Sustain-during-erase
Even with the use of the selective erase technique, the amount of time available for discharging the cells continue to impose a limitation on the brightness and contrast of the picture of an HD panel. To overcome these limitations, a new scanning technique has been developed known as ‘scan-during-sustain’, SDS. As the name suggests, with SDS, scanning and sustaining are carried out simultaneously.
In the SDS technique, the row electrodes are grouped into a number of blocks. At any one time, two of the blocks known as the scan blocks are addressed while the other blocks, known as sustain blocks are discharged. The process is then repeated with two different blocks being addressed while the remaining blocks are sustained and so on. Thus scan pulses are applied to the scan blocks simultaneously with the sustain pulses to the sustain blocks. For example, an SXGA panel which contains 1024 row elec- trode pairs and 1024 X 3 = 3840 data D electrode is divided into eight blocks: B1 – B8. Each block contains 128 pairs of S and C electrodes. In each block, the scan electrodes are driven separately while the common (sustain) electrodes are connected and driven together as shown in Figure 10.15. The odd numbered blocks use the left side of the panel for S and the other side for C electrode connections. The reverse is true for the even numbered blocks. With this arrangement, a single type of drive board can be used for both left and right sides of the panel.
Greyscale and colours
In digitised video applications, the number of colours that may be dis- played depends on the number of greyscale levels available and that of course is determined by the number of bits allocated to each colour. In broadcast application 8 bits are allocated to each primary colour making a total of 24 bits for the RGB video signal, hence the name 24–bit video. Each colour thus have 28 greyscale levels and hence a pixel with three colour
cells can produce 256 X 256 X 256 (or 224) = 16.778 million colours. A 10-bit video results in 210 X 210 X 210 = 230 = 1.07 billion colours and so on. In general, the number of colours = 2n where n is the total number of bits allocated to the video which for a 24-bit video is 24 bits. However, with the introduction of SFs, the number of greyscale levels and with it the number of colours is now dependent on the number of SFs which may be different than the original bit allocation at the analogue-to-digital converter stage. In modern plasma panels, 10, 11, 12 and even 13 SFs are used which allows manufacturers to claim astronomical number of colours. For instance, 10 SFs would produce 210 = 1024 greyscale levels and 1024 X 1024 X 1024 (or 230) = 1.07 billion colours. As for 12 SFs, the figure is 67.8 billion. Increasing the number of SFs does not improve the inherent quality of the picture as the amount of video information remains unchanged. It merely allows it to be presented differently, which as we will see later, does enhance the video experience.