Abstract:
A method and apparatus for driving a plasma display panel and improving the display characteristics through multi-discharge phenomenon is provided. The driving method is used for providing energy to light up at least a display unit in the plasma display panel and includes the following steps. Before providing any external energy, an energy recovery circuit provides internally stored energy so that the display unit has a first discharge through a resonance effect initiated by the internally stored energy. After the first discharge, external energy is provided to the display unit to trigger a second discharge. Thereafter, the energy recovery circuit stops providing internally stored energy to the display unit. Similarly, external energy to the display unit is also stopped. After the second discharge, the energy in the display unit is returned to the energy recovery circuit to serve as internally stored energy.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the priority benefit of Taiwan application serial no. 94136516, filed on Oct. 19, 2005. All disclosure of the Taiwan application is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a method and apparatus for driving a plasma display panel. More particularly, the present invention relates to a method for driving a plasma display panel and improving the display characteristics through multiple discharges.  
         [0004]     2. Description of the Related Art  
         [0005]     Plasma display panel (PDP) operates by producing gaseous discharge to light up a fluorescent agent. Therefore, PDP is also referred to as a gas discharge display. In general, a PDP comprises a plurality of display units as shown in  FIG. 1 .  FIG. 1  is a schematic diagram showing a conventional plasma display panel. The plasma display panel  10  in  FIG. 1  has a plurality of scan electrodes S 1 ˜Sn, a plurality of bulk electrodes B 1 ˜Bn and a plurality of addressing electrodes A 1 ˜Am. The bulk electrodes B 1 ˜Bn are also called the sustain electrodes. The scan electrodes S 1 ˜Sn and the bulk electrodes B 1 ˜Bn are interdigitated in parallel. The addressing electrodes A 1 ˜Am are aligned vertically with both of the scan electrodes S 1 ˜Sn and the bulk electrodes B 1 ˜Bn. The addressing electrodes A 1 ˜Am, the scan electrodes S 1 ˜Sn and the bulk electrodes B 1 ˜Bn are isolated from one another. The blocks intersected by the addressing electrodes A 1 ˜Am and the scan electrodes S 1 ˜Sn and the bulk electrodes B 1 ˜Bn are display units (for example, the display unit  110  in  FIG. 1 ). Each display unit is bounded by two glass panels on the top and the bottom and by the isolating panels at the front, rear, left and right sides to form a discharge space.  
         [0006]     In the process of driving the plasma display panel  100 , a resetting period, an addressing period and a sustaining period are sequentially executed in cycles. In general, the addressing period is also known as a scanning period. Each display unit can have a light-emitting state and a non-emitting state. For example, after all the display units of the PDP  100  have been reset (in the resetting period), whether the display unit  110  lights up or not has already been determined through the addressing by the addressing electrode A 2  and the scan electrode Sn (in the addressing period). After the addressing period, the sustaining period immediately commences. If the display unit  110  has been set to emit light through the addressing, it continues to emit in the sustaining period. During the sustaining period, the sustaining voltage of the sustain circuit of the scan side and bulk side (not shown) is transmitted respectively by the scan electrode Sn and the bulk electrode Bn in sequence so that these two electrodes produce alternating current discharge within the discharge space of the display unit  110 . The UV light generated by discharge bombard against the fluorescent material within the discharge space to produce visible light.  
         [0007]      FIG. 2  is a timing diagram showing the relation between the voltage Vp and the brightness level in a conventional sustaining period. The voltage difference between the scan electrode Sn and the bulk electrode Bn of the display unit  110  is represented by Vp. In the conventional method for driving a plasma display panel, a single discharge is used to produce ultraviolet (UV) light. By illuminating the fluorescent material inside the discharge space with UV light, visible light is produced. In  FIG. 2 , the line IR indicates the brightness level of the UV light from the display unit  110  as detected by an infrared ray sensor.  
         [0008]     Referring to  FIG. 2 , within the period PA, the bulk electrode Bn (or the scan electrode Sn) is connected to a ground and a ramp voltage is applied to the scan electrode Sn (or the bulk electrode Bn). At this time, the wall charges inside the display unit  110  continue to accumulate. During this period, the sum total of the energy provided and the energy of the internally accumulated wall charges is still insufficient to initiate a firing discharge. After the period PA, period PB commences. In the period PB, the total energy provided by the supplied energy and the energy of the internally accumulated wall charges exceeds the firing energy. Consequently, there is an internal discharge inside the display unit  110 . In general, the discharge energy in the PB period is provided through the sustain voltage.  
