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

The AFE4900 device is an analog front-end (AFE) for synchronized electrocardiogram(ECG), photoplethysmogram (PPG) signal acquisition. The device can also be used for opticalbio-sensing applications, such as heart-rate monitoring (HRM) and saturation of peripheralcapillary oxygen (SpO₂). The PPG signal chain supports up to four switchinglight-emitting diodes (LEDs) and up to three photodiodes (PDs). The LEDs can be switched on using afully integrated LED driver. The current from the photodiode is converted into voltage by thetransimpedance amplifier (TIA) and digitized using an analog-to-digital converter (ADC). The ECGsignal chain has an instrumentation amplifier (INA) with a programmable gain that interfaces to thesame ADC. A right-leg drive (RLD) amplifier set can be used to the bias for the ECG input pins. ACand dc lead-off detect schemes are supported. The ADC codes from the PPG and ECG phases can bestored in a 128-sample first in, first out (FIFO) block and read out using either anI²C 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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