A 455 nW 220 fJ/conversion-step 12 bits 2 kS/s SAR ADC for portable biopotential acquisition systems

An ultra-low power 12 bits 2 kS/s successive approximation register analog-to-digital converter (ADC)is presented. For power optimization, the voltage supply of the digital part is lowered, and the offset voltage of the latch is self-calibrated. Targeted for better linearity and lower noise, an improved digital-to-analog converter capacitor array layout strategy is presented, and a low kick-back noise latch is proposed. The chip was fabricated by using 0.18μm 1P6M CMOS technology. The ADC achieves 61.8 dB SNDR and dissipates 455 nW only, resulting in a figure of merit of 220 fJ/conversion-step. The ADC core occupies an active area of only 674×639 μm2.