Abstract:
An energy recovery circuit of a plasma display panel is disclosed, which can drive the sustain electrode of the plasma display panel during the sustain period. The energy recovery circuit includes a voltage source which can store electrical energy, a first channel for raising the voltage of the sustain electrode to high potential, a second channel for pulling the voltage of the sustain electrode down to ground, and other auxiliary circuits. When the first channel is turned on, the voltage source can transmit electrical energy to the sustain electrode. When the second channel is turned on, the voltage source retrieves the electrical energy from the sustain electrode. Thereby the sustain electrode is driven between high potential and ground. Moreover, the first channel and the second channel can share a part of common channel.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates in general to a technology for plasma display panel, and more particularly to an energy recovery circuit for a plasma display panel.  
           [0003]    2. Description of the Related Art  
           [0004]    A PDP device, which displays images by accumulating charges by electrode discharge, is an attention-getting flat display since it can have a large screen size display a full-color image.  
           [0005]    [0005]FIG. 1 is a cross-sectional diagram of a conventional PDP cell, in which the PDP is triple-electrode type. As shown in the drawing, the PDP is basically constituted by two glass substrates  1  and  7 . Inert gas such as Ne, Xe is filled in the cavity formed between the glass substrates  1  and  7 . Two electrodes including a sustain electrode X and a sustain electrode Yi are disposed parallel to each other on the glass substrate  1 . A dielectric layer  3  and a protective film  5  are formed covering the sustain electrode X and the sustain electrode Yi. Address electrodes Ai, which are perpendicular to the sustain electrode X and the sustain electrode Yi, are disposed on the glass substrate  7 . Partition wall  8  is used to isolate each PDP cell. Fluorescent material is placed between the partition walls to luminesce during the discharge process.  
           [0006]    [0006]FIG. 2 is a block diagram of a conventional PDP device. As shown in the drawing, the PDP  100  is driven by the sustain electrodes Y 1 ˜Yn and sustain electrode X parallel to each other and the address electrodes A 1 ˜Am across thereon. The reference numeral  10  indicates the display unit of the PDP  100 . Partition wall  8  is used to isolate each display unit  10 .  
           [0007]    Besides the PDP  100 , the PDP device includes the control circuit  110 , the Y scan driver  112 , the X common driver  114  and the address driver  116 . The control circuit  110  can generate the timing information necessary for every driver according to the external clock signal CLOCK, the video data signal DATA, the vertical synchronous signal VSYNC and the horizontal synchronous signal HSYNC. The clock signal CLOCK represents the data-transmitting clock. The video data signal DATA represents the display data. The vertical synchronous signal VSYNC and the horizontal synchronous signal HSYNC are used to define the timing of a single frame and a single scanning line. The control circuit  110  generates every clock and data to be displayed, which are sent to the corresponding drivers to generate the signals needed to drive the electrodes.  
           [0008]    [0008]FIG. 3 is diagram of driving the PDP to display a frame in the prior art. A frame is normally divided into several sub-fields. For instance, the frame of FIG. 3 is divided into 8 sub-fields SF 1 ˜SF 8 . Each sub-field is used to display the corresponding gray scales on all scanning lines. For example, 8 sub-fields can be used when 256 levels of gray scales corresponding to 8 bits are to be displayed. Each sub-field is constituted by three operating periods, i.e., the reset periods R 1 ˜R 8 , the address periods A 1 ˜A 8  and the sustain periods S 1 ˜S 8 . The residual charge left from the last field display is cleaned in the reset period. The wall charge is accumulated in the display cell through address discharge in the address period. The accumulated wall charge is sustained to maintain the display status in the sustain period. All display units on the PDP are simultaneously processed in the reset period R 1 ˜R 8  and the sustain period S 1 ˜S 8 . However, address operation is sequentially performed for the display units on the sustain electrodes Y 1 ˜Yn in the address periods A 1 ˜A 8 .  
