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Author

Chen Xu

Other affiliations: Micron Technology
Bio: Chen Xu is an academic researcher from Hong Kong University of Science and Technology. The author has contributed to research in topics: CMOS & CMOS sensor. The author has an hindex of 10, co-authored 22 publications receiving 270 citations. Previous affiliations of Chen Xu include Micron Technology.

Papers
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Journal ArticleDOI
TL;DR: In this article, a hybrid bulk/silicon-on-insulator (SOI) complementary metal oxide semiconductor (CMOS) active pixel image sensor has been fabricated and studied.
Abstract: A hybrid bulk/silicon-on-insulator (SOI) complementary metal oxide semiconductor (CMOS) active pixel image sensor has been fabricated and studied. The active pixel comprised of reset and source follow transistors on the SOI thin film while the photodiode is fabricated on the SOI handling substrate after removing the buried oxide. The bulk photodiode can be optimized for efficiency with the use of lightly doped SOI substrate without compromising the circuit performance. On the other hand, the elimination of wells on the SOI thin-film allows the use of PMOSFET without increasing the pixel size. The addition of a PMOSFET in the active pixel structure can reduce the minimum operating voltage of the circuit beyond that of conventional designs. With the combination of the high quantum efficiency of bulk photodiode and the low power advantage of SOI technology, the hybrid technology is attractive for scaled low voltage imaging applications.

50 citations

Journal ArticleDOI
TL;DR: In this paper, a complementary active pixel sensor (CAPS) architecture is developed to operate at a voltage below 1 V V/sub DD/ without using bootstrapping techniques.
Abstract: In this paper, an architecture to design a CMOS active-pixel sensor (APS) in an extremely low-voltage environment imposed by advanced CMOS technology is proposed. A complementary active pixel sensor (CAPS) architecture is developed to allow a CMOS active pixel to operate at a voltage below 1 V V/sub DD/ without using bootstrapping techniques. A fixed voltage deference (FVD) method with correlated double sampling is used to increase the dynamic range of the readout circuit. Both the CAPS and FVD readout circuits together, with an 8-b analog-to-digital converter, are implemented in a commercially available 0.25-/spl mu/m, single-poly and five-metal CMOS process. Measurement results show that the circuit is functional at a V/sub DD/ below 1 V with 15-dB added dynamic range compared with a conventional CMOS APS architecture.

43 citations

Journal ArticleDOI
TL;DR: In this paper, a silicon integrated circuit (IC) compatible DNA-detection platform using photodiode and ordinary optical illumination to detect DNA hybridization events occurred on the chip surface was proposed.
Abstract: In this paper, we had proposed a silicon integrated circuit (IC) compatible DNA-detection platform using photodiode and ordinary optical illumination to detect DNA hybridization events occurred on the chip surface. The method utilizes gold nanoparticle labeling and silver enhancement to generate opaque surface at area with target DNA hybridization. A photodiode fabricated underneath the supporting surface can then be used to detect the light intensity changes, before and after the silver enhancement. With this technique, we have successfully discriminated single base-mismatched DNA from matched DNA sequence, and the detection limit could be as low as 10 pM. By exploiting the advanced modern IC manufacturing technology and the well-established electrochemical immobilization of DNA, this approach has the potential to be used to construct a portable high-density DNA nanoarray system with fully electronic readout.

27 citations

Proceedings Article
01 Jan 2002
TL;DR: In this paper, a new correlated double sampling (CDS) technique based on fixed voltage difference (FVD) is introduced, which relieves the high resolution requirement of the subsequent A/D converter as a result of the limited voltage swing in advanced deep-submicron CMOS technologies.
Abstract: In this paper, a new Correlated Double Sampling (CDS) Technique based on Fixed Voltage Difference (FVD) is introduced. Compared with the traditional CDS technique with voltage sampling for A/D conversion, this method has the advantage of low voltage capability, which relieves the high resolution requirement of the subsequent A/D converter as a result of the limited voltage swing in advanced deep-submicron CMOS technologies. The new technique also allows the use of reference voltages to control the dynamic range of the circuit. The FVD CDS technique has been applied to the readout circuit of a low voltage CMOS Active Pixel Sensor (APS) circuits with an array size of 128×128 fabricated by a 0.25µm CMOS process from TSMC. The circuit is proven to be functional at extremely low V DD with added dynamic range.

21 citations

Journal ArticleDOI
TL;DR: In this paper, a backside illuminated lateral PIN photodiode on a silicon-on-sapphire (SOS) substrate is proposed and developed to address the low quantum efficiency problem due to very thin active film used, and the APS is demonstrated to function at 1.2 V, giving a dynamic range of 51 dB.
Abstract: In this paper, we propose a method to design charge-sensing elements for CMOS image sensor pixels on a silicon-on-sapphire (SOS) substrate. To address the low quantum efficiency problem due to very thin active film used, a backside illuminated lateral PIN photodiode on an SOS substrate is proposed and developed. It has the advantages of higher photo response with a PIN structure and improved optical transmission with a backside illumination through a transparent sapphire substrate. An active pixel sensor (APS) based on the PIN and backside illumination has been implemented in a commercially available SOS CMOS process. Acceptable sensitivity in optical conversion from the APS can be achieved, even with the ultrathin silicon film. The APS is demonstrated to function at 1.2 V, giving a dynamic range of 51 dB.

