一种用于CMOS图像传感器的高精度抗辐射自适应斜坡产生电路设计

一种用于CMOS图像传感器的高精度抗辐射自适应斜坡产生电路设计 Design of High Precision Radiation-Hardened Adaptive Ramp Generator Circuit for CMOS Image Sensor 1 first-author 李闯泽，男，博士生，现从事CMOS模拟集成电路设计、抗辐射CMOS图像传感器设计方面的研究。E-mail：li_chuang_ze@163.com 李闯泽，男，博士生，现从事CMOS模拟集成电路设计、抗辐射CMOS图像传感器设计方面的研究。E-mail：li_chuang_ze@163.com li_chuang_ze@163.com 2 1 1 corresp E-mail:wls771@163.com E-mail:wls771@163.com wls771@163.com 西安微电子技术研究所，陕西 西安 710072 西安微电子技术研究所，陕西 西安 710072 Xi’an Microelectronic Technology Institute, Xi’an 710072, Shaanxi， China Xi’an Microelectronic Technology Institute, Xi’an 710072, Shaanxi， China 西安电子科技大学 微电子学院，陕西 西安 710072 西安电子科技大学 微电子学院，陕西 西安 710072 School of Microelectronics， Xidian University, Xi’an 710072, Shaanxi， China School of Microelectronics， Xidian University, Xi’an 710072, Shaanxi， China 为解决空间辐射环境引起的列并行单斜式模拟数字转换器（analog to digital converter, ADC）中斜坡信号范围不能动态校正的问题，提出一种用于CMOS（complementary metal oxide semiconductor，互补金属氧化物半导体）图像传感器的高精度抗辐射自适应斜坡产生电路设计方法，并对该方法进行了理论分析和验证。仿真实验结果表明：通过dummy像元的设计可以实现输入到输出整个信号环路的闭环自适应负反馈调节；该斜坡产生电路能够在电离总剂量（total ionization dose, TID）效应影响情况下自动调整斜坡信号斜率，从而有效提高斜坡信号的精度。 In order to address the issue that the ramp range cannot be dynamically corrected in the column-parallel single-slope analog to digital converter (ADC) caused by space radiation environment, a design method of high precision radiation-hardened adaptive ramp generator circuit for complementary metal oxide semiconductor （CMOS） image sensor is proposed，theoretically analyzed and verified. The simulation results show that the closed-loop adaptive negative feedback adjustment of the entire signal loop from input to output can be realized by the design of the dummy pixel. And the ramp generator circuit can automatically adjust the slope of the ramp under the influence of the total ionization dose (TID) effect, thereby effectively improving the accuracy of the ramp signal. CMOS图像传感器 单斜ADC 斜坡发生器 抗辐射 自适应 微分非线性 积分非线性 complementary metal oxide semiconductor (CMOS) image sensor single-slope analog to digital converter （ADC） ramp generator radiation-hardened adaptive differential nonlinearity （DNL） integral nonlinearity （INL） 0　 引 言 1 列并行模拟数字转换器（analog to digital converter, ADC）是广泛应用于CMOS（complementary metal oxide semiconductor，互补金属氧化物半导体）图像传感器中的一种模拟数字转换器。常见的列级ADC有单/多斜式ADC、逐次逼近式（successive approximation register, SAR）ADC、Cyclic ADC及Pipeline ADC等多种结构 [ 1 1 ] ，其中，单/多斜式ADC因其具有结构简单、功耗低、占用面积小等优势，比较适合应用于CMOS图像传感器阵列类型的器件中。单/多斜式ADC电路的核心部分是斜坡产生电路，斜坡信号的线性度和精度高低直接决定单/多斜式ADC性能的优劣。斜坡产生电路一般包括电流源和积分电容两部分，通过电流源对积分电容进行充放电来产生斜坡信号。 斜坡产生电路在Buck转换器 [ 2 2 ] 、模拟数字转换器内置自检（built-in self-test，BIST） [ 3 3 , 4 4 ] 、单/多斜式ADC [ 1 1 , 5 5 , 6 6 , 7 7 , 8 8 ] 等多种功能电路中得到了广泛应用，但由于传统的斜坡产生电路受工艺、电压及温度（process-voltage-temperature, PVT）等因素的影响较大,造成斜坡信号精度不高、线性度比较差等问题，限制了该类型电路整体性能的提升。1999年，Provost 等 [ 3 3 ] 首次提出用于模拟数字转换器BIST的自适应斜坡产生电路，通过离散负反馈方式对斜坡产生电路进行动态校正，解决了传统斜坡信号随PVT、电流源及电容失配等因素变化的问题。2012年，Sordo等 [ 5 5 ] 提出了与文献[ 3 3 , 4 4 ]中类似的自适应斜坡产生电路，对该电路中的校正电路进行了改进和辐射加固设计 [ 5 5 ] ，但未考虑运算放大器的自身有限增益及运放失调对斜坡产生电路性能的影响。同年，Liu [ 9 9 ] 提出了采用开关电容模拟精确电阻的方法实现的斜坡产生电路，该方法产生的斜坡信号斜率与时钟频率、参考电压相关，消除了电容的绝对值对斜坡信号斜率的影响，但受PVT和时钟信号抖动的影响较大，不适合飞行时间（time of flight，TOF）测距及科学级成像等高精度应用。2019年，Deyan等 [ 10 10 ] 设计了一种采用编程方式调整斜坡信号范围的斜坡产生电路，但是存在两方面缺点：一是产生的斜坡信号斜率会受PVT因素的影响而改变；二是实际使用中采用数字模拟转换器（digital to analog converter，DAC）编程的方式对电流源大小进行调整比较繁琐。文献[ 1 1 , 2 2 , 3 3 , 4 4 , 5 5 , 6 6 , 7 7 , 8 8 , 9 9 ]提出的单/多斜式ADC中的斜坡产生电路都是采用固定的斜坡参考电压，导致电路不能动态地随着应用环境中电离总剂量（total ionization dose, TID）、PVT等因素的变化自动调节斜坡参考电压。尤其是在空间及医疗成像等辐射环境中，CMOS图像传感器易出现暗电流增大、MOS（metal oxide semiconductor，金属氧化物半导体）器件阈值电压产生漂移等现象，从而对其性能造成严重影响，因此需要针对此类特殊应用，对CMOS图像传感器进行优化设计，以满足空间和医疗成像应用中对图像传感器的设计要求。 针对上述问题，本文提出了一种用于CMOS图像传感器的斜坡产生电路设计方法。该方法首先采集当前环境中dummy像元电路输出信号的上下限目标电压，然后将目标电压作为斜坡产生电路的参考电压，最后建立起一种与应用环境相适应的斜坡产生电路；为了满足空间、医疗等辐射环境下斜坡产生电路的抗辐射要求，对电路进行了辐射加固设计；考虑到斜坡信号精度受PVT、失调电压等因素的影响 [ 3 3 , 4 4 ] ，采用离散负反馈技术对斜坡产生电路进行了优化设计。通过对环境自适应、辐射加固、离散负反馈技术3个方面的研究，以期获得一种用于CMOS图像传感器的高精度抗辐射自适应斜坡产生电路设计方法。 1　 TID对斜坡电路产生的影响及分析 1 1.1　影响 2 CMOS图像传感器在空间和医疗成像应用中若受到高能粒子的辐射作用，会对其功能和性能产生较大影响。辐射环境下产生的辐射效应大致分为3种 [ 11 11 , 12 12 ] ：1） TID效应；2） 单粒子效应：包括单粒子瞬态（single event transient，SET）、单粒子翻转（single event upset，SEU）、单粒子闩锁（single event latch-up，SEL）效应等；3） 位移损伤效应。因此需对CMOS图像传感器进行特殊辐射加固设计，以降低空间辐射环境中高能粒子对CMOS图像传感器造成的损伤和失效影响。 CMOS图像传感器作为一种典型的数模混合芯片，其模拟电路部分如像元和读出链路直接影响图像传感器的性能，而TID效应对模拟电路的性能影响较大，因此本文重点分析TID效应对CMOS图像传感器斜坡产生电路造成的影响，并针对这种影响提出对应的改进措施。 CMOS图像传感器在空间辐射环境中受到TID效应影响时，一方面，由于像元结构电路中拑位光电二极管（pinned photodiode，PPD）和传输栅（transfer gate，TG）管中Si-SiO 2 界面缺陷增多、P型外延（P epi ）与N + 形成的体区陷阱电荷增大形成扩散电流，以及PPD管耗尽区陷阱电荷增大形成热电流等多因素的影响，引起暗电流变大，使得图像传感器信噪比下降；另一方面，像素内MOS管阈值电压减小，会导致其漏电流变大 [ 13 13 , 14 14 , 15 15 , 16 16 , 17 17 ] ，严重影响CMOS图像传感器整体性能和成像质量，因此必须对像元结构电路进行辐射加固设计，从而保证在空间辐射环境下CMOS图像传感器良好的性能和成像质量。 1.2　分析 2 由于斜坡产生电路的参考电压是由dummy像元电路产生， dummy像元输出摆幅的变化会引起斜坡参考电压范围发生变化，因此，TID对像元输出的影响最终会影响单斜式ADC的有效位数。下面从TID对像元输出的影响和像元输出摆幅对单斜式ADC有效位数的影响两个方面进行分析，以期深入研究问题产生的机理。 1.2.1　TID对像元输出的影响 3 为了说明空间辐射环境下像元结构电路输出信号摆幅的动态变化过程， 本文以典型4T有源像素传感器（active pixel sensor，APS）像元结构为例进行分析，所提出的设计方法同样适用于5T-APS、6T-APS像元结构。典型4T-APS像元结构由PPD、TG管、复位管（reset，RST）及源极跟随器（source follower，SF）构成。 图1 图1 为辐射前后4T-APS像元势垒变化引起像元输出摆幅变化示意图，同时图中还给出了4T-APS像元结构中PPD、TG管的剖面图，在辐射前后4T-APS像元中PPD管光生电荷过程以及TG管势垒变化等。 