7.5 A 250fps 124dB Dynamic-Range SPAD Image Sensor Stacked with Pixel-Parallel Photon Counter Employing Sub-Frame Extrapolating Architecture for Motion Artifact Suppression
Jun Ogi, Takafumi Takatsuka, Kazuki Hizu, Yutaka Inaoka, Hongbo Zhu, Yasuhisa Tochigi, Yoshiaki Tashiro, Fumiaki Sano, Yusuke Murakawa, Makoto Nakamura, Yusuke Oike
Abstract
Photon-count imaging has been proposed as a promising technology to realize image capture with noiseless readout and high dynamic range (HDR) [1]-[7]. In addition, for industrial and scientific applications, a global shutter exposure with motion artifact suppression is essential. A single-photon avalanche diode (SPAD) image sensor is well matched to the photon-counting architecture by shrinking the SPAD pixel size and stacking a logic chip with pixel-parallel Cu-Cu connections. A pixel-parallel photon counter, however, requires many counter bits in a pixel for HDR operation. This makes it difficult to shrink the pixel size and lower the power consumption, owing to the substantial number of SPAD activations under high light conditions [2]. Inter-frame mode switching between digital photon count and analog accumulation avoids the power increase under high light conditions, but it suffers from a dip in the signal-to-noise ratio (SNR) and/or motion artifact in reproducing an HDR image [3], [4]. An approach reducing SPAD activations under high light conditions can reduce the power consumption [5]-[7], but the combination of long- and short-exposure frames for HDR [5], [6] still suffers from the dip in SNR like conventional multi-exposure image sensors [8], even if these techniques can suppress motion artifacts owing to sub-frame readout.