AFE4420 - Ultra-small integrated AFE with FIFO for multisensor wearable optical heart-rate monitoring

The AFE4420 is an analog front-end for optical bio-sensing applications, such asheart-rate monitoring (HRM) and saturation of peripheral capillary oxygen (SpO2). The devicesupports up to four switching light-emitting diodes (LEDs) and up to four photodiodes. Up to 16signal phases can be defined and the signal can be acquired from each phase in a synchronizedmanner and stored in a 128-sample First in, First out (FIFO) block. The FIFO can be read out usingeither an I2C or a SPI interface. The AFE also has a fully- integrated LED driver with an 8-bitcurrent control. The device has a high dynamic range transmit-and- receive circuitry that helpswith the sensing of very small signal levels.

• Supports Signal Acquisition of up to 16 Phases
• Flexible Allocation of LEDs and PDs in Each Phase
• Accurate, Continuous Heart-Rate Monitoring:
  • Up to 100-dB Dynamic Range
  • Low Current for Continuous Operation on a Wearable Device with a Typical Value
    • 15 µA for an LED, 20 µA for the Receiver
• Transmitter:
  • Supports Common Anode LED Configuration
  • 8-Bit Programmable LED Current with Range Adjustable from 50 mA to 200 mA
  • Mode to Fire Two LEDs in Parallel
  • Programmable LED On-Time
  • Simultaneous Support of 4 LEDs for Optimized SpO2, HRM, or Multi-Wavelength HRM
  • Programmable Control Signals to Extend Operation to 8 LEDs using External SPDT Switches
• Receiver:
  • Supports 4 Time-Multiplexed Photodiode Inputs
  • Individual DC Offset Subtraction DAC at TIA Input for each LED, Ambient with 7-bit Control and Range up to ±254 µA
  • Transimpedance Gain: 10 kΩ to 2 MΩ
  • Digital Ambient Subtraction at ADC Output to Suppress Ambient Tones
  • Noise Filtering with Programmable Bandwidth
• Supports External Clock and Internal Oscillator Modes
• Automatic Ambient Cancellation Mode (AACM) to Increase Receiver Dynamic Range
• Two Programmable GPIO Pins with Flexible Interrupt Generation
• FIFO with 128-sample Depth
• I²C, SPI Interfaces: Selectable by Pin
• Operating Temperature Range: –40°C to +85°C
• 2.6-mm × 2.1-mm DSBGA, 0.4-mm Pitch
• Supplies:
  • Rx:
    • 1.7 V to 1.9 V (LDO Bypass)
    • 1.9 V to 3.6 V (LDO Enabled)
  • Tx: 3 V to 5.5 V
  • IO: 1.7 V to RX_SUP

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