(a) Field of the Invention
The present invention relates to an alternating current (AC) plasma display panel (PDP). More specifically, the present invention relates to an apparatus and a method for driving scan electrodes of the AC PDP, which are capable of reducing the number of driving switches in a scan Y electrode driving circuit, to thus set the path of the flow of current between the PDP and the driving circuit.
(b) Description of the Related Art
In general, a plasma display panel (PDP) is a flat panel display for displaying characters or images using plasma gas discharges. Pixels ranging from hundreds of thousands to more than millions are arranged in the form of a matrix depending on the PDP size. PDPs are classified into a direct current (DC) PDP and an alternating current (AC) PDP based on the waveform shape of driving voltages and the discharge cell structure.
The most significant difference between the DC PDP and the AC PDP is that, in the DC PDP, the current directly flows in the discharge area while applying voltages, because electrodes are exposed to the discharge spaces. Therefore, a resistor that restricts the current must be used outside of the DC PDP. On the other hand, in the AC PDP, the current is restricted because capacitance is natually formed by the dielectric layer covering the electrodes. The AC PDP has a longer life than the DC PDP because the electrodes are protected against the ion shocks generated by the discharge. A memory characteristic is one of the important characteristics of the AC PDP and it is implemented by the capacity due to the dielectric layer covering the electrodes.
According to the light emission principle of the AC PDP, discharge occurs because an electric potential difference in the form of a pulse signal is formed in common electrodes (X electrodes) and scan electrodes (Y electrodes). At this time, vacuum ultraviolet (UV) rays generated in the discharge process excite red R, green G, and blue B fluorescent bodies. The respective fluorescent bodies emit light due to light combination. The discharge is affected by various parameters such as the kind and the pressure of the discharge gas inside the PDP, the secondary electron emission characteristic of an MgO protecting film, and the structures and the driving conditions of the electrodes.
In the AC PDP, because the common electrodes (the X electrodes) and the scan electrodes (the Y electrodes) for sustaining discharge operate as capacitive load, capacitance Cp is formed with respect to the X electrode and the Y electrodes. Reactive power other than power for discharge is necessary in order to apply waveforms for the sustain-discharge. A circuit for recovering and re-using the reactive power is referred to as a sustain-discharge circuit or a power recovery circuit.
FIG. 1 shows the arrangement of the electrodes of a common PDP.
The electrodes are in the matrix form of m columns and n rows. Address electrodes A1 through Am are arranged in the column direction, and scan electrodes SCN1 through SCNn and sustain electrodes SUS1 through SUSn of n rows are arranged in the row direction. The discharge area is positioned where the address electrodes and a pair of the scan electrode and the sustain electrode cross each other, and forms a discharge cell.
A conventional Y electrode driving circuit includes a power recovery unit, a reset pulse supplier, a scan buffer IC, and a scan pulse supplier.
The power recovery unit supplies power to a panel capacitor through switching operations based on the operation sequence, and recovers power after the discharge. The reset pulse supplier generates a reset pulse that resets each of the discharge cells. The scan buffer IC stores a scan pulse signal and outputs it according to predetermined timing. The scan pulse supplier selects the discharge cells to be turned on and the discharge cells not to be turned on.
According to the method for driving the panel by the Y electrode driving circuit, a frame comprises n sub-fields. Each sub-field includes a reset period, a scan period, a sustain period, and an erase period.
In the reset period, the address electrodes A1 through Am and the sustain electrodes SUS1 through SUSn are sustained at 0 V in the first half thereof. A ramp voltage that slowly increases from a voltage of no higher than a discharge starting voltage toward a voltage higher than the discharge starting voltage with respect to the sustain electrodes, is applied to the scan electrodes SCN1 through SCNn. In the latter half of the reset period, a ramp voltage that slowly decreases from the voltage of no higher than the discharge starting voltage of the sustain electrodes toward 0 V is applied to the scan electrodes.
In the scan period, all the Y electrodes are sustained at a predetermined voltage. An address voltage and a scan pulse voltage (0 V) are simultaneously applied to the address electrode and the Y electrode corresponding to the discharge cell to be displayed in the first row, respectively, to accumulate wall charges in the selected cells.
In the sustain period, a sustain pulse is applied to all the Y electrode and the X electrode to keep the sustain-discharge in the discharge cells according to the gray scales to be displayed.
In the erase period, an erase pulse is applied to all the X electrodes to stop the sustain-discharge.
In the driving circuit, to which such a panel driving method is applied, a plurality of switches are provided to the reset pulse supplier of a Y electrode driving circuit for generating a ramp waveform to be applied in the reset period. The switches open the path of the current that flows between the driving circuit and the panel, and they separate the power recovery unit from the scan pulse supplier when a reset waveform is generated.
In the conventional Y electrode driving circuit, switches play an important role in forming the circuit. However, a number of switches increase the manufacturing costs of the driving circuit. Also, the switches are located in the main current path, which is not desirable for the output characteristics of the respective driving signals.