           [0009]    [0009]FIG. 4 is the timing diagram of the control signals of the sustain electrodes X and Yi on a single sub-field of FIG. 3 such as SF 1 . After finishing the reset operation of all scanning lines, the address period starts. In the address period, i.e., A 1 , the X common driver  114  controls the sustain electrode X to output the voltage Vs. The scanning lines corresponding to the electrodes Y 1 , Y 2 , Y 3 , . . . , Yn sequentially output the address pulses AP including display data to the address electrodes A 1 , A 2 , . . . , Am through the address driver  116 . Therefore, a transient discharge occurs on the display unit  10  corresponding to the data to be displayed, and the wall charge is accumulated in the display unit  10 . After processing all of the scanning lines, the “data to be displayed” can be stored in the corresponding display unit  10  in the form of accumulated wall charge.  
           [0010]    After finishing the address period, the sustain period (i.e., S 1 ) starts. In the sustain period, the Y scan driver  112  and the x common driver  114  alternately send the sustain pulses to all of the sustain electrodes Yi and the common sustain electrode X. As shown in FIG. 4, a sustain pulse Xsus having a voltage level Vs is sent to the sustain electrode X. This action will be repeated during the sustain period of the sub-field. Moreover, this action involves all of the display units  10 , but only the display units  10  that have accumulated wall charges through the address discharge during the address period keep luminescing during the sustain period.  
           [0011]    Accordingly, the X common driver  114  periodically generates a sustain pulse Xsus during the sustain period. Normally, the sustain pulse Xsus is a signal of high frequency and high voltage, thus causing a considerable power consumption. There are many energy-recovery structures designed for this driving circuit currently. FIG. 5 is a circuit diagram of a prior-art energy-recovery structure for PDP driving circuit. As shown in the drawing, Cp indicates the capacitor-like load corresponding to the display units  10  of the PDP  100 . The capacitor Cp has one end connected to the Y scan driver  112 . The X common driver  114  includes the MOS transistors T 1 , T 2 , T 3  and T 4 , the inductance element  61  and the capacitor C 3 . The capacitor C 3  is an element storing and releasing energy. The transistors T 3  and T 4  are alternatively opened to raise up or pull down the voltage of the sustain electrode X. The operation is briefly described below.  
           [0012]    When the voltage of the sustain electrode X changes from 0 volts to Vs, i.e., the rising edge of the sustain pulse Xsus, the voltage of the capacitor C 3  maintains at Vs/2, and the voltage of the coil is 0 volts. At this time, the transistor T 3  is turned on, and the voltage Vs/ 2  of the capacitor is applied to one end of the coil  61 . Thus a current occurs on the coil  61  and the voltage of the sustain electrode X on the other end of the coil rises up. Since a counter electromotive force exists on the coil  61 , the voltage of the sustain electrode X, i.e., the other end of the coil, can theoretically be raised to Vs. However, the voltage cannot rise up to Vs in practice due to loss. The voltage of the sustain electrode X is raised to Vs by turning the transistor T 1  on if the voltage of the sustain electrode X is a little lower than Vs. That the voltage of the sustain electrode X suddenly rises to Vs will cause the problem of electromagnetic interference.  
           [0013]    On the other hand, when the voltage of the sustain electrode X changes from Vs to 0 volts, i.e., the falling edge of the sustain pulse Xsus, the voltage of the coil is Vs. At this time, the transistor T 4  is turned on, and the voltage Vs/ 2  of the capacitor C 3  is applied to one end of the coil  61 . Thus a reverse current occurs on the coil  61 , and the voltage of the sustain electrode X on the other end of the coil  61  falls down to  0  volts. However, the voltage of the sustain electrode X does not fall to 0 volts in practice due to loss. The voltage of the sustain electrode X can fall down to 0 volts by turning the transistor T 2  on if the voltage of the sustain electrode X is a little higher than 0 volts. That the voltage of the sustain electrode x suddenly falls to 0 volts will also cause the problem of electromagnetic interference.  
