A high-speed capacitive-sensor interface using a relaxation oscillator and a fast counter

Abstract

This paper presents the analysis and experimental results on the jitter of a capacitive-sensor interface. The interface is implemented with a simple relaxation oscillator, a fast counter and a microcontroller. The goal is to find the criteria to implement a low-noise system, so that, even with a short measuring time, a high-resolution can be obtained. Experimental results are performed in order to prove the validity of the theoretical predictions. The quantization noise of the 50 MHz counter predominates over the internal noise of the oscillator for measuring times shorter than 2 ms. The achieved resolution for measuring times of 2 ms and 20 ms is better than 16 bits and 18 bits, respectively