This paper presents a low power, high dynamic range (DR), reconfigurable light-to-digital converter (LDC) for photoplethysmogram (PPG), and near-infrared spectroscopy (NIRS) sensor readouts. The proposed LDC utilizes a current integration and a charge counting operation to directly convert the photocurrent to a digital code, reducing the noise contributors in the system. This LDC consists of a latched comparator, a low-noise current reference, a counter, and a multi-function integrator, which is used in both signal amplification and charge counting based data quantization. Furthermore, a current DAC is used to further increase the DR by canceling the baseline current. The LDC together with LED drivers and auxiliary digital circuitry are implemented in a standard 0.18 μm CMOS process and characterized experimentally. The LDC and LED drivers consume a total power of 196 μW while achieving a maximum 119 dB DR. The charge counting clock, and the pulse repetition frequency of the LED driver can be reconfigured, providing a wide range of power-resolution trade-off. At a minimum power consumption of 87 μW, the LDC still achieves 95 dB DR. The LDC is also validated with on-body PPG and NIRS measurement by using a photodiode (PD) and a silicon photomultiplier (SIPM), respectively.

中文翻译：

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119dB动态范围电荷计数光数字转换器，用于可穿戴PPG / NIRS监视应用。

本文提出了一种低功耗，高动态范围（DR），可重配置的光体积数字图像（PPG）的光数字转换器（LDC）和近红外光谱（NIRS）传感器读数。提出的LDC利用电流积分和电荷计数操作将光电流直接转换为数字代码，从而减少了系统中的噪声因素。该LDC由一个锁存比较器，一个低噪声电流基准，一个计数器和一个多功能积分器组成，用于信号放大和基于电荷计数的数据量化。此外，电流DAC用于通过消除基准电流来进一步增加DR。LDC与LED驱动器和辅助数字电路一起以标准的0.18μmCMOS工艺实现，并进行了实验表征。LDC和LED驱动器消耗的总功率为196μW，同时实现了最大119 dB的DR。电荷计数时钟和LED驱动器的脉冲重复频率可以重新配置，提供了广泛的功率分辨率折衷方案。在最低功耗为87μW的情况下，LDC仍可达到95 dB的DR。还分别通过使用光电二极管（PD）和硅光电倍增管（SIPM）对LDC进行了体内PPG和NIRS测量验证。