# Patent

## Title
Plasma display panel driving device having a zener diode

## Abstract

A plasma display panel driver for applying a Zener diode to a falling ramp driving circuit, and reducing a falling ramp driving initial voltage to a voltage that causes a discharge. The driver comprises a transistor having a first electrode coupled between a first terminal of a panel capacitor and a power source; a capacitor having a first terminal coupled to a control electrode of the transistor; and a first resistor, a diode, and a Zener diode coupled in parallel between a second terminal of the capacitor and the first electrode of the transistor.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application claims priority to and the benefit of Korean Patent Application No. 10-2003-0072323, filed on Oct. 16, 2003, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma display panel (PDP) driving device and method.
2. Discussion of the Related Art
Generally, among flat panel displays, PDPs are regarded as having better luminance and light emission efficiency, as well as wider view angles. Therefore, PDPs are being considered as the primary substitute for the conventional cathode ray tubes for large displays of greater than 40 inches.
The PDP uses plasma generated via a gas discharge process to display characters or images, and tens of thousands to millions of pixels may be provided in a matrix, depending on its size. PDPs are categorized into direct current (DC) PDPs and alternating current (AC) PDPs according to supplied driving voltage waveforms and discharge cell structures.
Since the DC PDPs have electrodes exposed in the discharge space, they allow a current to flow when a voltage is supplied, which requires resistors for current restriction. On the other hand, since the AC PDPs have electrodes covered by a dielectric layer, naturally formed capacitances restrict the current, and the dielectric layer also protects the electrodes from ion shocks due to discharging. Accordingly, they have a longer lifespan than the DC PDP.
FIG. 1 shows a perspective view of a conventional AC PDP.
As shown, parallel pairs of a scan electrode 4 and a sustain electrode 5, covered by a dielectric layer 2 and a protection film 3, are provided on a lower surface of a first glass substrate 1. A plurality of address electrodes 8, covered with an insulation layer 7, is formed on an upper surface of a second glass substrate 6. Barrier ribs 9 are formed in parallel with, and between, the address electrodes 8, on the insulation layer 7, and phosphor layers 10 are formed on the surface of the insulation layer 7 and the sides of the barrier ribs 9. The first and second glass substrates 1 and 6 are sealed together to form a discharge space 11 between them, and the scan electrode 4 and the sustain electrode 5 pair are orthogonal to the address electrode 8. Discharge cells 12 are formed in the discharge space at intersections of the address electrode 8 and the scan electrode 4 and the sustain electrode 5 pair.
FIG. 2 shows a typical PDP electrode arrangement.
As shown, the PDP electrodes have an m×n matrix configuration. Address electrodes A1 to Am are arranged in the column direction, and scan electrodes Y1, to Yn (Y electrodes) and sustain electrodes X1 to Xn (X electrodes) are alternately arranged in the row direction.
FIG. 3 shows a conventional PDP driving waveform.
Each subfield includes a reset period, an address period, and a sustain period.
The reset period erases wall charge states of a previous sustain and sets up wall charges in order to stably perform a next addressing operation. In the address period, the cells that are to be turned on are selected, and wall charges are accumulated to those selected cells. In the sustain period, discharges for actually displaying images on the PDP are performed.
The following describes operations of the conventional reset period. As shown in FIG. 3, the conventional reset period may include an erase period, a Y ramp rising period, and a Y ramp falling period.
(1) Erase Period
Positive charges are accumulated on the X electrodes, and negative charges are accumulated on the Y electrodes after finishing the last sustain discharge. In this state, an erase ramp voltage that gently rises from 0 V to the voltage of +Ve is applied to the X electrode, thereby eliminating the wall charges formed on the X and Y electrodes.
(2) Y Ramp Rising Period
During this period, the address electrode and the X electrode maintain 0V, and a ramp voltage gradually rising from the voltage of Vs to the voltage of Vset is applied to the Y electrode. While the ramp voltage rises, a first weak reset discharge is generated to all the discharge cells from the Y electrode to the address electrode and the X electrode. As a result, negative wall charges accumulate to the Y electrode, and positive wall charges accumulate to the address electrode and the X electrode.
(3) Y Ramp Falling Period
In the latter part of the reset period, a ramp voltage that gradually falls from the voltage of Vs to the 0V is applied to the Y electrode while the X electrode maintains a voltage of Ve. While the ramp voltage falls, a second weak reset discharge is generated at all the discharge cells.