图1 图1 中， <math id="M1"><mi mathvariant="normal">S</mi><mi mathvariant="normal">T</mi><mi mathvariant="normal">I</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422961&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422960&type= 6.34999990 2.70933342 （shallow trench isolation）表示浅槽隔离， <math id="M2"><msub><mrow><mi mathvariant="normal">N</mi></mrow><mrow><mi mathvariant="normal">P</mi><mi mathvariant="normal">P</mi><mi mathvariant="normal">D</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422963&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422962&type= 6.94266701 3.64066648 表示PPD管的N型掺杂注入，P + 表示P型重掺杂， <math id="M3"><msup><mrow><mi mathvariant="normal">N</mi></mrow><mrow><mo>+</mo></mrow></msup></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422965&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422964&type= 4.99533367 2.96333337 表示N型重掺杂（与 <math id="M4"><msub><mrow><mi mathvariant="normal">N</mi></mrow><mrow><mi mathvariant="normal">P</mi><mi mathvariant="normal">P</mi><mi mathvariant="normal">D</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422967&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422966&type= 6.94266701 3.64066648 的掺杂浓度大小不同）， <math id="M5"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">g</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422969&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422968&type= 4.14866638 3.64066648 表示TG管的栅极控制电压， <math id="M6"><mi mathvariant="normal">V</mi><mi mathvariant="normal">P</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422971&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422970&type= 5.16466665 2.70933342 表示TG管势垒大小。当TG管开启时，辐射前后浮动扩散（floating diffusion，FD）节点的电压分别为 <math id="M7"><mi mathvariant="normal">V</mi><mo>_</mo><mi mathvariant="normal">L</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422973&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422972&type= 7.11199999 3.13266659 和 <math id="M8"><mi mathvariant="normal">V</mi><mo>_</mo><msub><mrow><mi mathvariant="normal">L</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422975&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422974&type= 8.29733276 4.06400013 ；辐射前后FD节点的复位电压分别为 <math id="M9"><mi mathvariant="normal">V</mi><mo>_</mo><mi mathvariant="normal">H</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422977&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422976&type= 7.53533316 3.13266659 和 <math id="M10"><mi mathvariant="normal">V</mi><mo>_</mo><msub><mrow><mi mathvariant="normal">H</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422979&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422978&type= 8.72066689 4.06400013 ; <math id="M11"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">s</mi><mn mathvariant="normal">2</mn></mrow></msub><mo>=</mo><mi mathvariant="normal">V</mi><mo>_</mo><mi mathvariant="normal">H</mi><mo>-</mo><mi mathvariant="normal">V</mi><mo>_</mo><mi mathvariant="normal">L</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422981&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422980&type= 29.80266571 4.06400013 和 <math id="M12"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">s</mi><mn mathvariant="normal">1</mn></mrow></msub><mo>=</mo><mi mathvariant="normal">V</mi><mo>_</mo><msub><mrow><mi mathvariant="normal">H</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub><mo>-</mo><mi mathvariant="normal">V</mi><mo>_</mo><msub><mrow><mi mathvariant="normal">L</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422983&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422982&type= 32.17333221 4.06400013 分别表示辐射前后FD节点电压摆幅； <math id="M13"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">s</mi></mrow></msub><mo>=</mo><mi mathvariant="normal">V</mi><mo>_</mo><mi mathvariant="normal">H</mi><mo>-</mo><mi mathvariant="normal">V</mi><mo>_</mo><msub><mrow><mi mathvariant="normal">L</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422985&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422984&type= 29.97199821 4.06400013 是固定斜坡情况下读出电路采集到的信号摆幅。若辐射前后像元结构电路满阱容量（full well capacity，FWC）不发生变化，那么由满阱容量决定的信号摆幅也是不变的，因此 <math id="M14"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">s</mi><mn mathvariant="normal">1</mn></mrow></msub><mo>=</mo><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">s</mi><mn mathvariant="normal">2</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422987&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422986&type= 15.15533447 3.64066648 。像元结构电路信号摆幅不变时，由像元内MOS管阈值电压减小引起的信号摆幅变化就成为决定因素，因此受TID效应影响和RST复位管阈值电压减小引起的变化量为 <math id="M15"><mi mathvariant="normal">V</mi><mo>_</mo><msub><mrow><mi mathvariant="normal">L</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub><mo>-</mo><mi mathvariant="normal">V</mi><mo>_</mo><mi mathvariant="normal">L</mi><mo>=</mo><mi>m</mi><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">t</mi><mi mathvariant="normal">h</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422989&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422988&type= 32.85066605 4.06400013 ，其中， <math id="M16"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">t</mi><mi mathvariant="normal">h</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422991&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422990&type= 4.74133348 3.64066648 表示典型情况下MOS管的阈值电压， <math id="M17"><mi>m</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422993&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422992&type= 2.79399991 2.62466669 是介于0~1之间的比例因子。当采用固定的斜坡参考电压进行采集时，该变化量的一部分信号会在斜坡参考电压范围之外，使得有效信号丢失，从而导致ADC动态范围减小及信噪比降低。 1.2.2　像元输出摆幅对单斜式ADC有效位数的影响 3 图2 图2 为空间辐射环境下受TID效应影响时，像元结构电路输出信号摆幅变化示意图。 