Multitouch Using Single Layer Sensor

Feb. 14, 2011
IDT's LDS700x multitouch technology utilizes only a single layer sensor while providing reliable detection in any orientation.

IDT's approach eliminates ghosting

Multi-touch recognition and linearity

IDT LDS700x touch sensor product family

IDT combined sensor and chip design to implement multitouch support that requires only a single layer sensor system. It requires no shield layer and while retaining high noise immunity. It targets small form factor screens under 5-in making it ideal for cell phones and smartphones.

A typical capactive touch system employs three layers: shield, X axis electrodes and Y axis electrodes. IDT forgoes one electrode layer and the shield. This can cut costs by as much as $2. Fewer layers also reduce light attenuation providing a brighter display for less backlight power.

IDT uses a single layer pattern (Fig. 1) that provides unique signatures depending upon finger position. This elminates multitouch ghosting effects. There are other single layer approaches (Fig. 2) but they suffer from poor linearity.

The LDS700x family (Fig. 3) is matched to the sensor technology. It can handle single and dual touch applications. SPI and I2C interfaces are supported. The 30 channel LDS7000 comes in a 5mm by 5mm QFN package and only supports I2C. It is designed for screens up to 3.5-in. The 35 channel LDS7001 comes in a 6mm by 6mm QFN package.

At its core, the LDS700x has a 32-bit processor and a 10-bit ADC. The 8ms data rate supports 120Hz displays.

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