19 citations


Cited by
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Journal ArticleDOI
TL;DR: The biomimetic CMOS dynamic vision and image sensor described in this paper is based on a QVGA array of fully autonomous pixels containing event-based change detection and pulse-width-modulation imaging circuitry, which ideally results in lossless video compression through complete temporal redundancy suppression at the pixel level.
Abstract: The biomimetic CMOS dynamic vision and image sensor described in this paper is based on a QVGA (304×240) array of fully autonomous pixels containing event-based change detection and pulse-width-modulation (PWM) imaging circuitry. Exposure measurements are initiated and carried out locally by the individual pixel that has detected a change of brightness in its field-of-view. Pixels do not rely on external timing signals and independently and asynchronously request access to an (asynchronous arbitrated) output channel when they have new grayscale values to communicate. Pixels that are not stimulated visually do not produce output. The visual information acquired from the scene, temporal contrast and grayscale data, are communicated in the form of asynchronous address-events (AER), with the grayscale values being encoded in inter-event intervals. The pixel-autonomous and massively parallel operation ideally results in lossless video compression through complete temporal redundancy suppression at the pixel level. Compression factors depend on scene activity and peak at ~1000 for static scenes. Due to the time-based encoding of the illumination information, very high dynamic range - intra-scene DR of 143 dB static and 125 dB at 30 fps equivalent temporal resolution - is achieved. A novel time-domain correlated double sampling (TCDS) method yields array FPN of 56 dB (9.3 bit) for >10 Lx illuminance.

632 citations

Journal ArticleDOI
TL;DR: In this paper, CMOS Image Sensors are reviewed, providing information on the latest advances achieved, their applications, the new challenges and their limitations, leading to the State-of-the-art of CMOS image sensors.

546 citations

Book
22 Jul 2008
TL;DR: In this article, color theory is explained from its origin to the current state of the art, including image capture and display as well as the practical use of color in disciplines such as computer graphics, computer vision, photography, and film.
Abstract: This book provides the reader with an understanding of what color is, where color comes from, and how color can be used correctly in many different applications. The authors first treat the physics of light and its interaction with matter at the atomic level, so that the origins of color can be appreciated. The intimate relationship between energy levels, orbital states, and electromagnetic waves helps to explain why diamonds shimmer, rubies are red, and the feathers of the Blue Jay are blue. Then, color theory is explained from its origin to the current state of the art, including image capture and display as well as the practical use of color in disciplines such as computer graphics, computer vision, photography, and film.

182 citations

Journal ArticleDOI
TL;DR: The aim of this review is to highlight the most promising optical microarray biosensing techniques, as well as the most competitive commercial microarray systems, presented and compared with one another in the context of their detection system.
Abstract: Microarrays provide a powerful analytical tool for the simultaneous analyses of thousands of parameters, be they DNA or proteins, in a single experiment. However, a number of challenges continue to hinder the widespread application of microarray assays for analytical and diagnostic purposes. Advances in detection methods can help overcome some of these challenges by improving sensitivity and reliability in signal detection and by enabling real-time detection of binding events. Thus, the aim of this review is to highlight the most promising optical microarray biosensing techniques. The principles of techniques making use of labels, including scanner type, total internal reflection type, fiber-optics-based, and SPR-enhanced fluorescence, are described, along with a brief summary of labeling strategies. State of the art label-free techniques, including imaging SPR and imaging ellipsometry, are also reviewed. Examples of microarray-based assays using each technique are given to illustrate both their usefulness and their limits of detection. Furthermore, the most competitive commercial microarray systems are presented and compared with one another in the context of their detection system. Finally, a discussion of the remaining challenges as well as trends and future applications of microarrays are presented in the context of optical sensing. Copyright © 2006 John Wiley & Sons, Ltd.

165 citations

Journal ArticleDOI
TL;DR: An analytical model of mixing in the staggered herringbone mixer (SHM) was derived to estimate mixing parameters and provide practical expressions to guide mixer design and operation for a wide range of possible solutes and flow conditions.
Abstract: An analytical model of mixing in the staggered herringbone mixer (SHM) was derived to estimate mixing parameters and provide practical expressions to guide mixer design and operation for a wide range of possible solutes and flow conditions. Mixing in microfluidic systems has historically been characterized by the mixing of a specific solute system or by the redistribution of flow streams; this approach does not give any insight into the ideal operational parameters of the mixer with an arbitrary real system. For Stokes-flow mixers, mixing can be computed from a relationship between solute diffusivity, flow rate, and mixer length. Confocal microscopy and computational fluid dynamics (CFD) modeling were used to directly determine the extent of mixing for several solutes in the staggered herringbone mixer over a range of Reynolds numbers (Re) and Peclet numbers (Pe); the results were used to develop and evaluate an analytical model of its behavior. Mixing was found to be a function of only Pe and downstream position in the mixer. Required mixer length was proportional to log(Pe); this analytical model matched well with the confocal data and CFD model for Pe < 5 × 104, at which point the experiments reached the limit of resolution. For particular solutes, required length and mixing time depend upon Re and diffusivity. This analytical model is applicable to other solute systems, and possibly to other embodiments of the mixer, to enable optimal design, operation, and estimation of performance.

140 citations