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.