A Laser Doppler Blood Flow Measurement System With a 151.4 dBΩ Gain and 0.05% Nonlinearity for PAD Patients

This article presents a compact blood flow measurement system exploiting the Doppler effect and photocurrent sensing technique for wearable health monitoring. Specifically, it helps the patients suffering from peripheral artery disease (PAD) to monitor the blood flow continuously without involving a physician or medical expert. The system prototype integrates a laser diode, a photodiode, and an analog front-end (AFE) on a 54 mm
$\times64$
mm three-layer PCB using discrete components for proof of concept. The front-end is designed with two output modes providing simultaneous current-to-voltage and current-to-frequency conversion without requiring an external clock source. Moreover, this system does not require optical filters or fibers, dynamic artifacts are therefore significantly reduced. Drawing 33 mA current from a 3.3-V supply, the developed system offers a transimpedance gain of 151.4 dB
$\Omega $
for the voltage mode output. For the frequency output, a nonlinearity of 0.05% is achieved.