3538 IEICE TRANS. FUNDAMENTALS, VOL.E89–A, NO.12 DECEMBER 2006 PAPER Special Section on VLSI Design and CAD Algorithms A Sampling Switch Design Procedure for Active Matrix Liquid Crystal Displays Shingo TAKAHASHI † , Affiliate Member, Shuji TSUKIYAMA †a) , Masanori HASHIMOTO †† , Members, and Isao SHIRAKAWA ††† , Fellow, Honorary Member SUMMARY In the design of an active matrix LCD (Liquid Crystal Dis- play), the ratio of the pixel voltage to the video voltage (RPV) of a pixel is an important factor of the performance of the LCD, since the pixel voltage of each pixel determines its transmitted luminance. Thus, of practical im- portance is the issue of how to maintain the admissible allowance of RPV of each pixel within a prescribed narrow range. This constraint on RPV is analyzed in terms of circuit parameters associated with the sampling switch and sampling pulse of a column driver in the LCD. With the use of a minimal set of such circuit parameters, a design procedure is described dedicatedly for the sampling switch, which intends to seek an optimal sam- pling switch as well as an optimal sampling pulse waveform. A number of experimental results show that an optimal sampling switch attained by the proposed procedure yields a source driver with almost 18% less power consumption than the one by manual design. Moreover, the percentage of the RPVs within 100±1% among 270 cases of fluctuations is 88.1% for the optimal sampling switch, but 46.7% for the manual design. key words: active matrix LCD, CAD tool, column driver, sampling pulse, sampling switch 1. Introduction LCDs (Liquid Crystal Displays) have established a firm foothold on the market as flat panel displays, first for cal- culators, subsequently for personal computers, mobile ap- pliances, digital cameras, and so forth, and at present with increasing importance for TVs. Thus, development is con- tinuing further on improving the picture quality as well as on the picture function of LCDs, and hence the design automa- tion has to be enhanced more and more for column drivers which affect most the performance of LCDs [1], [2]. In a TFT (Thin Film Transistor)-addressed LCD, usu- ally called an active matrix LCD, as illustrated in Fig. 1, the grey shade of each pixel is controlled individually by a designated pixel voltage. In each column driver, a pair of nMOS TFT and pMOS TFT connected in parallel con- stitutes a sampling switch, as shown in Fig. 2, which is to sample the video signal and then to transmit the signal to the source line. Manuscript received March 17, 2006. Manuscript revised June 13, 2006. Final manuscript received July 31, 2006. † The authors are with the Dept. of Electrical, Electronic, and Communication Eng., Chuo University, Tokyo, 112-8551 Japan. †† The author is with the Graduate School of Information Sci- ence and Technology, Osaka University, Toyonaka-shi, 560-8531 Japan. ††† The author is with the Graduate School of Applied Informat- ics, University of Hyogo, Kobe-shi, 650-0044 Japan. a) E-mail: tsuki@elect.chuo-u.ac.jp DOI: 10.1093/ietfec/e89–a.12.3538 Fig. 1 Active matrix LCD. Fig. 2 Column driver in active matrix LCD. During the period when all pixels in a row are activated by a gate line, a video voltage is fed to each pixel in the row from column to column so as to display a designated gray shade, whereas all pixels in other rows are blocked by grounding their gate lines. Thus, during this period each column driver has to transmit a designated voltage to a pixel in the row, one at a time from left to right, and hence the Copyright c  2006 The Institute of Electronics, Information and Communication Engineers