JPS6126073B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit for operating an AC type gas discharge display panel, a so-called plasma display panel (PDP), by a time division drive method.

A plasma display panel consists of two sets of electrodes arranged in a matrix, facing each other with a dischargeable gas medium in between.The surface of each electrode in contact with the gas medium is covered with a dielectric layer, and an external voltage is applied. The voltage is configured to be coupled to the gas medium via the capacitance. Therefore, in order to cause a desired gas cell to discharge and emit light, an AC voltage is applied between a pair of opposing electrodes sandwiching the gas cell, and the cell intermittently discharges once each time the polarity of the applied voltage changes. and emit light.

In order to drive this type of plasma display panel in a time-division manner, first a voltage pulse train consisting of a plurality of pulses is sequentially applied to each electrode in one of the electrode groups in opposing rows or columns. Apply sequentially and scan at a repetition rate of about 60 or more times per second. When a voltage pulse train is applied to a certain electrode among these electrodes, that is, when it is in a selected state, all of the cells that determine which cells are to be emitted to emit light according to the content of display data are selected from among a row of gas cells determined by this electrode. By applying a voltage pulse train having a polarity opposite to that of the pulse train to the other opposite electrode of the cell to select a selective state, only a desired cell can be caused to discharge and emit light. By repeating the above operation each time each electrode in the former electrode group is scanned one by one, the desired display will appear on the entire screen.

Now, if the number of repetitions of scanning is a constant value R times per second, and the number of pulses assigned to each electrode in one scan is a, then the number of pulses applied to the cell that is to discharge and emit light is equal to As mentioned above, the gas cell discharges and emits light every time the polarity of the applied voltage changes, so it discharges twice with one pulse voltage, and thus discharges 2Ra times per second.

The luminance of each gas cell's light emission is proportional to the capacitance of the dielectric layer covering the electrode, but in order to prevent breakdown of the dielectric layer, it is necessary to have a certain thickness.
Since the capacitance does not exceed a certain value, there is a limit to the luminance of light emitted each time. At present, in order to obtain a level of brightness that can be put to practical use, it is necessary to perform about 50,000 discharges per second.

On the other hand, when the number of scanning electrodes is n, in order to cause the gas cell to discharge 2Ra times per second, the repetition frequency of the voltage pulse is nRa (Hz). In order to put the display panel into practical use, it is necessary to
Rna is nRa=n・2Ra/2=128×50000/2=320(K
Hz), and considering that the current drive voltage of plasma display panels is approximately 140V, this places a burden on the drive circuit to operate at high voltage and at high speed.

In order to solve this problem, conventionally, a drive circuit having a set of high voltage complementary transistors as its main element has been proposed. In other words, this circuit configuration, in which a PNP transistor and an NPN transistor are connected in series to perform switching and obtain a pulse output, can obtain high-speed pulses of 500KHz or more.
Moreover, it was extremely useful in that the power loss caused by the drive circuit itself was minimal.

However, with the recent demand for larger plasma display panels, the weaknesses of the complementary drive circuit have been exposed. In other words, as the size of the panel increases, the number of gas cells defined by one electrode on the scanning side increases, and the drive circuit must supply a current proportional to the number of gas cells. Due to the increase in stray capacitance inside and outside the panel, the output impedance of the drive circuit was required to be extremely low.
The complementary drive circuit cannot meet this requirement because it has a structure in which the output is obtained through a resistor, and there is a limit to the direct current amplification factor h _FE of the transistor.

SUMMARY OF THE INVENTION An object of the present invention is to provide a drive circuit with extremely low output impedance, high voltage, and high switching speed in order to drive a large-area plasma display panel in a time-division manner.

Furthermore, it is another object of the present invention to provide a drive circuit for a plasma display panel with very little internal power loss due to switching.

The present invention consists of two sets of electrodes that face each other with a dischargeable gas medium in between and are arranged in a matrix, the surface of each electrode in contact with the gas medium is covered with a dielectric layer, and an externally applied voltage is applied. A first PNP transistor and a first
The collectors of a first complementary transistor pair consisting of NPN transistors are connected via a resistor, the emitter of the first PNP transistor is connected to a high potential power supply, and the first complementary transistor pair is connected to each other through a resistor.
The emitters of the NPN transistors are connected to a low potential power supply, the bases of each pair of first complementary transistors are connected to the same pulse signal source through capacitors, and the emitters of the second PNP transistor and the second NPN transistor There is a second complementary transistor pair consisting of a second PNP transistor whose collector is connected to said low potential power supply, a second NPN transistor whose collector is connected to said high potential power supply, and a second
The base of the PNP transistor is connected to the node between the first PNP transistor and the resistor, the base of the second NPN transistor is connected to the node between the first NPN transistor and the resistor, and the base of the second NPN transistor is connected to the node between the first NPN transistor and the resistor. The purpose is achieved by connecting the emitters of the plasma display panel and extracting the pulse voltage output to be applied to each electrode of the plasma display panel from this node.

Next, it will be explained in detail using the drawings.

FIG. 1 is a diagram showing a conventional high voltage, high speed switching type driver circuit connected to a plasma display panel. In the figure, 1 is a drive circuit group for the scanning-side electrode group, and 2 is a drive circuit group for the data-side electrode group, but they differ only in the input signal timings supplied from the scanning signal generator and the data signal generator. Since the structure is exactly the same, the operation of the drive circuit 1 will be explained.

First, when an input signal with a voltage amplitude of TTL level or similar becomes high level, PNP transistor Q11 is turned off almost at the same time, and NPN
Since the transistor Q12 is turned on, the output terminal 12 of the driver circuit suddenly becomes a low level.
Flows the current from the panel to a low potential power source (earth). Next, when the input signal becomes low level, transistor Q11 turns on and transistor Q12 turns off almost at the same time, so the output terminal 12 suddenly becomes high level and goes from the high potential power supply (+V ₀ ) to the panel through resistor R3. Inject current.

