The AFE4460 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 32 switching light-emitting
diodes (LEDs) and up to four photodiodes (PDs). The AFE has two LED drivers each with 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. Up to 16 signal phase sets can be
defined, each phase set comprising a combination of LED and Ambient phases. Low noise offset
DACs at the receiver inputs can be automatically controlled to cancel DC from Ambient and
LED light. The current from each of the 4 PDs in each phase is converted into voltage by
TIAs, filtered, and then digitized using a common ADC. The ADC code can be stored in a
256-sample FIFO block. The FIFO can be read out using a SPI or I2C interface.