           [0014]    In order to improve on the drawbacks for the above energy-recovery structure, U.S. Pat. Nos. 5,438,290 and 5,828,353 disclose using a capacitor as a device storing and releasing energy to reduce the power consumption for repeatedly driving the sustain electrode X.  
         SUMMARY OF THE INVENTION  
         [0015]    Accordingly, an object of the present invention is to provide an energy-recovery driving circuit which is suitable for using in the driver of a PDP. The energy-recovery circuit can avoid the problem of electromagnetic interference since the transistors of the circuit switch are at zero voltage.  
           [0016]    According to the above object, the energy-recovery driving circuit of this invention alternatively applies a driving potential Vs and a reference potential VO to the sustain electrode X on a PDP. The sustain electrode connects to the capacitor-like load corresponding to the display units. The energy-recovery driving circuit includes a first voltage source for providing the driving potential; a second voltage source for providing a first potential which is lower than the driving potential and storing electrical energy; a first channel, including a first inductance element connected between the first voltage source and the electrode, for providing electrical energy to the electrode while the potential of the electrode changes from the reference potential to the driving potential; a second channel, including a second inductance element connected between the second voltage source and the electrode, for providing electrical energy by the electrode and storing the electrical energy in the second voltage source while the potential of the electrode changes from the driving potential to the reference potential; a first switch, connected between the first voltage source and the electrode, for connecting the first voltage source to the electrode while the potential of the electrode changes from the reference potential to the driving potential; and a second switch, connected between the second voltage source and the electrode, for connecting the electrode to the reference potential while the potential of the electrode changes from the driving potential to the reference potential. The first channel further includes a third switch for controlling the turn-on of the first channel. The second channel further includes a fourth switch for controlling the turn-on of the second channel.  
           [0017]    Furthermore, the first switch can be replaced by a unidirectional conductive element connected between the first voltage source and the electrode to control the charge direction. The second switch can be replaced by a second unidirectional conductive element connected between the second voltage source and the electrode to control the discharge direction.  
           [0018]    The first channel and the second channel may share a common channel. In other words, the first inductance element and the second inductance element can be replaced by a single inductance element. The common channel further includes a current direction control device for setting the conducting direction of the first channel and the conducting direction of the second channel. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The present invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:  
         [0020]    [0020]FIG. 1 is a cross-sectional diagram of the display cell in a conventional PDP;  
         [0021]    [0021]FIG. 2 is a block diagram of a conventional PDP device;  
         [0022]    [0022]FIG. 3 is a diagram illustrating the operation of showing a frame basing on the driving technology of a conventional PDP;  
         [0023]    [0023]FIG. 4 is a timing diagram of the control signal on the sustain electrodes X and Yi in a single sub-field such as SF 1  of FIG. 3;  
         [0024]    [0024]FIG. 5 is a circuit diagram of the energy-recovery structure for a prior-art PDP driving circuit;  
         [0025]    [0025]FIG. 6A is a circuit diagram of the energy-recovery structure of the X common driver according to the first embodiment of this invention;  
         [0026]    [0026]FIG. 6B is a diagram illustrating the waveforms of the control signals in the circuit of FIG. 6A;  
         [0027]    [0027]FIG. 7A is a circuit diagram of the energy-recovery structure of the X common driver according to the second embodiment of this invention;  
         [0028]    [0028]FIG. 7B is a diagram illustrating the waveforms of the control signals in the circuit of FIG. 7A;  
         [0029]    [0029]FIG. 8A is a circuit diagram of the energy-recovery structure of the X common driver according to the third embodiment of this invention;  
         [0030]    [0030]FIG. 8B is a diagram illustrating the waveforms of the control signals in the circuit of FIG. 8A; 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]    First Embodiment  
         [0032]    [0032]FIG. 6A is a circuit diagram of the energy-recovery structure of the X common driver according to this first embodiment. In FIG. 6A, the symbol “X” represents the sustain electrode X, the symbol “Yi” represents the sustain electrodes Yi, and the symbol “Cp” represents the capacitor-like load corresponding to the display units in the PDP. As shown in the drawing, voltage sources V 1  and V 2  are disposed in the X common driver, in which the voltage source V 2  supplies the voltage Vs and the voltage source V 1  provides a voltage lower than Vs/ 2 . Moreover, in this embodiment, the voltage source V 1  can retrieve electrical energy. Since the current in the inductance elements L 1 , L 2  can not instantly change its direction, the electrode X can be charged to the reference potential Vs to turn on the transistor Q 3  while charging through the path CHG, and the electrode X can be discharged to the reference potential GND to turn on the transistor Q 4  while discharging through the path DIC.  
