AFE4404 - 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