Tiny low-cost touch sensor for consumer hand-held applications

The QT100 can sense touch, or near proximity, through any kind of dielectric including glass, plastic, stone, ceramic or wood. Designers therefore have a high degree of flexibility in the physical and aesthetic design of their products. Furthermore, touch sensors eliminate the reliability and manufacturing complexity issues associated with electromechanical switches and membrane keypads.

The QT100 only needs three external passive components, two capacitors and a resistor, to complete the sensor. The sense electrode can be any conductive surface, from a simple printed circuit board pad or an area of conductive indium tin oxide (ITO) printed onto a transparent touch screen. Sensitivity is easily adjusted through the design of sense electrodes or by changing capacitor values.

The device features self-calibration on power-up with automatic drift compensation. A consensus filter, and the use of spread-spectrum signal acquisition, ensures high noise immunity and low RF emissions.
The QT100 operates from a single 2V to 5V supply and consumes only 10 micoAmps at 2V in low power mode, maximizing battery life in portable equipment. Where speed and response time are critical, the chip offers a fast mode with just 1 millisecond between bursts. A sync mode, where the device sleeps after each measurement burst, enables multiple QT100s to be synchronized, while preventing cross-interference. The operating mode is selected though the status of the sync pin.