JPH0243600A - Display driving circuit for plasma display panel - Google Patents

Abstract

PURPOSE:To remove unevenness on display and to improve picture quality by using a driven transistor(TR) in a current mirror circuit as a constant current source to supply display current to each picture element. CONSTITUTION:A display driving circuit 20 is provided with plural switching TRs 21 whose one ends are connected to respective picture elements 13 so as to be respectively opened/closed by pulse width corresponding to the value of a video tape and the current mirror circuit 22 consisting of a reference TR 23 and plural driven TRs 24 whose one ends are connected to a power supply point Vd with a prescribed voltage in common and connecting the other ends of respective driven TRs 24 to the other ends of the switching TRs 21. In accordance with the ON/OFF operation of the switching TRs 21, constant currents with pulse width values corresponding to video data are supplied from respective driven TRs 24 in the current mirror circuit 22 to respective picture elements 13. Consequently, display over the whole screen without unevenness can be attained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a display drive circuit particularly suitable for a DC type plasma display panel, that is, a display drive circuit that simultaneously scans pixels arranged in rows and columns within the plane of a plasma display panel in a predetermined direction. ijl to be done
The present invention relates to a circuit that drives each pixel by supplying a constant current with a pulse width corresponding to the value of video data to each pixel.

[Conventional technology]

The above-mentioned plasma display panel is a small and lightweight so-called flat display panel suitable for office automation equipment, etc.. Conventionally, it mainly displayed characters and figures consisting of bright and dark dots, but recently, A device that displays several levels of floor 81 has appeared, and its uses are rapidly expanding. Pixels are arranged in rows and columns in the plane of this plasma display panel, for example, 400 rows x 640 columns, and the pixels arranged in a predetermined direction, usually the row direction, are simultaneously or all at once scanned sequentially in the column direction at a frequency of, for example, 6011z. The sequential number of pixels, for example, 640 pixels, which are arranged along a specific row selected by this column direction scanning, are simultaneously driven for display by the signal display drive circuit that is the object of the present invention. Although this is well known, this procedure will first be explained with reference to FIG.

Plasma display panel 1 shown schematically at the bottom left of FIG.
0, a large number of scanning lines 11 running in the row direction and a large number of display drive lines 12 running in the column direction are provided, and three of each are shown in the figure to represent them. As is well known, the pixels 13 are formed at each intersection of the scanning line 11 and the display drive 112.

In the case of a DC type plasma display panel, the scanning line 11 is
) It is on the shadow side of each pixel 13, and a high negative scanning voltage v1 is applied to the scanning line 11 selected by scanning to determine the display state of the pixel at that time, and the resistance is maintained during other periods. Negative sustaining voltage v2 lower than the upper scanning voltage via 15
is to be given to this. The transistor 70 is for switching the scanning line 11, and the shift register 80
is used to advance scanning by sequentially turning on the scanning transistors 70 one by one using the outputs of the stages advanced one by one by the shift pulse SP.

A positive display voltage Vd is applied to the display drive line 12 on the anode side of each pixel 13 from the display drive circuit 20, which is the object of the present invention. The pulse width is given according to the video data, and for this purpose the shift register 60. A latch circuit 50 and a pulse width selection circuit 40 are provided. Each video data VD is a bit data DO in this example.
It has a 2-pixel configuration consisting of 0 and 01, and in principle it should be possible to specify four levels of gradation display for each pixel, but one of these is usually used to specify the so-called pilot discharge. Therefore, the number of gradations that can be used for actual display is the remaining three.

The shift register 60 has two shift registers 61 and 62 corresponding to the video data vD of the training.
It has a double structure in which 2 bits of video data vD are read and stored in each stage by a shift pulse SP. The launch circuit 50 is also an arrangement of latches that each store 2 bits, and the latch command LS
The video data v is sent from each stage of the shift register 60 according to
D is read all at once and held in each latch. The pulse width selection circuit 40 includes a pulse generation circuit 41 that generates four signals each having a different pulse width, and as schematically shown in the figure with a changeover switch, the pulse width selection circuit 40 selects each of the 2-bit video signals received from the launch circuit. One of the four pulse width signals is selected and output to the display drive circuit 20 according to the value of the data VD.

The display drive circuit 20 receives this pulse width signal and applies a positive display voltage Vd having the same pulse width to the display drive line 12 to discharge between the negative and anode poles of each pixel 13, thereby applying a display voltage to each pixel 13. Display is performed in gradation according to the pulse width of Vd.

