Date: 15th Jun 2011
ST's touchscreen tech detects atto-Farad
capacitance variation with noise immunity
STMicroelectronics has announced its new FingerTip technology,
which enables a single-chip solution for capacitive touch
screens up to 10 inches in diameter with multi-touch capability.
ST's MEMS sensors and FingerTip technology share a similar
architecture, in which a sensing element is connected to
a high-performance capacitance-sensing circuit. ST has leveraged
its know-how in analog and mixed-signal interface technology
to develop an innovative analog-front-end that is able to
detect variations of capacitance in atto-Farads ((10 to
power of -18) F) and to immunize the system against noise.
Touchscreen applications are subject to noise coming from
various sources, including the display, the system, human
touch, or battery chargers. Low-cost and 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 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.
The new FingerTip capacitive sensing technology employs
32-bit DSP (Digital Signal Processing) engine to eliminate
this sort of charger noise effect and reach higher immunity
levels. FingerTip 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, General Manager of MEMS, Sensors and
High Performance Analog Division. "Our leadership in
analog capacitive interface IP, developed for MEMS sensors,
will allow us to achieve higher noise rejection prior to
digital filtering. 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's new product family, based on the new technology, is
under evaluation with major customers that can benefit from
the FingerTip's: hand writing capability with a small stylus;
very fast response time; ultra-low power consumption; best
linearity and accuracy in noisy conditions; and tiny package
suitable for smart phones and 10-inch tablets.
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