Dirk Uwaerts

CMOS image sensors with logarithmic response are attractive devices for applications where a high dynamic range is required. Their strong point is the high dynamic range. Their weak point is the sensitivity to pixel parameter variations introduced during fabrication. This gives rise to a considerable fixed pattern noise (FPN) that deteriorates the image quality unless pixel calibration is used. In the present work a technique to remove the FPN by employing on-chip calibration is introduced, where the effect of threshold voltage variations in pixels is cancelled. An image sensor based on an active pixel structure with five transistors has been designed, fabricated, and tested. The sensor consists of 525/spl times/525 pixels measuring 7.5 /spl mu/m/spl times/10 /spl mu/m, and is fabricated in a 0.5-/spl mu/m CMOS process. The measured dynamic range is 120 dB while the FPN is 2.5% of the output signal range.

A 512/spl times/512 CMOS active pixel sensor (APS) was designed and fabricated in a standard 0.5-/spl mu/m technology. The radiation tolerance of the sensor has been evaluated with Co-60 and proton irradiation with proton energies ranging from 11.7 to 59 MeV. The most pronounced radiation effect is the increase of the dark current. However, the total ionizing dose-induced dark current increase is orders of magnitude smaller than in standard devices. It behaves logarithmically with dose and anneals at room temperature. The dark current increase due to proton displacement damage is explained in terms of the nonionizing energy loss of the protons. The fixed pattern noise does not increase with total ionizing dose. Responsivity changes are observed after Co-60 and proton irradiation, but a definitive cause has not yet been established.

In this paper, we report on the design and performance of a 1 cm², 90 × 92-pixel image sensor. It is made X-ray sensitive by the use of a scintillator. Its pixels have a charge packet counting circuit topology with two channels, each realizing a different charge packet size threshold and analog domain event counting. Here, the sensor's performance was measured in setups representative of a medical X-ray environment. Further, two-energy-level photon counting performance is demonstrated, and its capabilities and limitations are documented. We then provide an outlook on future improvements.

This paper discusses a 13.89 million pixels CMOS image sensor for digital SLR cameras. The pitch of the 3-transistor active pixel is 8 microns. The sensor has a full well charge of 117K electrons and 33 electrons temporal noise, and a dynamic range of 71 dB. The fixed pattern noise is 0.14 % RMS, obtained by an on-chip correction circuit. Color filters have been optimized for best photographic performance. The pixel array area is equal to the size of 35 mm film (36 x 24 mm 2). Essentially, this means that the photographer gets the same image with the digital camera as with film, without lens magnification factor. Two technological challenges have to be overcome to make a sensor of this size. The sensor size exceeds the field area of steppers used to fabricate sub-micron CMOS chips. To solve this, a stitching technique has to be applied during processing of this device. A second problem of such large devices is the variation of the angle-of-incidence of the light on the silicon, causing the efficiency of micro lenses to vary along the focal plane. To avoid this problem, a pixel design with an inherently high fill factor is used. The product of fill fact or and quantum efficiency on this pixel is 30%, a number that cannot be further increased by the use of micro lenses. 1.

In this paper, we outline the functionality of a new Fiber Bragg Grating (FBG) interrogator that has been developed based on requirements from the Flight Test Group of a major European aircraft manufacturer and give some performance figures regarding the dynamic measurement capabilities of the system. The interrogator is designed for sensing the wavelength of short apodized gratings at high sampling rates and with strict requirements on the signal quality in the frequency domain. In particular, the specifications on aliasing and phase distortion will be discussed, and an explanation on how the system can and does meet these specs over different sampling frequencies is given.