Patent Application
20070188414
1. Field of Invention
The present invention relates to a driving circuit of a plasma display panel (PDP), and particularly to a reset circuit of a PDP.
2. Description of the Related Art
When driving a Plasma Display Panel (PDP), a cycle of a sequential reset period, addressing period and sustaining period is repeated for driving operations. Wherein, the operation during the reset period is used for clearing and resetting wall charges of PDP display cells; the operation during the addressing period is used for addressing the display cells; the operation during the sustaining period is used for sustaining luminance of the addressed display cells.
The sustaining circuits 101 and 104 serve for providing the display cell 103 with AC sustaining voltage during the sustaining period. The reset circuit 102 serves for producing a reset signal to the display cell 103 during the reset period, wherein the reset signal is used for clearing and resetting wall charges. Cp represents an equivalent capacitance of the PDP in the display cell 103. As a switch Q1 is on, the current from a voltage source Vd would pass through a diode D1 and the switch Q1, which results in a RC resonance of a resistor R and the capacitance Cp, further producing a reset signal for clearing and resetting wall charges. In this embodiment, the reset signal is an exponential waveform. The detail for controlling switches Q1˜Q7 during driving the display cell 103 should be known to those skilled in the art and are not repeated herein.
The disadvantage of the above-described conventional scheme is when the wall charges are to be effectively cleared and reset, a feeble discharge is essentially needed, making the voltage applied to the capacitor Cp slowly fall. The slowly falling of the voltage requires a longer reset time, but the longer the reset period, the longer the backlight is up. Thus, the sustaining period affecting the average luminance of a display cell would be accordingly shorter and the display quality degrades. On the other hand, the equipped resistor R requires a more complex process and a higher cost.
Although the sustaining circuit 101 may provide an LC resonance between an inductor Ls and a capacitor Cp, the resonance frequency and reset waveform required by each is different. The resonance of the sustaining circuit 101 actually plays a much different role from the resonance to build up the reset signal, limiting and confining the application of the resonance of the sustaining circuit 101.
An object of the present invention is to provide a PDP reset circuit, suitable for significantly shortening the reset period and improving the display quality.
Another object of the present invention is to provide a PDP driving circuit, suitable for significantly shortening the reset period, reducing the circuit cost and easily adjusting the reset signal frequency.
To reach the above-described objects, the present invention provides a PDP reset circuit, which includes a first switch and an inductor. The first switch is electrically connected to a first voltage source, while the inductor is electrically connected between the first switch and a display cell of the PDP.
In the above-described reset circuit of an embodiment, a diode and a capacitor are further included. The diode is electrically connected between the first voltage source and the first switch, while the capacitor is electrically connected between the diode and a sustaining circuit.
In the above-described reset circuit of an embodiment, the sustaining circuit includes a fourth switch and a fifth switch, wherein the fourth switch is electrically connected between a second voltage source and the capacitor, while the fifth switch is electrically connected between the capacitor and the ground.
In the above-described reset circuit of an embodiment, to produce the reset signal, the operation requires three periods. During the first period, the first switch and the fourth switch are off, while the fifth switch is on. During the second period, the fifth switch is off, and then the fourth switch is on. During the third period, the first switch is on.
On the other hand, the present invention further provides a PDP driving circuit, which includes a reset circuit and a sustaining circuit. The reset circuit is electrically connected to a display cell of a PDP and produces a reset signal of the above-described display cell by means of an LC resonance (inductance-capacitance resonance). The sustaining circuit provides the above-described display cell with a sustaining voltage during the sustaining period.
According to an embodiment of the present invention, instead of a RC resonance (resistance-capacitance resonance) used in the prior art, the present invention uses an LC resonance, therefore the reset period can be significantly shortened. A shorter reset period would contribute to reducing the backlight and increasing dark room contrast ratio (DRCR). The saved time can be used for delivering more scan signals to support higher resolution or for delivering more sustaining signals to improve the chroma displayed. In short, due to a shorter reset period, the display quality is consequently advanced.
According to an embodiment of the present invention, another advantage in the present invention is no extra circuit required. In fact, only one component in the original circuit needs to be changed; that is, the resistor in the original reset circuit needs to be replaced by an inductor. Since the modified inductor process is simpler compared with the original resistor, a lower circuit cost is expected.
Moreover, the inductor in the reset circuit, not the original inductor in the sustaining circuit, is used in the present invention. Therefore, the circuit has higher modifiability, so that it is easier to adjust the reset signal frequency regardless of the operation frequency required by the original sustaining circuit and the function thereof.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve for explaining the principles of the invention.