As is clear from the above operation modes, in this circuit configuration, when one of the complementary transistors turns on, the other turns off almost simultaneously, so the rise and fall of the output voltage are steep, and the output voltage is high through Q11 and Q12. Since the current flowing directly from the potential power source to the low potential power source is very small, there is no waste of power, which is preferable.

However, as panels become larger and the required output current capacity increases, it is necessary to prevent Q11 and Q12 from momentarily turning on at the same time due to the on-state storage effect that appears transiently when the transistor is off, resulting in destruction. Due to the voltage drop caused by the inserted protective resistor R13, the slope of the voltage pulse waveform appearing at the output terminal 12 becomes dull.
The amplitude becomes smaller. Furthermore, the impedance of a transistor when it is on depends on the base current determined by the coupling capacitors C11 and C12 and the base resistors R11 and R12. The impedance cannot be lowered to an extreme level, and the collector-emitter saturation voltage increases, causing an increase in the output waveform and an increase in power loss. This results in a decrease in voltage amplitude.

In the drive circuit shown in Figure 1, the collector loss is 1W.
When using a transistor with a high withstand voltage, the value of resistor R13 can be lowered to 500Ω at most, and when driving a plasma display panel with a gas cell pitch of 1 mm, the number of cells that can be discharged simultaneously in one circuit is 50. number is the limit.

FIG. 2 shows an embodiment of the present invention.

In FIG. 2, 3 is a drive circuit group for the scanning side electrode group, and 4 is a drive circuit group for the data side electrode group. As is clear from the explanation of the time-division driving method described above, in one data side electrode, the discharge current flowing therein is at most one gas cell, and therefore, even if the panel is enlarged, the drive circuit 4 is The conventional configuration shown in the figure is sufficient to fulfill the role. On the other hand, the configuration of the scanning side drive circuit 3 is according to the present invention.

The operation of this circuit will be described next. First, a complementary transistor pair Q21 and Q22 connected in series via a resistor R23 connects to a capacitor C
21 and C22, which is alternately turned on and off by the scanning signals applied through C22, is exactly the same as described in the explanation of FIG. However, in this drive circuit, a PNP transistor Q23 and an NPN transistor Q24 are added. Now, if Q21 is off and Q22 is on, nodes 23 and 24
becomes low level, Q23 is turned off, Q24 is turned on, and the output terminal 22 becomes low level, dropping the current from the panel to the low potential power supply. Since Q24 is used as an emitter follower, output terminal 22 → Q24 emitter → Q24 base → R2
The current flowing in the path 3→Q22→low potential power supply, which is approximately determined by R23, can flow down from the output terminal to the low potential power supply, which is h _FE times the base current of Q24. Next, Q21 is on, Q2
2 is off, Q23 is on, Q2
4 is turned off, allowing a current h _FE times the current determined by R23 to flow from the high potential power supply to the panel through Q23.

That is, the output impedance of the drive circuit 3 shown in FIG. 2 has been lowered to 1/h _FE compared to the conventional circuit shown in FIG. The repetition frequency of the gas cell described above to drive the 1mm plasma display panel.
It is a natural result that 512 cells can be discharged and emitted at the same time under the conditions of inputting a high-speed pulse of 400KHz.

What is also noteworthy is that the buffer transistor Q
The bases of Q23 and Q24 are connected across each other to both ends of R23, so during the transition period of switching, due to the slight voltage drop across R23, the timing at which Q23 and Q24 turn on and off is shifted, causing them to turn on at the same time. There is no risk of the transistor becoming damaged.

FIG. 3 shows another embodiment of the invention. This circuit configuration includes a diode D1, a diode D1,
With the addition of D2, during the switching transition period,
A reverse bias is applied between the base and emitter of Q23 or Q24, which plays the role of preventing transistor deterioration such as a drop in _hFE and increasing the reliability of the circuit.

As described above, according to the present invention, when the gas cell pitch is 1 mm, a large-area plasma display panel having a cell count of about 512 x 160 can be driven in a time-division manner with extremely low output impedance and efficiency with extremely low power loss. A good drive circuit can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram of a conventional high-voltage, high-speed switching type drive circuit, FIG. 2 is a diagram showing one embodiment of the present invention, and FIG. 3 is a diagram showing another embodiment of the present invention. be.

Claims (1)

[Claims] 1 Consists of two sets of electrodes arranged in a matrix, facing each other with a dischargeable gas medium in between, and the surface of each electrode in contact with the gas medium is covered with a dielectric layer, and the externally applied voltage increases the capacitance. In a driving circuit for driving a plasma display panel in a time-sharing driving manner, the plasma display panel is configured to be coupled to a gas medium through a first PNP transistor and a first NPN transistor.
The collectors of a first complementary pair of transistors are connected via a resistor, the emitter of the first PNP transistor is connected to a high potential power supply, and the emitter of the first PNP transistor is connected to a high potential power supply.
The emitters of the NPN transistors are connected to a low potential power source, the bases of each pair of first complementary transistors are connected to the same pulse signal source through capacitors, and a second complementary transistor pair comprising: a collector of the second PNP transistor connected to the low potential power supply; a collector of the second NPN transistor connected to the high potential power supply; The base of the transistor is the first
The base of the second NPN transistor is connected to the node between the PNP transistor and the resistor, and the emitters of the second complementary transistor pair are connected to each other. A driving circuit for a plasma display panel, characterized in that the pulse voltage output to be applied to each electrode of the plasma display panel is extracted from this node.