Design of a Pseudo-Wide Dynamic Range CMOS Image Sensor by Using the Bidirectional Gamma Curvature Technique

Abstract

This brief presents a 640x480 CMOS image sensor (CIS) with in-circuit bidirectional gamma correction for use in computer vision applications. The conventional gamma correction method can saturate the bright region in an image, leading to the loss of bright image information. Using the proposed bidirectional gamma correction method, which can be implemented with a log-exponential counter, both bright and dark regions in an image can be simultaneously corrected. The transfer function of an 8-bit single-slope analog-to-digital converter can be selected considering either linear or bidirectional gamma curves with three different slope-change points to enhance the visibility in the pseudo-dynamic range. From the prototype sensor, we observed that the visibility of dark images was increased with proper bidirectional gamma curvatures. The CIS was fabricated in a 110 nm CIS process, and the full chip area was 5900 mu m x 5240 mu m. The total power consumption was 6 mW at a rate of 15 frames per second with an analog, pixel, and digital supply voltage of 3.3 V, 3.3 V, and 1.5 V, respectively.