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

In this paper, a column-parallel hybrid analog-to-digital converter (ADC) architecture taking the advantages of both successive-approximationregister (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-m 1-poly 5-metal standard CMOS process. The conversion time is 1.225 s with a maximum operation clock frequency of 40 MHz and it consumes 48 W. 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.