A 61-nW Level-Crossing ADC With Adaptive Sampling for Biomedical Applications

An ultra-low-power level-crossing analog-to-digital converter (LC-ADC) with on-chip adaptive sampling is presented. Different from conventional ADCs based on Nyquist sampling, LC-ADC utilizes sparsity of signals for low power data acquisition. To save power, the proposed adaptive sampling scheme is implemented with only one scaler and one high-precision comparator, which is in sharp contrast to conventional LC-ADCs that require an n-bit digital-to-analog converter and two comparators. Implemented in 0.18-um CMOS process, the proposed ADC consumes only 61 nW under 0.5V supply, and achieves 5.6 bits equivalent numbers of bits and 35 dB signal-to-noise and distortion ratio with an operating frequency up to 1 kHz.