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流片后的可编程开窗读出电路芯片与640×512元短波红外InGaAs探测器芯片成功实现了倒装焊互连,得到了红外焦平面探测器组件。搭建了图10中所示的红外焦平面测试系统,主要包括直流电源、5078时序发生器、数字采集卡、黑体光源和专用PCB测试板等,对640×512规模的InGaAs红外焦平面探测器组件进行开窗功能测试。
为了验证电路的开窗功能,在焦平面组件感光区域前放置了排针进行成像,分别验证了全画幅读出、左上角开窗、正中心开窗和开窗地址溢出等几种典型应用场景下的电路功能,得到的焦平面图像如图11所示。测试结果表明,整个640×512规模的InGaAs红外焦平面探测器组件功能正常,可编程开窗数字IP核的功能符合设计预期,可以实现指定区域开窗,有效提高读出电路帧频。列级输出电路的功耗主要来自输出缓冲器,测试结果表明,文中提出的分时选通技术有效降低了功耗,其中在3.3 V电源供电下,整个组件的总功耗低于80 mW,列级功耗仅为15 mW,读出速率达到15 MHz,电路相关测试参数如表1所示。
图 11 可编程随机开窗功能验证。(a)全画幅成像;(b)左上角开窗384×256;(c)正中心开窗256×256;(d)右下角溢出开窗128×128
Figure 11. Verification of programmable arbitrary windowing function. (a) Full-frame imaging; (b) Top left windowing 384×256; (c) Center windowing 256×256; (d) Bottom right windowing overflow test 128×128
表 1 可编程任意开窗红外焦平面组件主要性能参数
Table 1. The main performance parameters of the programmable arbitrary windowing IRFPA assembly
Parameter Measurement Array format 640×512 Technology 0.18 μm Pixel pitch 15 μm Readout mode ITR & IWR Input stage CTIA Read rate 15 MHz Power consumption 80 mW Frame rate
(typical windowing size)180 Hz (640×512)
3 kHz (128×128)
50 kHz (32×32)FPAs dynamic range >70 dB Output swing 2.5 V Chip area 12 mm×10.4 mm
Study of low-power readout circuit based on a programmable windowing IP core
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摘要: 红外焦平面探测器正朝着更大规模、高帧频、高集成度的方向发展。在高速目标跟踪探测、感兴趣区域成像等应用场景,需要解决高速读出时面临的功耗较高的难点。文中提出了一种数字IC的可编程开窗IP核设计,并通过采用列级分时选通技术,实现对640×512读出电路列模块的超低功耗优化。像素单元电路包含CTIA输入级、双采样保持结构和跟随输出,折衷优化了面积、噪声和增益等因素。相较于传统用门级电路定制设计实现的开窗方式,可编程开窗数字IP核对于不同面阵规格具有良好的可扩展性,并且可以借助后端软件综合优化版图布局,从而缩短设计周期。实际研制中采用0.18 µm 标准CMOS工艺完成了中心距15 µm的640×512读出电路设计及流片验证,并与640×512元短波红外InGaAs探测器芯片进行了耦合测试,结果表明分时选通技术有效降低了列级电路功耗,电路读出总功耗小于80 mW,列级功耗仅为15 mW,读出速率达到15 MHz,可编程开窗IP核功能正常,可以实现指定区域的开窗功能。Abstract:
Objective Infrared focal plane detectors are moving towards larger scale, higher frame rates, and higher levels of integration. In application scenarios such as high-speed target tracking and detection and region of interest imaging, the difficulty of high power consumption faced at high-speed readout needs to be addressed. As the spatial resolution of the infrared focal plane detectors has gradually increased to today's millions and even tens of millions of pixels, the size of the infrared focal plane arrays (IRFPA) has grown, and the need for high frame rate readout and random windowing has become increasingly urgent. At the same time, the increase in scale has also brought about a continuous increase in circuit power consumption, and the circuits that achieve these functions are becoming increasingly complex. The traditional design of digital readout integrated circuit (ROIC) modules from the transistor level is becoming increasingly difficult. Random windowing is an effective way to increase the IRFPA ROIC frame rate and enable the readout of regions of interest. As the need for increasingly complex IR detector customisation grows, the typical architecture of existing ROIC implemented at the chip level for random windowing has many limitations, such as long design cycles for customisation, poor scalability of different-sized arrays and the difficulty of achieving small cell sizes in terms of the occupied pixel area. Methods For large-format IRFPA high frame rate applications, this paper proposes a programmable windowing IP core design (Fig.7) based on the digital IC design flow implementation and achieves ultra-low power optimisation of the 640×512 readout circuit column module by using a column-level time-selection technology (Fig.5). The pixel cell circuit contains a CTIA input stage, a double sample-and-hold structure and a follow output structure (Fig.3), that compromises the optimisation of area, noise, gain, etc. A low-noise, high-speed programmable arbitrary