Development of 3+2 dynamic drive scheme for cholesteric liquid crystal displays

In order to achieve fast driving for reflective cholesteric liquid crystal display (Ch-LCD) we have developed a novel 3+2 dynamic driving scheme (3+2 DDS), which uses 3 and 2 level driver ICs for row and columns, respectively. From the transient dielectric study, the selection period of around 1.0 ms/line showed the best contrast ratio at 30 °C in our system. The time of the homeotropic to transient planar state is strongly dependent on temperatures. The row driver IC has 3 level outputs of R_H, R_M (R_H/2), and R_L; 32, 16, and 0 V, respectively. And the outputs of the column driver IC are composed of 2 levels. We found that a preparation period of more than 40 times and an evolution period of around 40 times of the selection period are suitable. Also, we have accomplished a stable gray scale by using, as we call it, the pulse position modulation (PPM) in which the root mean square (RMS) value of the applied field during the evolution period does not change, even under cross-talk pulses. The driving condition made by PPM is more stable than that made by the usual PHM and PWM techniques. By adopting the 3+2 DDS, we have made 8.4 in. foldable VGA Ch-LCD (640×480×2) that shows an addressing speed of around 1.0 ms/line.