Plasma display device and driving method thereof
View Patent ↗In conventional plasma display devices, reset by obtuse waves has been performed since discharge intensity becomes higher and background light emission is increased when reset by rectangular waves is performed. However, further improvement of the contrast to improve the image quality has been demanded. The present invention provides a driving method of a plasma display device using obtuse-wave reset in which sustain time of an achieved potential of the obtuse-wave reset is controlled in accordance with a display ratio of a video signal.
1. A driving method of a plasma display device having a reset period including a first period where a waveform in which a voltage is increased with time course is applied and a second period where an achieved potential of the waveform in which the voltage is increased is maintained,
wherein the second period is lengthened more in a case where a display ratio of an input signal is a second display ratio higher than a first display ratio than in a case where the display ratio is the first display ratio, and
an amount of increase in voltage per unit time of the waveform in which the voltage is increased is increased more in the case of the second display ratio than in the case of the first display ratio.
2. The driving method according to claim 1 , wherein the achieved potential is made higher in the case of the second display ratio than in the case of the first display ratio.
3. The driving method according to claim 1 , wherein the first period is shortened more in the case of the second display ratio than in the case of the first display ratio.
4. The driving method according to claim 1 , wherein the reset period further includes a period where a waveform of a negative potential in which a voltage is decreased with time course is applied.
5. The driving method according to claim 1 , wherein the reset period is substantially same in the case where the display ratio of the input signal is the first display ratio and in the case where the display ratio of the input signal is the second display ratio.
6. The driving method according to claim 1 , wherein the amount of increase in voltage per unit time of the waveform in which a voltage is increased with time course is made substantially constant by using a constant current source.
7. A plasma display device comprising:
a plasma display panel having a plurality of X and Y electrodes extending in a first direction and a plurality of address electrodes extending in a second direction intersecting the first direction;
a circuit for detecting a display ratio of an input signal;
a circuit for applying, to the Y electrodes, a reset waveform including a waveform in which a voltage is increased with time course; and
a control circuit for controlling the circuit for applying the reset waveform,
wherein the control circuit controls the circuit for applying the reset waveform so as to maintain an achieved potential of the waveform in which the voltage is increased,
wherein a period where the achieved potential is maintained is lengthened more in a case where the display ratio of the input signal is a second display ratio higher than a first display ratio than in a case where the display ratio is the first display ratio, and
wherein the circuit for applying the waveform in which the voltage is increased is controlled so that an amount of increase in voltage per unit time of the waveform in which the voltage is increased is increased more in the case of the second display ratio than in the case of the first display ratio.
8. The plasma display device according to claim 7 , wherein the control circuit controls the circuit for applying the waveform in which the voltage is increased so that the achieved potential is made higher in the case of the second display ratio than in the case of the first display ratio.
9. The plasma display device according to claim 7 , wherein the control circuit controls the circuit for applying the waveform in which the voltage is increased so that a period where the waveform in which the voltage is increased is applied is shortened more in the case where the display ratio of the input signal is the second display ratio than in the case where the display ratio of the input signal is the first display ratio.
10. The plasma display device according to claim 7 , wherein:
the circuit for applying the reset waveform includes a constant current source and a switch element connected to the constant current source,
the control circuit controls a current value of the constant current source thereby changing the amount of increase in voltage per unit time, and
the control circuit controls an on-time of the switch element, thereby changing the period where the achieved potential is maintained.
11. The plasma display device according to claim 7 , wherein the circuit for applying the reset waveform includes a variable resistor and a switch element connected to the variable resistor, and wherein the control circuit controls a resistance value of the variable resistor, thereby changing the amount of increase in voltage per unit time.
12. The plasma display device according to claim 7 , wherein the circuit for applying the reset waveform includes a plurality of resistors and switch elements connected to each of the plurality of variable resistors, and wherein the control circuit switches on and off the switch elements, thereby changing the amount of increase in voltage per unit time.