A 7.6-nW 1-kS/s 10-bit SAR ADC for Biomedical Applications

Abstract

This paper presents a 10-bit successive approximation register analogue-to-digital converter with energy-efficient switching scheme for biomedical applications. The energy-efficient switching scheme achieves an average digital-to-analog converter switching energy of 63.56 $CV_{ref}^{2}$ , achieving an reduction of 95.34% compared with the conventional capacitor switching scheme for CDACs. With the switching scheme, the ADC can lower the dependency on the accuracy of $V_{cm}$ and complexity of digital control logic and DAC driver circuit. Moreover, dynamic circuits are used to reduce power consumption of comparator and SAR digital logic. The prototype is designed and fabricated in a 180 nm CMOS with a core size of 500 µm x 300 µm (0.15 mm2). It consumes 7.6 nW at 1 kS/s sampling rate and 1.8-V supply with an achieved signal-to-noise-and distortion ratio of 45.90 dB and a resulting figure of merit of 51.7 fJ/conv.-step.