KR20010093019A - Apparatus for Controlling Radio Frequency of Plasma Display Panel and Method thereof - Google Patents

Abstract

PURPOSE: An apparatus and a method for controlling a high frequency power of a plasma display panel(PDP) are provided to uniformly maintain the high frequency power by varying a voltage level of a high frequency signal depending on current inputted to the PDP. CONSTITUTION: A switching mode power supply(SMPS)(32) and a direct current - direct current(DC-DC) inverting unit(33) are serially connected between an alternating current - direct current(AC-DC) inverting unit(31) and an amplifier(34). A filter(35) is connected to the output terminal of the amplifier(34). A current/voltage detecting unit(36) and storing unit(37) are serially connected to a feedback loop between the filter(35) and a controlling unit(38). A level shifter(39) is connected between the controlling unit(38) and the SMPS(32). An oscillator(40) is connected between the controlling unit(38) and the amplifier(34). An alternating current of a single phase or 3 phase is inputted to the AC-DC inverting unit(31). The alternating signal is inverted to a direct signal by the AC-DC inverting unit(31), and then is inputted to the SMPS(32). The SMPS(32) inverts the direct signal inputted from the AC-DC inverting unit(31) to a square wave signal as switching the direct signal by an on/off control signal inputted from the level shifter(39).

Description

Apparatus for Controlling Radio Frequency of Plasma Display Panel and Method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply control apparatus and method for a plasma display panel, and more particularly, to a high frequency power control apparatus and method for a plasma display panel suitable for high frequency power control of a high frequency plasma display panel.

Plasma Display Panels (hereinafter referred to as "PDPs") display an image including characters or graphics by emitting phosphors by ultraviolet rays of 147 nm generated upon discharge of He + Xe or Ne + Xe gas. Such a PDP is not only thin and easy to enlarge, but also greatly improved in quality due to recent technology development. PDPs are largely classified into direct current type and alternating current type according to their structure and discharge type. Among them, the AC-type PDP generates discharge by using wall charges accumulated in the dielectric and the electrode is protected by the dielectric, so that the driving voltage can be lowered and the service life is longer than the direct current type.

Referring to FIG. 1, an AC PDP includes a front substrate 1 having a sustain electrode 10 and a back substrate 2 having an address electrode 4 formed thereon. The front substrate 1 and the rear substrate 2 are spaced in parallel with the partition 3 therebetween. A mixed gas such as Ne-Xe, He-Xe, or the like is injected into the discharge space provided by the front substrate 1, the rear substrate 2, and the partition wall 3. Two sustain electrodes 10 are paired in one plasma discharge channel. One of the pair of sustain electrodes 10 causes an opposite discharge with the address electrode 4 in response to the scan pulse supplied in the address period, and the adjacent sustain electrode 10 in response to the sustain pulse supplied in the sustain period. It is used as a scan / sustain electrode which causes surface discharge. The other one of the sustain electrode pairs 10 is used as a common sustain electrode to which a sustain pulse is commonly supplied. The dielectric layer 8 and the protective layer 9 are stacked on the upper substrate 1 on which the sustain electrodes 10 are formed. The dielectric layer 8 serves to limit the plasma discharge current and to accumulate wall charges during discharge. The protective film 9 prevents damage of the dielectric layer 8 due to sputtering generated during plasma discharge and increases emission efficiency of secondary electrons. This protective film 9 is usually made of magnesium oxide (MgO). On the back substrate 2, partition walls 3 for dividing the discharge space extend vertically. On the surfaces of the back substrate 2 and the partition walls 3, phosphors 5 are excited by vacuum ultraviolet rays to generate visible light.

In this type of AC PDP, one frame is composed of a plurality of subfields, and gray levels are expressed by a combination of subfields. For example, in the case where 256 gray levels are to be realized, one frame period is time-divided into eight subfields. In addition, each of the eight subfields is divided into a reset period, an address period, and a sustain period. The full screen is initialized during the reset period. In the address period, cells in which data is to be displayed are selected by the address discharge. The selected cells are discharged in the sustain period. The sustain period is lengthened by a period corresponding to 2n according to the weight of each of the subfields. In other words, the sustain period included in each of the first to eighth subfields is lengthened at a ratio of 20, 21, 22, 23, 24, 25, 26, 27. To this end, the number of sustain pulses generated in the sustain period is increased to 20, 21, 22, 23, 24, 25, 26, 27 according to the subfields. The combination of these subfields determines the luminance and chromaticity of the display image.