图2 图2 中， <math id="M18"><mi mathvariant="normal">Δ</mi><msub><mrow><mi>V</mi></mrow><mrow><mn mathvariant="normal">0</mn></mrow></msub><mo>=</mo><mi mathvariant="normal">V</mi><mo>_</mo><msub><mrow><mi mathvariant="normal">L</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub><mo>-</mo><mi mathvariant="normal">V</mi><mo>_</mo><mi mathvariant="normal">L</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422995&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422994&type= 31.83466721 4.06400013 ， <math id="M19"><mi mathvariant="normal">Δ</mi><msub><mrow><mi>V</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub><mo>=</mo><mi mathvariant="normal">V</mi><mo>_</mo><msub><mrow><mi mathvariant="normal">H</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub><mo>-</mo><mi mathvariant="normal">V</mi><mo>_</mo><mi mathvariant="normal">H</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422997&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422996&type= 32.76599884 4.06400013 分别表示像元结构电路受TID效应影响时,输出信号下限和上限的最大变化量；不受TID效应影响时，像元结构电路输出最小电压值和最大电压值分别为 <math id="M20"><mi mathvariant="normal">V</mi><mo>_</mo><mi mathvariant="normal">L</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422999&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3422998&type= 7.11199999 3.13266659 和 <math id="M21"><mi mathvariant="normal">V</mi><mo>_</mo><mi mathvariant="normal">H</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423001&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423000&type= 7.53533316 3.13266659 ，输出摆幅为 <math id="M22"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">s</mi><mn mathvariant="normal">2</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423003&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423002&type= 4.99533367 3.64066648 ；受到TID效应影响时，像元结构电路输出最小电压值和最大电压值分别为 <math id="M23"><mi mathvariant="normal">V</mi><mo>_</mo><msub><mrow><mi mathvariant="normal">L</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423005&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423004&type= 8.29733276 4.06400013 和 <math id="M24"><mi mathvariant="normal">V</mi><mo>_</mo><msub><mrow><mi mathvariant="normal">H</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423007&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423006&type= 8.72066689 4.06400013 ，输出摆幅为 <math id="M25"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">s</mi><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423009&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423008&type= 4.99533367 3.64066648 。 为了覆盖最差情况下的像元输出摆幅，若使用固定的斜坡参考电压， <math id="M26"><mi mathvariant="normal">V</mi><mo>_</mo><msub><mrow><mi mathvariant="normal">H</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423014&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423013&type= 8.72066689 4.06400013 电压值的选择比正常值大 <math id="M27"><mi mathvariant="normal">Δ</mi><msub><mrow><mi>V</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423016&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423015&type= 6.68866634 3.64066648 ， <math id="M28"><mi mathvariant="normal">V</mi><mo>_</mo><msub><mrow><mi mathvariant="normal">L</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423018&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423017&type= 8.29733276 4.06400013 电压值的选择比正常值大 <math id="M29"><mi mathvariant="normal">Δ</mi><msub><mrow><mi>V</mi></mrow><mrow><mn mathvariant="normal">0</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423020&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423019&type= 6.68866634 3.64066648 。这种情况下 <math id="M30"><mi mathvariant="normal">Δ</mi><msub><mrow><mi>V</mi></mrow><mrow><mn mathvariant="normal">0</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423022&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423021&type= 6.68866634 3.64066648 与 <math id="M31"><mi mathvariant="normal">Δ</mi><msub><mrow><mi>V</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423024&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423023&type= 6.68866634 3.64066648 值的选取非常关键，选取的值过大会使单斜ADC的量化噪声增大，选取的值过小反而丢失信号。斜坡参考电压固定不变情况下，ADC的量化噪声RMS(V)、实际信噪比 <math id="M32"><mi mathvariant="normal">S</mi><mi mathvariant="normal">N</mi><msub><mrow><mi mathvariant="normal">R</mi></mrow><mrow><mi mathvariant="normal">a</mi><mi mathvariant="normal">c</mi><mi mathvariant="normal">t</mi><mi mathvariant="normal">u</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">l</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423026&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423025&type= 12.53066635 3.72533321 和有效位数ENOB分别为 <math display="block" id="M33"><mi mathvariant="normal">R</mi><mi mathvariant="normal">M</mi><mi mathvariant="normal">S</mi><mo>=</mo><mfrac><mrow><mi mathvariant="normal">F</mi><mi mathvariant="normal">S</mi><mi mathvariant="normal">R</mi></mrow><mrow><msup><mrow><mn mathvariant="normal">2</mn></mrow><mrow><mi>N</mi></mrow></msup><mroot><mrow><mn mathvariant="normal">12</mn></mrow><mrow/></mroot></mrow></mfrac></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423028&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423027&type= 25.73866653 8.55133343 其中，FSR(V)是斜坡参考电压的满量程范围，即下文提到的参考电压 <math id="M34"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">H</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423030&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423029&type= 7.78933334 3.64066648 和 <math id="M35"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">L</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423032&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423031&type= 7.53533316 3.64066648 之间的满摆幅； N 为ADC的位数。 <math display="block" id="M36"><mi mathvariant="normal">S</mi><mi mathvariant="normal">N</mi><msub><mrow><mi mathvariant="normal">R</mi></mrow><mrow><mi mathvariant="normal">a</mi><mi mathvariant="normal">c</mi><mi mathvariant="normal">t</mi><mi mathvariant="normal">u</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">l</mi></mrow></msub><mo>=</mo><mfrac><mrow><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">o</mi><mi mathvariant="normal">u</mi><mi mathvariant="normal">t</mi><mo>_</mo><mi mathvariant="normal">r</mi><mi mathvariant="normal">m</mi><mi mathvariant="normal">s</mi></mrow></msub></mrow><mrow><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">n</mi><mi mathvariant="normal">o</mi><mi mathvariant="normal">i</mi><mi mathvariant="normal">s</mi><mi mathvariant="normal">e</mi></mrow></msub></mrow></mfrac><mo>=</mo><mfrac><mrow><mo stretchy="false">(</mo><mi mathvariant="normal">F</mi><mi mathvariant="normal">S</mi><mi mathvariant="normal">R</mi><mo>-</mo><mi mathvariant="normal">Δ</mi><msub><mrow><mi>V</mi></mrow><mrow><mn mathvariant="normal">0</mn></mrow></msub><mo stretchy="false">)</mo><mo>/</mo><mn mathvariant="normal">2</mn><mroot><mrow><mn mathvariant="normal">2</mn></mrow><mrow/></mroot></mrow><mrow><mi mathvariant="normal">R</mi><mi mathvariant="normal">M</mi><mi mathvariant="normal">S</mi></mrow></mfrac></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423034&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423033&type= 66.63265991 8.97466660 <math id="M37"><mi mathvariant="normal">S</mi><mi mathvariant="normal">N</mi><msub><mrow><mi mathvariant="normal">R</mi></mrow><mrow><mi mathvariant="normal">a</mi><mi mathvariant="normal">c</mi><mi mathvariant="normal">t</mi><mi mathvariant="normal">u</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">l</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423036&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423035&type= 12.53066635 3.72533321 本身为一比值，无量纲，ADC中为了表达方便，通过取20lg（ <math id="M38"><mrow><mrow><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">o</mi><mi mathvariant="normal">u</mi><mi mathvariant="normal">t</mi><mo>_</mo><mi mathvariant="normal">r</mi><mi mathvariant="normal">m</mi><mi mathvariant="normal">s</mi></mrow></msub></mrow><mo>/</mo><mrow><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">n</mi><mi mathvariant="normal">o</mi><mi mathvariant="normal">i</mi><mi mathvariant="normal">s</mi><mi mathvariant="normal">e</mi></mrow></msub></mrow></mrow></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423038&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423037&type= 19.30399895 3.97933340 ）将其转换为对数的形式，单位为分贝（dB）。其中， <math id="M39"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">o</mi><mi mathvariant="normal">u</mi><mi mathvariant="normal">t</mi><mo>_</mo><mi mathvariant="normal">r</mi><mi mathvariant="normal">m</mi><mi mathvariant="normal">s</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423040&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423039&type= 9.73666668 3.64066648 （V)表示输入信号的有效值（以正弦波为例，理想情况下该值为FSR/2 <math id="M40"><mroot><mrow><mn mathvariant="normal">2</mn></mrow><mrow/></mroot></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423042&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423041&type= 5.58799982 3.97933340 ）； <math id="M41"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">n</mi><mi mathvariant="normal">o</mi><mi mathvariant="normal">i</mi><mi mathvariant="normal">s</mi><mi mathvariant="normal">e</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423044&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423043&type= 7.28133297 3.64066648 (V)表示ADC所有噪声的均方根值,仅考虑量化噪声对ADC有效位数的影响时，其值等于RMS。 <math display="block" id="M42"><mi mathvariant="normal">E</mi><mi mathvariant="normal">N</mi><mi mathvariant="normal">O</mi><mi mathvariant="normal">B</mi><mo>=</mo><mfrac><mrow><mi mathvariant="normal">S</mi><mi mathvariant="normal">N</mi><msub><mrow><mi mathvariant="normal">R</mi></mrow><mrow><mi mathvariant="normal">a</mi><mi mathvariant="normal">c</mi><mi mathvariant="normal">t</mi><mi mathvariant="normal">u</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">l</mi></mrow></msub><mo>-</mo><mn mathvariant="normal">1.76</mn></mrow><mrow><mn mathvariant="normal">6.02</mn></mrow></mfrac></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423046&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423045&type= 40.55533218 7.36599970 由（1)~(3)式可知，若 <math id="M43"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">s</mi><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423048&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423047&type= 4.99533367 3.64066648 和 <math id="M44"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">s</mi><mn mathvariant="normal">2</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423050&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423049&type= 4.99533367 3.64066648 下限电压变化所引起的变化量 <math id="M45"><mi mathvariant="normal">Δ</mi><msub><mrow><mi>V</mi></mrow><mrow><mn mathvariant="normal">0</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423052&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423051&type= 6.68866634 3.64066648 为200 mV，FSR满量程范围为0.8 V时，ADC的有效位数会从12位降低至11.58位，降低了0.42位。