Patent GB-1396486-A (GB)
Title: Display apparatus
IPC: H04N3/12
Filed: 1973-06-08
Abstract: 1396486 Television 0MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 8 June 1973 [8 June 1972 20 June 1972 (2) 20 Sept 1972] 27526/73 Heading H4F A matrix display panel 1 is controlled so that either the brightness of all the elements of an X-line, which is selected during the whole of one line period, is controlled during at least two separate portions of the line period (e.g. the line blanking and active line periods), or a plurality of X-lines (e.g. four) are sequentially selected during one line period, the most significant bits of the received video signal being appropriately delayed so that the brightness of the elements of each line are controlled more than once during each field and only by the information for that line. The matrix panel may be an electroluminescent panel, an array of light-emitting diodes or a plasma display panel. In a first embodiment, where one X-line is selected during the whole of one line period, video signals to be displayed are converted into 6-bit digital form by an analogue-to-digital converter 6 and registered in a memory MEM1. When a line of information has been written into memory MEM1 switches 8 and SwI-Swm are switched to the positions shown and a second memory MEM2 is set, the three least significant bits for each element thus being transferred from the memory MEM1 to the second memory MEM2. These three bits for each element are passed to respective AND gates in a respective circuit 3-j, to each of which gates is passed, from width control circuit 7, a respective one of three sequential signals of pulse width ratio 1: 2 : 4, to provide, for each element, one of eight pulse widths corresponding to numbers 0-7. At the end of the line blanking period switches 8 and Sw1- Swm are switched to their opposite positions, second memory MEM2 is set, and the three most significant bits are transferred from memory MEM1 to second memory MEM2, the output of width control circuit 7 again being three sequential signals of the same pulse width ratio as before, to provide a second brightness control signal for each element. In a second embodiment where four X-lines are sequentially selected during each line period (Fig. 4, not shown), the apparatus operates as above during the line blanking periods. The most significant bits from converter 6, are however, connected to memory MEM1 by respective delay lines such that the most significant bit is delayed by 180 line periods, the seond most significant bit is delayed by 120 line periods and the third most significant bit is delayed by 60 line periods. The thus delayed three most significant bits are stored in memory MEM2 for the active line period as before, but during this period width control circuit 7 provides three equal width sequential signals to the respective AND circuits, so that the third most significant bits are passed to the respective line elements during the first third of the active line period, during which time the appropriate X-line is selected, the second and first most significant bits similarly being passed by the AND gates during the second and third thirds of the active line period respectively. Each X-line is thus selected four times during each field.