windowing 640×512 ROIC with pixel pitch 15 µm is designed and fabricated in 0.18 µm CMOS technology (Fig.10). The ROIC is coupled with a short-wave infrared InGaAs detector chip to form an FPA assembly and tested at room temperature. Results and Discussions The infrared focal plane test system (Fig.11) consists of a DC power supply, a 5078 timing generator, a digital acquisition card, a blackbody light source and a dedicated PCB test board for the functional testing of the 640×512 scale InGaAs infrared focal plane detector assemblies with windowing. A row of pins was placed in front of the sensing area of the focal plane assembly for imaging to verify the circuit windowing function. The circuit function was verified in several typical application scenarios, such as full frame readout, upper left corner windowing, centre windowing and windowing address overflow, respectively, to obtain an IRFPA windowing image (Fig.12). The test results show that the entire 640×512 scale InGaAs IR detector assembly functions normally, and the programmable windowing digital IP core functions as expected, which can realise the specified area windowing and effectively improve the ROIC frame rate. The power consumption of the column-level output circuit mainly comes from the output buffer. The time-selection technology proposed in the paper effectively reduces the power consumption, in which the total power consumption of the whole assembly is less than 80 mW under the 3.3 V power supply. The power consumption of the column level is only 15 mW, and the readout rate reaches 15 MHz (Tab.1). Conclusions In this paper, a programmable windowing digital IP core module design is proposed based on the digital IC design flow implementation, which can achieve high frame rate readout in windowing mode. This programmable windowing IP core uses a row-address-controlled windowing architecture, allowing the windowing core algorithm to be reused for different-sized IRFPA readout circuits with good scalability and no pixel area occupation. At the same time, to address the problem of high power consumption in high frame rate readout, a time-selection technology is used to optimise the ultra-low power consumption of the column-level module of the ROIC. The programmable windowing IP core layout is integrated with the analogue pixel array layout to achieve a scale of 640×512, 15 µm low-power, high-speed programmable arbitrary windowing IRFPA readout circuit based on a 0.18 µm CMOS process. The ROIC is coupled with a short-wave infrared InGaAs detector chip to form an FPA assembly and tested at room temperature. The results show that the time-selection technology effectively reduces the power consumption of the column-level circuit, the total power consumption of the circuit readout is less than 80 mW while the power consumption of the column-level is only 15 mW, and the readout rate reaches 15 MHz. The programmable windowing digital IP core functions properly, allowing for the readout of specified areas. The work in this paper provides the technical basis for subsequent large-scale small-pitch IRFPA high frame rate low power ROICs. -
Key words:
- programmable arbitrary windowing /
- time-selection technology /
- ROIC /
- InGaAs /
- short-wave infrared
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表 1 可编程任意开窗红外焦平面组件主要性能参数
Table 1. The main performance parameters of the programmable arbitrary windowing IRFPA assembly
Parameter Measurement Array format 640×512 Technology 0.18 μm Pixel pitch 15 μm Readout mode ITR & IWR Input stage CTIA Read rate 15 MHz Power consumption 80 mW Frame rate
(typical windowing size)180 Hz (640×512)
3 kHz (128×128)
50 kHz (32×32)FPAs dynamic range >70 dB Output swing 2.5 V Chip area 12 mm×10.4 mm -
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