In such an AC-type PDP, the sustain electrode pair 10 is alternately supplied with a sustain pulse having a duty ratio of 1, a frequency of 200 to 300 kHz, and a pulse width of about 10 to 20 Hz. The sustain discharge occurring between the sustain electrode pairs 10 in response to the sustain pulse occurs only once at a very short moment per sustain pulse. Charged particles generated by the sustain discharge move along the discharge path between the sustain electrode pair 10 according to the polarity of the sustain electrode pair 10 and accumulate in the upper dielectric layer 8 to remain as wall charges. This wall charge lowers the driving voltage during the next sustain discharge, but reduces the electric field of the discharge space during the sustain discharge. Accordingly, when the wall charge is formed during the sustain discharge, the discharge is stopped. As such, the sustain discharge occurs only once at a very short moment compared to the width of the sustain pulse, and most of the time is spent in the preparation of the wall charge and the next sustain discharge. For this reason, in the conventional AC PDP, the actual discharge period becomes very short compared to the total discharge period, so that the luminance and the discharge efficiency are inevitably low.

In order to solve the low luminance and discharge efficiency problems of the AC-type PDP, a high frequency PDP (hereinafter referred to as "RFPDP") that causes sustain discharge using a high frequency signal of several tens to several hundred MHz has been proposed. In RFPDP, electrons vibrate in a cell by high frequency discharge.

Referring to FIG. 2, the RFPDP includes a front substrate 11 on which a high frequency electrode 13 is formed, and a back substrate 12 on which an address electrode 14 and a scan electrode 16 are formed in an orthogonal direction. A dielectric layer 15 is formed between the address electrode 14 and the scan electrode 16 to insulate the electrodes. A lattice-shaped partition wall 17 is formed between the front substrate 11 and the rear substrate 12. The phosphor 18 is coated on the surface of the partition 17.

In the RFPDP, cells are selected by the discharge between the address electrode 14 and the scan electrode 16 in the address period. The selected cells display an image by vibrating motion of electrons in the sustain period. At this time, a high frequency signal of several to tens of MHz is applied to the high frequency electrode 13, and a DC bias voltage of a predetermined level is applied to the scan electrode 46. The high frequency signal causes the electrons in the cell to vibrate in the discharge space according to the polarity of the high frequency signal. The discharge gas is continuously ionized by the vibrating motion of the electrons. The vacuum ultraviolet rays generated by this discharge excite the phosphor 26 and generate visible light as the phosphor 26 transitions. In this way, RFPDP generates a discharge continuously during a sustain period by using a high frequency signal, thereby increasing luminance and discharge efficiency as compared with an AC PDP.

In order to stabilize the high frequency discharge in the RFPDP, the power of the high frequency signal applied to the high frequency electrode 13 of the panel must be sufficiently large. For this purpose, the RFPDP includes an impedance matching circuit 23 connected between the high frequency generator 22 and the panel 24 as shown in FIG. The high frequency generator 22 generates a high frequency signal of tens to hundreds of MHz. This high frequency signal is amplified by an amplifier in the high frequency generator 22 and then input to the impedance matching circuit 23. The impedance matching circuit 23 matches the impedance of the high frequency signal with the impedance of the panel 24. Since the impedance of the input terminal and the output terminal of the high frequency signal is matched as described above, the high frequency signal input to the panel 24 has the maximum power value.

However, the conventional RFPDP has a problem that it is difficult to precisely control the power value of the high frequency signal according to the impedance variation of the panel 24. In other words, in the conventional method of controlling the high frequency signal power, the sampling is performed in the form of a combination of voltage and power, converted into active power, and then the power value of the high frequency signal is adjusted based on this. On the other hand, in the PDP, the current value of the high frequency signal changes due to the load change that varies depending on the luminance value of the data or the discharge of the cell. On the other hand, the voltage value of the high frequency signal hardly changes even with the load variation of the PDP. Accordingly, since the power value of the high frequency signal does not change significantly when the load of the panel 24 changes, the method of controlling the high frequency signal based on the power value of the high frequency signal fed back from the panel 24 may reduce the precision of the control. There is no choice but to.

