N. Faramarzpour

Fully Integrated Single Photon Avalanche Diode Detector in Standard CMOS 0.18-

Avalanche photodiodes (APDs) operating in Geiger mode can detect weak optical signals at high speed. The implementation of APD systems in a CMOS technology makes it possible to integrate the photodetector and its peripheral circuits on the same chip. In this paper, we have fabricated APDs of different sizes and their driving circuits in a commercial 0.18-mum CMOS technology. The APDs are theoretically analyzed, measured, and the results are interpreted. Excellent breakdown performance is measured for the 10 and 20 m APDs at 10.2 V. The APD system is compared to the previous implementations in standard CMOS. Our APD has a 5.5% peak probability of detection of a photon at an excess bias of 2 V, and a 30 ns dead time, which is better than the previously reported results.

\mu

An analysis of the active pixel sensor (APS), considering the doping profiles of the photodiode in an APS fabricated in a 0.18 mum standard CMOS technology, is presented. A simple and accurate model for the junction capacitance of the photodiode is proposed. An analytic expression for the output voltage of the APS obtained with this capacitance model is in good agreement with measurements and is more accurate than the models used previously. A different mode of operation for the APS based on the dc level of the output is suggested. This new mode has better low-light-level sensitivity than the conventional APS operating mode, and it has a slower temporal response to the change of the incident light power. At 1 muW/cm2 and lower levels of light, the measured signal-to-noise ratio (SNR) of this new mode is more than 10 dB higher than the SNR of previously reported APS circuits. Also, with an output SNR of about 10 dB, the proposed dc level is capable of detecting light powers as low as 20 nW/cm2, which is about 30 times lower than the light power detected in recent reports by other groups.

m Technology

Fluorescence-based spectroscopy and imaging techniques provide qualitative and quantitative diagnostic information on biological systems. In this paper, we report on the design, fabrication, and testing of a miniaturized wireless fluorescence imaging device for noninvasive clinical diagnosis and screening of diseases in the gastrointestinal tract. The system includes three submodules: optical imaging, electronics control and image acquisition, and information processing and transmission. These modules were individually developed and tested before being integrated into a battery-powered wireless device. The final integrated system is mounted in a customized, compact cylindrical housing. The performance of each individual module and the overall integrated system has been evaluated using fluorescent phantoms. It has been demonstrated that the miniaturized device can acquire spectrally resolved fluorescence images and transmit the image stream wirelessly. An important outcome of this feasibility study is the identification of important technological issues and pathways for future prototype development.

CMOS-Based Active Pixel for Low-Light-Level Detection: Analysis and Measurements

A new approach for lossless compression of DNA microarray images is proposed in this work. First DNA image spots are automatically detected and extracted. Then employing a new scanning technique called spiral path, 2D spots are converted into 1D sequences. Linear interpolation method is used in the prediction coding of the 1D sequence. Finally the prediction residual sequence is divided into spot and background parts and Huffman coded. Two stages of local optimization result in excellent compression which not only outperforms ordinary compression engines, but also previous works in this area.

Toward a Miniaturized Wireless Fluorescence-Based Diagnostic Imaging System

CMOS photodetectors are compact, cheap, and of low power, making them good candidates for many biomedical applications. However, many of these applications require the capability of detecting low-level light. Therefore, the noise in CMOS sensors must be carefully considered. This paper presents a detailed analysis of the signal and noise properties in active pixel sensor (APS) elements. An optimum signal-to-noise ratio (SNR) of 54 dB is achieved by varying the integration time. Based on a rigorous reset-time analysis of the APS, the dc level of the sense node is proposed as the new output signal, which is more sensitive to low-level light than existing APS techniques. By varying the reset time, an optimum SNR of 56 dB is achieved for a 30-ms integration time. This approach can achieve higher SNR for the same APS structure than the previous reports found in the literature

Lossless DNA microarray image compression

CMOS photodetectors and imaging systems have shown that they possess adequate performance characteristics to replace CCDs or PMTs in some biomedical applications, thereby providing low power, portable, and cheap integrated bioimaging systems. Some advanced solutions, like novel active pixel sensors that detect ultra-low light levels, and avalanche photodiodes that are integrated in CMOS and perform single photon detection, are addressed in this paper.

An Approach to Improve the Signal-to-Noise Ratio of Active Pixel Sensor for Low-Light-Level Applications

The silicon-based gate-controlled lateral bipolar junction transistor (BJT) is a controllable four-terminal photodetector with very high responsivity at low-light intensities. It is a hybrid device composed of a MOSFET, a lateral BJT, and a vertical BJT. Using sufficient gate bias to operate the MOS transistor in inversion mode, the photodetector allows for increasing the photocurrent gain by 106 at low light intensities when the base-emitter voltage is smaller than 0.4 V, and BJT is off. Two operation modes, with constant voltage bias between gate and emitter/source terminals and between gate and base/body terminals, allow for tuning the photoresponse from sublinear to slightly above linear, satisfying the application requirements for wide dynamic range, high-contrast, or linear imaging. MOSFETs from a standard 0.18-μm triple-well complementary-metal oxide semiconductor technology with a width to length ratio of 8 μm /2 μm and a total area of ~ 500 μm2 are used. When using this area, the responsivities are 16-20 kA/W.

CMOS imaging for biomedical applications

This paper presents a new approach for lossless and lossy compression of DNA microarray images. A DNA microarray is a single stranded DNA fragments, arranged on a glass or nylon slide where the hybridized spots can be detected and extracted by laser scanning of the microarray. The spatial optimization techniques and transforms are employed to achieve excellent compression ratio.

Photodetection With Gate-Controlled Lateral BJTs From Standard CMOS Technology

The active pixel sensor (APS) structure is the most common pixel element for photodetection systems in standard complementary metal-oxide semiconductor technology. The focus of our work is on finding functional characteristics for low-light level design. Shot, reset, thermal, and 1∕f noise sources are considered in APS noise modeling. We also consider a higher-order empirical model for the p-n junction capacitance to accurately calculate the signal value. Signal-to-noise ratio curves are then determined for various values of integration time, signal level, and other design parameters. These curves can lead to the optimum operating point of the APS element.

Lossless and lossy compression of DNA microarray images

With the advances in deep submicron CMOS technologies, CMOS-based active-pixel sensors (APS) have become a practical alternative to charge-coupled devices (CCD) imaging technology. Key advantages of CMOS image sensors are that they are fabricated in standard CMOS technologies, which allow full integration of the image sensor along with the analog and digital processing and control circuits on the same chip and that they are of low cost. Since there is a practical limit on the minimum pixel size (4~5 mum), then CMOS technology scaling can allow for an increased number of transistors to be integrated into the pixel. Such smart pixels truly show the potential of CMOS technology in imaging applications, especially for high-speed applications. This work discusses various active-pixel sensors (APS) and shows the feasibility of using the DC-level to increase the sensitivity of the pixel for low-level light applications. Avalanche-photodiodes (APDs) are described, in addition to a discussion of the breakdown mechanism and microplasma in avalanche breakdown for single photon APDs. A fully integrated, 16 times 16 pixel CMOS camera-on-a-chip, fabricated in a standard CMOS 0.18 mum technology is also shown in this work. The array is based on 256 APS with a pixel size of 20 mum times 30 mum, a fill-factor of 60% with all digital and analog blocks implemented on-chip.