A Fully Differential PPG Readout Amplifier with a Reconfigurable Bandwidth for Power Minimization

This paper presents a low-power, full voltage range, fully differential optical sensor readout amplifier for photoplethysmography (PPG) recordings. The proposed system architecture employs a novel bias circuit together with a three-stage fully differential amplifier based transimpedance amplification stage. The bias circuit provides a DC biasing voltage for photodiode (PD) and isolates the large PD parasitic capacitance from the core amplifier, without reducing the output voltage range. The three-stage amplifier provides a high gain and its output stage exploits a class AB topology, increasing the driving capability. Moreover, the bandwidth of the system can be reconfigurable by changing the feedback components, which can improve the signal to noise ratio (SNR) and reduce the system power consumption. The amplifier and auxiliary circuit are implemented in a standard 55nm CMOS process. The simulation results show that the readout system consumes a total power of 46µA current from 1.2V supply. Also, the correlated double sampling based ambient cancellation functionality is realized successfully.