors virtually increases the shunt resistance and so restores the decreased closed loop gain and settling accuracy. The bootstrapping technique will be shown and the noise characteristics will be analyzed and compared to the traditional solutions.

The camera group of the DLR--Institute of Space Sensor Technology and Planetary Exploration is developing imaging instruments for scientific and space applications. One example is the ROLIS imaging system of the ESA scientific space mission `Rosetta', which consists of a descent/downlooking and a close-up imager. Both are parts of the Rosetta-Lander payload and will operate in the extreme environment of a cometary nucleus. The Rosetta Lander Imaging System (ROLIS) will introduce a new concept for the sensor electronics, which is referred to as MOSES (Modula Sensor Electronics System). MOSES is a 3D miniaturized CCD- sensor-electronics which is based on single modules. Each of the modules has some flexibility and enables a simple adaptation to specific application requirements. MOSES is mainly designed for space applications where high performance and high reliability are required. This concept, however, can also be used in other science or commercial applications. This paper describes the concept of MOSES, its characteristics, performance and applications.

This paper describes a linear CMOS IR multiplexer comprising four spectral bands, each with 480 channels of 12 TDI elements. The multiplexer is designed to interface with high R₀A InSb detectors manufactured by Litton EOS, Tempe, AZ. The requirement to handle a wide range of photocurrents down to 100 fA, yet maintaining a signal bandwidth in excess of 2.5 kHz imposed significant demands on the input buffer amplifier design. In addition, each detector cell incorporates a sample/hold stage to allow snapshot operation mode. These features lead to a challenging layout for the 32 micrometers pitch to be met. To optimize dynamic range, each band may be independently operated with one of three gain settings set by switchable capacitors within the unit cell. Other architectural features of the array include bi- directional scanning, externally controllable integration time and electrical test. The array dissipates less than 50 mW of power and exhibits less than 65 noise electrons at high gain setting. A 0.7 micrometers silicon technology was used. Special design techniques were employed to allow operation at 7.5 V, thereby enhancing dynamic range. IR cameras incorporating the multiplexer are currently being delivered to the customer.

We report on the fabrication and characterization of analog multi-pixel optical position-sensitive detectors (PSDs) for sensing the 2D position of a light spot over the sensor area. Computer simulations were performed to understand the influence of the geometrical layout of the device on the linearity of response. Standard CMOS technology was chosen for fabrication so that the detectors are compatible with reliable low-cost and low-power electronics for integration with processing electronics. Three chessboard-like 5 X 5- pixel structures, with different pixel layouts have been implemented. The response linearity was calculated and measured over 80% of the detector active area. It was shown that chessboard-like structures are not suitable for spot diameters below 2 pixels. For a light spot diameter comparable with the device size, the best linearity of response--RMS deviation of less than 4%--among all three structures is achieved by the structure with vertical phototransistors as the photo-sensing elements. We also implemented a PSD with two complementary spiral structures, providing sensing for both coordinates in each pixel. With this layout we achieved RMS non-linearity of less than 3.5% for a spot size comparable with pixel size in close agreement to the simulations. The computer model indicates that the non-linearity for all structures studied decreases with the number of pixels.

A prototype solid-state multi-chip-module (MCM) optical sensor circuit is described. The MCM is designed to sample the optical signals from a fiber-optic array at rates up to 200 MHz. The fiber-optic inputs interface to the MCM avalanche-photodiode (APD) sensor array. The prototype 40 pixel MCM stores approximately 1000 samples from each fiber before readout. This is done on the MCM using high-speed charge-injection input CCD delay line ICs. The MCM is designed to be cooled to 0 degrees C. This stabilizes the APD gain and minimizes dark current generation in the APD and the CCD delay line.

A backside illuminated time delay integration (TDI) charge coupled device (CCD) technology has been developed. Imagers have been demonstrated at 13 pm pixel size and 8 pm pixel size. Photocomposition (stitching) has been employed to realize TDI iinagers of length < 60 mm. Performance has been enhanced in the areas of quantum efficiency, dynamic range, modulation transfer function (MTF), and line scan rates. The focus of this work has been to develop this new generation of line scan imagers for advanced reconnaissance applications. The enhancements permit the deployment of new camera systems with higher sensitivity, and higher resolution. To support the deployment of this technology into rugged environments, a custom packaging technology has been 'developed. The packages provide a hermetic enclosure for the CCD and establish precise alignment of the CCD pixels to the package mounting fixture. This paper will summarize the design features of the 13 pm pixel and 8 jim pixel TDI arrays. Measured performance will be presented. Future plans for this backside illuminated TDI technology will be discussed.

An ultra-high resolution 14,400 pixel trilinear image sensor is under development to meet customer requirements as they progress into next generation, high-end color scanning systems. High-performance features being incorporated into this device include an enhanced color filter scheme providing improved blue and green responsivity, electronic exposure control, and antiblooming protection. To our knowledge, this will be the highest resolution trilinear sensor to date and is being designed to provide common optical length to Kodak's current line of long trilinear imagers.