應用於大尺吋電容式觸控面板之前端感測電路設計

Abstract

本論文目的為設計大尺寸投射電容式觸控螢幕之感測讀取電路與系統實現，並提供兩種方法實現觸控面板的讀取電路。電容式觸控螢幕是由銦錫氧化物（ITO）透明導電薄膜所構成，由於手指接觸面板後所產生ITO電極間的電容變化大小來判斷物體的移動情形。大尺吋電容式觸控面板之特別之處在於ITO所構成的阻值甚大(>200KΩ)，將使微小電容變化之訊號衰減，不易判斷是否手指有觸碰，且大尺吋電容式觸控面板除了阻值大之外，亦會受到周遭溫度、濕度…等環境干擾的因素，使得面板量測出的ITO電容值並不固定，會隨週遭環境改變。以往對於電容式觸控電路設計多採取直流方式對電容充放電，進而量測其觸碰前後之變化，此種方法可適用於小尺吋面板，因為其ITO所造成的阻值較小(10KΩ)。本論文所提出的大尺寸電容式觸控面板前端感測電路是針對12吋以上投射電容式觸控面板而設計，改以交流的形式進行面板電容值的偵測，如此可以大幅減少直流驅動造成的電容充放電時間。本論文提出的兩種感測電路分別是積分器感測電路與差動比較感測電路，兩種電路均搭配其前端的低干擾掃描陣列，此陣列可降低環境對觸控面板上ITO所所造成的干擾，而電路前端之觸控面板則由奇菱科技公司所提供的12.1吋投射電容式觸控面板來進行實際量測。在積分器感測電路部分，由低干擾掃描陣列與電容-電壓轉換電路所構成,而差動比較電路的部分則由低干擾掃描陣列、電容橋式電路與差動放大電路所組成，並經由下線實作成IC進行量測。最後再由FPGA撰寫UART傳輸晶片與VB程式語言來進行對電腦的串列資料傳輸，並傳送數值給電腦分析。本論文所提之感測電路部分皆已成功下線至台積電0.35um 2P4M 3.3V混合訊號互補式金氧半導體製程，並結合前端12.1吋電容式觸控面板與後端程式構成整個系統，並已實際測試其可行性。研究下線晶片經由財團法人國家實驗研究院晶片系統設計中心贊助，兩次下線的晶片面積分別為1.281×1.281 mm2 以及 0.91×0.775 mm2。

The study proposes the sensing circuit for a large-sized capacitive touch panel. The panel consists of two parallel Indium Tin Oxide (ITO) film layers which are separated by a sensor glass layer. Our goal is to design a capacitive sensing circuit for a large-sized capacitive touch panel (PCT) (more than 12in.), where large electrode resistance (> 200kΩ) and capacitance shifts due to environmental disturbance are commonly presented to make extreme difficult a successful touch detection. The method of DC charge and discharge into the ITO capacitance is adopted for smaller-size (< 7in.) ITO panels, where a lower resistance (< 90kΩ) is presented. A new AC sensing technique is developed herein to enable the touch sensing in a larger-size (> 12in.) ITO touch panel. For the sensing circuit design, integrator’s and differential methods are developed. Both methods have low-disturbance sensing arrays to eliminate the effect of the environments. A 12.1" projected capacitive touch panel is provided by CHILIN Co. Ltd. for testing. All the sensing circuits are accomplished via IC taped-out and realized for the projected capacitive touch panel. The output is transmitted from the IC by Universal Asynchronous Receiver/Transmitter (UART) chip of FPGA. A personal computer displays whether or not the touch panel is touched via a set of serial data transmitted from the FPGA module and Visual Basic (VB) program. Finally, the circuit is also accomplished by using Taiwan Semiconductor Manufacturing Company (TSMC) 0.35μm 2P4M 3.3V mixed‐signal CMOS process. The proposed chips, with the die area of 1.281×1.281 mm2 and 0.91× 0.775 mm2, are carried out by National Chip Implementation Center (CIC).