AFE4405 - Ultra-Small Integrated AFE With FIFO for Wearable Optical Heart-Rate Monitoring and Biosensing

The AFE4405 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 up to two photodiodes. 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 stored in a 240-sample first in, first out (FIFO) block with programmable depth. The FIFO depth can be partitioned to accommodate the phases that must be stored. 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.

To request a full data sheet or other design resources: request AFE4405

• Transmitter:
  • Supports Common Anode LED Configuration
  • Dynamic Range: 100 dB
  • 8-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:
  • Supports 2 Time-Multiplexed Photodiode
    Inputs
  • 24-Bit Representation of the Current Input from
    the Photodiode in Twos Complement Format
  • Individual DC Offset Subtraction DAC
    (±15.75-µA Range) at TIA Input for Each LED,
    Ambient
  • Digital Ambient Subtraction at ADC Output
  • Transimpedance Gain: 10 kΩ to 2 MΩ
  • Dynamic Range: 100 dB
  • Dynamic Power-Saving Mode to Reduce
    Receiver Current to 200 µA
• Pulse Frequency: 5 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
• FIFO with 240 Sample Depth:
  • Programmable Partitioning Across Phases
• I²C, SPI™ Interfaces: Selectable by Pin
• Operating Temperature Range: –20°C to +70°C
• 2.6-mm × 2.1-mm DSBGA, 0.4-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