According to the conventional reset method shown in FIG. 3, a reset discharge is generated in the Y ramp rising period and the Y ramp falling period to control the amount of wall charges within the cell, and hence, an accurate addressing operation may be carried out subsequently.
In the Y falling ramp period, however, the discharge is not generated until the voltage at the Y electrode reaches a predetermined voltage. As shown in FIG. 3, during the Y ramp falling period, the voltage at the Y electrode falls to the voltage of Vs and maintains that voltage for a short period before gradually falling.
However, the voltage for actually generating the second discharge may be lower than the voltage of Vs. Hence, an unneeded period in which no discharge is generated may be provided after applying the Y ramp falling pulse, which increases the length of the reset period and the total driving time.
SUMMARY OF THE INVENTION
The present invention provides a PDP driver that may reduce a length of time for the reset period.
Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention.
The present invention discloses a PDP driver for applying a reset driving waveform in a ramp pulse format to a panel capacitor, comprising a transistor having a first electrode coupled between a first terminal of the panel capacitor and a power source and a capacitor having a first terminal coupled to a control electrode of the transistor. A first resistor, a diode, and a Zener diode are coupled in parallel between a second terminal of the capacitor and the first electrode of the transistor.
The present invention also discloses a PDP driver for applying a reset driving waveform in a ramp pulse format to a panel capacitor comprising a transistor having a first electrode coupled between a first terminal of the panel capacitor and a power source, and a capacitor having a first terminal coupled to a control electrode of the transistor. A second terminal of the capacitor is coupled in series to a zener diode, and a first resistor and a diode are coupled in parallel between the first electrode and the Zener diode.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.
FIG. 1 shows a partial perspective view of a conventional AC PDP.
FIG. 2 shows a typical PDP electrode arrangement.
FIG. 3 shows a conventional PDP driving waveform.
FIG. 4 shows a PDP according to a first exemplary embodiment of the present invention.
FIG. 5 shows a Y electrode driving circuit of the PDP according to the first exemplary embodiment of the present invention.
FIG. 6 shows a a falling ramp driving circuit according to the first exemplary embodiment of the present invention.
FIG. 7 shows a PDP driving waveform according to the first exemplary embodiment of the present invention.
FIG. 8 shows a a falling ramp driving circuit according to a second exemplary embodiment of the present invention.
FIG. 9 shows a PDP driving waveform according to the first and second exemplary embodiments of the present invention.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following detailed description shows and describes exemplary embodiments of the invention, simply by way of illustration of the best mode contemplated by the inventors of carrying out the invention. As will be realized, the invention is capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are illustrative in nature, and not restrictive. To clarify the present invention, parts that are not described in the specification are omitted, and parts for which similar descriptions are provided have the same reference numerals.
A PDP driving method according to the first exemplary embodiment of the present invention will be described in detail with reference to FIG. 4, FIG. 5 and FIG. 6.
FIG. 4 shows a PDP according to the first exemplary embodiment of the present invention.
As shown, the PDP comprises a plasma panel 100, an address driver 200, a Y electrode driver 320, an X electrode driver 340, and a controller 400.
The plasma panel 100 comprises a plurality of address electrodes Al to Am arranged in the column direction, and a plurality of Y electrodes Y1 to Yn and X electrodes X1 to Xn alternately arranged in the row direction.
The controller 400 receives external video signals and generates an address driving control signal SA, a Y electrode driving signal SY, and an X electrode driving signal SX, and transmits them to the address driver 200, the Y electrode driver 320, and the X electrode driver 340.
The address driver 200 receives the address driving control signal SA and applies a display data signal to the respective address electrodes for selecting a discharge cell to be displayed.
The Y electrode driver 320 and the X electrode driver 340 receive a Y electrode driving signal SY and an X electrode driving signal SX and apply them to the Y and X electrodes.
FIG. 5 shows a detailed diagram of the Y electrode driver 320 according to the first exemplary embodiment of the present invention, FIG. 6 shows a falling ramp driving circuit according to the first exemplary embodiment of the present invention, and FIG. 7 shows a reset driving waveform applied to the Y electrode by the falling ramp driving circuit of the first exemplary embodiment of the present invention.
