AFE4900

• 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: 2.15 to 12.92
  • 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
  • IEC 60601 Test report available on request
• 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
• 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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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.