The versatility of Synaptics' capacitive sensing technology makes it suitable for handheld devices which require a clear, durable touchscreen sensor optimized for finger-only use. This includes cell phones, MP3 players, digital still cameras, and digital video cameras.

Synaptics' transparent capacitive sensors, such as the ClearPad™ product family, provide all the functionality and performance of Synaptics' TouchPad devices touch screen applications in portable handheld devices. Compared to resistive touch screens, Synaptics capacitive sensors offer superior durability and stunning optics --- the screen stays brighter and crisper, with less optical distortion.

Our transparent capacitive position sensing technology operates in a manner very similar to the Synaptics capacitive sensing technology. To locate a finger, sense wires are formed using transparent conductors. Most commonly, indium tin oxide (ITO) is used. The ITO traces are implemented on a clear substrate such as polyester (PET) film, polycarbonate, or glass.

Our two-dimensional transparent capacitive position sensing technology utilizes a grid of these sensors to accurately locate the X, Y and "pressure" of a finger on a sensor. Typically, ITO-coated PET is etched to form arrays of wires. This provides a simple, clear, and thin sensor that can be laminated underneath the protective lens that is in front of a display. (Figure 1)

Figure 1

The most common alternative to transparent capacitive sensing is resistive technology. In a typical resistive touch screen, two layers of ITO-coated PET are separated by an air gap. When the screen in pressed, the top layer bends to make contact with the bottom layer (Figure 2). The point of contact can be calculated by placing a voltage gradient across the top ITO layer, and then measuring the voltage on the bottom layer.

Figure 2

Advantages of Synaptics' Transparent Capacitive Position Sensing Technology

Synaptics' capacitive solution offers several fundamental technical advantages. Capacitive sensing is completely solid state, with no moving parts---this contributes to its high reliability and durability. In contrast, resistive screens are physical switches that must flex and rub in use, decreasing their useful lifetime.

Because capacitance can be sensed through most non-conductive materials, designers are not limited to pliable surface materials as required by resistive sensing technology. Capacitive sensing operates even when the sensor is placed underneath a durable surface, such as polycarbonate or acrylic. In this situation, the capacitive sensor has the environmental durability of its rigid overlay, allowing it to function in environments where other technologies fail.

Synaptics' transparent capacitive sensors are optically superior to most resistive touch screens. Refractive index-matched adhesives, anti-reflective coatings, and the lack of an air gap and spacer dots, provide for fewer internal reflections. Absorption of light is also minimized, since very thin conductive layers are used. In contrast, the physical stack-up of a resistive panel requires the use of an air gap, and steps must be taken to minimize internal reflections and the loss of light as it passes through layers with differing refractive indices.

Lastly, unlike resistive sensors, Synaptics sensors can work underneath slightly curved surfaces without loss of functionality. This allows device designers to incorporate touchscreen functionality into their device with virtually no compromise to the industrial design of the device; devices can retain the "smooth and sleek" aesthetic used in typical handheld devices. Because of these differences, the Synaptics technology allows designers to add inexpensive and simple touch sensing in applications that other technologies cannot approach.

ClearTouch Product Family

Onyx Concept