14-bit 3M/s High Accuracy Pipeline Analog-to-Digital Converter Design

Digital signal has a high noise resistance. It is susceptible to the interference from environment noise and clock noise in mixed digital-analog system and digital signal is supported by algorithms to achieve complex signal processing. So analog signal is always converted into digital signal. Analog-to-digital converter(ADC) is the circuit to change analog signal into digital analog. Pipeline ADC is a high speed and high precision ADC structure.This paper describes the design processing of a 14bit-3M/s pipeline ADC used in glimmer CMOS image sensor with 300K pixels. The ADC precision has an effect on the resolution in the pixels. So in order to get the image in glimmer, the ADC must have enough precision. The circuit has 13 stages, 1.5bit per stage. There are several innovative methods adopted to improve precision. First, calibration with extra bit of redundancy is used and the comparator threshold is changed to prevent the overflow caused by gain error. Second, add a background calibration to eliminate fixed pattern noise and improve precision by double sampling and multiply sampling. In addition, differential circuit and complementary switches are also used to improve the circuit performance.There is a high current through the amplifier in the front stage considering the precision consuming large power. Progressively decreasing is used in the amplifier and sampling capacitor in each stage to reduce power consumption and the calibration can also reduce the pressure of analog circuit design.The circuit is fabricated in SMIC 0.18μm CMOS process, which occupies a die area of 1.36mm2 and consumes a power dissipation of 1.05W in static state. The measured SNR and ENOR are improved to 78.2dB and 12.9 respectively.