Kwan-young Oh

CCFL backlight solution for low-cost liquid crystal televisions without image artifacts

Recently, a single-phase CCFL (cold cathode fluorescent lamp) driving method has been adopted to provide a low cost implementation. However, whereas dual-phase driving compensates the coupling effect on the pixel electrodes, single-phase high voltage driving signals are coupled to pixel electrodes through parasitic capacitance between the lamps and panel electrodes. As a result, image artifacts appear on the display screen. This paper describes the analysis results of this phenomenon. Furthermore, the proposed automatic delay compensation scheme eliminates the artifacts caused by the coupling effect, regardless of how much delay is generated by the lamp driving circuit.

Analytic solution to remove flickers on a liquid crystal display television

Flickers have been critical issues on liquid crystal displays (LCDs) which use a backlight unit (BLU) under a panel. The luminance modulation of the backlight and the transmittance of the panel are independently investigated in frequency domain to look for an analytic solution to remove flickers on the LCD panel. The transmittance of the panel depends on how to drive the LC molecules and how the LC molecules respond. We shows there are three frequency components caused by only the panel driving. It is shown that the flicker can be generated by the inter-modulation effect between two different frequency groups from the BLU and the panel. To remove flickers on LCD TV panels, the frequency of the PWM backlight signal should be carefully chosen so that the inter-modulation frequencies may be higher than 60 Hz. It is shown that it is impossible to perceive flickers on an LCDTV operating at 120 Hz refresh rate if the frequency of the PWM signal is 120 Hz or 180 Hz.

P‐53: Automatic LCD Gamma Curve Optimization

To achieve completely consistent LCD panel-to-panel color performance in mass production, novel algorithms have been developed for automated tuning and programming of LCD gamma. Optimal gamma is derived using a digital gamma buffer (DGB) and a linear scan method (LSM) as a simple but accurate solution. Another approach uses a V-T curve interpolation method to achieve shorter tact time.

P‐54: Automated Flicker Reduction for Large TFT‐LCDs

A new algorithm and an automatic Vcom optimization method have been developed to minimize flicker in large TFT-LCDs. The region of acceptable flicker must be close to the minimum average flicker level with low variance of the flicker value on multiple panel locations. The method is processed by using a digitally adjustable Vcom controller in conjunction with a luminance measurement tool.