1. Field of the Invention
This invention relates to a display driving device which performs scan driving of a plasma display panel (hereafter “PDP”) or other display panel, and in particular relates to a display driving device incorporated into an integrated circuit.
2. Description of the Background
A PDP uses light emission at the intersections of a matrix of electrodes accompanying a rare gas plasma discharge, causing light emission at the intersections of row electrodes and column electrodes selected by a scan driver and a data driver respectively. FIG. 7 is a block diagram showing the configuration of a scan driver IC of the prior art in such a PDP.
A scan driver IC comprises numerous unit circuits (output circuits); the unit circuits, or their output, are called bits. Scan data (DATA) input from the data terminal of a scan driver IC is transferred, in the direction of the arrow in the figure, to shift registers SR1 to SRN (where N is an integer) in synchronization with a clock signal (CLK). The ith bit (i=1 to N) comprises a selection circuit SEi, level shifter LSi, H (high) side pull-up switching element Nui, and L (low) side pull-down switching element Ndi, and bit outputs Do1 to DoN are obtained. The selection circuits SEi perform selection and switching of display mode operation and write mode operation, and execute control of delay time (dead time) such that the pull-up switching element Nui and pull-down switching element Ndi are not turned on simultaneously.
FIG. 8 shows the configuration of the output circuit for one bit in the above scan driver IC. IGBTs are preferably used for the pull-up switching element Nu and pull-down switching element Nd, but it will be appreciated by those skilled in the art that other types of devices may be used instead. Ci indicates the load capacitance.
In the shift registers SR1 to SRN, when data transferred to Si is at a high or H level, the pull-down switching element Ndi is turned on and the output Doi goes to a low or L level, and when the data transferred to SRi is at the L level, the pull-up switching element Nui is turned on and the output Doi is at the H level. Further, when in scanning mode as shown in FIG. 9, in the N-bit output Doi (i=1 to N), the L-level output is outputted in sequence. FIG. 9 is a timing chart showing operation of a scan driver IC of the prior art. When the output Doi is at the L level, the corresponding row of the PDP is selected.
However, in recent years there have been urgent demands to reduce the costs of the above scan driver ICs, accompanying falling prices for PDP televisions. Reduction of the chip size is an effective means of lowering the cost of scan driver ICs. Hence it has been proposed that the H-side pull-up switching elements Nu1 to NuN be replaced with resistance elements R1 to RN. FIG. 10 is a block diagram showing the configuration of another such scan driver IC of the prior art. Also, FIG. 11 shows the configuration of the output circuit for one bit in the scan driver IC of FIG. 10.
By replacing the pull-up switching elements Nui with resistance elements Ri, the H-side pull-up switching elements Nui are eliminated, and the level shifters LSi driving them also become unnecessary and can be omitted. In the case of a scan driver IC, the total area occupied by the level shifters LS1 to LSN, which convert logic signals at approximately 5 V to high-voltage signals at approximately 120 V, is approximately 15% of the total, and so elimination of these level shifters LS1 to LSN is effective for reducing costs.
In addition, in order to reduce the chip size of driving voltage supply circuitry for line-sequential driving with large currents in the above-described display driving device, without requiring special circuit elements or processes, it has been proposed that the resistance elements Ri of FIG. 11 be replaced with diodes Di, and that the cathodes of the diodes Di be connected to the pull-down switching elements Ndi, while also providing pull-up PMOS transistors connected in common to a plurality of diode anodes between this connection point and the driving voltage VDH (see for example Japanese Patent Laid-open No. 2005-129121).