Analysis of luminance variation with display load and display pattern in AC-plasma display panels
Introduction
The luminance of current plasma display panels (PDPs) is controlled by the number of applied sustain pulses. Theoretically, if the number of applied sustain pulses is constant, the luminance should also remain constant, regardless of the display load determined by the ratio of the displayed area to the entire panel area. However, in the case of current ac-PDPs, the luminance varies according to the display load, even when applying the same number of sustain pulses [1], [2]. Furthermore, the luminance also varies according to the display pattern, even under the same display load. As a result, the gray level expression of ac-PDPs is degraded, along with the quality of dynamic and static images. Therefore, this problem needs to be solved urgently to improve the image quality of ac-PDPs. In previous experimental results, the current authors found that the luminance variation according to the display load or display pattern was strongly related to the distortion of the sustain waveform, especially the distortion of the rising slope of the sustain waveform [3], meaning that a change in the display load or display pattern causes a variation in the sustain discharge characteristics, thereby inducing different luminance levels.
Accordingly, this paper investigates the luminance variation relative to the display load and relative to the display pattern under a consistent display load (8%) in a 50-in. full-HD PDP. To identify the cause for the luminance variation with the display load or display pattern, the distortions of the sustain waveforms and related IR emission characteristics are measured relative to the display load or display pattern. In particular, the changes in the resistance and capacitance relative to the display pattern are measured and calculated to identify the cause for the distortion of the sustain waveform. Finally, the rising slopes of the sustain waveforms are properly controlled using an energy recovery circuit to compensate for the luminance variation resulting from the display load or display pattern.
Section snippets
Experiments
The pixel pitch of the 50-in. full-high definition (full-HD) ac-PDP used in this study was 576 × 192 μm. The discharge gas composition was a Ne + He (35%) + Xe (15%) gas mixture, and the gas pressure was 420 Torr. The 50-in. test panel included box-type barrier ribs and three electrodes: two sustain (X, Y) and one address (A). The sustain frequency was 200 kHz.
Fig. 1 shows the test patterns relative to the display load, ranging from 10% to 100%. Here, the display load means the ratio of the displayed
Luminance variation according to display load
Fig. 3 shows the changes in the luminance relative to the display load. In this study, the number of applied sustain pulses was fixed at 256, regardless of the variations in the display load. As shown in Fig. 3, the luminance decreased with an increase in the display load. In particular, when the display load was increased from 30% to 70%, which is typical when displaying a dynamic image, the corresponding luminance was decreased by about 43%, representing a severe degradation of the gray level
Conclusion
When increasing the display load, the sustain waveform, especially the rising slope of the sustain waveform, was severely distorted and the resultant IR emission intensities reduced, resulting in luminance variation according to the display load. Thus, the higher luminance with a display load below 50% could be significantly compensated by adopting a sustain waveform with a slower rising slope, whereas the lower luminance with a display load above 50% could be significantly compensated by
Acknowledgement
This study was supported by the BK 21 Project.
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