从上述分析可知，斜坡参考电压范围的选取直接影响单斜式ADC的有效位数，进而影响其整体性能。 综合上述分析，为提升单斜式ADC的整体性能，使图像传感器具有良好的成像质量，本文提出一种用于CMOS图像传感器的高精度抗辐射自适应斜坡产生电路设计方法，以期通过该方法提高斜坡电路的空间辐射环境适应性和易用性，同时降低单斜ADC的量化噪声，提高单斜式ADC的有效位数和CMOS图像传感器的信噪比，进而提高ADC的精度，提升CMOS图像传感器的成像质量。 2　 电路设计 1 从1.2节对辐射引起的像元输出变化的分析可知，在辐射环境下，需要采取相应的措施来解决像元输出信号摆幅动态变化的问题。针对该问题，本文提出利用dummy像元获取输出信号摆幅上下限，然后根据得到的参考电压产生相应的斜坡信号。下面分别从斜坡参考电压产生电路、高精度自适应斜坡产生电路及辐射加固3个方面进行分析和设计。 2.1　斜坡参考电压产生电路设计 2 由1.1节可知，CMOS图像传感器工作在空间辐射环境时，由于受到空间环境中各种高能粒子的影响，图像传感器像元电路的功能退化，输出的像元信号范围发生变化。为此，本文设计了能够表征有效像元阵列输出信号摆幅的上下限参考电压产生电路。 图3 图3 是利用有效像元阵列四周的dummy像元获得的自适应斜坡产生电路参考电压 <math id="M46"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">H</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423054&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423053&type= 7.78933334 3.64066648 和 <math id="M47"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">L</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423056&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423055&type= 7.53533316 3.64066648 的示意图。 图3 图3 中，中间部分（黄色区域）的电路表示有效像元阵列，有效像元阵列四周的电路表示dummy像元。一般，CMOS图像传感器为了保证有效像元电路的性能，会在有效像元阵列四周放置dummy像元，dummy像元在电路结构、功能和性能等方面与有效像元是相同的，只起匹配作用。 图3 图3 中顶部和底部的dummy像元分别用来产生斜坡参考电压 <math id="M48"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">H</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423061&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423060&type= 7.78933334 3.64066648 和 <math id="M49"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">L</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423063&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423062&type= 7.53533316 3.64066648 。由于 <math id="M50"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">H</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423065&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423064&type= 7.78933334 3.64066648 和 <math id="M51"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">L</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423067&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423066&type= 7.53533316 3.64066648 均是利用dummy像元产生，因此没有额外增加芯片版图面积。 图4 图4 是通过采集dummy像元输出信号获得 <math id="M52"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">H</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423069&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423068&type= 7.78933334 3.64066648 和 <math id="M53"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">L</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423071&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423070&type= 7.53533316 3.64066648 的原理图。其中，VDD表示电源电压，TX表示TG管栅极控制信号，RST表示复位管栅极控制信号，RS表示行选开关控制信号，COUNTER表示12 bit数字计数器，CLK表示时钟信号。 图4 图4 中左侧电路为dummy像元电路（dummy pixel unit），中间部分为12 bit单斜式ADC（single-slope ADC，SS-ADC）电路，右侧为6 bit DAC电路。 如 图4 图4 所示，斜坡参考电压产生电路工作过程如下：采用最大强度光照射像元阵列，当开关 <math id="M54"><msub><mrow><mi>S</mi></mrow><mrow><mi mathvariant="normal">a</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423076&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423075&type= 3.21733332 3.64066648 闭合 <math id="M55"><msub><mrow><mi>S</mi></mrow><mrow><mi mathvariant="normal">b</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423078&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423077&type= 3.30199981 3.64066648 打开时，首先由12 bit 单斜式ADC采集有效像元阵列顶部的dummy像元输出电压，然后通过时钟信号扫描的方式驱动右侧6 bit DAC电路输出对应的参考电压，当参考电压与dummy像元输出电压相等时，将12 bit SS-ADC输出的数字码存储在寄存器LATCH_H中，再通过12 bit DAC将寄存器LATCH_H中的数字量转换为模拟量，最后得到斜坡参考电压 <math id="M56"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">L</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423080&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423079&type= 7.53533316 3.64066648 ；在无光照情况下，当开关 <math id="M57"><msub><mrow><mi>S</mi></mrow><mrow><mi mathvariant="normal">b</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423082&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423081&type= 3.30199981 3.64066648 闭合 <math id="M58"><msub><mrow><mi>S</mi></mrow><mrow><mi mathvariant="normal">a</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423084&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423083&type= 3.21733332 3.64066648 打开时，同样的原理，通过SS-ADC采集有效像元阵列底部的dummy像元输出电压可以得到斜坡参考电压 <math id="M59"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">H</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423086&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423085&type= 7.78933334 3.64066648 。由于12 bit DAC输出的参考电压 <math id="M60"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">H</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423088&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423087&type= 7.78933334 3.64066648 及 <math id="M61"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">L</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423090&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423089&type= 7.53533316 3.64066648 驱动能力较弱，因此需要在 <math id="M62"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">H</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423092&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423091&type= 7.78933334 3.64066648 和 <math id="M63"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">L</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423094&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423093&type= 7.53533316 3.64066648 后面增加一级模拟缓冲器驱动电路(非电路主要部分，故未在 图4 图4 中给出)，以提高斜坡参考电压的驱动能力。 