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Capacitive touch sensors enable smart user interfaces

Posted: 25 Jun 2007 ?? ?Print Version ?Bookmark and Share

Keywords:capacitive touch sense ICs? PCB? touch sensor? user interfaces?

STMicroelectronics launches the QST108, the first IC in a family of capacitive touch sense products that will enable contemporary and innovative user interfaces for many markets.

The QST family of products enable easy creation of sealed, back-lit sensing surfaces, enabling manufacturers to reduce touch-panel costs while creating dramatic, contemporary interfaces.

Intuitive sensor
First in ST's QST capacitive touch-sensor series, QST108 uses a pure digital, firmware-based solution that implements Quantum Research Group 's patented and field-proven charge-transfer QProx capacitive technology and provides an intelligent single-chip control interface that responds to users' touch.

Quantum's QProx technology involves charging an electrically conducting sensing electrode, usually a copper area on a PCB and 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 QST108 sensor device allows users to create capacitive touch-panels of up to eight 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. 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.

Unique design
QST devices require no production line or user calibration. They incorporate sophisticated drift compensation, auto-calibration, noise filtering and adjacent key suppression to ensure maximum usability and control integrity. Device configuration allows flexibility in panel thickness, from ultrathin 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.

The QST108 touch sense controller requires no additional software development and allows different sensing modes selected in firmware and by option resistors. Providing a solid-state alternative to mechanical switches, QST gives great flexibility in user interface design and offers a stable, reliable capacitive touch solution that can be easily soft-customized for product designs and easily re-configured for variants. QST standard solutions significantly reduce the development time and cost, allowing designers to concentrate their creativity on the system design.

Initially available in a 32-pin LQFP package, QST108 drives up to eight LEDs. It 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 I?C interface.

I?C allows QST108 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 I?C commands.

Over time, ST plans to expand the QST family with products offering different key counts and new features such as capacitive wheels and sliders. Later, ST will offer one-, two- and four-key products and a more complex product offering seven keys and a wheel or slider. Higher keycounts will be supported using Quantum's QMatrix technology.

QST108KT6 is sampling now for major OEM customers and will be available to all in Q4. Available in a 32-pin LQFP package, QST108KT6 is priced around $1.80 in quantities of 10,000 pieces through distribution.

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