应用于监控安防领域的CMOS图像传感器关键技术研究
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摘要
进入新世纪以来，我国的综合国力和人民的生活水平不断提高。国家的国有资产和人民群众的个人财产和安全，都需要得到保护。整体社会的监督管理网络，也需要不断地完善。正因为如此，安防监控系统的应用越来越广泛，几乎遍布城市的每个角落。这些系统设备，充分而有效地保障了整个社会生活的顺利进行。随着微电子学的发展，图像传感器芯片在监控安防系统中的作用越来越重要，图像传感器相当于监控设备的“心脏”，它的性能好坏直接决定着监控设备能否发挥其应有的作用。因此，本文针对监控安防系统的应用，分析了监控CMOS图像传感器需要解决的关键技术问题，并提出了相应的解决方案。
首先，针对监控领域对于低噪声的要求，分析了CMOS图像传感器的影响性能的主要几种噪声来源，提出了消除主要噪声的理论方法和电路结构实现。其次，针对监控领域对于大动态范围的要求，介绍了动态范围对于CMOS图像传感器的重要性，分析了造成CMOS图像传感器动态范围偏低的主要原因，并提出了提高动态范围指标的多种方法。再次，针对监控领域对于高灵敏度的要求，介绍了提高CMOS图像传感器像素灵敏度的几种方法。最后，通过实际的芯片产品测试结果，证明了本文提出的方法可以有效地提高CMOS图像传感器的灵敏度，降低噪声和扩展动态范围，使得监控领域应用最为看重的这三个性能指标得到了根本性的改善。
本文在分析和提高监控CMOS图像传感器最为看重的噪声，动态范围和灵敏度三个重要指标基础上，提出了主要的几个创新方面：
第一，提出了一种新颖的具有低噪声和高电源抑制比(PSRR)的电路结构，在模拟域大幅降低了CMOS图像传感器的图像噪声，提高了图像质量；并且依据暗电流噪声的相关性，提出了一种应用暗电流比例系数矩阵来消除暗电流噪声的方法，即节省了硬件资源，又提高了暗场下的图像质量。
第二，根据多次曝光提高动态范围的理论，提出了一种新颖的组合穿插式多次曝光技术，在有效提高动态范围的同时，又保证了帧频不降低，硬件资源不过多消耗。
第三，针对监控系统应用场合的不同，提出了一种新型的可变浮动节点电容值的灵敏度增强技术，实现了一颗芯片在多种监控环境下应用的可行性。
Since the beginning of the new century, the country's comprehensive nationalstrength and people's living standards are improved continuously. The state-ownedassets and the personal property and safety of the masses are in need of protection. Thesupervision and management network of the whole society must be improvedconstantly. So the security surveillance system is used widely, almost everywhere inthe city. The social life’s smoothness is effectively guaranteed by these equipments.With the development of the microelectronics, the image sensor plays an importantrole in the security surveillance system, likes the heart, and the performance of theimage sensor derectly decides the effect of the surveillance equipment. So this paperaims at the application of the security surveillance system, analyzes the key technicalproblems of CMOS image sensor, and puts forward the solution.
First, against the low-noise requirement of the surveillance system, the mainnoise sources of CMOS image sensor are analyzed. And the theoretical methods andcircuit implementation of noise elimination are presented. Secondly, against the widedynamic range requirement of the surveillance system, the importance of the dynamicrange of CMOS image sensor is introduced, the main reasons of low dynamic range ofCMOS image sensor are analyzed and some methods to improve the dynamic rangeare presented. Again, against the high sensitivity requirement of the surveillancesystem, some methods for increasing the sensitivity of CMOS image sensor arerecommended. At last, through the actual chip test, the theory and methods which thispaper presents are proved that the sensitivity, noise and dynamic range are effectivelyenhanced.
This paper has analyzed and improved the noise, dynamic range and sensitivitywhich are more important in CMOS iamge sensor in surveillance field and advancedthe some main creative points below.
First, a new low noise and high PSRR circuit configuration is presented, whichreduces the analog circuit noise of CMOS image sensor and improves the imagequality. And according to the correlation of dark current, a method of eliminating thedark current noise by applicating dark current proportional coefficient matrix ispresented, which not only saves hardware resources, but also improves the imagequality under a dark condition.