FIG. 3 shows a display drive circuit 20 according to the prior art.
creates a display voltage Vd with a pulse width specified by the switching command SS received from the pulse width signal selection circuit 40,
It drives the pixels 13 by being placed on the display drive line 12 of the display panel 10 via a resistor 31, and as shown in the figure, it includes a driver 25 that receives a switching command SS, and a switching transistor 2 that receives the output and performs a switching operation.
In this example, a pnp type bipolar transistor is used as the switching transistor 21.

By the way, the display of the pixel 13 is of course caused by plasma discharge, and as is well known, this plasma discharge has negative voltage and current characteristics, so the scanning transistor 70 is turned on and the negative scanning voltage v1 is applied to the scanning. line 11 and when the display voltage Vd is applied from the display drive circuit 20 to the display drive line 12, the plasma current in the pixel 13 will run out of control. The resistor 31 is a current limiting resistor for preventing this, and is usually a high resistance of about several hundred ohms to limit the plasma current to about several hundred DA. During the off-period of the scanning transistor 70, the scanning voltage vi is switched to the above-mentioned sustaining voltage v2 and is applied to the pixel 13 via the common line 14, but at this time the resistor 15 acts as a current limiter.

Note that this display drive circuit 20 is similar to the pulse width selection circuit 40. in FIG. By incorporating the latch circuit 50, shift register 60, etc. into a B i CMO3 type integrated circuit device in this example, it is possible to downsize the plasma display panel drive circuit and save labor in assembling it. Since the resistor 31 has a high resistance and is not suitable for being incorporated into an integrated circuit, a plurality of resistors 31 are combined into a resistor circuit 30 and separated from the integrated circuit device.

[Problem to be solved by the invention]

However, the display drive circuit described above has the problem that it takes time and effort to connect the resistor circuit 30 to the plasma display panel 10 and the resistor drive circuit 20, and the display tends to be uneven due to variations in the resistance value of the resistor 31.

As mentioned above, the plasma display panel 10 has about 640 display drive lines 12, so if the resistance circuit 30 is separate from the display drive circuit 20, the effort and effort required to connect the display drive lines increases by the number of display drive lines. You will also need space. resistance 31
As mentioned above, is for current limiting, but its resistance value determines the plasma current value flowing to the pixel, so if there is variation in resistance value, the display will be uneven, so it is necessary to make this unevenness less noticeable visually. It is necessary to keep the error in resistance value within about 5%. Display drive circuit 2 with resistance circuit 30
If the resistor 31 is built into the integrated circuit device along with 0, it is almost impossible to match the resistance value of the resistor 31 with such precision, so it is temporary to attach it externally to the integrated circuit device as described above. Resistor circuit 3
Even if 0 is manufactured, the resistance value tends to vary by about 10% and the display is likely to be uneven.If such an external resistor is used, it is possible to make the resistance value uniform by means of a trimming shade. Of course, adjusting the resistance value also requires some effort.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and provide a display drive circuit for a plasma display panel that does not require a resistor for each display drive line.

[Means to solve the problem]

According to the present invention, this purpose is to arrange pixels arranged in rows and columns within the plane of a plasma display panel in a predetermined direction as described at the beginning, and to obtain video data values for each pixel for each of a plurality of pixels that are simultaneously scanned. The display drive circuit of the plasma display panel is driven by supplying a constant current with a pulse width corresponding to the value of the video data.The display drive circuit of the plasma display panel is driven by supplying a constant current with a pulse width corresponding to the value of the video data. It consists of a transistor, a reference transistor whose one end is commonly connected to a power supply point of a predetermined voltage, and a plurality of driven transistors, and a current mirror circuit whose other end of each driven transistor is connected to the other end of a switching transistor. , When the switching transistor is controlled to be turned on, a constant current corresponding to the current set by the reference transistor of the current mirror circuit is supplied from each driven transistor to each pixel through the corresponding switching transistor as plasma for display. achieved by.

