AFE4410 - Ultra-Small Integrated AFE With FIFO for Wearable Optical Heart-Rate Monitoring and Biosensing

The AFE4410 is an analog front-end for optical biosensing applications, such asheart-rate monitoring (HRM). The device supports up to four switching light-emitting diodes (LEDs)and up to three photodiodes (PDs). The current from the photodiode is converted into voltage by thetransimpedance amplifier (TIA) and digitized using an analog-to-digital converter (ADC). The ADCcode is stored in a 128-sample first in, first-out block (FIFO) with programmable depth. The FIFOcan be read out using either an I²C interface or a serial peripheralinterface (SPI). The AFE also has a fully integrated LED driver with 8-bit current control. Thedevice has high dynamic range transmit-and-receive circuitry offering a dynamic range of up to 100dB that enables accurate heart-rate sensing. The AFE achieves extremely low current levels byoperating an ultralow power (ULP) mode set by using the ENABLE_ULP register bit.

• Accurate, Continuous Heart-Rate Monitoring:
  • Up to 100-dB Dynamic Range for Accurate Heart-Rate Detection
  • Low Current for Continuous Operation on a Wearable Device With a Typical Value:
    • 30 µA for an LED, 25 µA for the Receiver
• Transmitter:
  • 4 LEDs in Common Anode Configurations
  • 8-Bit Programmable LED Current to 200 mA
  • Mode to Fire Two LEDs in Parallel
  • Programmable LED On-Time
  • Simultaneous Support of 3 LEDs for Optimized SpO₂, HRM, or Multiwavelength HRM
  • Average Current of 30 µA Adequate for a Typical Heart-Rate Monitoring Scenario:
    • 20-mA Setting, 60-µs Pulse Duration,
      25-Hz Sampling Rate
• Receiver:
  • Supports 3 Time-Multiplexed PD Inputs
  • 24-Bit Representation of Current Input From PD in Two’s-Complement Format
  • Individual DC Offset Subtraction DAC
    (Up to ±127-µA Range) at TIA Input for Each LED, Ambient
  • Digital Ambient Subtraction at ADC Output
  • Transimpedance Gain: 10 kΩ to 2 MΩ
  • Noise Filtering With Programmable Bandwidth
  • Receiver Operates at Approximately 1-µA/Hz Sampling Rate (Example, 25 µA at 25 Hz)
  • Hardware Power-Down Mode: Approximately 0-µA Current
• Flexible Pulse Sequencing and Timing Control
• Clocking Via External Clock or Internal Oscillator
• FIFO With 128-Sample Depth:
  • Programmable Partitioning Across Phases
• Pin-Selectable I²C, SPI Interface
• Operating Temperature Range: –20°C to +70°C
• 2.6-mm × 2.1-mm, 0.4-mm Pitch DSBGA Package
• Supplies:
  • Tx: 3 V to 5.25 V
  • Rx: 1.8 V to 1.9 V (LDO Bypass),
    2.0 V to 3.6 V (LDO Enabled)
  • IO: 1.7 V to Rx_SUP

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