【作者】 尚玉全；

【导师】 曾云；

【作者基本信息】 湖南大学 ， 微电子学与固体电子学， 2005， 硕士

【摘要】 概述了国内外CMOS图像传感器发展历史、现状和趋势,比较了CMOS图像传感器与CCD图像传感器的性能特点,指出了本课题的研究意义。在介绍半导体光电知识的基础上,深入探讨了用于CMOS图像传感器的半导体光电二极管和双极光栅晶体管的光电转换特性,指出了影响光电二极管光电特性的因素和提高光电二极管特性的方法,建立了新型光电器件——双极光栅晶体管的等效电路模型,利用电子电路仿真软件PSPICE对其光电特性进行了模拟,由于引入P~+N注入结,双极光栅晶体管的光响应特性优于传统光栅晶体管,随着入射光功率的增加,其光电流成指数关系增加。介绍了CMOS图像像素采集单元的各种电路形式,提出了针对双极光栅晶体管的新型像素单元电路并对其噪声特性进行了分析。通过在每列总线上增加两个晶体管,使之与像素内的行选通晶体管和源跟随晶体管形成一个输入输出短接的差动放大器,提高了像素内的光电转换增益。相关双取样电路中,用单位增益采样器代替PMOS列选电路,不但克服了开关晶体管的非理想效应,而且进一步提高了系统的光电转换增益,并设计了一个用于将信号送入模数转换器的列输出缓冲器。设计了一个适合应用于CMOS图像传感器的列并行8位低功耗模数转换器,该转换器采用逐次逼近型结构,量化速度为1M,信噪比为42dB,微分非线性度和积分非线性度分别为0.5LSB和1LSB。电压比较器采用完全差分三级结构,第一、二级为预放大级,第三级为放大级,数模转换器采用电荷定标,并且采用新型的电容分布形式,大大减少了单位电容的使用量,逐次逼近寄存器采用最少的逻辑单元完成,所有这些措施使得系统的功耗大大降低,仅为350μW。本设计有利于降低CMOS图像传感器整体电路的功耗,避免了由于局部电路功耗过大而使芯片局部过热影响图像触感器的性能,使芯片的功耗、噪声、面积、速度达到一个很好折衷。更多还原

【Abstract】 In this paper, the developing history, present situation and trends of CMOS image sensor inside and outside of China were summarized. The characteristics between CMOS image sensor and CCD image sensor were compared and the research meaning was pointed out. On the basis of introducing semiconductor photoelectric effect, the light-transfer characteristics of photodiode and photogate transistor used in CMOS image sensor were deeply discussed, the factors affecting the light-transfer characteristics of photodiode and the methods increasing the light-transfer characteristics of photodiode were analyzed. The equivalent circuit model of new photoconducting device—bipolar junction photogate transistor (BJPHGT) was proposed, by utilizing electronic circuit simulation software PSPICE, the current-illumination characteristics of BJPHGT were simulated. Due to the introduced P+N injection junction, the photoresponse characteristic of BJPHGT is better than that of traditional photogate transistor. The photocurrent density increases exponentially with the incident light power. After every kind of pixel unit circuit was introduced, the new pixel unit circuit for BJPHGT was brought forward and its noisiness was analyzed. By means of adding two transistors in each column bus, making them form a short-circuit differential amplifier with source follower transistor and row switch transistor inside of pixel, the photoelectric conversion gain is increased by this method. In the correlated double sample circuit, by substituting unity gain sampler for PMOS column gate, not only the nonideal effect of switch transistor was depressed but also the photoelectric conversion gain was further increased. A column output buffer used to drive large input capacity of analog-digital converter (ADC) and a column parallel, 8-bits resolution, low consumed power successive approximation type ADC for CMOS image sensor were designed. Its sample speed, signal-to-noise ratio, differential and integration nonlinear are 1MS/s, 42dB, 0.5LSB and 1LSB respectively. The comparator was designed to be a fully differential multilevel structure, the first and second level are pre-magnification, and the third one is amplifiers. The charge-scaling digital-analog converter has a new capacity distribution, which make its specific capacitance decrease greatly. The successive approximation register is made up by least logic elements. All these methods leads to very low power consumption which is 350μW.This design have a perfect compromise of power consumption, noise, area and speed and is propitious to reduce the power consumption of CMOS image sensor system, avoid producing hot spot due to high power consumption of the local circuit which damages the performance of CMOS image sensor.更多还原