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制造、划片和封装后的读出电路芯片如图7所示。随后搭建测试平台并对多功能ROIC进行测试验证。
图8 (a)为CTIA电路在低增益模式下的积分波形图。电路在复位信号RST下降沿时复位、上升沿时开始积分。结果表明CTIA电路的积分功能正常,积分信号Vout1具有良好的线性度,输入电流超量程后输出电压摆幅达到最大,为2.18 V。
图 8 (a) CTIA电路测试结果; (b) CTIA电路噪声测试结果; (c) ALPD电路测试结果; (d) TLRF电路测试结果
Figure 8. (a) Test result of CTIA circuit; (b) Noise test result of CTIA circuit; (c) Test result of ALPD circuit; (d) Test result of TLRF circuit
随后测试电路噪声,观察零电流输入条件下的输出电压。图8 (b)是CTIA电路在低增益模式下的噪声测试结果,图中F1通道为输出电压的直方图统计结果。在积分阶段的中间时刻,示波器会检测并记录输出电压,如图中红色箭头所示,随后进行均方根运算,这样即可得到读出电路的噪声均方根。测试结果显示,低增益模式下噪声均方根为873.2 μV。
代入公式(1),可以计算出低增益模式下读出电路的动态范围DR为67.94 dB。
$$ DR = 20{\log _{10}}\left( {{{{V_{max}}} \mathord{\left/ {\vphantom {{{V_{max}}} {{V_{noise,rms}}}}} \right. } {{V_{noise,rms}}}}} \right) $$ (1) 式中:Vmax为输出摆幅;Vnoise,rms为噪声均方根。
通过同样的方法,得出高增益模式下读出电路的动态范围是60 dB。
图8 (c)为异步激光脉冲检测电路的测试结果,复位信号RST出现上升沿时输出端Out复位,一旦电流脉冲Ipulse到来,检测电路即刻输出高电平信号。测试中,异步激光脉冲检测电路可有效检测脉宽为2.2 ns、幅值为0.8 μA的脉冲电流。
图8 (d)为二维激光测距电路的测试结果。RAMP为时间幅度转换器产生的斜坡信号,Vout2是与TOF相关的模拟电压信号。图中复位信号RST变为低电平时,斜坡信号开始线性上升,Vout2跟随斜坡信号变化。一旦检测到电流脉冲,Out就变为高电平,同时Vout2停止变化,这样就能根据Vout2获得TOF,计算出被探测目标的距离信息。
测试结果显示,文中设计的多功能读出电路具有四种成像模式,能够满足特定场合下的应用需求。该多功能读出电路与国际先进产品的性能对比如表1所示。对比显示,文中设计的新型多功能ROIC具有一定先进性和实用性,同时芯片的部分性能具有一定优势。
表 1 文中电路与国际先进产品的性能对比
Table 1. Performance comparison between the circuit in this paper and international advanced products
Parameters 2011[11] 2016[12] 2021[13] This work Array size 640×512 1280×1024 128×128 64×64 Technology/μm CMOS 0.18 CMOS 0.18 CMOS 0.18 CMOS 0.35 Imaging mode Active and passive Active and passive Active and passive Active and passive Supply voltage/V − − 5 3.3 Pixel pitch/μm 15 10 50 30 Maximum frame rate Passive imaging − 350 Hz Active imaging − 640 Hz
Passive imaging − 160 Hz− Active imaging − 12.5 kHz
Passive imaging − 500 HzDynamic range/dB High gain − 49
Low gain − 70High gain − 49
low gain − 69- High gain − 60
Low gain − 68Well capacity High gain − 12 ke−
Low gain − 600 ke-High gain − 10 ke−
low gain − 1 Me−Fixed gain − 7 Me− High gain − 203 ke−
Low gain − 1.63 Me−
Design of multifunctional infrared FPA ROIC
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摘要: 主/被动成像系统具备多种成像模式,集成度高、成本低、系统运行效率高,应用前景良好。设计了一种64×64规模的多功能红外焦平面阵列读出电路,在30 μm像元中心距的限制下实现了日光标准成像、微光成像、异步激光脉冲检测和二维激光测距四种成像功能。基于TSMC 0.35 μm工艺,完成了多功能读出电路的芯片设计与流片验证。电路复用设计和像素共享架构显著降低了版图面积。CTIA的T型开关有效减小漏电流,改善了红外被动成像电路的动态范围,高增益模式下动态范围达60 dB,低增益模式下动态范围达68 dB。并且满阱电荷容量分别为203 ke−和1.63 Me−。三级push-pull运放和MOS反馈电阻使RTIA兼具高增益和小尺寸。芯片测试结果表明,电路具备主/被动成像功能,性能良好,可应用于红外焦平面激光雷达成像系统。Abstract: The active/passive imaging system has two imaging modes, with high integration, low cost, high system operation efficiency and good application prospect. A 64×64 multifunctional infrared focal plane array (FPA) readout integrated circuit (ROIC) was presented. Under the limitation of 30 μm pixel center distance, four imaging functions had been realized on this ROIC: Daylight standard imaging, low light level imaging, asynchronous laser pulse detection and two-dimensional laser ranging. Based on the TSMC 0.35 μm process, the chip design, tape out and test verification of multifunctional ROIC were completed. The layout area was significantly reduced by using circuit reuse design and pixel sharing architecture. The T-switch of CTIA was adopted to effectively reduce the leakage current and to improve the dynamic range of infrared passive imaging circuit, which made the dynamic range up to 60 dB in high gain mode and 68 dB in low gain mode. And the well capacity reached 203 ke− in high gain mode and 1.63 Me− in low gain mode. Three-stage push-pull amplifier and MOS feedback resistor made RTIA have both high gain and small layout area. The test results show that the circuit has active/passive imaging functions and good performances. It can be applied to infrared FPA lidar imaging system.
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Key words:
- ROIC /
- infrared thermal imaging /
- laser active imaging /
- active and passive imaging
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表 1 文中电路与国际先进产品的性能对比
Table 1. Performance comparison between the circuit in this paper and international advanced products
Parameters 2011[11] 2016[12] 2021[13] This work Array size 640×512 1280×1024 128×128 64×64 Technology/μm CMOS 0.18 CMOS 0.18 CMOS 0.18 CMOS 0.35 Imaging mode Active and passive Active and passive Active and passive Active and passive Supply voltage/V − − 5 3.3 Pixel pitch/μm 15 10 50 30 Maximum frame rate Passive imaging − 350 Hz Active imaging − 640 Hz
Passive imaging − 160 Hz− Active imaging − 12.5 kHz
Passive imaging − 500 HzDynamic range/dB High gain − 49
Low gain − 70High gain − 49
low gain − 69- High gain − 60
Low gain − 68Well capacity High gain − 12 ke−
Low gain − 600 ke-High gain − 10 ke−
low gain − 1 Me−Fixed gain − 7 Me− High gain − 203 ke−
Low gain − 1.63 Me− -
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