Introduction to QTouch® Peripheral Touch Controller (PTC)

The QTouch® Peripheral Touch Controller (PTC) offers built-in hardware for capacitive touch measurement on sensors that function as buttons, sliders, and wheels. The PTC has been designed to perform capacitive touch acquisition on sensors independently from the CPU, resulting in low CPU utilization and reduced power consumption.

Capacitive Measurement Techniques

The PTC supports two methods of capacitance measurement:

  • Self-capacitance
  • Mutual capacitance

Self-capacitance Method

The self-capacitance method involves charging a sense electrode (Y line) of unknown capacitance to a known potential. The resulting charge is transferred into a measurement circuit. By measuring the charge with one or more charge-and-transfer cycles, the capacitance of a sense plate can be determined.

A self-capacitance button is formed using one Y channel, whereas a slider or a wheel requires 3 Y channels.


To get a position on sliders or wheels, the relative signal strength of the sensors is measured. Below is an illustration of signal versus finger position on a slider.


Mutual Capacitance Method

The mutual capacitance method uses a pair of sensing electrodes (X-Y lines). One electrode (X line) acts as an emitter into which a charge consisting of logic pulses is driven in burst mode. The other electrode (Y line) acts as a receiver that couples to an emitter using the overlying panel dielectric. When a finger touches the panel, field coupling is reduced, and touch is detected.

Mutual capacitance buttons use one X-Y channel whereas sliders and wheels can be configured to use 3 to 8 X-Y channels, depending on the sensor size.


While the mutual capacitance method does require two electrodes per sensor surface, it is possible to have many sensors connected to the same X line and Y line in a matrix of sensors. When the layout is done correctly, the mutual capacitance method also offers a better signal to noise ratio on sensors. This makes it possible to get longer tracks from the sensor to the device. In addition, the sensing field of a mutual capacitance sensor does not extend as far away from the sensor, which again can reduce noise compared to the self-capacitance method.

© 2024 Microchip Technology, Inc.
Notice: ARM and Cortex are the registered trademarks of ARM Limited in the EU and other countries.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.