Touchscreen technology limits electrical noise

The company has developed an analogue front end that is able to detect variations of capacitance in atto-Farads and to immunise the system against noise. Touchscreen applications are subject to noise coming from various sources, including the display, the system, human touch, or battery chargers. Poor quality chargers, in particular, are a source of noise that can be as high as tens of volts and can affect normal operations when a finger touches the screen. When this occurs, a strong periodic noise - which could be in the range of 100V (peak to peak) and in the frequency range from 1kHz to 1MHz – enter into the touchscreen controller's analogue front end and result in 'false' finger touches. According to ST, the new FingerTip capacitive sensing technology is able to eliminate this sort of charger noise effect and reach higher immunity levels without reducing performance in terms of accuracy, frame rate and power consumption. The device has a 32bit dsp engine and has also been designed to eliminate noises from displays and works with both 'in cell' and 'on cell' display technologies. "Noise from battery chargers pose a special issue for touchscreens, resulting in a poor user experience," said Benedetto Vigna, pictured, general manager of MEMS, Sensors and High Performance Analog Division. "This new FingerTip technology is able to achieve faster response time, low power consumption and higher noise rejection required for high end portable applications." ST is developing a range of products based on the new technology which is currently under evaluation.