Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1998-05-22
2001-12-04
Liang, Regina (Department: 2774)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S090000, C345S098000
Reexamination Certificate
active
06326959
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display panel driver for driving a liquid crystal display panel or the like, and particularly to a display panel driver having a voltage step-up circuit
2. Description of the Prior Art
A display panel such as a liquid crystal display device is driven by a driver IC (integrated circuit) to achieve display. Such a driver IC is supplied with a power source voltage by a battery, and is controlled by a microcomputer to produce driving signals.
The driver IC includes a voltage step-up circuit for stepping up the power source voltage. The produced stepped-up voltage is fed to a display voltage producing circuit.
The voltage step-up circuit steps up the power source voltage in such a way that voltages stepped-up by different factors appear at different ports for output.
This conventional display panel driver, however, has the following disadvantage. The power source voltage supplied from the battery to the driver IC varies with the type of the battery. Accordingly, within the driver IC, to allow the display voltage producing circuit to receive an appropriate voltage in any situation, the voltage step-up circuit is provided with a plurality of output ports to output a plurality of voltages stepped-up by different factors.
For example, consider a case where the battery voltage Vin is 3.3 V and this voltage needs to be stepped up by a factor of three by the voltage step-up circuit to obtain a display voltage of 8.0 V from the display voltage producing circuit. In this case, if replacing the battery, for example, ends in reducing the power source voltage to 2.0 V, then it is impossible to obtain a voltage higher than 6.0 V simply by stepping up the power source voltage by a factor of three, and thus it is impossible to achieve display on the display panel.
One way to obtain a display voltage of 8.0 V at the maximum even when the battery voltage is 2.0 V is to set the voltage step-up circuit to step up the voltage by a factor of five, feed the stepped-up voltage to the display voltage producing circuit, and adjust it to 8 V by the use of an appropriate adjusting circuit. In this case, however, if the battery voltage Vin is 3.3 V, the voltage step-up circuit steps it up by a factor of five, that is, to 16.5 V. Such excessive stepping up of the voltage leads to unduly high current consumption.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a display panel driver that does not produce an excessively high stepped-up voltage and that does not require the provision of a plurality of output ports.
To achieve the above object, in one embodiment of the present invention, a display panel driver is provided with a control means for monitoring the power source voltage supplied from the power source and outputting a control signal in accordance with the power source voltage. The control signal is fed to a voltage step-up circuit. The voltage step-up circuit steps up the power source voltage supplied from the battery by a factor specified by the control signal, and outputs a stepped-up voltage. From the voltage outputted from the voltage step-up circuit, a display panel driver circuit produces signals for driving a display panel.
In this construction, it is possible to set an appropriate voltage step-up factor in accordance with the power source voltage, and thus it is possible to avoid excessive stepping-up of the voltage and thereby obtain an appropriately stepped-up voltage.
Moreover, according to the present invention, it is also possible to detect the ambient temperature around the display panel by the use of a temperature sensor so that the control circuit will output the control signal in accordance with the ambient temperature.
In this construction, even with a display panel such as a liquid crystal display panel whose response varies with the ambient temperature, the control circuit can compensate for such variation, and thus it is possible to obtain an appropriately stepped-up voltage.
REFERENCES:
patent: 4123671 (1978-10-01), Aihara et al.
patent: 5198747 (1993-03-01), Height
patent: 5317332 (1994-05-01), Kanno et al.
Arent Fox Kintner & Plotkin & Kahn, PLLC
Dinh Duc Q
Liang Regina
Rohm & Co., Ltd.
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