SLAA843A August 2018 – March 2019 MSP430FR2512 , MSP430FR2512 , MSP430FR2522 , MSP430FR2522 , MSP430FR2532 , MSP430FR2532 , MSP430FR2533 , MSP430FR2533 , MSP430FR2632 , MSP430FR2632 , MSP430FR2633 , MSP430FR2633
This application report describes the fundamental concepts of sensitivity, signal-to-noise ratio (SNR), and design margin. It then describes how to use these concepts as tools to evaluate the reliability and robustness of capacitive touch applications that are built with CapTIvate™ touch sensing MCUs.
CapTIvate is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
Capacitive touch sensing is the process of periodically monitoring for changes in the capacitance of a sensing electrode over time and determining if those changes are due to a user's touch or some other non-touch phenomena. This process executes periodic capacitance-to-digital conversions to obtain digital values that represent the capacitance of the sensing electrode over time, and post processing algorithms interpret the measurement results and differentiate a true touch or proximity detection from long term drift and background noise.
It is important for the designer of a capacitive touch interface to understand the basic concepts of sensitivity, signal-to-noise ratio (SNR), and design margin and, more importantly, how to leverage these metrics to ensure that a capacitive touch solution is reliable and robust. This document provides an overview of these performance metrics as they relate to capacitive touch sensing, with a focus on providing a methodology to assess the reliability and robustness of a capacitive touch solution built using CapTIvate MCUs.
The primary objective of a capacitive touch design engineer is to develop a system that:
Often, the designer focuses on the first three objectives the most during product development and does not focus on the last two objectives (reliability and robustness) until much of the design work is complete and the qualification phase is beginning. This document primarily focuses on the last two objectives but does not consider them as separate activities to be completed after the other objectives are met. Rather, these objectives should be assessed throughout the design and development phases.