In addition, the conventional RFPDP has a problem in that the manufacturing cost increases when the impedance matching circuit 23 is configured as a variable matching circuit that varies the capacitive impedance value according to the impedance of the panel.

Accordingly, an object of the present invention is to provide an apparatus and method for controlling high frequency power of a PDP that is suitable for power control of a high frequency signal supplied to an RFPDP.

1 is a perspective view showing a conventional AC plasma display panel.

2 is a perspective view showing a conventional high frequency plasma display panel.

FIG. 3 is a block diagram illustrating a high frequency generator and an impedance matching circuit for supplying a high frequency signal to the high frequency plasma display panel shown in FIG.

4 is a block diagram showing a high frequency generator according to an embodiment of the present invention.

FIG. 5 is a block diagram illustrating a plasma display panel generating discharge by using the high frequency generator and the high frequency signal shown in FIG. 4.

<Description of Symbols for Main Parts of Drawings>

1,11: Front board 2,12: Back board

3,17 partition 4,14 address electrode

5,18 phosphor 8,15 dielectric layer

9: protective film 10: sustain electrode

16: scan electrode 22, 50: high frequency generator

23: impedance matching circuit 24, 60: panel

31: AC-DC converter 32: SMPS

33: DC-DC converter 34: amplifier

35 filter 36 current / voltage detection unit

37: storage unit 38: control unit

In order to achieve the above object, the high frequency power control apparatus of the PDP according to the present invention includes a detection means for detecting a current value of the high frequency signal input to the panel, and a high frequency for changing the voltage level of the high frequency signal according to the current variation of the high frequency signal And signal control means.

The high frequency power control method of the PDP according to the present invention includes detecting a current value of a high frequency signal input to a panel, and varying a voltage level of the high frequency signal according to a current variation of the high frequency signal.

Other objects and features of the present invention in addition to the above object will become apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 4 and 5.

Referring to FIG. 4, the high frequency generator of the PDP according to the present invention is a switching mode power supply connected in series between an AC-DC converter (hereinafter referred to as an "AC-DC converter") 31 and an amplifier 34 ( Switching Mode Power Supply (hereinafter referred to as " SMPS ") 32 and a DC-DC-conversion section (hereinafter referred to as a " DC-DC conversion section ") 33 and a filter connected to the output terminal of the amplifier 34 ( 35, a current / voltage detector 36 and a storage 37 connected in series on a feedback loop between the filter 35 and the controller 38, and connected between the controller 38 and the SMPS 32. The level shifter 39 and the oscillator 40 connected between the control part 38 and the amplifier 34 are provided. The AC-DC converter 31 receives single-phase or three-phase AC signals. The AC signal is converted into a DC signal by the AC-DC converter 31 and then input to the SMPS 32. The SMPS 32 converts the DC signal input from the AC-DC converter 31 into a square wave signal by switching the on / off control signal input from the level shifter 39. The DC-DC converter 33 rectifies the square wave signal from the SMPS 32 and then boosts the voltage to supply the amplifier 34 to the amplifier 34. The oscillator 40 generates a high frequency signal of a predetermined frequency under the control of the controller 38 and supplies it to the amplifier 34. The amplifier 34 amplifies the high frequency signal from the oscillator 40 by the voltage level of the supply voltage input from the DC-DC converter 33 and supplies it to the filter 35. The filter 35 removes harmonic components mixed in the high frequency signal input from the amplifier 34. The current / voltage detector 36 separates and detects the current I and the voltage V from the high frequency signal RF output from the filter 35. The current I and the voltage V of the high frequency signal RF thus detected are temporarily stored in the storage unit 37 and then supplied to the control unit 38. The control unit 38 causes the square wave generated from the SMPS 32 to be pulse width modulated (“PWM”) according to the current I of the high frequency signal input from the storage unit 37. In detail, the current value of the high frequency signal RF varies according to the load variation of the RFPDP. The control unit 38 supplies the level shifter 39 with the pulse width of the PWM control signal varying according to the level change of the current I from the storage unit 37. The level shifter 39 shifts the voltage level of the PWM control signal from the controller 39 to the drive voltage level of the SMPS 32. This level shifter 39 may be composed of a photo coupler. In this manner, the SMPS 32 adjusts the on / off time of the DC signal input from the AC-DC converter 31 by the PWM control signal input to the SMPS 32. Since the pulse width of the square wave signal generated from the SMPS 32 is changed by the PWM control, the voltage level of the supply voltage supplied to the amplifier 34 is changed. At this time, when the pulse width of the square wave is reduced, the supply voltage level of the amplifier 34 is lowered, while the supply voltage level is increased when the pulse width of the square wave is increased. The oscillator 40 serves to generate a high frequency signal of a predetermined frequency under the control of the controller 38.