The major difference of the reset circuit 202 in
The reset circuit 202 includes a diode D1, switches Q1˜Q3, an inductor Ld and a capacitor Cd. Wherein, the anode of the diode D1 is electrically connected to a voltage source Vd. The switch Q1 is electrically connected between the cathode of the diode D1 and the upper end of the inductor Ld. The upper end of the inductor Ld is electrically connected to the switch Q1, while the lower end thereof is electrically connected to the switch Q3 and the scan end of the display cell 203. The upper end of the capacitor Cd is electrically connected to the cathode of the diode D1 and the switch Q1, while the lower end thereof is electrically connected to the switch Q2 and both switches Q4 and Q5 of the sustaining circuit 201. The left end of the switch Q2 is electrically connected to the lower end of the capacitor Cd and both switches Q4 and Q5 of the sustaining circuit 201, while the right end thereof is electrically connected to the switch Q3. The right end of the switch Q3 is electrically connected to the lower end of the inductor Ld and the scan end of the display cell 203.
The components in the sustaining circuit closely related to the embodiment are the switches Q4 and Q5. The upper end of the switch G4 is electrically connected to a voltage source Vs, the lower end thereof is electrically connected to the lower end of the capacitor Cd and the upper end of the switch G5. The upper end of the switch G5 is further electrically connected to the lower end of the capacitor Cd, while the lower end thereof is grounded.
By means of an LC resonance induced by the inductor Ld and the capacitor Cp, the reset circuit 202 generates a reset signal for the display cell 203. The capacitor Cp is the equivalent capacitance of the PDP in the display cell 203. During the reset period, the switches Q2 and Q3 are off all the time. The process for the reset circuit to generate a reset signal includes three phases.
In the first phase, the switches Q1 and Q4 are off, while the switch Q5 is on. At the point, the upper end of the capacitor Cd is electrically connected to the voltage source Vd, while the lower end thereof is grounded. Meanwhile, the capacitor Cd starts to be charged until the voltage at both ends of the capacitor raise to the voltage of the voltage source Vd. In the second phase, the switch Q5 is off, and then the switch Q4 is on, which makes the lower end of the capacitor Cd coupled to the voltage source Vs. The voltage of the capacitor can not be transiently changed, therefore the voltage level at the upper end of the capacitor Cd would immediately surge to the voltage of (Vd+Vs). In the embodiment, the voltage of Vd is 60 V and the voltage of Vs is 180 V, thus the voltage at the upper end of the capacitor Cd is transiently 240 V. In the third phase finally, the switch Q1 is on. The storage energy in the capacitor Cd herein is capable of inducing a resonance between the inductor Ld and the capacitor Cp. As the capacitor Cd is discharged, the current passing the inductor Ld can not quickly follow the change in time, therefore the discharge energy is restricted and only a feeble discharge is generated. In this way, the reset signal can be generated for the purpose of clearing and resetting the wall charges of the display cell 203.
Except for the above-described process, a 240 V high voltage can be provided at the voltage source Vd in the embodiment. With such high voltage, the reset signal can be directly generated without the above pulling-up voltage process.
Except for replacing the original resistor in a reset circuit with an inductor, the embodiment further needs to modify the original driving code for rearranging the control signals of the switches Q1˜Q7. The driving code modification should be well known for those skilled in the art after reviewing the presented circuit layout in
The following table 1 lists some experiment comparison results between the conventional circuit and the one provided by the embodiment. It can be seen from the table, that for a totally black screen display, the average luminance of the embodiment is about a half of that using the conventional circuit, the power consumption of the embodiment is less than that of the conventional circuit and the reset time of the embodiment is dramatically shorter than that of the conventional circuit. Besides, supposing the peal luminance of a regular PDP is 1500 cd/m2, then the dark room contrast ratio (DRCR) for the conventional circuit is 1500/0.25=6000, while the dark room contrast ratio (DRCR) for the circuit of the embodiment is 1500/0.13=11538, thus a significantly larger DRCR is obtained.
Although the reset circuit 202 of the embodiment is electrically connected to the scan end of the display cell 203 in the embodiment, it is not limited thereof. In the other embodiments of the present invention, the reset circuit can be alternatively electrically connected to the bulk end of the display cell. The corresponding driving circuit layout at the scan end and rearranging the control signals of the switches should be known to those skilled in the art, hence are omitted herein for simplicity.
It can be seen from the above described that the LC resonance of the embodiment, instead of the RC resonance in the prior art, makes the reset period significantly shorter. Along with a shorter reset period, the backlight is reduced and the dark room contrast ratio (DRCR) is increased. The saved time can be used for delivering more scan signals to support higher resolution or for delivering more sustaining signals to improve the chroma displayed. In short, along with a shorter reset period, the display quality can be enhanced.
Another advantage of the present invention is that to implement the present invention, no extra circuit is required. In the original circuit, only one component needs to be changed; that is, the resistor of the original reset circuit is replaced by an inductor. Since the inductor process is relatively simpler, the circuit cost is expected to be reduced as well.
A further advantage of the present invention is that a newly equipped inductor in the reset circuit is employed without using the original inductor in the sustaining circuit, which provides higher modifiability for adjusting the reset signal frequency without the restriction of operation frequency and the function of the original sustaining circuit. Moreover, the resonance energy can be directly supplied by the voltage source, which is much better than using capacitor storage energy in the sustaining circuit.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the specification and examples to be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims and their equivalents.