2.2　高精度自适应斜坡产生电路设计 2 通过 图4 图4 所示电路动态采集dummy像元输出可获得相应的斜坡参考电压，利用 图5 图5 所示高精度自适应斜坡产生电路可以动态地调整斜坡信号斜率，使得斜坡输出信号跟随斜坡参考电压的变化而动态地改变，从而提升单斜式ADC的信噪比，改善CMOS图像传感器的成像质量。所要产生的斜坡信号斜率为 <math display="block" id="M64"><msub><mrow><mi>K</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">m</mi><mi mathvariant="normal">p</mi></mrow></msub><mo>=</mo><mfrac><mrow><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">H</mi></mrow></msub><mo>-</mo><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">L</mi></mrow></msub></mrow><mrow><msub><mrow><mi>t</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">m</mi><mi mathvariant="normal">p</mi></mrow></msub></mrow></mfrac></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423096&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423095&type= 33.44333649 7.95866680 其中， <math id="M65"><msub><mrow><mi>t</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">m</mi><mi mathvariant="normal">p</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423098&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423097&type= 5.33399963 3.55599999 (μs)是斜坡信号的积分时间。 图5 图5 中，开关 <math id="M66"><msub><mrow><mi>M</mi></mrow><mrow><mn mathvariant="normal">0</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423103&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423102&type= 4.57200003 3.64066648 和 <math id="M67"><msub><mrow><mi>M</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423105&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423104&type= 4.57200003 3.64066648 控制斜坡模式切换，分别实现产生下降斜坡和上升斜坡信号的功能；开关 <math id="M68"><msub><mrow><mi>S</mi></mrow><mrow><mn mathvariant="normal">0</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423107&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423106&type= 3.38666677 3.64066648 和 <math id="M69"><msub><mrow><mi>S</mi></mrow><mrow><mn mathvariant="normal">0</mn></mrow></msub><mi mathvariant="normal">'</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423109&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423108&type= 4.31799984 4.23333359 在斜坡产生电路初始化阶段控制PMOS（P型金属氧化物半导体，P-type metal oxide semiconductor）晶体管（ <math id="M70"><mi mathvariant="normal">P</mi><msub><mrow><mi mathvariant="normal">M</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423111&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423110&type= 6.94266701 3.64066648 ）或NMOS（N型金属氧化物半导体，N-type metal oxide semiconductor）晶体管（ <math id="M71"><mi mathvariant="normal">N</mi><msub><mrow><mi mathvariant="normal">M</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423113&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423112&type= 7.45066643 3.64066648 ）漏极初始电压；开关 <math id="M72"><msub><mrow><mi>S</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423115&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423114&type= 3.38666677 3.64066648 、 <math id="M73"><msub><mrow><mi>S</mi></mrow><mrow><mn mathvariant="normal">2</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423117&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423116&type= 3.38666677 3.64066648 及 <math id="M74"><msub><mrow><mi>S</mi></mrow><mrow><mn mathvariant="normal">3</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423119&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423118&type= 3.38666677 3.64066648 是斜坡信号进行周期校正时的切换开关。电容 <math id="M75"><msub><mrow><mi>C</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423121&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423120&type= 3.72533321 3.64066648 用来采集运算放大器（简称“运放”） <math id="M76"><msub><mrow><mi>A</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423123&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423122&type= 4.06400013 3.72533321 的输入失调电压； <math id="M77"><msub><mrow><mi>C</mi></mrow><mrow><mi mathvariant="normal">f</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423125&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423124&type= 3.38666677 3.64066648 是斜坡信号进行周期校正时的采样电容； <math id="M78"><msub><mrow><mi>C</mi></mrow><mrow><mn mathvariant="normal">2</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423127&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423126&type= 3.72533321 3.64066648 是第一级积分器的积分电容； <math id="M79"><msub><mrow><mi>C</mi></mrow><mrow><mn mathvariant="normal">3</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423129&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423128&type= 3.72533321 3.64066648 是第二级积分器的积分电容。整个自适应斜坡产生电路是一个离散负反馈控制系统，由两个跨导电容（ <math id="M80"><msub><mrow><mi>g</mi></mrow><mrow><mi mathvariant="normal">m</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423131&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423130&type= 3.64066648 4.40266657 -C）积分器组成，其中第一级积分器由 <math id="M81"><msub><mrow><mi>A</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423133&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423132&type= 4.06400013 3.72533321 和 <math id="M82"><msub><mrow><mi>C</mi></mrow><mrow><mn mathvariant="normal">2</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423135&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423134&type= 3.72533321 3.64066648 构成，其输出信号控制 <math id="M83"><mi mathvariant="normal">P</mi><msub><mrow><mi mathvariant="normal">M</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423137&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423136&type= 6.94266701 