6.6 A 320×256 6.9mW 2.2mK-NETD 120.4dB-DR LW-IRFPA with Pixel-Paralleled Light-Driven 20b Current-to-Phase ADC
Yi Zhuo, Hangyu Lu, Ding Ma, Zheng Zhou, Linxiao Shen, Yacong Zhang, Zhongjian Chen, Xixin Cao, Yimao Cai, Ning Li, Wengao Lu
Abstract
Long-wavelength (LW) cryogenic (from 80 down to 40K) infrared focal plane arrays (IRFPAs) are extensively employed because of their sensitivity and rapid response. Readout circuits (ROIC) with high dynamic range (HDR) can significantly improve the signal-to-noise ratio (SNR) of LW-IRFPAs due to enhancement of well capacity. However, neither conventional current-voltage nor current-frequency modulation can avoid analog circuits, making the ROIC susceptible to interference [1]–[8]. In these ROICs, active analog circuits are usually the primary power consumption item. Moreover, the long data transfer bus with a high swing across the pixels consumes power and introduces crosstalk. To address these issues, an LW-IRFPA architecture with pixel-paralleled light-driven current-to-phase A/D conversion (IP-ADC) is implemented in this work. The key circuit includes: 1) a light-current-controlled oscillator (LCO) based modulator for IP-ADC that is powered only by photocurrent without extra power supply; 2) a phase-reconstruction circuit to enhance low-light performance while reducing quantization noise by sub-phase extraction; 3) a pixel-level 20b asynchronous gray-code counter for high equivalent full well capacity during phase quantization; and 4) a low-swing bus data transfer circuit to reduce transmission power consumption and crosstalk. Overall, this work demonstrates a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$320\times 256,\ 30\mu \mathrm{m}$</tex> pixel pitch, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10.55\mu\mathrm{m}$</tex> wavelength quantum-well infrared photodetector (QWIP) IRFPA. The ROIC used in IRFPA is fabricated in a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.18\mu \mathrm{m}$</tex> standard CMOS process. The performance of this IRFPA achieves 120.4dB HDR, 2.2mK noise equivalent temperature difference (NETD) within a typical 6.9mW power consumption.