Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
2000-05-30
2003-10-14
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C315S169300
Reexamination Certificate
active
06633287
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a power supply circuit of an electro-optical device, a driving circuit of an electro-optical device, a method of driving an electro-optical device, an electro-optical device, and an electronic equipment, in which a reduced number of components are mounted.
2. Description of Related Art
In general, electro-optical devices can be classified into various types according to the driving method or the electrode structure. In an electro-optical device of the simplest type, a plurality of scanning electrodes (scanning lines) are formed on one substrate, a plurality of data electrodes (data lines) are formed on the other substrate, and an electro-optical material such as a liquid crystal is disposed between these two substrates, whereby an image is displayed by means of an electro-optical change caused by a potential difference between the two electrodes.
In such an electro-optical device, a selection voltage required to drive the electro-optical material is generally in the range of 20 to 25 V, which is much higher than input voltages of 3 to 5 V applied to logic circuits. In order to obtain such a high selection voltage, electro-optical devices generally include a power supply circuit using a charge pump circuit which generates the selection voltage by stepping up a voltage supplied from a single power supply.
However, the technique of generating the selection voltage using the charge pump circuit needs as many capacitors as the voltage stepping-up factor. In electro-optical devices, as described above, the input voltage has to be stepped up by a large factor to obtain the selection voltage, and thus the charge pump circuit needs a large number of capacitors.
Capacitors used in power supply circuits are generally large in size, and thus it is difficult to form them on semiconductor substrates. In most cases, therefore, capacitors of power supply circuits are not integrated on semiconductor chips, but they are instead mounted as external components. Therefore, if a large number of capacitors are used, the result is an increase in the total cost and an increase in complexity of the assembly process which causes a reduction in the production efficiency.
SUMMARY OF THE INVENTION
In view of the above problems, it is an object of the present invention to provide a power supply circuit of an electro-optical device, a driving circuit of an electro-optical device, a method of driving an electro-optical device, an electro-optical devices and an electronic equipment using an electro-optical device, which need a less number of externally mounted components and thus which allows simplification of the assembly process and a reduction in cost.
According to a first aspect of the present invention, to achieve the above object, there is provided a power supply circuit for supplying a potential to an electro-optical device which includes a plurality of scanning lines and a plurality of data lines, the scanning lines crossing the data lines, and the potential serving as a selection voltage for selecting a scanning line. The power supply circuit may consist of a voltage generation circuit for generating one of a selection voltage having a positive polarity and a selection voltage having a negative polarity, defined with respect to a median value of signal voltages applied to the data lines; a voltage storage element for storing a voltage based on the one selection voltage generated by the voltage generation circuit; and an inverter circuit for inverting the polarity of the voltage stored in the voltage storage element with respect to a predetermined reference value and outputting the inverted voltage as another one of the selection voltage having a positive polarity and the selection voltage having a negative polarity. The voltage generation circuit may consist of a switching element; and an inductor that stores electric power between a first input voltage and a second input voltage when the switching element turns on, and that releases the stored electric power when the switching element turns off, whereby, using the electric power released from the inductor, the voltage generation circuit generates the one of selection voltage having a positive polarity and the selection voltage having a negative polarity with respect to the median value of signal voltages applied to the data lines.
In the power supply circuit according to the first aspect, either one of the selection voltages having positive and negative polarities applied to the scanning lines is generated by the voltage generation circuit using electric power which is released from the inductor when the switching element is turned off. This allows the one selection voltage to become greater than the difference between the first and second input potentials. Furthermore, in the power supply circuit according to the first aspect, the other selection voltage is generated by the inverter circuit by inverting the polarity of the one selection voltage stored in the voltage storage element after being generated by the voltage generation circuit. Thus, in the power supply circuit according to the first aspect of the present invention, it is possible to reduce the number of components such as voltage storage elements which cannot be formed on a semiconductor substrate, and thus, which have to be externally mounted without causing an increase in electric power consumption. Therefore, the first aspect of the present invention allows the components to be mounted in a simpler fashion, and brings about cost reduction. As for the voltage storage element used in the present invention, a capacitor or a secondary battery capable of charging and discharging may be employed. The capacitor is more desirable because it can be produced in a small form.
In the power supply circuit according to the first aspect, the voltage generation circuit preferably further includes a control circuit for controlling a turning-on/off operation of the switching element in accordance with a comparison result of a voltage based on the electric power released from the inductor with respect to a target voltage. In this circuit configuration, the turning-on/off of the switching element is controlled by feeding back the output voltage, thereby regulating the selection voltage having the inverted polarity as well as the selection voltage having the non-inverted polarity, regardless of the load.
Preferably, the switching element is turned on and off using a pulse signal such that the generated electric power is controlled by adjusting the pulse width or the pulse intervals.
According to a second aspect, to achieve the above-described object, there is provided a power supply circuit for supplying a voltage to an electro-optical device including a plurality of scanning lines and a plurality of data lines, the scanning lines crossing the data lines, and the potential serving as a selection voltage for selecting a scanning line from the plurality of scanning lines. The power supply circuit may consist of a voltage generation circuit for generating one of a selection voltage having a positive polarity and a selection voltage having a negative polarity, defined with respect to a median value of signal voltages applied to the data lines; a voltage storage element for storing a voltage based on the one selection voltage generated by the voltage generation circuit; and an inverter circuit for inverting the polarity of the voltage stored in the voltage storage element with respect to a predetermined reference value, and outputting the inverted voltage as another one of the selection voltage having a positive polarity and the selection voltage having a negative polarity. The voltage generation circuit may consist of a transformer which inputs a pulse signal via a primary side of the transformer, the voltage generation circuit generating the one of the selection voltage having a positive polarity and the selection voltage having a negative polarity using a voltage output from a secondary side of the transformer.
In the power s
Yamazaki Katsunori
Yamazaki Suguru
Yatabe Satoshi
Jorgensen Leland
Oliff & Berridg,e PLC
Saras Steven
Seiko Epson Corporation
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