Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1998-09-23
2001-11-27
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S204000
Reexamination Certificate
active
06323851
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circuit and a method for driving a display device, more particularly to a circuit and a method for driving a display device which can prevent undesired bright lines or spots from appearing on a display screen when power supply is cut off
2. Description of the Related Art
A display device is driven with a voltage which is higher than a source voltage supplied from a battery or the like. To obtain such a drive voltage, a drive circuit of the display device comprises a booster circuit for boosting a source voltage from a battery or the like up to a plurality of predetermined high voltages. The drive circuit has its power source circuit and it outputs a plurality of different voltages because the display device needs different voltages to its scanning electrodes and signal electrodes for time-sharing addressing.
A booster circuit or a dividing circuit is used as such a power source circuit which outputs a plurality of different voltages. The booster circuit boosts a source voltage into a plurality of different voltages. The booster circuit boosts a voltage by switching connection of a plurality of capacitors so that charged voltages in the capacitors are added to each other. The dividing circuit divides a previously boosted voltage into a plurality of different voltages. The dividing circuit divides a boosted source voltage with a series circuit of resistors or capacitors.
A capacitor-based booster or dividing circuit is advantageous to reduce its power consumption.
Each of output lines of the power source circuit has a plurality of capacitors in order to output stable voltages.
SUMMARY OF THE INVENTION
In a conventional drive circuit, charges remaining in capacitors on the drive circuit are supplied to a display device when the device is turned off and the supplied charges cause irregular bright spots or lines on a display screen.
For example, switch elements in the display device are in unstable state immediately after the device is turned off and some of them are in on-state irregularly. Charges in the capacitors are applied to the display device via thus activated switch elements. This causes the bright spots or lines which irregularly appear on the display screen. This unnecessary display is kept until the charges in the capacitors are almost discharged.
The present invention has been made in consideration of the above, and it is an object to prevent irregular display caused by power-off action of the device from occurring.
It is another object of the present invention to terminate activity of the display device without irregular display after the device is turned off.
To achieve the above objects, a driving circuit for a display device according to a first aspect of the present invention comprises: drive voltage generating means, to which electricity is supplied, for generating and outputting drive voltages for driving a display device;
drive means for driving the display device with the drive voltages from said drive voltage generating means; and
power-off state detection means for detecting that the power supply to the drive voltage generating means is cut off, and for outputting a detection signal to at least one of the drive voltage generating means and the drive means so as to execute predetermined power-off processing for controlling the display device not to light.
According to thus structured present invention, at least one of the drive voltage generating means and the drive means executes predetermined processing which causes the display device not to be lit when the power supply to the drive voltage generating means is cut off. This prevents irregular bright lines or spots from appearing on the display device after the device is turned off.
In the case where the circuit for driving the display device further comprises charge means, it is preferable that at least one of the drive voltage generating means and the drive means executes the predetermined power-off processing with the electricity charged in the charge means.
According to this structure, the charges in the charge means are exhausted because they are used for executing the predetermined processing. Thus, the irregular display caused by the charges is prevented from occurring. Moreover, the charge means is native to there for driving the display device, therefore, additional preparation of the charge means is not required.
In order to prevent the irregular display after the power-off from occurring, the drive voltage generating means may comprise power-off processing means which generate and output in response to the detection signal from the power-off state detection means a plurality of voltages which cause the display device not to light.
The drive voltage generating means may comprise, for example, capacitors to which electricity is supplied and are charged with the supplied electricity, and control means for generating a plurality of drive voltages. which drive the display device with the voltages charged in the capacitors.
The control means may include discharge control means which discharge the capacitors in response to the detection signal from said power-off state detection means.
In this case, the discharge control means connect both terminals of each of the capacitors, or connect the both terminals of each of the capacitors via a resistive load.
The control means may fix a voltage of at least one terminal of each of the capacitors to a predetermined voltage in response to the detection signal from the power-off state detection means. Thus, the charges which cause the irregular display are eliminated.
In the case where the drive voltage generating means comprises boost means which boost supplied voltages and the boosted voltages are output as the drive voltages, the drive voltage generating means may comprise control means which controls in response to the detection signal from the power-off state detection means the boost means to terminate the outputs of the boosted voltages or to reduce the boosted voltages.
The drive voltage generating means may comprise dividing means which has boost means for boosting the supplied voltage and outputting the boosted voltage, and means for dividing the boosted voltage into a plurality of voltages and controlling the boost means to terminate the output of the boosted voltage in response to the detection signal from the power-off state detection means. In this case, the output of the divided voltages may be terminated.
The drive voltage generating means may comprise dividing means which has boost means for boosting the supplied voltage and outputting the boosted voltage, and means for dividing the boosted voltage into a plurality of voltages and controlling the boost means to reduce the boosted voltage in response to the detection signal from the power-off state detection means. In this case, the divided voltages may be reduced.
The drive means may comprise power-off processing means which generate in response to the detection signal from the power-off state detection means voltages which cause the display device not to light and supply the generated voltages to the display device.
In the case where the display device lights when a voltage which is applied between opposing two electrodes is equal to or greater than a threshold voltage, the drive means may apply a voltage which is smaller than the threshold voltage between the opposing two electrodes in the display device in response to the detection signal from the power-off state detection means. That is, the voltage which does not cause the display device to light is applied between the opposing two electrodes of the display device after the display device is turned off, thus, the display device is turned to be in non-display state. This prevents irregular bright lines or spots from appearing on the display device.
The drive voltage generating means may comprise means for reducing an externally supplied voltage when the power-off state detection means detects that the power supply is cut off.
A method for driving a displa
Casio Computer Co. Ltd.
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Osorio Ricardo
Shalwala Bipin
LandOfFree
Circuit and method for driving display device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Circuit and method for driving display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Circuit and method for driving display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2618174