Ultra-low-power integrated analog front end (AFE) for wearable optical biosensing with FIFO and SPI

The AFE44S30 is an analog front-end for optical bio-sensing applications, such as heart-rate monitoring (HRM) and saturation of peripheral capillary oxygen (SpO2). The device supports up to eight switching light-emitting diodes (LEDs) and up to four photodiodes. Up to 24 signal phases can be defined and the signal can be acquired from each phase in a synchronized manner. The current from the photodiode is converted into voltage by the transimpedance amplifier (TIA) and digitized using an analog-to-digital converter (ADC). The ADC code can be stored in a 128-sample First in, First out (FIFO) block. The FIFO can be read out using a SPI interface. The AFE also has a fully-integrated LED driver with an 8-bit current control. The device has a high dynamic range transmit-and-receive circuitry that helps with the sensing of very small signal levels.