Ultra-Small Integrated AFE for Wearable, Optical Heart-Rate Monitoring and Biosensing



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 fully-integrated 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.


  • 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

View more

Parametrics Compare all products in Photodiode Sensing

# Input Channels
Resolution (Bits)
Sample Rate (max) (SPS)
Number of LEDs
Package Group
Operating Temperature Range (C)
Package Size: mm2:W x L (PKG)
AFE4404 AFE4403 AFE4405 AFE4410 AFE4490 AFE4900
1    1    2    3    1    3   
24    22    24    24    22    24   
I2C    SPI    I2C
Serial SPI    SPI
1KSPS    2KSPS    1KSPS    1KSPS    5KSPS    1KSPS   
3    3    3    4    2    4   
DSBGA    DSBGA        VQFN     
Catalog    Catalog    Catalog    Catalog    Catalog    Catalog   
-20 to 70    -20 to 70    -20 to 70    -20 to 70    -40 to 85    -20 to 70   
See datasheet (DSBGA)    See datasheet (DSBGA)        40VQFN: 36 mm2: 6 x 6(VQFN)     
Optical biosensing    Optical biosensing    Optical biosensing    Optical biosensing    Optical biosensing    Optical biosensing