A silicon photomultiplier-based analog front-end for DC component rejection and pulse wave recording in photoplethysmographic applications

The growing attention towards healthcare and the constant technological innovations in the field of semiconductor components have allowed a widespread availability of smaller devices, suitable to be worn and able to continuously acquire physiological signals. Wearable devices are, however, more prone to yield signals corrupted by artifacts caused by movement. This issue is particularly relevant in photoplethysmographic (PPG) applications where also, to exploit the whole dynamic range of the acquisition device, the DC component of the signal should be removed and the AC component amplified. In this context, we have designed and realized an analog front-end (AFE) suitable to be integrated within PPG wearable devices able to minimize these problems by reducing the ambient light and the factors that can vary the average value of the current output from a silicon photomultiplier in a PPG system using a green LED. DC component elimination is pursued by a signal conditioning circuit realized by the design and the implementation of a transimpedance amplifier and a Miller integrator capable of following and subsequently subtracting the average value of the acquired signal, so as to obtain an output signal that fluctuates around zero. The step response of the feedback circuit was studied carrying out a PPG acquisition on wrist with promising preliminary results.