A Column-Parallel Hybrid Analog-to-Digital Converter Using Successive-Approximation-Register and Single-Slope Architectures with Error Correction for Complementary Metal Oxide Silicon Image Sensors

Abstract

In this paper, a column-parallel hybrid analog-to-digital converter (ADC) architecture taking the advantages of both successive-approximation-register (SAR) and single-slope (SS) architectures has been developed for CMOS image sensors. The proposed architecture achieves high conversion speed and low power consumption without requiring a high clock frequency and a large number of capacitors. Moreover, an error correction methodology has been presented to calibrate capacitance mismatches in a SAR capacitor array for linearity improvement. An 11-bit hybrid prototype ADC has been implemented in a 0.18-µm 1-poly 5-metal standard CMOS process. The conversion time is 1.225 µs with a maximum operation clock frequency of 40 MHz and it consumes 48 µW. With the proposed error correction, the measured differential nonlinearity (DNL) and integral nonlinearity (INL) are +0.40/-0.44 least significant bit (LSB) and +1.21/-1.12 LSB, respectively.