Ultra-small, integrated AFE for optical bio-sensing

The AFE4462 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 16 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.