1 Features
1• Transmitter:
– Supports Common Anode LED Configuration
– Dynamic Range: 100 dB
– 6-Bit Programmable LED Current to 50 mA
(Extendable to 100 mA)
– Programmable LED On-Time
– Simultaneous Support of 3 LEDs for Optimized
SpO2, HRM, or Multi-Wavelength HRM
• Receiver:
– 24-Bit Representation of the Current Input from
a Photodiode in Twos Complement Format
– Individual DC Offset Subtraction DAC at TIA
Input for Each LED and Ambient Phase
– Digital Ambient Subtraction at ADC Output
– Programmable Transimpedance Gain:
10 kΩ to 2 MΩ
– Dynamic Range: 100 dB
– Average Current Less Than 200 μA for PPG
Signal Acquisition
• Pulse Frequency: 10 SPS to 1000 SPS
• Flexible Pulse Sequencing and Timing Control
• Flexible Clock Options:
– External Clocking:
4-MHz to 60-MHz Input Clock
– Internal Clocking: 4-MHz Oscillator
• I2C Interface
• Operating Temperature Range: –20°C to 70°C
• 2.6-mm × 1.6-mm DSBGA Package, 0.5-mm Pitch
• Supplies: Rx: 2 V to 3.6 V, Tx: 3 V to 5.25 V,
IO: 1.8 V to 3.6 V

2 Applications
• Optical Heart-Rate Monitoring (HRM)
• Heart-Rate Variability (HRV)
• Pulse Oximetry (SpO2 Measurement)
• VO2 Max
• Calorie Expenditure

3 Description
The AFE4404 is an analog front-end (AFE) for optical
bio-sensing applications, such as heart-rate
monitoring (HRM) and saturation of peripheral
capillary oxygen (SpO2). The device supports three
switching light-emitting diodes (LEDs) and a single
photodiode. 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 read out
using an I2C interface. The AFE also has a fullyintegrated
LED driver with a 6-bit current control. The
device has a high dynamic range transmit and
receive circuitry that helps with the sensing of very
small signal levels.