Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1999-11-12
2002-09-17
Wu, Xiao (Department: 2674)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S205000
Reexamination Certificate
active
06452590
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a device for driving a display panel such as a plasma display panel (PDP), a plasma addressed liquid crystal (PALC), a liquid crystal display (LCD) or a field emission display (FED).
The display panel is widely used as a device that can substitute for a CRT in various fields. For example, a PDP is available in the market as a flat type television set having a wide screen above 40 inches. One of the challenges for making the wide screen with high definition is to control capacitance between electrodes.
2. Description of the prior art
The display panel has an electrode matrix including scan electrodes for row selection and data electrodes for column selection. On each cross point of the scan electrodes and the data electrodes, a single display portion having a display element is disposed. The display element of a PDP and a PALC is a discharging cell. An LCD has a liquid crystal cell as the display element and the FED has a field emitter as the display element. A surface discharge type PDP that is available in the market has two electrodes for each row. However, only one of the two electrodes is used for row selection. Therefore, the electrode arrangement of the surface discharge type PDP is regarded as a single matrix similar to the others from the viewpoint of selecting the display element.
Contents of the display is decided by the selective addressing (i.e., addressing of row). An addressing period of one frame is divided into row selection periods of the number same as the number of rows of the screen. Each scan electrode is biased to a predetermined potential in one of the row selection periods so as to be active. In synchronization with this row selection, display data for the row is output from all data electrodes. In other words, potentials of data electrodes are controlled simultaneously in accordance with the display data. The most typical method for controlling the potentials of the data electrodes is to dispose a switching device between each output terminal of plural power sources having different potentials and the data electrode, and to control the switching device by a pulse signal synchronizing with the row selection so as to connect or disconnect the output terminal of the power source and the data electrode.
A driving method in which the addressing and sustaining required for an AC type PDP are separated on the time axis is widely used for the AC type PDP. The addressing is performed for forming charge distribution corresponding to the display data, and then discharge in gas is generated utilizing wall electric charge by the number of times corresponding to intensity. In the sustaining period, a voltage pulse is applied to a pair of two electrodes alternately, so that the relative potential between the electrodes changes periodically. Along with this change of the relative potential, a capacitance between the electrodes (hereinafter, referred to as an interelectrode capacitance) is charged and discharged repeatedly. The charging and discharging of the interelectrode capacitance are waste of electric power that cannot contribute to light emission. In order to reduce the power loss, the PDP has a power recycling circuit including a capacitor and an inductor having predetermined capacitance and inductance. The charge of the interelectrode capacitance is discharged into the capacitor for recycling, and the charge of the capacitor is retrieved to charge the interelectrode capacitance for reusing repeatedly. The inductor is disposed between the capacitor and the interelectrode capacitance so as to form a resonance circuit that speeds up the movement of the charge and enlarges an amplitude and a reuse ratio of the charge (i.e., a power recycling ratio).
In the above-mentioned sustaining period, a constant pattern of voltage pulse is applied to the plural electrodes wothout depending on the display data. Therefore, only one power recycling circuit is necessary for the electrodes. However, in the case of addressing, the potential of each data electrode depends on the display data, and the relative potential between the neighboring data electrodes is not constant. Therefore, in order to reduce the power consumption due to the interelectrode capacitance in the addressing, each data electrode requires one power recycling circuit. Since the capacitor and the inductor having a sufficient capacitance or inductance are difficult to be packed into an IC chip, the driving device becomes large size, and the number of man-hours required for manufacturing becomes a large. In addition, in order to avoid floating of a logic circuit for generating switching signals, isolation is needed between the logic circuit and the power recycling circuit, resulting in a complicated and expensive circuit configuration. For this reason, the conventional display panel available in the market does not recycle the power for addressing.
High definition and wide screen are being promoted for display panels, so that the number of data electrode and driving frequency is increasing. Therefore, power consumption of the. interelectrode capacitance is being a big problem. Especially, for PDPs, the power consumption in the addressing period is coming close to that in the sustaining period, so the power recycling will be necessary for the addressing too. If trying to reduce the power consumption without the power recycling, the number of displayed colors or the intensity should be restricted, which affects the display quality.
SUMMARY OF THE INVENTION
The object of the present invention is to reduce the power consumption due to the interelectrode capacitance in the addressing period, and decrease the number of components in the driving circuit.
In the present invention, for each of plural data electrodes, a discharging path to a power recycling circuit and a charging path from the power recycling circuit are disposed, and these paths are used separately in accordance with display data. In addition, if the q-th data and the (q+1)th data are the same in the display data given to each data electrode sequentially in synchronization with row selection of addressing, both the discharging path and the charging path are opened so as to keep the electrode potential.
Basically, providing four switches to each data electrode enables controlling connection between the data electrode and the power supply line or the ground line, and controlling connection with the power recycling circuit, so that plural data electrodes can share one power recycling circuit.
Furthermore, each data electrode can have two switches for controlling connection with the power recycling circuit, so that data electrode can share the switch for controlling connection with the power supply line or the ground line. In this configuration, electric power can be recycled without depending on the combination of display data by providing diodes adequately so that currents between data electrodes can be prevented. However, it is not always necessary to prevent the current between data electrodes. Namely, if the number of objects to be charged and the number of objects to be discharged are not the same in plural data electrodes that share one power recycling circuit, a potential difference is generated between the common connection node of the plural data electrodes and the recycling capacitor, so that charging current or discharging current will appear. Therefore, recycling efficiency is not zero. Only when the number of objects to be charged and the number of objects to be discharged are the same coincidentally, the potential of the common connection node becomes substantially the middle potential between the power source potential and the ground potential due to the current between data electrodes, and neither the charging current or the discharging current appears.
The switches for the data electrodes are packed into an IC chip. Thus, the driving circuit of the display panel having plural data electrodes can be realized in a small size. The switches t
Awamoto Kenji
Sakita Koichi
Yoshikawa Kazuo
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