         [0009]     The period PB can be divided into a period A and a period B for better description. The period starting from the excitation of the fluorescent material by the UV rays to the production of visible light is period A and the period starting from the appearance of visible light to the end of the excitement of the fluorescent material is period B. Because a time period A and definite energy within that period is required to excite the fluorescent material before any visible light is produced, the length of the period A and the energy dosage within this period will directly affect the efficiency and brightness level produced by the fluorescent material in the subsequent period B. In other words, it is essential to minimize the energy used by the sustain voltage in period A and extend the length in period B (the period where the fluorescent material emits light) so that the display characteristics of the plasma display panel can be improved.  
       SUMMARY OF THE INVENTION  
       [0010]     Accordingly, at least one objective of the present invention is to provide a method for driving a plasma display panel (PDP) and improving the display characteristics of the PDP. Through multiple discharges, the fluorescent material inside the display unit of the PDP can have a higher light-emitting efficiency and brightness level.  
         [0011]     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for driving a plasma display panel (PDP). The method utilizes multiple discharge phenomena to improve the display characteristics of the PDP and provides energy to light up at least one display unit in the PDP. The driving method includes the following. Before providing any external energy, an energy recovery circuit provides internally stored energy so that the display unit has a first discharge through a resonance effect initiated by the internally stored energy. After the first discharge, external energy is provided to the display unit to trigger a second discharge. Thereafter, the energy recovery circuit stops providing internally stored energy to the display unit. Similarly, external energy to the display unit is also stopped. After the second discharge, the energy in the display unit is returned to the energy recovery circuit to serve as internally stored energy.  
         [0012]     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a appratus for driving a plasma display panel (PDP). The method utilizes multiple discharge phenomena to improve the display characteristics of the PDP and provides energy to light up at least one display unit in the PDP. The driving appratus includes an energy recovery circuit and a sustain circuit. The energy recovery circuit electrically connects to the PDP for providing internally stored energy so that the display unit has a first discharge through a resonance effect initiated by the internally stored energy. The sustain circuit electrically connects to the PDP for providing external energy to the display unit to trigger a second discharge. Wherein, after the second discharge, the energy in the display unit is returned to the energy recovery circuit to serve as internally stored energy.  
         [0013]     In the present invention, the energy recovery circuit provides internally stored energy so that sufficient wall charges are accumulated to produce a weak discharge before the external energy (for example, the sustain voltage) generates a full discharge. In other words, the fluorescent material inside the display unit of the PDP is excited to a light-emitting state through internally stored energy. Thus, the discharge energy provided by the external energy can be completely utilized to produce light via the fluorescent material for the full discharge period. As a result, the light-emitting efficiency and brightness level of the fluorescent material inside the PDP is increased and the display characteristics of the PDP are improved.  
         [0014]     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     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 to explain the principles of the invention.  
         [0016]      FIG. 1  is a schematic diagram showing a conventional plasma display panel.  
         [0017]      FIG. 2  is a timing diagram showing the relation between the voltage Vp and the brightness level in a conventional sustaining period.  
         [0018]      FIG. 3  is a diagram showing the scan side and bulk side driving circuit for a plasma display panel according to one embodiment of the present invention.  
         [0019]      FIG. 4  is a timing diagram showing the timing relationship of the on-off switches, the display unit voltage and the light-emitting state for the circuit in  FIG. 3  during the sustaining period. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
         [0021]      FIG. 3  is a diagram showing the scan side and bulk side driving circuit for a plasma display panel according to one embodiment of the present invention. In  FIG. 3 , only a display unit  300  and its associated circuits that electrically connect with a scan electrode and a bulk electrode of the display unit  300  is used to describe the display unit and related driving circuit of a PDP (for example, the PDP  100  in  FIG. 1 ). The capacitance of the capacitor Cp is equivalent to the capacitance between the scan electrode and the bulk electrode of the display unit  300 . The voltage Vp represents the voltage difference between the scan side electrode and the bulk side electrode of the display unit  300 . The method of operating the circuits is explained in the following.  
         [0022]     For example, in the sustaining period, the scan side sustain circuit  310  and the bulk side sustain circuit  320  transmit sustain voltage Vs to the two terminals of the capacitor Cp in the display unit  300  through the scan electrode and the bulk electrode alternately. Thus, the two electrodes generate an alternating discharge current in the discharge space within the display unit  300  and excite the fluorescent material to produce visible light. In general, the sustain voltage Vs is set to a high potential level (for example, between 170˜200V). To reduce the energy loss due to switching the switches SW 3  and SW 4  within the sustain circuit  310  (or the switches SW 5  and SW 6  within the sustain circuit  320 ), the scan side has an energy recovery circuit ERC 1  and the bulk side has another energy recovery circuit ERC 2 .  