As such, since the voltage level of the high frequency signal RF is changed according to the current value of the high frequency signal RF, the power of the high frequency signal RF supplied to the RFPDP is always maintained even when the load of the RFPDP is changed.

On the other hand, the controller 38 performs the PWM control according to the current value of the high frequency signal RF when the load variation of the RFPDP is small, but when the load of the RFPDP changes significantly, the high frequency signal input to the RFPDP Since the voltage value of is changed, PWM control is performed according to the voltage variation of the high frequency signal.

As described above, since the voltage of the high frequency signal is adaptively changed according to the load variation of the RFPDP, the power of the high frequency signal input to the panel is always maintained at the maximum, thereby eliminating the impedance matching circuit as shown in FIG. 5. In other words, the high frequency generator 50 and the panel 60 are connected in series. When an impedance matching circuit is provided between the high frequency generator 50 and the panel 60, this impedance matching circuit is composed of a fixed impedance matching circuit having a fixed capacitive impedance value.

As described above, the high frequency power control apparatus of the PDP according to the present invention changes the voltage level of the high frequency signal according to the current value of the high frequency signal input to the panel. When the high frequency power control device is applied as a high frequency signal source of the RFPDP, the power of the high frequency signal supplied to the panel is kept at a constant maximum. Accordingly, the high frequency power control apparatus and method of the PDP according to the present invention is adapted to the RFPDP which causes the discharge by using the high frequency signal. In addition, when the high frequency power control apparatus according to the present invention is applied as a high frequency signal source of the RFPDP, a low cost fixed impedance matching circuit may be installed instead of an expensive variable impedance matching circuit, and an impedance matching circuit may be omitted.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (7)

In a plasma display panel that generates a discharge by using a high frequency signal, Detecting means for detecting a current value of a high frequency signal input to the panel; And a high frequency signal control means for varying a voltage level of the high frequency signal in response to a current variation of the high frequency signal. The method of claim 1, The high frequency signal control means includes: a square wave generator for converting a DC signal into a square wave signal; A DC-DC converter for rectifying and boosting the square wave signal to generate a DC-type supply voltage; An amplifier for amplifying the high frequency signal according to a supply voltage from the DC-DC converter; And a control unit for modulating the pulse width of the square wave signal generated from the square wave generator based on the current variation of the high frequency signal. The method of claim 2, The high frequency signal control means includes an AC-DC converter for converting an AC input signal into a DC signal and supplying the square wave generator; And a filter for removing harmonic components of the high frequency signal output from the amplifier. The method of claim 2, And a storage unit for temporarily storing the current value and the voltage value of the high frequency signal detected by the detection means. The method of claim 2, An oscillator for supplying a high frequency signal of a predetermined frequency to the amplifier further comprises a high frequency power control apparatus for a plasma display panel. The method of claim 2, And a level shifter for suitably converting a voltage level of a pulse width modulation control signal input from the controller to the square wave generator, to suit the square wave generator. In the high frequency signal control method of a plasma display panel that generates a discharge by using a high frequency signal, Detecting a current value of a high frequency signal input to the panel; And varying a voltage level of the high frequency signal in response to a current variation of the high frequency signal.