Meaning
Systemic phase shifts in modulated light or radio signals represent the constant delay introduced by internal electronics and physical transceiver components during distance measurements. Determining the time-of-flight phase offset is necessary to prevent systematic errors.
Hardware Delay
The propagation delay of signal traces, amplifiers, and bandpass filters adds a constant phase shift to the measurement. These internal delays are often larger than the time of flight being measured, making them the dominant source of error if left uncalibrated. This time-of-flight phase offset is measured during factory test sequences by placing the device at a known reference distance in a calibration fixture.
Thermal Sensitivity
The phase response of electronic components changes with temperature, which introduces drift into the distance measurements. An uncompensated sensor will report different distances as the device warms up during operation. To prevent this drift, the firmware uses a temperature sensor to apply a dynamic correction to the time-of-flight phase offset based on calibration curves stored in non volatile memory.
Calibration Procedure
Field calibration routines allow the system to recalculate the baseline offset after integration into an enclosure. The cover glass or protective lens of the product can reflect a portion of the signal back into the receiver, creating a phase shift. Recording this reflection in a controlled environment allows the device to nullify the effect, restoring the accuracy of the measurements.