         [0033]    The X common driver can change the potential of the sustain X from 0 volts (ground) to Vs or from Vs to 0 volts the first channel CHG and the second channel DIC as shown in FIG. 6A. The first channel CHG, which includes a MOS transistor Q 1  controlled by the signal CQ 1 , a diode D 1  and the inductance element L 1 , is a charge path for controlling the voltage source V 2  to release electrical energy to the sustain electrode X. The second channel DIC, which includes a MOS transistor Q 2  controlled by the signal CQ 2 , a diode D 2  and the inductance element L 2 , is a retrieving path for controlling the sustain electrode X to retrieve electrical energy and store the electrical energy in the voltage source V 1 .  
         [0034]    The function of the elements in the first path CHG is described below. The inductance element Ll functions similar to the inductance element  61  of FIG. 5 to raise the voltage of the sustain electrode X to Vs. The diode D 1  is used to ensure the direction of the charge current. The MOS transistor Q 1  is controlled by the control signal CQ 1  to control the turn-on time of the first channel CHG. When the first channel CHG is turned on, the voltage of the sustain electrode X gradually rises to Vs and the body diode included in the MOS transistor Q 3  is turned on so that the voltage of the sustain electrode X is fixed at Vs. At this time, a control signal CQ 3  is applied to turn on the MOS transistor Q 3 , the MOS transistor Q 3  is zero-voltage switching, thus the problem of electromagnetic interference existed in the prior art of FIG. 5 can be avoided.  
         [0035]    Next, the function of the elements in the second path DIC is described below. The inductance element L 2  functions similar to the inductance element  61  of FIG. 5 to retrieve electrical energy to pull down the voltage of the sustain electrode X to 0 volts. The diode D 2  is used to ensure the direction of retrieving electrical energy, that is, the current direction of retrieving electrical energy from the sustain electrode X to the voltage source V 1 . A control signal CQ 2  is used to control the MOS transistor Q 2  to control the turn-on time of the second channel. When the second channel DIC is turned on, the sustain electrode X releases the electrical energy to the voltage source V 1  through the second channel DIC. When the voltage of the sustain electrode X gradually falls down to 0 volts (ground), the body diode included in the MOS transistor Q 4  is turned on, thus the voltage of the sustain electrode X is fixed at 0 volts. At this time, a control signal CQ 4  is used to turn on the MOS transistor Q 4 , the NOS transistor Q 4  is zero-voltage switching, thus the problem of electromagnetic interference existed in the prior art of FIG. 5 can be avoided.  
