Stuart Mcleod

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 Photon Detection Efficiency and Dynamic Range in SPAD-Based Visible Light Receivers

We investigate the photon detection efficiency (PDE) and the dynamic range for digital silicon photomultipliers (dSiPMs) over a selection of design parameters: dSiPM unit cell dead time, PDE, unit cell area and fill factor, number of cells, and total dSiPM active area. Two receiver scaling scenarios are considered: varying the number of cells for 1) a fixed unit cell area or 2) a fixed total dSiPM area. Theoretical and simulated results are confirmed with experimental data from a selection of dSiPMs realised on a test chip in 130-nm CMOS process.

Digital Silicon Photomultipliers With OR/XOR Pulse Combining Techniques

A recently proposed XOR-based digital silicon photomultiplier (dSiPM) is compared against the OR-based counterpart. We show experimental data from a set of single-photon avalanche diode (SPAD) pixel arrays in 130-nm CMOS process with selectable OR tree and XOR tree for direct comparison. We demonstrate how XOR-based dSiPMs solve the limitation caused by monostable circuits and reach higher maximum count rates compared with optimized OR-based dSiPMs. The increased throughput of the SPAD array allows higher sampling rates for the digitization of the light signal enhancing dynamic range and linearity.

A Simulation Model for Digital Silicon Photomultipliers

We propose a simulator model to estimate the performance of digital Silicon Photomultipliers (dSiPM) based on Single Photon Avalanche Diodes (SPADs) in terms of detection rate of photons incident on the sensor. The work provides guidelines for efficient array structure depending on: the number of SPADs, fill factor, area of both SPADs and array. A comparison of the main techniques present in the literature to digitally combine multiple outputs into single channel is included with simulated results showing promising higher detection rates for XOR-based dSiPMs. Mathematical expressions are derived to estimate dSiPM parameters such as maximum detection rate and detector dead time as functions of the mentioned design parameters.