JSSC 2014第1期Power Management

A0 . 5V 4 W CMOS Light-to-Digital Converter Based on a Nonuniform Quantizer for a Photoplethysmographic Heart-Rate Sensor Mohammad Alhawari, Nadya A. Albelooshi, and Michael H. Perrott , Senior Member , IEEE

基于非均匀量化器的0.5V CMOS光数字转换器，实现高灵敏度和低功耗

0.5V CMOS, 4 W功耗, 30 dB SNR, 0.45%瞬时周期抖动

光数字转换器非均匀量化器CMOS低功耗高灵敏度

▸创新点1：非均匀量化器设计（电路创新）——采用基于梯级逆变器量化器（LIQAF）的非均匀量化器，不仅实现了高精度量化，还集成了低噪声前端放大和滤波功能，显著提升了信号处理效率和信噪比（SNR）。

▸创新点2：宽范围对数数字-电阻转换器（电路创新）——通过多比特数字调制技术，实现了对数数字-电阻转换器的宽范围和高分辨率，支持从4 nA到3.5 A的光电二极管偏置电流范围，确保了系统的灵活性和适应性。

▸创新点3：低噪声前端放大器与滤波器一体化（电路创新）——将低噪声前端放大器和滤波器集成到非均匀量化器中，简化了电路结构，降低了功耗（<4 W），同时提高了系统的灵敏度和抗干扰能力。

▸创新点4：基于环境光的心率检测（系统创新）——利用高灵敏度的光-数字转换器（LDC），仅通过环境光即可检测手指按压光电二极管时的心率信号，实现了无源、低功耗的心率监测，瞬时周期抖动小于0.45%（rms）。

Abstract

A 0.5 V CMOS light-to-digital converter (LDC) based on a nonuniform quantizer and off-chip photodiode enables a pho- todiode bias current range spanning 4 nA to 3.5 A while consuming less than 4 W of power. Using an off-chip LED as a modulated light source, measurements with a photodiode cur- rent signal having modulation frequency of 1.2 Hz (72 beats per minute) and 0.5% peak-to-peak amplitude relative to per- formed at the low and high end of the range con ﬁrm over 30 dB of SNR for an integration bandwidth spanning 0.5 to 5 Hz. Using off-chip digital signal proc essing of the LDC output, instan- taneous period jitter (a proxy for i nstantaneous heart rate) is mea- sured to be less than 0.45% (rms) of the period, and the high sen- sitivity of the LDC allows detection of the heart-rate signal from a ﬁnger pressed against the off-chip photodiode using only ambient light. Key circuit components of the LDC include a wide range logarithmic digital-to-resistance c onverter (DRC) utilizing digital multibit modulation to achieve ﬁne resolution and a nonuni- form quantizer based on a laddere d inverter quantizer (LIQAF) which also acts as a low-noise front-end ampli ﬁer and ﬁlter.