3.64066648 或 <math id="M84"><mi mathvariant="normal">N</mi><msub><mrow><mi mathvariant="normal">M</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423139&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423138&type= 7.45066643 3.64066648 的栅极电压，产生相应的积分电流；第二级积分器由 <math id="M85"><msub><mrow><mi>A</mi></mrow><mrow><mn mathvariant="normal">2</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423141&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423140&type= 4.06400013 3.72533321 和 <math id="M86"><msub><mrow><mi>C</mi></mrow><mrow><mn mathvariant="normal">3</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423143&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423142&type= 3.72533321 3.64066648 构成，其输出信号即为所产生的斜坡信号 <math id="M87"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">m</mi><mi mathvariant="normal">p</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423145&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423144&type= 7.28133297 3.64066648 。 单斜式ADC斜坡产生电路时钟信号采用互不交叠时钟设计，其中， <math id="M88"><msub><mrow><mi>S</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423147&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423146&type= 3.38666677 3.64066648 由时钟信号 <math id="M89"><msub><mrow><mi>ϕ</mi></mrow><mrow><mn mathvariant="normal">1</mn></mrow></msub></math> 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http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423198&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423197&type= 29.80266571 9.14400005 2.3　辐射加固设计 2 空间辐射环境对CMOS图像传感器整体功能和性能会产生很大影响，因此必须对CMOS图像传感器各个功能电路模块进行辐射加固设计。一般来说，辐射加固设计可以分为3个方面 [ 16 16 , 18 18 , 19 19 , 20 20 ] ：1) 电路级辐射加固设计；2） 器件级辐射加固设计；3） 工艺级辐射加固设计。 本文重点针对TID效应对自适应斜坡产生电路造成的影响进行辐射加固设计。由于dummy像元的输出是高精度自适应斜坡产生电路的参考电压，因此将dummy像元结构电路作为斜坡产生电路的一部分，由于dummy像元电路采用的是应用广泛且成熟的4T-APS像元结构，不涉及新型器件级结构辐射加固设计，因此下面仅从工艺级和电路级两个方面对自适应斜坡产生电路进行辐射加固设计和分析。 1） 工艺级辐射加固设计。本文提出的电路基于55 nm工艺，其中，数字电路部分采用的最小沟道长度为55 nm，模拟电路部分采用的最小沟道长度为0.35 <math id="M113"><mi mathvariant="normal">μ</mi><mi mathvariant="normal">m</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423200&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423199&type= 4.99533367 3.47133350 。由于达到100 nm以下工艺节点时，体硅CMOS器件的SiO 2 栅氧厚度变得较薄, TID对数字电路的阈值电压影响较小，因此不需要对数字电路进行抗TID加固设计。但是TID效应所引起的MOS管阈值电压漂移对模拟电路部分影响较大 [ 12 12 ] ，因此需要对高性能模拟电路部分进行设计加固。 2） 电路级辐射加固设计。从4个方面对dummy像元结构电路和自适应斜坡产生电路部分进行辐射加固设计： ① 采用PPD结构，通过在PD管N + 区表面上覆盖一层高浓度P + 掺杂注入，可以极大降低PD管表面漏电； ② 利用负电压驱动TG管，在负压（-2 ~-0.5 V）驱动时可以有效降低TG管自身漏电，从而减小由TG管贡献的暗电流； ③ 像元结构电路内MOS管采用环栅结构，可有效降低由条形栅结构引起的边缘漏电； ④ 对于dummy像元结构中尾电流偏置电路及自适应斜坡电路中的NMOS和PMOS管采用保护环设计，以防止单粒子闩锁。 3　 仿真结果和分析 1 为了验证本文提出电路的有效性，本节将从TID效应对源极跟随器SF输出的影响、自适应斜坡产生电路的性能及斜坡信号非线性特性等方面进行仿真实验及分析。 3.1　TID效应对源极跟随器输出的影响 2 1.2.1节对像元电路受TID的影响进行了定性分析，本节将对上文提出的相关电路进行定量仿真验证。由于4T-APS像元受TID效应影响时，dummy像元电路内复位管RST和源极跟随器SF中的氧化层中会累积陷阱空穴，从而使MOS管的阈值电压发生变化 [ 21 21 ] ，因此本文通过改变像元电路MOS管阈值电压的方式来模拟TID效应对像元电路SF输出的影响。 为分析在TID效应影响情况下，MOS管阈值电压漂移对SF输出电压的影响，比较以下3种情况下SF输出电压随其输入电压的变化： 1） 典型情况下（温度为27 °C，典型工艺角条件，下同）MOS管阈值电压为典型值（由于不同工艺开发包（process design kit，PDK）下MOS晶体管的阈值电压都不完全相同，但是不同PDK下阈值电压引起的输出摆幅变化趋势是一致的，故从结论的通用性考虑，本文未给出特定工艺下阈值电压的典型值）； 2） 典型情况下MOS管阈值电压下降100 mV（相较于典型值）； 3） 典型情况下阈值电压下降200 mV（相较于典型值）。 通过比较3种情形下像元电路SF输出电压的变化，可以定量评估TID对SF输出的影响程度，进而针对该影响提出有效的解决方法。 仿真实验步骤：首先，修改PDK工艺模型库中MOS管阈值电压（分别对应上述3种情形），然后利用Cadence公司的Spectre仿真验证工具进行仿真实验。 仿真实验结果如 图7 图7 所示， 图7 图7 中 V in 表示SF输入电压， V out 表示SF的输出电压值。为了进一步深入定量分析和对比3种不同阈值电压下SF输出电压的变化范围，对 图7 图7 的仿真结果进行数据处理得到 表1 表1 。 序号 仿真条件 SF管输出电压下限值/V SF管输出电压上限值/V SF管输出电压摆幅/V 1 典型情况下阈值电压为典型值 0.225 2.014 1.789 2 典型情况下阈值电压下降100 mV 0.299 2.095 1.796 3 典型情况下阈值电压下降200 mV 0.374 2.176 1.802 从 图7 图7 和 表1 表1 中可以看出，TID效应引起的MOS管阈值电压减小会使得SF输出电压上下限均呈增大趋势。相较于MOS管阈值电压典型值，当阈值电压降低200 mV时，SF输出电压下限值的变化量为0.149 V；SF输出电压上限值变化量为0.162 V；SF输出电压摆幅的变化比较小，其变化量仅为0.013 V。从仿真实验结果可知，TID对像元输出摆幅的影响较大，而像元输出摆幅决定着单斜式ADC的斜坡参考电压范围，因此，需要通过动态获取所需的斜坡参考电压来自适应校正斜坡信号，才可以避免采用固定斜坡参考电压的传统方法带来的单斜式ADC量化噪声较大和有效位数较低的问题。 3.2　高精度自适应斜坡产生电路自适应校正性能仿真 2 下面对本文提出的高精度抗辐射自适应斜坡产生电路的性能进行测试，通过动态修正斜坡产生电路参考电压，验证本文电路中斜坡信号可随斜坡参考电压的变化而自动校正的功能。使用Cadence公司的仿真工具Spectre进行仿真实验，得到如 图8 图8 所示的自适应斜坡信号随参考电压变化波形。 图8 图8 （a）和 图8 图8 （b）分别表示自适应斜坡产生电路随斜坡参考电压变化而产生的自适应下降斜坡信号和自适应上升斜坡信号。分析 图8 图8 （a）中的自适应上升斜坡信号可知，在时刻2 ms时，斜坡参考电压上限 <math id="M114"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">H</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423210&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423209&type= 7.78933334 3.64066648 由2.700 V变为2.850 V，斜坡参考电压下限 <math id="M115"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mo>_</mo><mi mathvariant="normal">L</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423212&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423211&type= 7.53533316 3.64066648 由1.400 V变为1.549 V，此时自适应斜坡产生电路产生的斜坡信号 <math id="M116"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">m</mi><mi 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http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423217&type= 7.53533316 3.64066648 由1.549 V变为1.300 V；从时刻3 ms到3.2 ms，即经过200 μs（文中设计的斜坡信号周期是40 μs时，约经过5个周期的自适应修正）后斜坡信号 <math id="M119"><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">m</mi><mi mathvariant="normal">p</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423220&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423219&type= 7.28133297 3.64066648 的范围也动态地变为2.406 ~1.266 V。 与 图8 图8 （a）的分析类似，从 图8 图8 （b）的仿真结果可知，自适应上升斜坡信号也会随着斜坡参考电压的变化而动态地校正斜坡输出信号，能够满足CMOS图像传感器中单斜式ADC对上升斜坡的功能要求。 