Capacitive Touch Sensors - STMicroelectronics

June 20, 2007

STMicroelectronics announced the QST108 capacitive touch sensor controller. QST capacitive touch sensors family are all-digital standard products based on QProx technology from Quantum Research Group. The QST108 touch sense controller requires no additional software development and allows different sensing modes selected in firmware and by option resistors.

Capacitive touch sensors will enable contemporary and innovative user interfaces for many embedded system applications. It is rapidly becoming the solution to replace electro-mechanical switches. Capacitive touch sensors allow designers to create attractive, elegant, functional and economical user interfaces of embedded devices where ease of use, durability, and price are important considerations. The QST family of products will allow the easy creation of sealed, back-lit sensing surfaces, enabling manufacturers to dramatically reduce touch-panel costs while also creating dramatic, contemporary interfaces.

The QST108 capacitive touch sensor uses a pure digital, firmware-based solution that implements QProx capacitive technology and provides an intelligent single-chip control interface that responds to users' touch. The QST108 sensor IC allows users to create capacitive touch-panels of up to 8 keys for their product user interfaces, using conventional or flexible printed circuit board. The sense electrodes can be part of the PCB layout or can even be printed using conductive ink, with flexibility in electrode sizes and shapes. The QST108 detects finger touch using an electrode behind a non-conductive front panel made from materials such as glass or plastic. External component count is low, with only one sampling capacitor and one resistor per channel being required.

Charge-Transfer Capacitive Sensing
QProx technology involves charging an electrically conducting sensing electrode, usually a copper area on a printed circuit board - then transferring that charge to a fixed-value sample capacitor. The charge-transfer is carried out in a patented - burst mode through the controlled switching of I/O transistors. The presence of any external capacitance, caused by an object such as a finger, affects the flow of charge and hence the capacitive reading, allowing the object to be detected. The switching process is the only one in existence today that is 100% digital in nature, making it highly reliable and robust, while also allowing very low price points even for high numbers of keys.

QST capacitive touch sensor devices incorporate auto-calibration, drift compensation, noise filtering and Adjacent Key Suppression (AKSTM). Device configuration allows flexibility in panel thickness, from extremely thin plastics to 10mm or more of glass. QST users also benefit from a range of panel construction methods pioneered and patented by Quantum that are available to ST customers.

QST108 capacitive touch sensor controller is available in a 32-pin LQFP package. It able to drives up to 8 LEDs. It also features PWM capability to drive a beeper output or to control LED brightness. De-bounced touch detection results are accessible through individual outputs or through the I2C interface.

I2C allows the QST108 capacitive touch sensors IC to communicate with the application host controller. User configurable parameters and control functions such as detection threshold, detection integrator, sensor recalibration, low power mode activation, AKS mode and key states and configuration are accessible using simple I2C commands.

The QST108KT6 capacitive touch sensor chip (32-pin LQFP) is sampling now. Volume production will be available in Q4 2007. Priced: around $1.80 each for 10K unit qty.

More information, here you can download the datasheet of ST108 Capacitive Touch Sensor Controller [PDF, 452KB]