1 Features

• Supports signal acquisition of up to 12 phase sets

• Supports up to 4 LEDs, 3 PDs

• Flexible allocation of LEDs, PDs in each phase

• Simultaneous signal acquisition from different

sensors at different data rates

• Accurate, continuous PPG monitoring:

– Low current for continuous heart-rate

monitoring on a wearable device with a typical

value: 12 μA for the receiver

– Peak system SNR of 115 dB in 0.5-10 Hz band

enables high-accuracy SpO2 measurement

• Transmitter:

– 8-Bit Programmable LED current with range

adjustable from 25 mA to 250 mA

– Mode to fire two LEDs in parallel with

independent per-phase current control

– Programmable LED on-time per-phase

– Simultaneous support of 4 LEDs for SpO2,

Multi-Wavelength HRM

• Receiver:

– Supports 3 Time-Multiplexed PD Inputs

– 2 parallel receivers (2 sets of TIA/filter)

– Individual ambient offset subtraction DAC at

each TIA Input with 8-bit per-phase control and

range adjustable up to 255-μA

– Individual LED offset subtraction DAC at each

TIA input with 9-bit per-phase control and 64-

μA range

– Digital ambient subtraction at ADC output

– Noise filtering with programmable bandwidth

– Transimpedance gain: 3.7 kΩ to 1 MΩ

• Supports external clock or internal oscillator

• Option to acquire data synchronized with a system

clock

• Automatic cancellation of DC from Ambient, LED

• FIFO with 160-sample depth

• SPI™ interface/ I2C interface

• 1.9-mm × 1.8-mm DSBGA, 0.35-mm Pitch

• Supplies: Rx:1.7 - 1.9 V, Tx: 3-5.5 V

2 Applications

• Optical Heart-Rate Monitoring (HRM) for

wearables, hearables

• Heart-Rate Variability (HRV)

• Pulse Oximetry (SpO2) measurements

3 Description

The AFE4432 is an analog front-end for optical biosensing

applications, such as heart-rate monitoring

(HRM) and saturation of peripheral capillary oxygen

(SpO2). The device supports up to 4 switching lightemitting

diodes (LEDs) and up to three 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 12

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 the 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 160-sample FIFO block. The

FIFO can be read out using a SPI or I2C interface.