从 图8 图8 （a）和 图8 图8 （b）可知，自适应斜坡信号首次达到稳定（从0 μs到200 μs期间）需要5~6个斜坡信号周期，自适应斜坡信号的稳定时间跟采样电容 <math id="M120"><msub><mrow><mi>C</mi></mrow><mrow><mi mathvariant="normal">f</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423222&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423221&type= 3.38666677 3.64066648 和反馈电容 <math id="M121"><msub><mrow><mi>C</mi></mrow><mrow><mn mathvariant="normal">2</mn></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423224&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423223&type= 3.72533321 3.64066648 的比例及斜坡信号周期有关，若自适应斜坡信号周期减小，那么相应达到稳定状态的时间就会减小。自适应斜坡产生电路在实际使用时一般会选择在系统上电初始化完成后的一段时间内使其达到稳定状态，因此正常工作时不会因为稳定时间的问题影响单斜式ADC的速度。自适应斜坡信号在受到空间辐射、PVT等因素影响时，在首次达到稳定后，通过负反馈调节能够在2个斜坡信号周期时间内达到稳定状态。 3.3　斜坡信号非线性特性仿真 2 对本文提出电路的周期性斜坡信号进行非线性特性测试，该测试最主要的2个参数是微分非线性（differential nonlinearity，DNL）和积分非线性（integral nonlinearity，INL），单位均为LSB（least significant bit，最低有效位），其中INL是对非线性特性影响最大的参数。 <math display="block" id="M122"><mi mathvariant="normal">D</mi><mi mathvariant="normal">N</mi><mi mathvariant="normal">L</mi><mo>=</mo><mfenced open="|" close="|" separators="|"><mrow><mfrac><mrow><msub><mrow><mi>V</mi></mrow><mrow><mi>D</mi><mo>+</mo><mn mathvariant="normal">1</mn></mrow></msub><mo>-</mo><msub><mrow><mi>V</mi></mrow><mrow><mi>D</mi></mrow></msub></mrow><mrow><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">L</mi><mi mathvariant="normal">S</mi><mi mathvariant="normal">B</mi><mo>-</mo><mi mathvariant="normal">I</mi><mi mathvariant="normal">D</mi><mi mathvariant="normal">E</mi><mi mathvariant="normal">A</mi><mi mathvariant="normal">L</mi></mrow></msub></mrow></mfrac><mo>-</mo><mn mathvariant="normal">1</mn></mrow></mfenced><mo>，</mo><mn mathvariant="normal">0</mn><mo><</mo><mtext> </mtext><mi>D</mi><mtext> </mtext><mo><</mo><msup><mrow><mn mathvariant="normal">2</mn></mrow><mrow><mi>N</mi></mrow></msup><mo>-</mo><mn mathvariant="normal">2</mn></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423226&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423225&type= 69.93466949 9.05933285 <math display="block" id="M123"><mi mathvariant="normal">I</mi><mi mathvariant="normal">N</mi><mi mathvariant="normal">L</mi><mo>=</mo><mfenced open="|" close="|" separators="|"><mrow><mfrac><mrow><msub><mrow><mi>V</mi></mrow><mrow><mi>D</mi></mrow></msub><mo>-</mo><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">Z</mi><mi mathvariant="normal">E</mi><mi mathvariant="normal">R</mi><mi mathvariant="normal">O</mi></mrow></msub></mrow><mrow><msub><mrow><mi>V</mi></mrow><mrow><mi mathvariant="normal">L</mi><mi mathvariant="normal">S</mi><mi mathvariant="normal">B</mi><mo>-</mo><mi mathvariant="normal">I</mi><mi mathvariant="normal">D</mi><mi mathvariant="normal">E</mi><mi mathvariant="normal">A</mi><mi mathvariant="normal">L</mi></mrow></msub></mrow></mfrac><mo>-</mo><mi>D</mi></mrow></mfenced><mo>,</mo><mn mathvariant="normal">0</mn><mo><</mo><mi>D</mi><mo><</mo><msup><mrow><mn mathvariant="normal">2</mn></mrow><mrow><mi>N</mi></mrow></msup><mo>-</mo><mn mathvariant="normal">1</mn></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423228&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=3423227&type= 66.88667297 9.05933285 其中， N 表示ADC的位数， D 表示ADC的数字输出码，V LSB-IDEAL 表示相邻数字码值之间的理想间隔电压，V ZERO 表示数字码输出全零时对应的最小模拟输入电压。 首先对产生的斜坡信号进行4 096点离散采样，然后根据（7）式和（8）式，利用MATLAB软件，对采样得到的4 096点数据的DNL和INL进行计算和分析，结果如 图9 图9 所示。 ADC中DNL的理想设计要求是其值介于±0.5 LSB之间，理论上就不会引起引起丢失码现象 [ 22 22 ] 。从 图9 图9 可知，该斜坡信号的DNL最小值和最大值分别为-0.026 LSB和0.163 LSB,其值介于±0.5 LSB之间，满足设计要求。INL方面，按照本文中图像传感器非线性小于0.05%的要求，对于12位精度ADC 而言，只要INL不大于0.05%×4 096=2.048 LSB就可以满足设计要求。由 图9 图9 可知，在整个动态响应范围内斜坡信号的INL最大值低至1.152 LSB，满足设计要求。 3.4　性能对比 2 从斜坡信号产生原理、斜坡信号校正技术及易用性等方面，将本文提出的电路与文献[3,5,9,23]中的斜坡产生电路进行性能对比，结果如 表2 表2 所示。 性能参数 本文 文献[ 3 3 ] 文献[ 5 5 ] 文献[ 9 9 ] 文献[ 23 23 ] 工艺/nm 350 180 350 180 180 斜坡产生原理 电流源对 电容充放电 电流源对 电容充放电 电流源对 电容充放电 电流源对电容充放电（开关电容实现） 电流源对 电容充放电 斜坡校正技术 dummy像元+负反馈 负反馈 负反馈 无 无 可编程性及易用性 高 中等 中等 低 低 斜坡精度提升/bit 0.42 无 无 无 无 辐射损伤补偿 有 无 无 无 无 功耗/mA 1.58 3.4 未提 8.87 未提 从 表2 表2 可知，上述5种斜坡产生电路都是基于电流源对电容进行充放电的方法设计实现；从斜坡信号校正技术及斜坡产生电路易用性来看，与文献[3,5,9,23] 中的传统方法相比，本文方法设计的自适应斜坡产生电路能够解决因TID等因素导致的斜坡信号精度降低问题，同时具有动态修正斜坡产生电路参考电压的优点；从辐射损伤补偿方面来看，本文的斜坡产生电路采用了辐射加固设计能够满足空间任务的抗辐射需求，并且该电路模块消耗的电流仅为1.58 mA。综合上述分析，本文提出的斜坡产生电路可以满足空间任务应用对单斜式ADC斜坡产生电路高精度、抗辐射及低功耗的需求。 4　 结 语 1 本文设计的电路能够随着空间辐射环境的变化动态采集dummy像元输出，修正自适应斜坡产生电路的参考电压。与采用无斜坡参考电压修正技术和负反馈校正技术的斜坡产生电路相比，本文电路不但省去片外编程调整斜坡斜率的不便，而且提升了斜坡信号的精度，在空间辐射环境中受到TID效应时，仍然能够保持单斜式ADC的有效精度和位数，改善了CMOS图像传感器的性能。 参考文献 SHOJI K . 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Linearity Research of a CMOS Image Sensor 10.14188/j.1671-8836.2019.0055 TN492 A 1671-8836（2020）03-0304-11 LI Chuangze,HAN Benguang,HE Jie, et al .Design of High Precision Radiation-Hardened Adaptive Ramp Generator Circuit for CMOS Image Sensor [J]. J Wuhan Univ （ Nat Sci Ed ）,2020,66(3):304-314. DOI: 10.14188/j.1671-8836.2019.0055 http://dx.doi.org/10.14188/j.1671-8836.2019.0055 (Ch). LI Chuangze,HAN Benguang,HE Jie,et al.Design of High Precision Radiation-Hardened Adaptive Ramp Generator Circuit for CMOS Image Sensor [J].J Wuhan Univ（Nat Sci Ed）,2020,66(3):304-314. DOI:10.14188/j.1671-8836.2019.0055(Ch). 李闯泽,韩本光,何杰, 等.一种用于CMOS图像传感器的高精度抗辐射自适应斜坡产生电路设计[J].武汉大学学报（理学版）,2020,66(3):304-314. DOI:10.14188/j.1671-8836.2019.0055 李闯泽,韩本光,何杰, 等.一种用于CMOS图像传感器的高精度抗辐射自适应斜坡产生电路设计[J].武汉大学学报（理学版）,2020,66(3):304-314. DOI:10.14188/j.1671-8836.2019.0055 国家重大科技产业工程计划（2017ZX01006101-001）；陕西省教育厅科学研究计划（19JC029） 2019-03-24 2020-06-24 2020-09-30 武汉大学学报（理学版） 3 66