David Renshaw

Extended Dynamic Range From a Combined Linear-Logarithmic CMOS Image Sensor

A CMOS image sensor that can operate in both linear and logarithmic mode is described. Two sets of data are acquired and combined in the readout path to render a high dynamic range image. This is accomplished in real-time without the use of frame memory. A dynamic range in excess of 120 dB was achieved at 26 frames/s (352times288-array). The system addresses the problems of high fixed pattern noise (FPN), slow response time, and low signal-to-noise ratio (SNR) in logarithmic mode. FPN has been effectively reduced by single and two parameter calibration, the latter achieving FPN of 2% per decade. A novel on-chip method of deriving a reference point has been implemented. The system is fabricated in a 0.18-mum 1P4M process and achieves a pixel pitch of 5.6 mum with 7 transistors per pixel

A Single-Photon Avalanche Diode in 90-nm CMOS Imaging Technology With 44% Photon Detection Efficiency at 690 nm

A CMOS and back-side illumination-compatible single-photon avalanche diode (SPAD) is reported in 90-nm imaging technology with a peak photon detection efficiency of ≈ 44% at 690 nm and better than ≈20% at 850 nm. This represents an approximately eightfold improvement in near infrared sensitivity over existing CMOS SPADs. This result has important implications for optical communications, time-of-flight ranging, and optical tomography applications. The 6.4-μm-diameter SPAD also achieves the following: low dark count rates of ≈100 Hz with ≈51-ps FWHM timing resolution and a low after-pulsing probability of ≈0.375%.

CMOS driven micro-pixel LEDs integrated with single photon avalanche diodes for time resolved fluorescence measurements

We describe a single chip approach to time resolved fluorescence measurements based on time correlated single photon counting. Using a single complementary metal oxide silicon (CMOS) chip, bump bonded to a 4 × 16 array of AlInGaN UV micro-pixellated light-emitting diodes, a prototype integrated microsystem has been built that demonstrates fluorescence excitation and detection on a nanosecond time scale. Demonstrator on-chip measurements of lifetimes of fluorescence colloidal quantum dot samples are presented.

Individually Addressable AlInGaN Micro-LED Arrays With CMOS Control and Subnanosecond Output Pulses

We report the fabrication and characterization of an ultraviolet (370 nm) emitting AlInGaN-based micro-light- emitting diode (micro-LED) array integrated with complementary metal-oxide-semiconductor control electronics. This configuration allows an 8 × 8 array of micro-LED pixels, each of 72-mum diameter, to be individually addressed. The micro-LED pixels can be driven in direct current (dc), square wave, or pulsed operation, with linear feedback shift registers (LFSRs) allowing the output of the micro-LED pixels to mimic that of an optical data transmitter. We present the optical output power versus drive current characteristics of an individual pixel, which show a micro-LED output power of up to 570 muW in dc operation. Representative optical pulse trains demonstrating the micro-LEDs driven in square wave and LFSR modes, and controlled optical pulsewidths from 300 ps to 40 ns are also presented.

Analysis of CMOS Photodiodes. II. Lateral photoresponse

For pt.I see ibid., vol.50, no.5, p.1233-38 (2003). In Part I of this paper, an improved one-dimensional (1-D) analysis and a semiempirical model of quantum efficiency for CMOS photodiode was illustrated. In this part of the paper, the lateral photoresponse in CMOS photodiode arrays is investigated with test linear photodiode arrays and numerical device simulations. It is shown that the surface recombination and mobility degradation along the Si-SiO/sub 2/ interface are important factors in determining the lateral photoresponse of CMOS photodiodes. The limitations of traditional analytical approaches are briefly discussed in this context, and a novel three-dimensional (3-D) analysis of lateral photoresponse is presented. Given the significant dependence of lateral photoresponse on the Si-SiO/sub 2/ interface quality, an empirical characterization method is proposed as a more reliable solution to modeling lateral photoresponse.

A Microsystem for Time-Resolved Fluorescence Analysis using CMOS Single-Photon Avalanche Diodes and Micro-LEDs

Although microfluidics and microarray technologies are revolutionizing the throughput, sensitivity and cost in many areas of biodiagnostics, they are still reliant on bulky and expensive fluorescence analysis instrumentation. Conventional fluorescence intensity measurements are prone to misinterpretation due to illumination and fluorophore concentration non-uniformities. Thus, there is a growing interest in time-resolved fluorescence detection, whereby the characteristic fluorescence decay time-constant (or lifetime) in response to an impulse excitation source is measured.

Implementation of wireless power transfer and communications for an implantable ocular drug delivery system

A wireless power transfer and communication system based on near-field inductive coupling has been designed and implemented. The feasibility of using such a system to remotely control drug release from an implantable drug delivery system is addressed. The architecture of the wireless system is described and the signal attenuation over distance in both water and phosphate buffered saline is studied. Additionally, the health risk due to exposure to radio frequency (RF) radiation is examined using a biological model. The experimental results demonstrate that the system can trigger the release of drug within 5 s, and that such short exposure to RF radiation does not produce any significant (<or= 1 degrees C) heating in the biological model. The conclusion of the work is that this system could replace a chemical battery in an implantable system, eliminating the risks associated with battery failure and leakage and also allowing more compact designs for applications such as drug delivery.

A Comprehensive Tool for Modeling CMOS Image-Sensor-Noise Performance

Accurate modeling of image noise is important in understanding the relative contributions of multiple-noise mechanisms in the sensing, readout, and reconstruction phases of image formation. There is a lack of high-level image-sensor system modeling tools that enable engineers to see realistic visual effects of noise and change-specific design or process parameters to quickly see the resulting effects on image quality. This paper reports a comprehensive tool, written in MATLAB, for modeling noise in CMOS image sensors and showing the effect in images. The tool uses accepted theoretical/empirical noise models with parameters from measured process-data distributions. Output images from the tool are used to demonstrate the effectiveness of this approach in determining the effects of various noise sources on image quality

Analysis of CMOS Photodiodes. I. Quantum efficiency

An improved one-dimensional (1-D) analysis of the CMOS photodiode has been derived in which the effect of the substrate, which forms a high-low junction with the epitaxial layer, has been included. The analytical solution was verified with numerical simulations based on parameters extracted from a standard 0.35 /spl mu/m CMOS process. Two empirical parameters are suggested to offset the unavoidable inaccuracies in the extracted parameter values. The derived semiempirical expression exhibits a good agreement with the measured spectral response. In Part II of this paper, a three-dimensional (3-D) analysis of lateral photoresponse in CMOS photodiode arrays is presented along with an empirical modeling method utilizing test linear photodiode arrays.

Combined linear-logarithmic CMOS image sensor

A 352/spl times/288 pixel array achieves >120 dB dynamic range through merging sequential linear and logarithmic images. Calibration is used to match offset and gain. A 7-transistor pixel is built in a 0.18 /spl mu/m 1P4M CMOS process.