A DPS array with programmable resolution and reconfigurable conversion time

A CMOS digital pixel sensor (DPS) with programmable resolution and reconfigurable conversion time is described. The chip features a unique architecture based on the pulse width modulation (PWM) technique and operates with either an 8-b or 4-b accuracy. The 8-b conversion mode is used for high-precision imaging while the 4-b conversion mode provides a shorter conversion time and a two times increase in spatial resolution. Two quantization schemes are studied, namely, the uniform and the nonuniform time-domain quantizers, which are referred to as UQ and NUQ, respectively. It is shown that the latter scheme not only permits to linearize the nonlinear response of the PWM sensor, but also allows to significantly speed up the conversion time, particularly for wide dynamic range and low coding resolutions. A prototype of 32 x 32/64 x 32 pixels has been fabricated using 1-poly, 5-metal CMOS 0.35-mu m n-well standard process. Power dissipation is 10 mW at V-DD = 3.3 V, dynamic range is dB, while dark current was measured at I pA. The reconfiguration features of the chip have been verified experimentally

CMOS image system wiht high responsivity and high dynamic range

Orientador: Jacobus Willibrordus SwartTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de ComputaçãoResumo: O trabalho apresentado nesta tese endereça dois importantes desafios impostos pela evolução da tecnologia CMOS, a diminuição da responsividade das junções e a redução da tensão de alimentação. Um fotodetector de alta responsividade e um sistema de imagem CMOS multiamostrado no domínio do tempo são propostos nesta tese. Como fototransistor de elevada responsividade propõem-se nesta tese o uso do Transistor Bipolar Lateral Controlado por Porta (GC-LBJT) operando como fototransistor de 4 terminais. Apresenta-se a análise do princípio de funcionamento e o desenvolvimento de um circuito equivalente CC. A fotoresposta do GC-LBJT é investigada em duas diferentes configurações, coletor-comum com tensão porta-base constante e emissor-comum com tensão porta-emissor constante. A característica da fotoresposta é associada às equações do dispositivo em ambas as configurações mostrando os principais parâmetros do dispositivo que determinam o ganho. Na configuração coletor-comum, a característica da fotoresposta varia de aproximadamente linear a sublinear por meio da tensão de controle VGB. Na configuração emissor-comum, o dispositivo apresenta fotoresposta sublinear e baixa excursão para toda faixa de tensão de controle (VGB) utilizada. Explorando a característica controlável do GC-LBJT em ambas as configurações, o fototransistor GC-LBJT pode apresentar ganho e responsividade maiores do que 10+6 e 10+4 A/W respectivamente. Propõe-se o método de múltipla-amostragem para sistemas de imagem CMOS no domínio do tempo. O pixel é composto por um comparador e um circuito de memória de um bit. O método de múltipla-amostragem no domínio do tempo permite reduzir o circuito de memória integrado ao pixel de 8 bits tipicamente para um único bit. O resultado da amostra armazenado na memória de um bit no pixel é lida externamente de forma síncrona e o valor do sinal do pixel é codificado de acordo com o instante da amostra no tempo. O número de bits e a velocidade de operação do circuito limitam a dimensão máxima da matriz. Além disso, este trabalho apresenta a influência da não-linearidade da capacitância do fotodiodo na característica da fotoresposta dos sistemas de imagem CMOS no domínio do tempo. Estudo do comportamento do ruído de padrão fixo e o temporal em sistema de imagem no domínio do tempo também são apresentadosAbstract: This thesis adresses two important challenges imposed by CMOS technology trends, the reduction of the junctions's responsivity and voltages levels. A new photodetector with high responsivity and a multi-sampling time domain image system are investigated. This thesis proposes to use the gate controlled lateral bipolar junction transistor (GCLBJT) as a four terminal phototransistor as photodetector with high responsivity. This work presents the photopolarization principle, gain current mechanism of the GC-LBJT in conjuction with DC equivalent circuit development. The GC-LBJT photo response is analysed in two different configurations, common colector with constant gate-base voltage and common emmiter with constant gate-emitter voltage. The photoresponse is related to device equations in both configurations. In the common colector with constant gate-base voltage configuration the photo response characteristic changes from linear to sublinear according to the VGB control voltage. In the common emmiter configuration, the device presents sublinear photo response and small changes for full range of the VGB control voltage used. Exploring the GC-LBJT controllable characteristic, the GC-LBJT phototransistor presents high and controllable gain all over the range of irradiation used, for both configurations. The multi-sampling method for time domain CMOS image systems is proposed. The pixel's architecture is composed by a comparator and a single bit memory circuit. The multisampling method in time-domain allows reducing memory circuits integrated per pixel with eight bit tipically to a single bit. The sample result stored in the single bit memory of the pixel is externally read in a synchronous way and the pixel signal value is coded according to the sampling instant. The number of the bits and the speed of circuit's operation define the upper limit of the matrix size. In addition, this work presents the influence of non-linearity on photoresponse characteristic for systems operating in time domain. The behavior of fixed and temporal pattern noise study in time domain image system is also presentedDoutoradoEletrônica, Microeletrônica e OptoeletrônicaDoutor em Engenharia Elétric

Active pixel sensors for breast biopsy analysis using x-ray diffraction.

Breast cancer diagnosis currently requires biopsy samples to be analysed by a histopathologist a time consuming, highly specialised process. X-ray diffraction is a quantitative technique that can distinguish between healthy and diseased breast biopsy samples using the change in proportions of fat and fibrous tissue that occurs when cancer invades. A semi-automated breast biopsy analysis system based on X-ray diffraction could yield a faster patient diagnosis. Recording X-ray diffraction patterns is a challenging task needing low noise, large area, and wide dynamic range detectors. Scientific complementary metal oxide semiconductor (CMOS) Active Pixel Sensors will soon be able to meet all of these demands in a single device. Characterization of two novel Active Pixel Sensors that advance towards an ideal X-ray diffraction detector is presented. 'Vanilla' exhibits a low read noise of 55e r.m.s. and high quantum efficiency of up to 70% so was selected for the design and implementation of the first 'Active Pixel X-ray Diffraction' (APXRD) system. Following on from Vanilla, the 'Large Area Sensor' (LAS) covered an area of over 29cm2 and had a wide dynamic range of over 95dB. The first linear systems model of an Active Pixel Flat Panel Imager (scintillator coupled APS) was formulated in the design of the APXRD system, to select filters to narrow the spectral width of the X-ray beam and predict the recorded scatter intensity. Following system implementation, scatter signatures were recorded for numerous breast tissue equivalent samples. A multivariate analysis model calibrated with these was able to predict the percentage fat content of an 'unknown' sample to within 3% a very promising result. The width of the filtered polychromatic X-ray spectrum had only a minor influence on the APXRD scatter signatures indicating that the system preserves all relevant structural information