Ultra-Low-Power Integrated AFE for Wearable Optical, Electrical Biosensing

Ultra-Low-Power Integrated AFE for Wearable Optical, Electrical Biosensing - AFE4900

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The AFE4900 device is an analog front-end (AFE) for synchronized electrocardiogram (ECG), photoplethysmogram (PPG) signal acquisition. The device can also be used for optical bio-sensing applications, such as heart-rate monitoring (HRM) and saturation of peripheral capillary oxygen (SpO2). The PPG signal chain supports up to four switching light-emitting diodes (LEDs) and up to three photodiodes (PDs). The LEDs can be switched on using a fully integrated LED driver. The current from the photodiode is converted into voltage by the transimpedance amplifier (TIA) and digitized using an analog-to-digital converter (ADC). The ECG signal chain has an instrumentation amplifier (INA) with a programmable gain that interfaces to the same ADC. A right-leg drive (RLD) amplifier set can be used to the bias for the ECG input pins. AC and dc lead-off detect schemes are supported. The ADC codes from the PPG and ECG phases can be stored in a 128-sample first in, first out (FIFO) block and read out using either an I2C or a serial programming interface (SPI) interface.


  • Synchronized PPG, ECG Signal Acquisition at Data Rates Up to 1 kHz
  • ECG Signal Chain:
    • Standalone ECG Acquisition Up to 4 kHz
    • Input Bias: 1-Lead ECG With RLD Bias
    • Programmable INA Gain: 2 to 12
    • Input Noise (1 Hz to 150 Hz): 2.5 µVrms at 1 kHz, 1.25 µVrms at 4-kHz Data Rate
    • AC, DC Lead-Off Detect: 12.5-nA to 100-nA
  • PPG Receiver:
    • Supports Three Time-Multiplexed PD Inputs
    • 24-Bit Representation of Current From PD
    • DC Offset Subtraction DAC (Up to ±126-µA) at TIA Input for Each LED, Ambient
    • Digital Ambient Subtraction at ADC Output
    • Noise Filtering With Programmable Bandwidth
    • Transimpedance Gain: 10 kΩ to 2 MΩ
    • Dynamic Range Up to 100 dB
    • Receiver Operates in PPG-Only mode at Approximately 1-µA/Hz Sampling Rate
    • Power-Down Mode: Approximately 0 µA
  • PPG Transmitter:
    • Four LEDs in Common Anode Configuration
    • 8-Bit LED Current Up to 200 mA
    • Mode to Fire Two LEDs in Parallel
    • Programmable LED On-Time
    • Simultaneous Support of Three LEDs for SpO2, 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
  • Clocking Using an External or Internal Clock
  • FIFO With 128-Sample Depth for ECG and PPG
  • I2C, SPI Interfaces: Selectable by Pin
  • Operating Temperature Range: –20°C to +70°C
  • 2.6-mm × 2.1-mm, 0.4-mm Pitch DSBGA Package
  • Supplies:
    • Rx: 1.8 V to 1.9 V (LDO Bypass),
      2.0 V to 3.6 V (LDO Enabled)
    • Tx: 3 V to 5.25 V
    • IO: 1.7 V to Rx_SUP

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Parametrics Compare all products in Photodiode Sensing

# Input Channels
Resolution (Bits)
Number of LEDs
Package Group
Operating Temperature Range (C)
Package Size: mm2:W x L (PKG)
AFE4900 AFE4403 AFE4404 AFE4405 AFE4410 AFE4490
3    1    1    2    3    1   
24    22    24    24    24    22   
SPI    I2C    I2C
Serial SPI   
4    3    3    3    4    2   
  DSBGA    DSBGA        VQFN   
-20 to 70    -20 to 70    -20 to 70    -20 to 70    -20 to 70    -40 to 85   
  See datasheet (DSBGA)    See datasheet (DSBGA)        40VQFN: 36 mm2: 6 x 6(VQFN)   
Optical biosensing    Optical biosensing    Optical biosensing    Optical biosensing    Optical biosensing    Optical biosensing