A low voltage ultra low power SAR ADC for wearable medical devices

A low-voltage ultra-low power SAR ADC with 0.5 V power supply, 2 kS/s sampling rate and 10 bit accuracy is designed for wearable medical devices. The design uses bootstrap sampling switch to achieve high linear sampling. In the low-power strategy, a voltage of 0.5 V is used to supply power, so that most of the transistors in the circuit are in the sub threshold region. The resulting extremely low current plays a key role in reducing the overall power consumption. Another low-power strategy is that in the selection and design of each module, the 5~5 segmented and bit by bit split DAC capacitor array is used to reduce its own energy consumption while omitting the reference circuit and reducing the overall power consumption. The comparator and SAR logic adopt the dynamic structure without static power consumption to reduce the energy consumption. In addition, an energy-efficient control circuit with control state detection is proposed. The circuit not only solves the problem of comparator misjudgment due to improper timing processing, but also can control four capacitors per module, which improves the control efficiency and reduces the energy consumption. Based on SMIC 0.18 μm CMOS process, the design and post simulation results show that under 0.5 V power supply and 2 kS/s sampling rate, the circuit can achieve ENOB of 9.68 bit, SNDR of 60.1 dB, power consumption of 15.45 nW and FOM of 9.4 fJ/conv-step.