Publication: Design of integrator and comparator in pixel readout circuit
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Date
2012-06-01
Authors
Mohamed Ghazali, Su'aidah
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Abstract
Recently, CMOS technology has been widely used in many applications including image sensor. For X-ray images, CMOS technology is used in the readout circuit of the sensors. The basic structure of a CMOS image sensor contains of two dimensional array of pixels and peripheral circuits. Converting the image into electrical signals is performed by a group of pixels that are arranged in a structure of a rectangular form called an array. Since the array of pixels largely determines the image quality of a CMOS sensor, it is important to detail the internal structure. The pixel structure used can be categorized into three types, which are Passive Pixel Sensor (PPS), Active Pixel Sensor (APS) and Digital Pixel Sensor (DPS). DPS is latest ] structure and has many advantages compared with PPS and APS. In DPS, each pixel contains the photodetector, the A/D conversion system and sometimes the digital memory to keep the value of this conversion. The A/D conversion system that has been proposed is Sigma-delta structures which have better resolutions and allows the data-conversion circuitry to be simple and insensitive to process variations. Sigma-delta modulator consists of three main circuits which are integrator,comparator and 1-bit digital-to-analog converter (DAC) circuits. This thesis will
focus on Integrator and comparator in the Sigma-delta modulator circuit and the analysis of both circuits.