A nanowatt successive approximation ADC with a calibrated capacitor array for biomedical applications

An 8-bit successive approximation analog-to-digital converter (ADC) with offset correction circuitry and a tunable capacitor is presented for biomedical applications. The ADC is designed in a standard 0.13 mum CMOS process technology and operates with voltage supplies down to 0.30 V using MOSFETs operating in their sub-threshold region of operation to achieve ultra low power dissipation. Post layout simulations were used to determine that the ADC achieves 8.5 pJ/cycle energy dissipation operating at 20 kS/s with a 0.4 V supply. An offset correction circuit is included for the comparator which significantly reduces the offset voltage as a result of process and mismatch variation. The attenuation capacitor is digitally tuned and post layout simulation results show the advantage of tuning to adjust linearity and dynamic performance for the ADC.