Design of a CMOS Image Sensor Based on a 10-bit Two-Step Single-Slope ADC

Abstract

Abstract-In this paper, a high-speed CMOS Image Sensor (CIS) based on a 10-bit two step Single Slope A/D Converter (SS-ADC) is proposed. The A/D converter is composed of both 5-bit coarse ADC and a 6-bit fine ADC, and the conversion speed is 10 times faster than that of the single-slope A/D convertor. In order to reduce the pixel noise, further, a Hybrid Correlated Double Sampling (H-CDS) is also discussed. The proposed A/D converter has been fabricated with 0.13um 1-poly 4-metal CIS process, and it has a QVGA (320 x 240) resolution. The fabricated chip size is 5 mm x 3 mm, and the power consumption is about 35 mW at 3.3 V supply voltage. The measured conversion speed is 10 us, and the frame rate is 220 frames/s.

High Frame Rate VGA CMOS Image Sensor using Three Step Single Slope Column-Parallel ADCs

“…The single slope ADC (SS-ADC) is commonly employed for the column-parallel ADC of CIS, because SS-ADC has small chip area, low noise, and low power consumption [7][8][9]. However, SS-ADC has a very low conversion speed, especially when high resolution is required.…”