Hisao Fujiwara

A new low‐image‐lag drive method for large‐size LCTVs

— A new low-image-lag drive method is proposed for large-size LCTVs, taking into account the input signal and inter-field differential signal dependence of the response time. It was shown that the gray-level response time was 30–60 ms, which is 2–3 times as long as the ON-OFF bi-level response time, and was expressed as a linear function of the input voltage. With the new level adaptive overdrive (LAO) method, the response time was reduced to 17 ms, which is about one-half to one-third that of the conventional method and is satisfactory for TV applications. A 10.4-in. panel has been used to verify the effect of LAO on image quality. Moving images have been clearly observed using the LAO method.

Low‐temperature poly‐Si TFT‐LCD with an integrated analog circuit

— We have developed a 6-bit D/A converter and amplifier integrated low-temperature poly-Si TFT-LCD in which an integrated signal-line driver is driven by a 5-V power supply. We have employed a D/A converter including a new capacitor array and an original amplifier comprised of serially connected comparators to achieve high accuracy. The D/A converter performs gamma correction using upper significant bits of input data. Control signals for these circuits were generated by the integrated timing circuit. These advances in integration have been achieved for the first time using 3-μm design rule and improved LTPS TFT technologies and provide an advanced display system with lower power consumption, smaller module size, and higher durability.

Equivalent Circuit Model for Thresholdless Antiferroelectric Liquid Crystal Displays

For high quality displays, analog responding liquid crystals with spontaneous polarization need to be coupled with active matrix driving schemes. Our goal is to investigate the possibilities for optimizing liquid crystal materials, thin film transistors, and driving schemes. In this paper, the electrooptical properties of thresholdless antiferroelectric (TLAF) liquid crystal displays (LCDs), which are analog responding, are modeled using an electric circuit which can be applied to conventional simulators. A novel procedure for deducing the circuit parameters on the basis of the experimental results is discussed. It was found that the voltage-dependent capacitance due to the induced spontaneous polarization is important for describing the static and dynamic behavior at different applied voltages. It is shown that our equivalent circuit model reproduces the pixel voltage as well as the transmittance of active-addressed TLAF-LCDs.

A 15‐in. XGA thresholdless antiferroelectric LCD addressed by TFTs and using the quasi‐dc driving method

— A 15-in. TFT-LCD with XGA resolution using thresholdless antiferroelectric liquid crystal (TLAF) has been developed. TLAF materials show V-shaped switching and enable display of analog gray scale, wide viewing angle, and fast response. However, in the case that high-resolution TFT-LCDs using materials with large spontaneous polarization such as TLAF were driven by the conventional method, alternating current (ac) driving, the obtained contrast ratio was limited because of a sharp decline of holding voltage due to the growth of a depolarization field. In order to enhance the contrast ratio, a novel driving method referred to as quasi-dc driving was proposed. In the quasi-dc driving, the polarity of the applied voltage to liquid crystals inverts at certain intervals of several seconds. Moreover, the applied voltage and the charging time at the time of polarity inversion are increased more than the intended signals. By this method, the 15-in. TFT-LCD using TLAF with high contrast ratio (more than 100:1) and wide viewing angle was realized.

New high‐quality drive methods for high‐resolution LCTVs

— New flicker-reduction and high-speed drive methods are proposed for use in high-resolution liquid-crystal TVs. The new flicker-reduction delta-inversion drive method changes the drive polarity in every line and field. In addition, one of the three color pixels in the same line is driven in reverse polarity. In this method, the plain flicker due to field-inversion driving is transformed into a column flicker similar to the column-inversion drive method. The column-flicker spatial frequency in our method is the highest of that in any other flicker-reduction drive method for high-resolution LCTVs with more than 1000 horizontal pixels. The high-speed preparatory drive method is achieved by driving individual pixels twice per field. The first drive is a dummy drive made two lines before the actual drive. The second drive is the actual drive. The drive time can be virtually twice as long as that for conventional methods, if the vertical image correlation is strong. The combination of these two methods yields high-quality images for large-size and high-resolution LCTVs.

A high-speed LCD drive method for HDTVs.

高精細液晶テレビ用高速駆動法を考案し, 解析した.本駆動法は, 画像信号の垂直方向の相関を利用し, 2ライン前で予備駆動を行うことを特徴としている.本駆動法により, 3000 (H) ×1000 (V) ドットを持つ40インチ高精細液晶テレビの駆動周波数を最低でも22%高速化することができた.