A binary readout circuit for photo detector equipped LCD panel

• Main Authors: Chia-Feng Chen, 鄭家豐
• Other Authors: Huey-Liang Hwang
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/54791386001397737404

碩士 === 國立清華大學 === 產業研發碩士積體電路設計專班 === 95 === Recently, for interactive purposes, detecting devices are been developed on the existing TFT-LCD panels. Many of them are based on resistive, capacitive or inductive touch technology. All these solutions require externally added components or one more layer of screen, which add the cost and degrade the optical performance. In our study, we use a novel approach by building an additional TFT photo-diode in the existing LCD display pixel as a detecting element. This diode can be embedded during the panel manufacturing process and incurring no additional cost. After the post-product evaluation, this diode also shows no impediment to the light efficiency. In this way, by using the photo-diode array and by going with a designed detecting circuit, the imaging signal that appears on the panel can then be read out. In this study we investigate a binary read out circuit that can be used to distinguish an ON/OFF signal that comes from a light beam spot shone on a photo detector array equipped in a LCD panel. In this structure, because the back light source can cause error during the signal read out period, here we used the correlated double sample (CDS) method to reduce the noise. By this way we can trace the moving light spot locus on the panel and transfer the coordinate data to the following processor for further processing. Besides, we used the hysteresis comparator as an analog to binary signal converter. This comparator circuit has designed with a bistable characteristic that has an adjustable threshold, so that the other noise influence such as thermal noise and dark current that comes from the LCD panel can be minimized. The parameters that influence the threshold variations and loop of hysteresis are observed. The circuit proposed above is design in a TSMC 0.35um process and verified by HSPICE program.