         [0036]    Referring to FIG. 6A, the control signals CQ 1 , CQ 2 , CQ 3  and CQ 4  for controlling the MOS transistors Q 1 , Q 2 , Q 3  and Q 4  are used to drive the sustain electrode X. FIG. 6B is the waveform diagram of the control signals CQ 1 , CQ 2 , CQ 3  and CQ 4  and the voltage of the sustain electrode X in FIG. 6A. As shown in the drawing, the voltage of the sustain electrode X is 0 volts before the time t 1 . At the time t 1 , the control signal CQ 1  turns on the MOS transistor Q 1 , the first channel CHG is turned on. Therefore the voltage of the sustain electrode X changes from 0 volts to Vs through the first channel CHG. The body diode included in the MOS transistor Q 3  is turned on, thus the voltage of the sustain electrode X is fixed at Vs. At the time t 2 , the control signal CQ 3  turns on the MOS transistor Q 3 . The voltage source V 2  directly charges the sustain electrode X to maintain the voltage of the sustain electrode X at Vs.  
         [0037]    Next, at the time t 3 , the control signal CQ 2  turns on the MOS transistor Q 2 , thus the voltage of the sustain electrode X is pulled down from Vs to 0 volts. The body diode included in the MOS transistor Q 4  is turned on therefore the voltage of the electrode X is fixed at 0 volts. At the time t 4 , the control signal CQ 4  turns on the MOS transistor Q 4  to maintain the voltage of the sustain electrode X at 0 volts.  
         [0038]    Accordingly, the control signals CQ 1 , CQ 2 , CQ 3  and CQ 4  can be used to alternatively open the channels, so that the sustain electrode X is repeatedly driven between Vs and  0  volts to meet the output requirement of the X common driver. Moreover, the rising time and the falling time of the voltage of the sustain electrode X can be adjusted by changing the parameters of the first channel CHG and the second channel DIC. The object for recovery electrical energy can be achieved by repeatedly retrieving the electrical energy.  
         [0039]    Second Embodiment  
         [0040]    In the first embodiment, four MOS transistors Q 1 , Q 2 , Q 3  and Q 4  controlled by various control signals are used to drive the sustain electrode X. In this embodiment, two diodes are used to replace the MOS transistors Q 3  and Q 4  used in the first embodiment.  
         [0041]    [0041]FIG. 7A is the circuit diagram of the energy-recovery structure of the X common driver in this embodiment. As shown in FIG. 7A, the diodes D 3  and D 4  are used to replace the MOS transistors Q 3  and Q 4  of FIG. 6A. The positive electrode and the negative electrode of the diode D 3  are respectively connected to the sustain electrode X and the voltage source V 2 . The positive electrode and the negative electrode of the diode D 4  are respectively connected to the ground and the sustain electrode X.  
         [0042]    Since the diodes D 3  and D 4  need no control signal, only the control signal CQ 5  used to control the MOS transistor Q 1  and the control signal CQ 6  used to control the MOS transistor Q 2  are required in FIG. 7A. FIG. 7B is the waveform diagram of the control signals CQ 5  and CQ 6  of FIG. 7A. As shown in the drawing, the control signal CQ 5  is used to control driving the sustain electrode X from 0 volts to Vs, and the control signal CQ 6  is used to control driving the sustain electrode X from Vs to 0 volts.  
         [0043]    At the time t 5 , the control signal CQ 5  turns on the MOS transistor Q 1  so that the first channel is turned on. The voltage source V 2  releases the electrical energy to the sustain electrode X through the first channel CHG. The voltage of the sustain electrode X gradually rises to Vs, then the diode D 3  is turned on, and the voltage of the sustain electrode X is fixed at the voltage Vs of the voltage source V 2 . Therefore, the problem of electromagnetic interference as caused by sudden switching of voltage in the prior art of FIG. 5 will not occur. At the time t 6 , the control signal CQ 6  turns on the MOS transistor Q 2 , so that the second channel DIC is turned on. The sustain electrode X retrieves the electrical energy to the voltage source V 1  through the second channel DIC. The voltage of the sustain electrode X gradually falls down to 0 volts, then the diode D 4  is turned on, and the voltage of the sustain electrode X is fixed at 0 volts. Alternatively controlling the turn-on status of the first channel CHG and the second channel DIC can alternatively drive the sustain electrode X between Vs and 0 volts to meet the output requirement of the X common driver. The object for recovery electrical energy can be achieved by repeatedly retrieving the electrical energy. Moreover, the number of transistors can be reduced since the diodes are used to replace the MOS transistors used in the first embodiment. The NMOS transistors Q 3  and Q 4  used in the first embodiment can be used in parallel with the diodes D 3  and D 4  used in this embodiment to provide the same effect.  
