LED thermal drift is normally expected within the first few minutes of operation due to the heating of the LED package, especially when driven with high current or long integration times (TINT). As the LED temperature increases, its luminous intensity decreases over time, leading to a reduction in photodetector current readings. Consequently, even with a constant LED current driven by the AFE, the PPG reading (ADC counts) diminishes over time.
To mitigate this, it is recommended to collect data for about 1 minute (or longer) and wait for the LED temperature to stabilize. Applying a first-order polynomial fit to the last 10 seconds of data can further reduce the effects of LED temperature drift when calculating the signal-to-noise ratio (SNR) of the application.
