TIDUF16 December   2023

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Photodiode, TIA, and ADC
      2. 2.2.2 LED Driving
      3. 2.2.3 Power
      4. 2.2.4 Display, Orientation, and Communication Features
      5. 2.2.5 Software
        1. 2.2.5.1 Timing Structure
        2. 2.2.5.2 Oversampling and Digital Filtering to Increase Dynamic Range
        3. 2.2.5.3 Calculating Vitals
    3. 2.3 Highlighted Products
      1. 2.3.1 MSPM0L1306
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Software Requirements
      1. 3.2.1 TI GUI
      2. 3.2.2 CCS Project
      3. 3.2.3 Analog Engineers Calculator
    3. 3.3 Test Setup
    4. 3.4 Test Results
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks

2.2.5.1 Timing Structure

Figure 2-5 illustrates the coded timing structure for pulse oximeter operation.

  • To capture the natural frequencies of a PPG signal, which can vary but are generally single-digit frequencies, photodiode samples for both red and IR light are captured at 125 Hz.
  • During the 8-ms period between captures, which is managed by the TIMG0 block (named T8) of the MSPM0L1306, Figure 2-5 details the operational status of several components involved in obtaining the photodiode sample.
  • TIMG1 block (named T1) runs twice at the start of the 8-ms period, each time for 1 ms, to denote the on time of each red and IR LEDs, respectively.
  • T1 and T8 utilize interrupts to manage activation and DAC output level timing as well as the start time for 256 ADC sample captures per LED.
  • Once the captured ADC data from both LEDs is stored and the second interrupt from T1 arrives, the MSPM0L1306 deactivates both LEDs to conserve power and begin data processing and calculations.
  • During this time, the ADC can switch to monitoring the internal voltage or transmitting serial data (or both) before the cycle repeats.
GUID-20231204-SS0I-WZ3P-QHTQ-36C5LBQN0H4M-low.svgFigure 2-5 TIDA-010267 Timing Diagram