Touch technology stifles electrical noise

STMicroelectronics (ST) unveiled a new FingerTip technology that enables a single-chip solution for capacitive touchscreens of up to 10 inches in diameter with multitouch capability.

ST said the FingerTip technology shares a similar architecture with MEMS sensors, in which a sensing element is connected to a high-performance capacitance-sensing circuit. ST added that it made use of its know-how in analog and mixed-signal interface technology while developing the FingerTip technology that is described to have an innovative analog-front-end.

The interface is able to detect variations of capacitance in atto-Farads (10-[18] F) and to immunize the system against noise which is a major concern for touchscreen applications. Touchscreen applications are subject to noise coming from various sources such as the display, the system, and human touch and battery chargers. Particularly, ST said low-cost and poor-quality chargers 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 happens, a strong periodic noise—which could be in the range of 100V (peak-to-peak) and in the frequency range from 1kHz to 1MHz—will enter into the touchscreen controller's analog front-end and result in 'false' finger touches.

According to ST, the new Fingertip capacitive sensing technology with its powerful 32bit DSP (Digital Signal Processing) can eliminate this charger noise effect. It is also 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, MEMS general manager for sensors and high performance analog division. Vigna noted that the new FingerTip technology allows for faster response time, low-power consumption and higher noise rejection required for high-end portable applications.

Major customers are now testing the technology.