1 Features

1• Supports signal acquisition of up to 16 phases

• Flexible allocation of LEDs and PDs in each

phase

• Accurate, continuous heart-rate monitoring:

– Up to 100-dB dynamic range

– 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 50 mA to 200 mA

– Mode to fire two LEDs in parallel

– Programmable LED on-time

– Simultaneous support of 4 LEDs for optimized

SpO2, HRM, or multi-wavelength HRM

– Programmable control signals to extend

operation to 8 LEDs using external SPDT

switches

• Receiver:

– Supports 4 time-multiplexed photodiode inputs

– Individual DC offset subtraction DAC at TIA

input for each LED, ambient with 7-bit control

and range up to ±254 μA

– Transimpedance gain: 10 kΩ to 2 MΩ

– Digital ambient subtraction at ADC output to

suppress ambient tones

– Noise filtering with programmable bandwidth

• Supports external clock and internal oscillator

modes

• Automatic ambient cancellation mode (AACM) to

increase receiver dynamic range

• Two programmable GPIO pins with flexible

interrupt generation

• FIFO with 128-sample depth

• I2C, SPI interfaces: selectable by pin

• Operating temperature range: –40°C to +85°C

• 2.6-mm × 2.1-mm DSBGA, 0.4-mm pitch

• Supplies:

– Rx:

– 1.7 V to 1.9 V (LDO bypass)

– 1.9 V to 3.6 V (LDO enabled)

– Tx: 3 V to 5.5 V

– IO: 1.7 V to RX_SUP

2 Applications

• Optical heart-rate monitoring (HRM) for

wearables, hearables

• Heart-rate variability (HRV)

• Pulse oximetry (SpO2) measurements

• Maximum oxygen consumption (VO2 Max)

• Calorie expenditure

3 Description

The AFE4420 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 four switching

light-emitting diodes (LEDs) and up to four

photodiodes. Up to 16 signal phases can be defined

and the signal can be acquired from each phase in a

synchronized manner and stored in a 128-sample

First in, First out (FIFO) block. The FIFO can be read

out using either an I2C or 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.