Second, On the basis of the theory that multiple exposures could enhance thedynamic range, a new interlaced multiple exposures way is creatively put forward. While the dynamic range effectively improved, this method also can guarantee theframe rate not to be slow down, and the hardware not to be excessive consumption.
At last, for different applications, a new sensitivity boosting technology bychanging the capacitor of the floating node of the pixels is introduced, which achievesthe feasibility of that one chip can apply to the various surveillance conditions.
首先，针对监控领域对于低噪声的要求，分析了CMOS图像传感器的影响性能的主要几种噪声来源，提出了消除主要噪声的理论方法和电路结构实现。其次，针对监控领域对于大动态范围的要求，介绍了动态范围对于CMOS图像传感器的重要性，分析了造成CMOS图像传感器动态范围偏低的主要原因，并提出了提高动态范围指标的多种方法。再次，针对监控领域对于高灵敏度的要求，介绍了提高CMOS图像传感器像素灵敏度的几种方法。最后，通过实际的芯片产品测试结果，证明了本文提出的方法可以有效地提高CMOS图像传感器的灵敏度，降低噪声和扩展动态范围，使得监控领域应用最为看重的这三个性能指标得到了根本性的改善。
本文在分析和提高监控CMOS图像传感器最为看重的噪声，动态范围和灵敏度三个重要指标基础上，提出了主要的几个创新方面：
第一，提出了一种新颖的具有低噪声和高电源抑制比(PSRR)的电路结构，在模拟域大幅降低了CMOS图像传感器的图像噪声，提高了图像质量；并且依据暗电流噪声的相关性，提出了一种应用暗电流比例系数矩阵来消除暗电流噪声的方法，即节省了硬件资源，又提高了暗场下的图像质量。
第二，根据多次曝光提高动态范围的理论，提出了一种新颖的组合穿插式多次曝光技术，在有效提高动态范围的同时，又保证了帧频不降低，硬件资源不过多消耗。
第三，针对监控系统应用场合的不同，提出了一种新型的可变浮动节点电容值的灵敏度增强技术，实现了一颗芯片在多种监控环境下应用的可行性。
Since the beginning of the new century, the country's comprehensive nationalstrength and people's living standards are improved continuously. The state-ownedassets and the personal property and safety of the masses are in need of protection. Thesupervision and management network of the whole society must be improvedconstantly. So the security surveillance system is used widely, almost everywhere inthe city. The social life’s smoothness is effectively guaranteed by these equipments.With the development of the microelectronics, the image sensor plays an importantrole in the security surveillance system, likes the heart, and the performance of theimage sensor derectly decides the effect of the surveillance equipment. So this paperaims at the application of the security surveillance system, analyzes the key technicalproblems of CMOS image sensor, and puts forward the solution.
First, against the low-noise requirement of the surveillance system, the mainnoise sources of CMOS image sensor are analyzed. And the theoretical methods andcircuit implementation of noise elimination are presented. Secondly, against the widedynamic range requirement of the surveillance system, the importance of the dynamicrange of CMOS image sensor is introduced, the main reasons of low dynamic range ofCMOS image sensor are analyzed and some methods to improve the dynamic rangeare presented. Again, against the high sensitivity requirement of the surveillancesystem, some methods for increasing the sensitivity of CMOS image sensor arerecommended. At last, through the actual chip test, the theory and methods which thispaper presents are proved that the sensitivity, noise and dynamic range are effectivelyenhanced.
This paper has analyzed and improved the noise, dynamic range and sensitivitywhich are more important in CMOS iamge sensor in surveillance field and advancedthe some main creative points below.
First, a new low noise and high PSRR circuit configuration is presented, whichreduces the analog circuit noise of CMOS image sensor and improves the imagequality. And according to the correlation of dark current, a method of eliminating thedark current noise by applicating dark current proportional coefficient matrix ispresented, which not only saves hardware resources, but also improves the imagequality under a dark condition.
Second, On the basis of the theory that multiple exposures could enhance thedynamic range, a new interlaced multiple exposures way is creatively put forward. While the dynamic range effectively improved, this method also can guarantee theframe rate not to be slow down, and the hardware not to be excessive consumption.
At last, for different applications, a new sensitivity boosting technology bychanging the capacitor of the floating node of the pixels is introduced, which achievesthe feasibility of that one chip can apply to the various surveillance conditions.
引文
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