Multi-touch Solutions Of Capacitive Touch Panel

As a human machine interactive input device, the touch panel is taking the replace ofkeyboard and mouse, and becoming an important part of electronic product gradually. Thecapacitive touch panel has the process of sputtering ITO on the empty glass,etching circuit onthe board, hot pressing the FPC(flexible printed circuit), laminating the cover glass and ITOsensor with OCA(Optical Clear Adhesive). The capacitive touch panel has more developmentin recent years, as the advantage of better transmission, supporting multi touch, a longerlife etc..Projective and mutual touch panel(projective touch technology, and mutual method)canrealize multi touch, has a better anti interference, may become the main touch technology inthe future. Now the main problem of projective and mutual touch panel is power commonmode interference. The key of projective touch panel is to find the proper detecting circuit,more excellent algorithm to realize reporting accurate coordinate of touch place, also have alower cost and power dissipation. As the development of capacitive touch panel in china isjust two to three years, the technology is immature. Some key technologies and patents setsome barriers to the development of capacitive touch panel.The theory and method study to capacitive touch panel can push the development ofcapacitive touch panel, and promote the international competition of touch panel.This study has a discussion on the realized method to multi touch, and give some solutionsto the anti interference in the design stage.(1) This study introduces three detections circuit of projective capacitive touch panel:switched capacitor method, charge transfer method and relaxation oscillator method. Giveexplanations to the principle and specialty. The relaxation oscillator method has moreapplication because has no barriers of patent.(2) Have an introduction to the structure and the design,including the design of coverglass, The main pattern design of ITO sensor and the reformed solution to the ITO patterndesign to improve interference by reducing the channel impedance. Also have an introductionto the structure of FPC, and the regulation of layout. Also have a introduction to the OCA.(3) The detective circuit collects the raw data, median filtering and take modified barycenter arithmetic method to the data, to get the more actual coordinate of touch place.At the last of this study, it give two examples, introduces the design examples of4.3inches and9.75inches and the demo effect of multi touch.