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CapTIvate™ Touch Getting Started Manual
7
Copyright © 2021, Texas Instruments Incorporated
2
Basic knowledge and principles of capacitive touch
A common capacitive touch sensor is shown in Figure 2-1, and generally uses copper on the PCB as electrodes.
Structurally, the top layer will be covered with a non-conductive protective layer, such as glass or plastic, and glued
to the PCB. In addition, there will be a grid ground around the sensor.
Figure 2-1 Capacitive touch structure
Based on the type of capacitance detected, capacitive touch can be divided into self-capacitive detection
(detecting the capacitance value between a single electrode and power line ground) and mutual-capacitive
detection (detecting the capacitance value between two electrodes).
2.1
Self-capacitive detection
Figure 2-2 Self-capacitive detection
Taking the simplest single button as an example, the detection schematic diagram of the self-inductive capacitor is
shown in Figure 2-2, and the detection model is shown in Figure 2-3. The self-inductive capacitor uses a single
electrode (receiving electrode Rx) formed by copper coating to detect the change in capacitance of the electrode
to the power line ground. The initial capacitance of the button to power line ground is C
p
. When a human hand
touches it, C
t
, C
h
and C
g
will be introduced into the entire loop, thereby
increasing
the capacitance of the button to
ground.
Figure 2-3 Self-capacitive detection model
Note: The solid line indicates the actual routing, and the dashed line indicates the non-real routing. Gray
components indicate equivalent capacitance or resistance.
