Improved Switching Energy Reduction Approach in Low-Power SAR ADC for Bioelectronics

Low-power analog-to-digital converter (ADC) is a crucial part of wearable or implantable bioelectronics. In order to reduce the power of successive-approximation-register (SAR) ADC, an improved energy-efficient capacitor switching scheme of SAR ADC is proposed for implantable bioelectronic applications. With sequence initialization, novel logic control, and capacitive subconversion, 97.6% switching energy is reduced compared to the traditional structure. Moreover, thanks to the top-plate sampling and capacitive subconversion, 87% input-capacitance reduction can be achieved over the conventional structure. A 10-bit SAR ADC with this proposed switching scheme is realized in 65 nm CMOS. With 1.514 KHz differential sinusoidal input signals sampled at 50KS/s, the ADC achieves an SNDR of 61.4 dB and only consumes power of 450 nW. The area of this SAR ADC IP core is only 136 mu m x 176 mu m, making it also area-efficient and very suitable for biomedical electronics application.