QMatrix

QMatrix devices are touch sensor ICs that detect touch using a scanned passive matrix of electrode sets. Electrodes are typically areas of copper on a printed circuit board but can also be areas of clear conductive indium tin oxide (ITO) on a glass or plastic touch screen. A single QMatrix device can drive a large number of keys, enabling a very low cost-per-key to be achieved.

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QMatrix technology replaces mechanical switches on all kinds of control panel, from domestic appliances to mobile phones. It offers a robust, reliable, and aesthetically flexible approach to control panel design. Panels can be up to 50mm thick. Key shapes and key placement can be arbitrary to suit the aesthetics and functionality of the end product. Lit and backlit keys are easily accommodated.

How the Technology Works
QMatrix uses a pair of sensing electrodes for each channel. One is an emitting electrode into which a charge consisting of logic pulses is driven in burst mode. The other is a receive electrode that couples to the emitter via the overlying panel dielectric. When a finger touches the panel the field coupling is reduced, and touch is detected.

QMatrix chips contain drive, receive and processing logic, so require very few external components. They output data in serial SPI or I²C form. Uniquely, the technology includes design diagnostics that can be viewed on any PC via a USB interface.

Where several touch keys are close together, an approaching finger causes a change in capacitance around more than one key. Quantum's patented adjacent key suppression – AKS™ - uses an iterative technique to repeatedly measure the capacitance change on each key, compare the results and determine which key the user intended to touch. AKS™ then suppresses or ignores signals from all other keys, providing that the signal from the selected key remains above the threshold value. This prevents false touch detections on adjacent keys. AKS™ is selectable by the system designer.

Key Advantages
QMatrix circuits offer tremendous signal-to-noise ratios, high levels of immunity to moisture films, extreme levels of temperature stability, superb low power characteristics, ease of wiring, and small IC package sizes for a given key count. For these reasons, QMatrix circuits are highly prized for automotive, kitchen appliance, and mobile applications.