A 13.92-ENOB 762ksps Bottom Sampling Capacitive SAR ADC for Medical Applications

This paper presents the design of a bottom-sampling 762ksps 13.92-ENOB capacitive SAR Analog-to-Digital Converter with embedded autocalibration tailored for medical applications. The IP has been developed using a HCMOS9A 130 nm technology from STMicroelectronics, but has been designed using the HCMOS9A GO2 option which only includes 500 nm minimum length MOS and require a 1.8 V supply. The proposed Converter achieves high resolution and speed, fulfilling the stringent demands of the PPG (photoplethysmogram) channel which requires at least 14-bit resolution and power-saving features such as the ability to turn OFF during inactive periods. The IP exhibits an average power dissipation of 4.86 mW during the conversion from 1.8 V supply and area employment of 0.806 mm 1.2. Conversion time is 1.3125 μs, comprising 0.3125 μs for the sampling and 16 clock cycles at 16MHz for the approximations. Simulation results have shown linearity and noise performances of a 14-bit converter, proving the goodness of the design. An auto-calibration technique improves the ADC’s linearity up to 16 bits, ensuring that INL does not degrade the ENOB.