SAM D21 Peripheral Touch Controller Overview
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 supports both mutual and self-capacitance measurement without the need for any external component. It offers superb sensitivity and noise tolerance, as well as self-calibration, and minimizes your sensitivity tuning effort.
The PTC is intended for autonomously performing capacitive touch sensor measurements. The external capacitive touch sensor is typically formed on a PCB, and the sensor electrodes are connected to the analog charge integrator of the PTC using the device I/O pins. The PTC supports mutual capacitance sensors organized as capacitive touch matrices in different X-Y configurations, including Indium Tin Oxide (ITO) sensor grids. In Mutual Capacitance mode, the PTC requires one pin per X-line (drive line) and one pin per Y-line (sense line). In Self-Capacitance mode, the PTC requires only one pin with a Y-line driver for each self-capacitance sensor.
Features
Implements low-power, high-sensitivity, environmentally robust capacitive touch buttons, sliders, and wheels
- Supports mutual capacitance and self-capacitance sensing
- Up to 32 buttons in Self-Capacitance mode
- Up to 256 buttons in Mutual Capacitance mode
- Supports lumped mode configuration
- One pin per electrode - no external components
- Load compensating charge sensing
- Parasitic capacitance compensation for Mutual Capacitance mode
- Adjustable gain for superior sensitivity
- Zero drift over the temperature and VDD range
- No need for temperature or VDD compensation
- Hardware noise filtering and noise signal de-synchronization for high-conducted immunity
- Microchip-provided QTouch Library firmware and QTouch Composer tool
PTC and its Benefits
Mixed Hardware and Firmware Solution
- Allows you to define sensor configuration
- PTC with the QTouch Library
PTC Runs Data Acquisition Autonomously,
- Resulting in low CPU utilization and power consumption
- User-controlled power-performance trade-off
- CPU can sleep during acquisition to save power
- Alternatively, the CPU can perform other time-critical operations during touch acquisition
Robust noise performance
Self-Capacitance Block Diagram
The PTC block diagram for self-capacitance measurement is shown in the accompanying figure. Only the Y-lines can be connected to self-capacitance sensors and are selected using the Input control. X-lines are unused and can be utilized for any other GPIO functionality. The acquisition module along with the compensation circuit helps in measuring the change in capacitance due to user touch.
Mutual Capacitance Block Diagram
The PTC block diagram for mutual capacitance measurement is shown in the accompanying figure. Both X-lines and Y-lines should be connected to mutual capacitance sensors and are selected using the Input control.
