Capacitive Touch Sensor

Topics: Touchscreen, Permittivity, Capacitor Pages: 13 (2792 words) Published: January 14, 2013
Internal Use Only

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Technical T1

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Capacitive Touch Sensor In BD Player Pla er
Today, in the world of globalization, Mechanical Tactile Switch have evolved and started to change to more advance technology which is Capacitive Touch Sensor. C S Capacitive T iti Touch S h Sensor currently is widely use in consumer product such as MP3 Player, mobile phone and other portable devises. More and more, this technology is utilized in further application fields such as household appliances as well as automotive and industrial application. As part of the top consumer product, Sony BD Player is not lack behind and implemented Capacitive Touch Sensor technology in their latest, high end model BDP-S790.

By Koh Hong Lee Electrical Design 2 Dept, Design Div, D i 1 Di Video Design Sector


Basic Principle
The simplest form of a capacitor consists of two conductor and separated by an insulator. The following formula shows the parameter which influence capacitance. i fl it

How Capacitive Touch Sensor Work?
The electrode of a touch sensor represents one plate of such a capacitor. The corresponding second g plate is represented by the environment of the sensor electrode (to form a parasitic C0) and another conductive object, like human finger for example (to form touch capacitor C T ). The sensor electrode is connected to an IC ( B D pl a ye r is us i n g A T A 5 0 8 8 & ATA5010) . The capacitance of the sensor pad is measured periodically. If a conductive object approaches or touches the electrode, the measured capacitance will increase. This change is detected by the IC and converted into a trigger signal. Considering the Capacitance formula, a bigger pad and thinner overlaying cover material leads to a bigger touch capacitance CT and as a result, a bigger capacitance diff bi it difference b t between touch and untouched sensor pad. In other words, the size of the electrode and the covering material influence the sensitivity of the sensor.

What is Capacitive Sensor?
Capacitive Sensor (Capacitive Sensing) by definition is a technology based on capacitive coupling that is used for detecting proximity, position, etc. ( In BD Player, Capacitive Touch Sensor i s u s ed t o r e p l a c e c o n v e n t i on a l Mechanical Tactile Switch and detect human capacitance. This change make the BD Player achieve a high level, simple and elegant outlook (below diagram). Structure mechanically is simplified and robust design due to no holes or other openings are necessary. Idle Condition

From the Capacitance Formula, - Capacitance, C is direct proportional to Area of Plate, A, which mean the bigger the Area, the bigger the capacitance. - Capacitance, C is inverse proportional to Distance between Plate, d, which mean the smaller the Distant, d the bigger the Capacitance, C - Relative Dielectric Constant,εr (A.K.A Relative Permittivity), is the insulating material between the plates. Table below shows the common materials a n d...
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