         [0023]     The energy recovery circuit ERC 1 , for example, comprises a capacitor CSS 1 , a first switch SW 1 , a second switch SW 3 , a first diode D 1 , a second diode D 2  and an inductor L 1 . The capacitor CSS 1  is used for storing internally stored energy. A first terminal of the switches SW 1  and SW 2  are electrically connected to the capacitor CSS 1 . In the period when the internally stored energy is provided, the switch SW 1  channels the internally stored energy to a second terminal of the switch SW 1 . In the period when the internally stored energy is returned, the switch SW 2  channels the energy of the display unit  300  from a second terminal of the switch SW 2  to the first terminal of the switch SW 2 . The anode of the diode D 1  is electrically connected to the second terminal of the switch SW 1  and the cathode of the diode D 1  is electrically connected to the second terminal of the switch SW 2 . A first terminal of the inductor L 1  is electrically connected to the cathode of the diode D 1  and a second terminal of the inductor L 1  is electrically connected to the display unit  300 .  
         [0024]      FIG. 4  is a timing diagram showing the timing relationship of the on-off switches SW 1 ˜SW 8 , the display unit voltage and the light-emitting state for the circuit in  FIG. 3  during the sustaining period. In  FIG. 4 , IR represents the state of the ultraviolet (UV) light emitted by the display unit  300  and detected by an infrared ray sensor. In the positive discharging period of the sustaining period, the switches SW 6 ˜SW 8  are maintained in an off state while the switch SW 5  is maintained in a conductive state. The switch SW 4  is cut off before the switch SW 3  is turned on (before providing external energy). Then, the switch SW 1  is turned on (start entering into P 1  region in  FIG. 4 ). At this moment, the energy recovery circuit ERC 1  transmits the internally stored energy inside the capacitor CSS 1  via the switch SW 1 , the diode D 1  and the inductor L 1  to the display unit  300 . Utilizing the resonance effect between the capacitor Cp and the inductor L 1 , the released internally stored energy is able to increase the display unit voltage Vp in a resonance manner. Thus, the energy loss in the switching process due to a large voltage difference when the switch SW 3  starts to turn on will be minimized. After the switch SW 3  is turned on, that is, the switch SW 3  starts to provide external energy (for example, provides a sustain voltage Vs), the switch SW 1  can be immediately turned off. When the switch SW 3  is turned off, the switch SW 2  is made to turn on. Hence, the energy within the capacitor Cp can be returned to the capacitor CSS 1  via the inductor L 1 , the diode D 2  and the switch SW 2  to serve as internally stored energy. Therefore, the terminal voltage Vss of the capacitor CSS 1  in the energy recovery circuit ERC 1  can be returned to the original potential level (for example, half of the sustain voltage Vs). Through the resonance effect between the capacitor Cp and the inductor L 1 , the display unit voltage Vp is decreased in a resonance manner. As a result, the energy loss in the switching process due to a large voltage drop when the switch SW 4  being turned on is minimized. Meanwhile, the switch SW 2  can be turned off once the switch SW 4  is turned on.  
         [0025]     In the negative discharging period of the sustaining period, the switches SW 1 ˜SW 3  are maintained in a cut-off state while the switch SW 4  is maintained in a conductive state. The switch SW 5  is cut-off before the switch SW 6  is turned on (before providing external energy). Thereafter, the switch SW 8  is turned on. At this moment, the energy recovery circuit ERC 2  transmits the internally stored energy inside the capacitor CSS 2  via the switch SW 8 , the diode D 3  and the inductor L 2  to the display unit  300 . Utilizing the resonance effect between the capacitor Cp and the inductor L 2 , the released internally stored energy is able to increase the display unit voltage Vp in a resonance manner. Thus, the energy loss in the switching process due to a large voltage difference when the switch SW 6  starts to turn on will be minimized. After the switch SW 6  is turned on, that is, the switch SW 6  starts to provide external energy (for example, provides a sustain voltage Vs), the switch SW 8  can be immediately turned off. When the switch SW 6  is turned off, the switch SW 7  is made to turn on. Hence, the energy within the capacitor Cp can be returned to the capacitor CSS 2  via the inductor L 2 , the diode D 4  and the switch SW 7  to serve as internally stored energy. Therefore, the terminal voltage Vss of the capacitor CSS 2  in the energy recovery circuit ERC 2  can be returned to the original potential level (for example, half of the sustain voltage Vs). Through the resonance effect between the capacitor Cp and the inductor L 2 , the display unit voltage Vp is decreased in a resonance manner. As a result, the energy loss in the switching process due to a large voltage drop when the switch SW 5  conducts is minimized. Meanwhile, the switch SW 7  can be turned off once the switch SW 5  is turned on.  
         [0026]     In the following, the positive discharge period of the sustaining period is used as an example. The multi-discharge phenomenon is divided into four time regions P 1 ˜P 4  and explained individually. In the first time period P 1 , the energy recovery circuit ERC 1  provides internally stored energy. During this period, the voltage level in resonance with the energy recovery circuit and the wall charge voltage inside the display unit  300  continues to accumulate. Because the sum of the voltage level of the energy recovery circuit and the wall charges inside the display unit  300  together still have not reached the firing voltage, no discharge occurs in the display unit  300  yet.  
