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An Activity-Triggered 95.3 dB DR - 75.6 dB THD CMOS Imaging Sensor With Digital Calibration

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4 Author(s)
Jie Yuan ; Electron. & Comput. Eng. Dept., Hong Kong Univ. of Sci. & Technol., Kowloon, China ; Ho Yeung Chan ; Sheung Wai Fung ; Bing Liu

Imaging sensors are being used as data acquisition systems in new biomedical applications. These applications require wide dynamic range (WDR), high linearity and high signal-to-noise ratio (SNR), which cannot be met simultaneously by existing CMOS imaging sensors. This paper introduces a new activity-triggered WDR CMOS imaging sensor with very low distortion. The new WDR pixel includes self-resetting circuits to partially quantize the photocurrent in the pixel. The pixel residual analog voltage is further quantized by a low-resolution column-wise ADC. The ADC code and the partially quantized pixel codes are processed by column-wise digital circuits to form WDR images. Calibration circuits are included in the pixel to improve the pixel linearity by a digital calibration method, which requires low calibration overhead. Current-mode difference circuits are included in the pixel to detect activities within the scene so that the imaging sensor captures high quality images only for scenes with intense activity. A proof-of-concept 32 times 32 imaging sensor is fabricated in a 0.35 mum CMOS process. The fill factor of the new pixel is 27%. Silicon measurements show that the new imaging sensor can achieve 95.3 dB dynamic range with low distortion of -75.6 dB after calibration. The maximum SNR of the sensor is 74.5 dB. The imaging sensor runs at frame rate up to 15 Hz.

Published in:

Solid-State Circuits, IEEE Journal of  (Volume:44 ,  Issue: 10 )