AFE4490 - Integrated Analog Front End (AFE) for Pulse Oximeters

The AFE4490 is a fully-integrated analog front-end (AFE) that is ideally suited for pulse-oximeter applications. The device consists of a low-noise receiver channel with a 22-bit analog-to-digital converter (ADC), an LED transmit section, and diagnostics for sensor and LED fault detection. The device is a very configurable timing controller. This flexibility enables the user to have complete control of the device timing characteristics. To ease clocking requirements and provide a low-jitter clock to the device, an oscillator is also integrated that functions from an external crystal. The device communicates to an external microcontroller or host processor using an SPI™ interface.

The device is a complete AFE solution packaged in a single, compact VQFN-40 package (6 mm × 6 mm) and is specified over the operating temperature range of –40°C to 85°C.

• Fully-Integrated Analog Front-End for
  Pulse Oximeter Applications:
  • Flexible Pulse Sequencing and
    Timing Control
• Transmit:
  • Integrated LED Driver (H-Bridge, Push, or Pull)
  • 110-dB Dynamic Range Across Full Range (Enables Low Noise at Low LED Current)
  • LED Current:
    • Programmable Ranges of 50 mA, 75 mA, 100 mA, 150 mA, and 200 mA,
      Each with 8-Bit Current Resolution
  • Low Power:
    • 100 µA + Average LED Current
  • LED On-Time Programmability from
    (50 µs + Settle Time) to 4 ms
  • Independent LED2, LED1 Current Reference
• Receive Channel with High Dynamic Range:
  • Input-Referred Noise:
    50 pA_RMS (at 5-µA PD Current)
  • 13.5 Noise-Free Bits (at 5-µA PD Current)
  • Analog Ambient Cancellation Scheme with Selectable 1-µA to 10-µA Ambient Current
  • Low Power: < 2.3 mW at 3.0-V Supply
  • Rx Sample Time: 50 µs to 4 ms
  • I-V Amplifier with Seven Separate LED2 and LED1 Programmable Feedback R and C Settings
  • Integrated Digital Ambient Estimation and Subtraction
• Integrated Fault Diagnostics:
  • Photodiode and LED Open and
    Short Detection
  • Cable On or Off Detection
• Supplies:
  • Rx = 2.0 V to 3.6 V
  • Tx = 3.0 V or 5.25 V
• Package: Compact VQFN-40 (6 mm × 6 mm)
• Specified Temperature Range: –40°C to 85°C