         [0027]     When the sum of the resonance voltage level of the energy recovery circuit and the wall charge voltage inside the display unit  300  is greater than the firing voltage, the time period P 2  begins. In the second time period P 2 , the energy recovery circuit ERC 1  continues to provide internally stored energy. At this time, the internally stored energy produces a first discharge (a weak discharge) in the display unit  300  through the resonance of the serially connected capacitor Cp and the inductor L 1 . The UV light produced by the weak discharge starts to excite the fluorescent substance inside the display unit  300 . The labeled period C in  FIG. 4  indicates the period when the fluorescent substance is excited by the UV light until the visible light is produced. The labeled period D indicates the duration from the start of the emission of visible light from the fluorescent substance to the end of the excitation. In the period P 2 , the display unit  300  starts to produce visible light at the end of the period C. Due to the current-limiting function of the inductor L 1 , both the voltage Vp and the current IL 1  drop. Because of the weak discharge and the wall discharge inside the display unit  300 , the sum of the resonance voltage level of the energy recovery unit and the wall charge voltage is lower than the firing voltage. Consequently, the period P 2  ends and the period P 3  begins.  
         [0028]     In the time period P 3 , the voltage Vp and the wall charge voltage of the display unit continues to accumulate. Because the period P 3  is rather short in the present embodiment, the discharge condition will not be satisfied. As soon as the switch SW starts to turn on, the period P 3  ends and the period P 4  begins.  
         [0029]     In the time period P 4 , external energy (for example, the sustain voltage Vs) is transmitted to the display unit  300 . Because the illumination of the fluorescent material increases slowly and non-linearly, the intensity of the illumination in the second discharge resulted from the application of the external energy is based on the previous illumination level of the fluorescent substance. Therefore, the period D when the fluorescent material generates visible light can be extended from the second period P 2  to the period P 4 . In addition, because the period C has already ended before providing the external energy, the external energy supplied in the period P 4  can be completely used for exciting the fluorescent material to produce light. Hence, the light-emitting efficiency and brightness of the fluorescent material is significantly increased.  
         [0030]     In the following, an experimental comparison between the conventional single discharge driving technique and the multiple discharge driving technique according to the present invention is provided. The infrared signals IR obtained through an infrared sensor are used for the comparison. Table 1 shows the data obtained from an electrical experiment on the same type of plasma display panel modules.  
                             TABLE 1                           A comparison of experimentally determined electrical data       between identical plasma display panel modules driven by       conventional single discharge technique and the multiple       discharge driving technique according to the present       invention (Vs = 175 V, Vxg = 175 V, Vw = 60 V).            Power apc:   Full white pattern   Full black pattern       205 W (for 46 AVC)   Power consumption   Power consumption               Single discharge   253 W     80 W       Multiple discharges   197 W   65.3 W                  
 
         [0031]     According to Table 1, no matter whether the pattern is full white or full black, there is a dramatic drop in the power consumption in the present invention. In addition, Table 2 shows a comparison of experimentally determined optical data between identical plasma display panel modules.  
                                                           TABLE 2                           A comparison of experimentally determined optical data between identical       plasma display panel modules driven by conventional single discharge       technique and the multiple discharge driving technique according to the       present invention (Vs = 175 V, Vxg = 175 V, Vw = 60 V).            Power                       apc:       Light-       205 W (46   Full white   emitting   IR signal area   IR signal area       AVC)   illumination   efficiency   (Scan side)   (Bulk side)                    Single   127.11 cd/m2   0.904   8.47 n volt-sec    7.9 n volt-sec       discharge       Multiple   143.56 cd/m2   1.31   9.65 n volt-sec   9.55 n volt-sec       discharges                  
 
         [0032]     According to Table 2, the optical characteristics in the present invention are much better than the ones provided through the conventional technique. Furthermore, the measured IR signaling area with multiple discharges is also higher than one with single discharge. All in all, the light-emitting efficiency and the brightness level of the multiple discharge driving method is better than the conventional single discharge driving technique.  
         [0033]     In summary, the conventional single discharge driving technique utilizes a sustain voltage to provide the energy needed for exciting the fluorescent material during the excitation period and the light-emitting period; and moreover, the excitation period and the light-emitting period are completed in a single discharge. Hence, overall light-emitting efficiency and brightness level is poor. In the present invention, the energy recovery circuit provides weak discharge energy to complete the excitation period and the light-emitting period of the fluorescent material before the discharge of the sustain voltage. Therefore, there is no need for the subsequent sustain voltage to enter into an excitation period so that the fluorescent material can emit visible light in no time. As a result, the present invention can improve the display characteristics of the plasma display panel and increase the light-emitting efficiency and brightness level of the panel.  
         [0034]     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 present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.