         [0044]    Third Embodiment  
         [0045]    In the first embodiment, the electric energy is transmitted and retrieved through the first channel CHG and the second channel DIC which are established independently. In this embodiment, the first channel CHG and the second channel DIC share a part of common channel in this embodiment. Further, in order to reduce the number of elements, a single inductance element is used to replace the inductance element L 1  of the first channel CHG and the inductance element L 2  of the second channel DIC.  
         [0046]    [0046]FIG. 8A is the circuit diagram of the energy-recovery structure for the X common driver of this embodiment. As shown in the drawing, the difference of this embodiment to the first embodiment and the second embodiment is that the first channel CHG and the second channel DIC share a common channel COM. The common channel COM includes an inductance element L 3  and a current direction control device including a MOS transistor Q 5  and a diode D 5 . In other words, a single inductance element L 3  is used to replace the inductance elements Ll and L 2  used in the first embodiment and the second embodiment. The MOS transistor Q 5  of the current direction control device is controlled by the control signal CQ 9 . The diode D 5  is disposed along the current direction of the first channel CHG. The diode D 5  and the MOS transistor Q 5  respectively correspond to the conductive directions of the first channel CHG and the second channel DIC. When the MOS transistor Q 5  is turned off, the MOS transistor Ql, the diode D 5  and the inductance element L 3  constitute the first channel CHG. When the MOS transistor Q 5  is turned on, the inductance element L 3 , the MOS transistor Q 5  and the MOS transistor Q 2  constitute the second channel DIC.  
         [0047]    [0047]FIG. 8B is the waveform diagram for the control signals CQ 7 , CQ 8  and CQ 9  of FIG. 8A. The control signals CQ 7  and CQ 8  are respectively used to control the MOS transistors Q 1  and Q 2 . It should be noted that the control signals CQ 8  and CQ 9  are synchronous. As shown in the drawing, at the time t 7 , the control signal CQ 7  turns on the MOS transistor Q 1 , and the MOS transistor QS is turned off so that the first channel CHG is turned on. The voltage source V 2  releases the electrical energy to the sustain electrode X through the first channel CHG. The voltage of the sustain electrode X gradually rises to Vs, then the diode D 3  is turned on and the voltage of the sustain electrode X is fixed at the voltage Vs of the voltage source V 2 . Therefore, the problem of electromagnetic interference caused by sudden switching of voltage in the prior art of FIG. 5 will not occur in this embodiment. Next, at the time t 8 , the control signal CQ 8  turns on the MOS transistor Q 2  and the control signal CQ 9  turns on the MOS transistor QS so that the second channel DIC is turned on. The sustain electrode X transmits the electrical energy to the voltage source Vl through the second channel DIC. The voltage of the sustain electrode X gradually falls down to 0 volts, then the diode D 4  is turned on and the voltage of the sustain electrode X is fixed at 0 volts. Alternatively controlling the turn-on status of the first channel CHG and the second channel DIC can alternatively change the voltage of the sustain electrode X between Vs and 0 volts to meet the output requirement of the X common driver. The object for recovery electrical energy can be achieved by repeatedly retrieving the electrical energy. Moreover, the number of elements can be reduced by using the common channel COM. It should be noted that although the diodes D 3 , D 4  are used in the circuit of FIG. 8A, they can be replaced by using the MOS transistors Q 3  and Q 4  or the parallel thereof to constitute the energy-recovery driving circuit of this embodiment.  
         [0048]    Finally, while the invention has been described by way of examples and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.