As shown in FIG. 5, the Y electrode driver 320 comprises transistors M1 and M2 coupled in series between the sustain discharge voltage of Vs and a ground voltage, and a transistor M3 is coupled between a node of the transistors M1 and M2 and a Y electrode of the panel capacitor Cp. In this case, the panel capacitor Cp represents a capacitance component between the X and Y electrodes. Additionally, the X electrode of the panel capacitor Cp is shown coupled to the ground terminal for ease of description, but it is actually coupled to the X electrode driver 340.
A first terminal of a capacitor C1 is coupled to the node of the transistors M1 and M2, and a diode D1 is coupled between a voltage of (Vset−Vs) and a second terminal of the capacitor C1. A transistor M4, for applying a rising ramp voltage to the Y electrode, is formed between the first terminal of the panel capacitor Cp, which corresponds to the Y electrode, and the second terminal of the capacitor C1. The transistor M4 is coupled to a ramp switch that includes a capacitor formed between a drain and a gate to supply a constant current between a source and the drain.
A falling ramp driving circuit 321, which includes a transistor M5 for applying a falling ramp voltage to the Y electrode, is coupled between the first terminal of the panel capacitor Cp, which corresponds to the Y electrode, and the ground voltage. The transistor M5 is coupled to a ramp switch that includes a capacitor formed between a drain and a gate to supply a constant current between a source and the drain.
As shown in FIG. 6, the falling ramp driving circuit 321 comprises a resistor R1, a diode D2, and a Zener diode D3 coupled in parallel between a first terminal of the capacitor C2 and a drain of the transistor M5. Additionally, a resistor R2 is coupled in series to the Zener diode D3. The resistor R1 forms a charging path of the capacitor C2, the diode D2 forms a discharging path thereof, and the Zener diode D3 operates as a constant voltage source in the breakdown region. The resistor R2 prevents the voltage charged in the capacitor C2 from discharging in the region where the Zener diode D3 functions as a general diode.
A driving method according to the first exemplary embodiment will be described in further detail with reference to FIG. 5, FIG. 6 and FIG. 7.
At time t1, the transistors M2, M3 and M5 turn off, and the transistors M1 and M4 turn on. The voltage of Vs is supplied to the first terminal of the capacitor C1, and the voltage at the second terminal of the capacitor C1 reaches the voltage of Vset since the capacitor C1 is charged with the voltage of (Vset−Vs) before time t1. The voltage of Vset is also supplied to the Y electrode of the panel capacitor Cp through the transistor M4. Between times t1 and t2, a ramp voltage rising from the second voltage of Vs to the third voltage of Vset is applied to the Y electrode of the panel capacitor Cp since a constant current flows between the source and the drain of the transistor M4.
During times t1 and t2, the capacitor C2 is charged with a voltage supplied from the voltage source of Vs through the resistor R1, and the Zener diode D3 stays off until the voltage at the resistor R1 reaches the breakdown voltage of the Zener diode D3. Once the voltage at the resistor R1 reaches the breakdown voltage, the Zener diode D3 turns on, a subsequent voltage at the resistor R1 is fixed at the breakdown voltage, and the capacitor C2 is charged with a third voltage of Vc, which equals a difference between the voltage at the Y electrode of the capacitor Cp and the breakdown voltage of the Zener diode D3.
The voltage of Vc may be a voltage at which a weak reset discharge is generated, and it may be controlled by controlling the breakdown voltage of the Zener diode D3.
At time t2, the transistors M2, M3 and M5 turn on, the transistors M1 and M4 turn off, and the voltage of Vc is applied to the Y electrode. At time t2, with the transistor M1 off and the transistors M3 and M5 on, a reverse current flows to the Zener diode D3, and it operates like a general diode. Therefore, the voltage at the Y electrode of the panel capacitor Cp is instantly reduced to the charging voltage of Vc at the capacitor C2. Since a constant current flows between the drain and the source of the transistor M5 due to the influence of the capacitor C2, the voltage at the Y electrode of the capacitor Cp falls to the ground voltage from the voltage of Vc in a ramp manner. Also, since the resistor R2 is coupled in series to the Zener diode D3, the voltage of Vc charged in the capacitor C2 is discharged through the diode D2 and the drain-source path of the transistor M5.
According to the reset driving method of the first embodiment as described above, the Zener diode D3 controls the voltage charged in the capacitor C2 in the Y ramp rising period, thus reducing the initial voltage of the Y ramp falling period to a voltage at which a weak reset discharge is generated, thereby reducing the length of the reset period.
The Zener diode D3 and the resistor R2, which are coupled in series, are coupled in parallel to the diode D2 and the resistor R1 in the first exemplary embodiment. As shown in FIG. 8, they may also be coupled in series between the capacitor C2, and the diode D2 and the resistor R1, which are coupled in parallel.
FIG. 8 shows a circuit diagram of a Y falling ramp driving circuit according to a second exemplary embodiment of the present invention.
