1 Features

1• Supports signal acquisition of up to 24 phases

• Flexible allocation of 8 LED, 4 PD in each phase

• Simultaneous signal acquisition from different

sensors at different data rates

• Accurate, continuous heart-rate monitoring:

– System SNR up to 108-dB at 16 μA PD current

– Low Current for Continuous Operation on a

Wearable Device with a Typical Value: 15 μA

for an LED, 20 μA for the Receiver

• Transmitter:

– Supports common anode LED configuration

– 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 8 LEDs for SpO2,

HRM, or multi-wavelength HRM

• Receiver:

– Supports 4 Time-Multiplexed Photodiode

Inputs

– 2 parallel receivers (two 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 5-bit per-phase control and 15.5-

μA range

– Close to 100 dB ambient rejection up to 10 Hz

– Noise filtering with programmable bandwidth

– Transimpedance Gain: 3.7 kΩ to 1 MΩ

• Supports external clock and internal oscillator

modes

• Option to acquire data synchronized with a system

master clock

• Automatic cancellation of DC from ambient, LED

• FIFO with 128-sample depth

• SPI interface

• 2.6-mm × 2.1-mm DSBGA, 0.4-mm pitch

• Supplies: Rx: 1.7 V-1.9 V (LDO bypass); 1.9 V-3.6

V (LDO enabled), Tx: 3 V-5.5 V, IO: 1.7-3.6 V

2 Applications

• Optical heart-rate monitoring (HRM) for

wearables, hearables

• Heart-rate variability (HRV)

• Pulse oximetry (SpO2) measurements

3 Description

The AFE44S30 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 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.