Energy-efficient Spread Second Capacitor Capacitive-Dac for SAR ADCs

An energy-efficient capacitive-digital-to-analog converter (C-DAC) switching with low common-mode voltage variation switching method is proposed for successive approximation register analog-to-digital converters (SAR ADCs). In the proposed spread second capacitor capacitive-DAC (SSC C-DAC), a role of capacitor for second conversion step is spread to all capacitors except the most significant bit (MSB) capacitor. The proposed SSC C-DAC achieves 98.1% more efficient switching energy and can be comprised of the number of quarter unit capacitor compared with conventional scheme. Furthermore, in order to achieve low variation of common-mode voltage, the proposed switching method adopts only one side of tri-state switching method in differential-type SAR ADC after second conversion.