Regarding operation of the Y electrode driver 320, the capacitor C2 is charged through the path in the order of the resistor R1, the Zener diode D3, and the resistor R2 in the rising ramp period.
Similar to the first embodiment, the Zener diode D3 stays off until reaching its breakdown voltage. Upon reaching its breakdown voltage, the Zener diode D3 turns on and remains fixed at the breakdown voltage, and the capacitor C2 is charged with the voltage of Vc, which is a difference between the voltage at the Y electrode of the capacitor Cp and the breakdown voltage of the Zener diode D3.
Also, with the transistor M1 off and the transistors M3 and M5 on in the falling ramp period, a reverse current flows to the Zener diode D3, and the Zener diode D3 operates like a general diode. Therefore, the voltage at the Y electrode of the panel capacitor Cp is instantly reduced to the charged voltage of Vc of the capacitor C2. Since a constant current flows between the source and the drain of the transistor M5 because of the influence of the capacitor C2, the voltage at the Y electrode of the capacitor Cp is reduced to the ground voltage from the voltage of Vc in a ramp manner. The voltage Vc charged in the capacitor C2 is discharged through the resistor R2, the Zener diode D3, the diode D2 and the drain-source path of the transistor M5.
When dividing a field into eight subfields and driving them, a falling ramp pulse may be applied after a rising ramp pulse in the reset period of the first subfield. On the other hand, a falling ramp pulse may be applied without the rising ramp pulse in the reset period of the second to eighth subfields, as disclosed in U.S. Pat. No. 6,294,875. While first and second exemplary embodiments of the present invention describe the falling ramp pulse applicable to the first subfield, the present invention is also applicable to the falling ramp pulse of the second to eighth subfields.
As shown by “A” of FIG. 9, a falling ramp may be applied, after a sustain discharge voltage is applied in the latter part of the sustain discharge period of a previous subfield, without applying a rising ramp pulse in the reset period of the second to eighth subfields. However, a reset discharge may not be generated until a period of time after applying the falling ramp pulse, and since the capacitor C2 is to be sufficiently charged before the falling ramp is applied, the voltage at the Y electrode may be maintained at the sustain discharge voltage Vs during the time t1 in which the capacitor C2 is charged.
However, when the falling ramp driving circuit according to the first and second exemplary embodiments is utilized, as shown by “B” of FIG. 9, the time for charging the capacitor C2 may be reduced to a time of t2 since the capacitor C2 may be charged with a voltage of Vc′, which is the difference between the voltage at the Y electrode of the capacitor Cp and the breakdown voltage of the Zener diode D3.
Also, when the transistor M5 is turned on in the falling ramp period, similar to the first and second exemplary embodiments, the voltage at the Y electrode of the capacitor Cp may be instantly reduced to the charged voltage of Vc′, and the voltage at the Y electrode of the capacitor Cp is then further reduced to the ground voltage by a falling ramp. Accordingly, the length of time of the falling ramp period may be reduced.
As described, the initial voltage of the Y ramp falling period may be reduced to a voltage at which a weak reset discharge is generated by controlling, through a zener diode, a voltage charged in a capacitor in a Y ramp rising period, thereby eliminating an unnecessary time during which no discharge is generated in the initial part of the Y ramp falling period and reducing a time of the reset period. Also, reducing the reset time may reduce the total driving time.
It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

## Claims

1. A plasma display panel driver for applying a reset driving waveform in a ramp pulse format to a panel capacitor, comprising:
a transistor having a drain electrode coupled to a first terminal of the panel capacitor and a source electrode coupled to a power source;
a capacitor having a first terminal coupled to a gate electrode of the transistor;
a Zener diode having an anode coupled to a second terminal of the capacitor; and
a first resistor and a diode coupled between a cathode of the Zener diode and the drain electrode of the transistor, wherein the first resistor and the diode are coupled in parallel to each other.

2. The plasma display panel driver of claim 1, wherein a voltage at the panel capacitor is reduced by a breakdown voltage of the Zener diode when the transistor is turned on.

3. The plasma display panel driver of claim 1, wherein the capacitor is charged with a voltage that is less than the voltage applied to the first terminal of the panel capacitor by an amount of a breakdown voltage of the Zener diode.

4. The plasma display panel driver of claim 1, wherein the power source supplies a final voltage of a falling ramp reset pulse driving waveform.

5. The plasma display panel driver of claim 1, further comprising a second resistor coupled in series between the second terminal of the capacitor and the anode of the Zener diode.