Measurement error analysis and uncertainty reduction for period- and time-interval-to-digital converters based on microcontrollers

This paper analyses individual error components contributing to the total error for period (or time-interval)-to-digital converters based on common microcontrollers. Two new error components are considered for measurements based on starting/stopping the timer by software: (1) the error because of the latency time between the occurrence of the interrupt request and the beginning of the interrupt machine cycle, and (2) the error due to the time delay between the beginning of the interrupt machine cycle and the start (or stop) of the time/counter. Both errors happen for any signal waveform, including rectangular signals. Solutions for their reduction are also described, such as the use of the capture module embedded in some modern microcontrollers. An advanced method to estimate the overall converter measurement error, based on Lyapunov's characteristic functions and a piece-wise linear approximation of probability distribution functions, increases the accuracy of the error estimation and reduces the uncertainty interval by 20–40%.