capacitive sensor circuit
Touch-screen chain
Summary
This White Paper provides overview of the supply chain of a touch screen. Describes the key elements of supply chain and touch screen modules available on the market.
Introduction
Detailed understanding of the capacity supply chain touch screen is vital for customers to view products touch the end. Engagement model chosen should match the in-house design capabilities, components, supplier of value added services and options available for the module design and power.
Controller IC Supplier
Capacitive touch controls are solid state devices, that senses finger position on the touch sensor. Different silicon architectures and sensing methods are used in a variety of suppliers, which is beyond the scope of this document. Capacitive controllers can be divided into two major categories.
Projected Capacitive
This method senses finger position sensor in the electric field projected through the substrate. This is typically done with one or more patterned ITO layer, applied to one or more transparent substrates. Projected capacitance is very resistant, because users touch the top of the glass or plastic substrate, while the ITO layer is protected below. Coordinates are calculated from measurements of signals off patterned ITO with deterministic position. It is planned shooting more accurate and reproducible than other capacitive sensing methods. Projected capacitive regulators generally require more input pins to capture a larger screen. In practice, This means that they are limited to around 10 "diagonal in a single chip solution. Alternative using the controller IC or more unique patterned ITO are also possible.
Surface Capacitive
This method uses a single sheet of transparent conductor used in the sensor substrate, typically ITO on glass, film, or plastic. This method is effective cost and suitable for high-volume production of many well-known techniques. Since the finger position is determined by four sensors in the corners or edges boards, touchscreens can be reduced to thirty inches or more without increasing the controller IC pin count. There are also important disadvantages, especially for smaller screens. Firstly, the scanning is done using ITO on top of the touchscreen substrate. Although ITO can be protected by a thin, hard coat, it is prone to scratches from fingers, rings, keys, and so on. Apart from owns a non-linearity of the measuring field for the surface capacitance must be repaired when the border patterns, software, hardware, or methods. This linearization effect becomes more pronounced with smaller screens. Other implementation details such as the proximity effect and the shadow of the finger must be also addressed.
Flex Supplier
Flexible printed circuit assemblies (Flex) is used for connections touch sensor system controller board. FLEX has ever touchscreen controller connected to supply a "flex module. Alternatively, a simple flex circuit without a regulator can be supplied to the sensor manufacturer, in this case, the regulator IC is built into the board customers' system controller.
Sensor Supplier
Typically referred to as "Glass" or "movie" a supplier that the supply chain has an in-house capability to create a conductive pattern on a transparent substrate material. The most common conductor is indium-tin oxide (ITO), used for its relatively low resistance and high optical clarity. Other transparent conductors are in use or under development, but not yet mainstream. Typical sensors are substrates glass, film, or polycarbonate plastic derivatives. Some vendors have more vertical integration of sensors, such as touch screens controller IC ASIC products, electronics for the controller board, LCD supply flex connector power module or complete integration.
LCD Supplier
Touch screens are usually used in conjunction with a video screen, so it is logical for the manufacturer of LCD is important in the supply chain. Their core competencies have included the imposition of patterned ITO on glass and flex circuits LCD production. Therefore, it is much easier for them to vertically integrate these key elements of the chain, the touch screen menu. LCD manufacturers decided to simply offer to appear on third parties for integration into the touch screen modules, or integrated controller, the sensor glass, or flex circuits into their assembly.
Supply chain, logistics
Supply Chain Logistics Touchscreen production has several variations, depending on the supplier-customer sales engagement, the customer prefers to trade model, and vertical integration of suppliers. Customers can initially consider touchscreen controllers, sensors, and Flex LCD directly from different suppliers, and perform their own design and integration. Although it may be perceived cost advantages, puts all design, performance and quality issues directly to the customer. Each touch-screen design is unique, and therefore the controller must be configured to work correctly with the sensor characteristics, LCD noise, environmental factors and industrial design. It is often beyond the capacity customers' design for the first time. More frequently used approach is for customers to purchase custom designed and tested known good "touch screen module, from one of the members of the supply chain.
Touchscreen Modules
Touchscreen modules are sold in three main varieties depending on the final customers:
Flex Module
It is the combination of the controller IC and the flexible printed circuit. Flex modules are mostly purchased ITO sensor suppliers to reduce design cycle time touch and increase the yield touchscreen. FLEX module consists of a flexible circuit is attached touch screen controller IC, tested as a known good unit. Flex modules are typically supplied by manufacturers or customers ITO design completion controller IC via distribution channels. For the Asian market, it is a typical "intensity repeat," who works as a combination of manufacturer Representatives and value-added supply chain managers.
Touchscreen Module
This product combines flex sensor module and the ITO. Using flex module improves time to market and product reliability, while maintaining flexibility for sensor design. Touchscreen modules are usually offered by suppliers of ITO glass sensor or film to a large OEM and ODM customers to design end. Some controller IC manufacturers We also offer a full touch screen modules to facilitate the engineering design, although this range is usually limited to large direct customers. Most large customers have very specific market demands of industrial design and manufacture of 'look'. Subsequently, very few companies use off-the-shelf touch screen module. Most of them are custom designed by the component suppliers.
Touchscreen LCD Module
This is the highest level of integration. It combines a touch-screen LCD module with a complete touch screen devices. Design end-user customers will see this device as a black box, which is capable of displaying pictures and sending touch coordinates of the main system. It is highly desirable in terms of product reliability, because each Unit provides known good display and touch interface. Some manufacturers offer this type of LCD module as a product of the general market. For large volume OEM customers, manufacturers of touch-sensor on the LCD shipment and produce touch-screen LCD module glass, flex components and controller IC.
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