AFE4400 - Integrated Analog Front End (AFE) for Heart-Rate Monitors and Low-Cost Pulse Oximeters

The AFE4400 is a fully-integrated analog front-end (AFE) ideally suited for pulse oximeter applications. The device consists of a low-noise receiver channel with an integrated 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 AFE4400, 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 0°C to 70°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)
  • Dynamic Range: 95 dB
  • LED Current:
    • Programmable to 50 mA with 8-Bit Current Resolution
  • Low Power:
    • 100 µA + Average LED Current
  • Programmable LED On-Time
  • Independent LED2 and LED1 Current Reference
• Receive Channel with High Dynamic Range:
  • 13 Noise-Free Bits
  • Low Power: < 670 µA at 3.3-V Supply
  • Integrated Digital Ambient Estimation and Subtraction
  • Flexible Receive Sample Time
  • Flexible Transimpedance Amplifier with Programmable LED Settings
• Integrated Fault Diagnostics:
  • Photodiode and LED Open and
    Short Detection
  • Cable On and Off Detection
• Supplies:
  • Rx = 2.0 V to 3.6 V
  • Tx = 3.0 V to 5.25 V
• Package: Compact VQFN-40 (6 mm × 6 mm)
• Specified Temperature Range: 0°C to 70°C