Renesas RX Series User Manual

R01UH0823EJ0100 Rev.1.00 Page 1490 of 1823
Jul 31, 2019
RX23W Group 43. Capacitive Touch Sensing Unit (CTSU)
43. Capacitive Touch Sensing Unit (CTSU)
The capacitive touch sensing unit (CTSU) measures the electrostatic capacitance of the touch sensor. Changes in the
electrostatic capacitance are determined by software, which enables the CTSU to detect whether a finger is in contact
with the touch sensor. The electrode surface of the touch sensor is usually enclosed with a dielectric so that a finger does
not come into contact with the electrode.
As shown in
Figure 43.1, electrostatic capacitance (parasitic capacitance) exists between the electrode and the
surrounding conductors. Because the human body is an electrical conductor, when a finger is placed close to the
electrode, the value of electrostatic capacitance increases.
Figure 43.1 Increased Electrostatic Capacitance Due to Presence of Finger
Electrostatic capacitance is detected by the following methods: Self-capacitance and mutual capacitance.
In the self-capacitance method, the CTSU detects electrostatic capacitance generated between a finger and a single
electrode. In the mutual capacitance method, two electrodes are used as a transmit electrode and a receive electrode, and
the CTSU detects the change in the electrostatic capacitance generated between the two when a finger is placed close to
them.
Figure 43.2 Self-Capacitance Method and Mutual Capacitance Method
Electrostatic capacitance is measured by counting a clock signal whose frequency changes according to the amount of
charged/discharged current, for a specified period.
For details on the measurement principles of the CTSU, refer to
section 43.3.1, Principles of Measurement
Operation
.
In this section, “PCLK” is used to refer to PCLKB.
MCU
Touch
electrode
Circuit board pattern
Metal enclosure
Ground (earth)
Touch
electrode
Circuit board pattern
Metal enclosure
Ground (earth)
MCU
Finger
Electrode
board
MCU
MCU
(transmission)
(reception)
Self-capacitance method
Mutual capacitance method
Dielectric
(panel)
Touch electrode

Renesas RX Series Specifications

General

Brand	Renesas
Model	RX Series
Category	Microcontrollers
Language	English