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Texas Instruments AFE44I3x Ultra-Low-Power Analog Front End (AFE)

Texas Instruments AFE44I3x Ultra-Low-Power Integrated Analog Front End is designed for optical bio-sensing applications, such as heart-rate monitoring (HRM) and peripheral capillary oxygen saturation (SpO2). The AFE44I3x supports up to six switching light-emitting diodes (LEDs) and up to four photodiodes. Up to 24 signal phases can be defined, and the signal can be acquired from each phase in a synchronized manner. The current from the photodiode is converted into a voltage by the transimpedance amplifier (TIA) and digitized using an analog-to-digital converter (ADC). The ADC code can be stored in a 128-sample First-In, First-Out (FIFO) block. The FIFO can be read out using an I2C interface.

The Texas Instruments AFE44I3x includes a fully-integrated LED driver with an 8-bit current control. The device features a high dynamic range transmit-and-receive circuitry that helps with sensing of very small signal levels.

Features

  • Accurate, continuous heart-rate monitoring
    • System SNR up to 108dB at 16µA PD current
    • Low current for continuous operation on a wearable device with a typical value (15µA for an LED, 20µA for the receiver)
  • Transmitter
    • Supports common anode LED configuration
    • 8-bit programmable LED current with a range adjustable from 25mA to 250mA
    • Mode to fire two LEDs in parallel with independent per-phase current control
    • Programmable LED on-time per-phase
    • Simultaneous support of 6 LEDs for SpO2, HRM, or multi-wavelength HRM
  • Receiver
    • Supports four time-multiplexed photodiode inputs
    • Two parallel receivers (two sets of TIA/filter)
    • Individual ambient offset subtraction DAC at each TIA Input with 8-bit per-phase control and range adjustable up to 255µA
    • Individual LED offset subtraction DAC at each TIA input with 5-bit per-phase control and 15.5µA range
    • Close to 100dB ambient rejection up to 10Hz
    • Noise filtering with programmable bandwidth
    • 3.7kΩ to 1MΩ transimpedance gain 
  • Supports signal acquisition of up to 24 phases
  • Flexible allocation of 6 LED, 4 PD in each phase
  • Simultaneous signal acquisition from different sensors at different data rates
  • Supports external clock and internal oscillator modes
  • Option to acquire data synchronized with a system master clock
  • Automatic cancellation of DC from ambient, LED
  • FIFO with 128-sample depth
  • I2C interface
  • 2.6mm × 2.1mm DSBGA, 0.4mm pitch
  • Supplies: Rx: 1.7V-1.9V (LDO bypass); 1.9V-3.6V (LDO enabled), Tx: 3V-5.5V, IO: 1.7V-3.6V

Applications

  • Optical heart-rate monitoring (HRM) for wearables, hearables
  • Heart-rate variability (HRV)
  • Pulse oximetry (SpO2) measurements

Block Diagram

Block Diagram - Texas Instruments AFE44I3x Ultra-Low-Power Analog Front End (AFE)
Published: 2020-04-13 | Updated: 2024-06-04