Analysis of pixel gain and linearity of CMOS image sensor using floating capacitor load readout operation
Analysis of pixel gain and linearity of CMOS image sensor using floating capacitor load readout operation
复制标题
DOI：
10.1117/12.2083111
复制
发表时间：
2015-03
期刊：
影响因子：
--
通讯作者：
Shunichi Wakashima;Fumiaki Kusuhara;R. Kuroda;S. Sugawa
中科院分区：
文献类型：
--
作者：
Shunichi Wakashima;Fumiaki Kusuhara;R. Kuroda;S. Sugawa
本文论证了浮动电容负载读出操作比传统的像素读出操作具有更高的读出增益和更宽的线性范围，并报告了其原因。像素信号读出增益由像素内驱动晶体管的跨导、后门跨导和输出电阻以及负载电阻决定。在浮动电容负载读出操作中，由于没有电流源，负载仅为采样/保持电容，因此负载电阻接近无穷大。因此读出增益比常规读出操作大。在浮电容负载读出操作中，无电流源，压降量小于常规读出操作。因此，与传统的读出操作相比，高电压和低电压的线性范围都扩大了。当降低电源电压以降低功耗时，线性范围扩大的效果更有利。为了证实这些效果，我们使用0.18um 1-Poly - 3-Metal CMOS工艺技术与钉住PD制作了原型芯片。结果，我们证实了浮动电容负载读出操作增加了读出增益和线性范围。
In this paper, we demonstrate that the floating capacitor load readout operation has higher readout gain and wider linearity range than conventional pixel readout operation, and report the reason. The pixel signal readout gain is determined by the transconductance, the backgate transconductance and the output resistance of the in-pixel driver transistor and the load resistance. In floating capacitor load readout operation, since there is no current source and the load is the sample/hold capacitor only, the load resistance approaches infinity. Therefore readout gain is larger than that of conventional readout operation. And in floating capacitor load readout operation, there is no current source and the amount of voltage drop is smaller than that of conventional readout operation. Therefore the linearity range is enlarged for both high and low voltage limits in comparison to the conventional readout operation. The effect of linearity range enlargement becomes more advantageous when decreasing the power supply voltage for the lower power consumption. To confirm these effects, we fabricated a prototype chip using 0.18um 1-Poly 3-Metal CMOS process technology with pinned PD. As a result, we confirmed that floating capacitor load readout operation increases both readout gain and linearity range.