[Function] The above-mentioned resistor has the dual functions of limiting the plasma current and adjusting it to a constant value, but the present invention can perform both of these functions by controlling the plasma current to a predetermined constant current value. For this reason, we abandoned the conventional idea of applying a display voltage from the display drive circuit to the pixel, and instead applied a constant current from the display drive circuit to the pixel as a plasma current for display, for example. By supplying this constant current from the side and generating this constant current using the current mirror circuit referred to in the above configuration, there is no need to interpose a resistor between the display drive circuit and the pixel. In other words, the present invention has succeeded in solving the above-mentioned problems by using the display drive circuit as a current supply source instead of the conventional voltage supply source.

Of course, since the display on a plasma display panel is based on plasma discharge, it is absolutely necessary to apply a voltage that generates a discharge to the pixel, but fortunately, one of the two electrodes of the pixel, for example, the positive side, is supplied with a constant current. Even if it is only supplied, for example, by selecting the scanning voltage to be applied to the cathode, which is the other electric bridge, when the scanning transistor is turned on, the voltage necessary for discharge can be sufficiently applied to the pixel from the cathode side.

Also, in the present invention, the plasma discharge time is made to correspond to the value of video data, but in order to do this, the switching transistor in the above configuration is turned on and off, and a constant current from the driven transistor of the current mirror circuit is is supplied to the pixels with a pulse width depending on the value of the video data.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to FIG.

This figure shows the display drive circuit 20 of FIG. 2 and its peripheral circuits.
11. Display drive lines 12 and pixels 13 are shown, and the lower cathode in the figure within each pixel 13 is actually connected to scan line 11.
As mentioned above, the scanning transistor 70
During this selection period, an eclipse display voltage v1 is applied to it, and when the scanning transistor 70 is off, a negative sustain voltage v2 lower than the display voltage is applied to it through the resistor 15. For example, display voltage Vl
is -200V and the maintenance voltage is -100V. In addition, only one scanning line 11 is shown in FIG. 1 as a representative of the many scanning lines of the plasma display panel, and the pixels 13 are also divided into three pixels at both ends and the center among the plurality of pixels arranged in the row direction. Only pieces are shown.

The display drive circuit 20 shown surrounded by a dashed line is provided for each of, for example, 64 pixels lined up in the row direction, and is composed of only MOS transistors in this embodiment, so the corresponding pulse width of FIG. Selection circuit 40° launch circuit 50. It can be housed in one MOS integrated circuit device together with the shift register 60, etc., and since there is no circuit that specifically handles high voltage, the integrated circuit device can be an inexpensive one for low voltage. In the display drive circuit 20, each pixel 13
In this example, P-channel MO3) transistors are provided as the switching transistors 21 corresponding to A switching command SS is respectively received from the circuit 40, which assumes a pulse width corresponding to the value of the video data VD.

Current mirror circuit 22 shown above display drive circuit 20
receives a low tfX voltage Vd, and its one reference transistor 23 and a plurality of driven transistors 24 have a
All P-channel MOS transistors are used in this example, and one end of these MOS transistors, in this example the source, is connected to the voltage point it, and the driven transistor 24
The other end, the drain in this example, is connected to the other end of the switching transistor 21, the source in this example. The gates of reference transistor 23 and driven transistor 24 are all connected in common to form a current mirror circuit, and are connected to the other end of reference transistor 23, in this example the drain.

Between the other end of the reference transistor 23 and the ground potential point,
A setting resistor 23a is provided for setting the reference current flowing through the reference transistor. The setting resistor 23a may be a fixed resistor within the integrated circuit device, but in this embodiment, an external resistor whose resistance value can be adjusted is used.

By using the setting resistor 23a as an adjusting resistor in this way, it is possible to finely adjust the reference current value and, accordingly, the plasma current value supplied from each driven transistor 24 to the pixel.
When a plasma display panel is driven by a plurality of display drive circuits 20, for example, about 10 display drive circuits 20, display unevenness can be prevented.

Of course, all the driven transistors 24 in the current mirror circuit 22 have the same configuration, and each has a reference transistor 23.
The operating characteristics of the MOS transistor as the driven transistor 24 are determined exclusively by its channel length and channel width, and such channel dimensions are determined by the integrated circuit device. Since the constant current value generated by the driven transistor 24 can be controlled with high accuracy using a photomask during the manufacturing process, it is possible to align the constant current value generated by the driven transistor 24 with much higher precision than in the case of the above-mentioned resistance value.

The display drive circuit 20 configured as described above controls the current mirror circuit 22 according to the on/off operation of the switching transistor 21 whose gate is controlled by the switching command SS.
By supplying a constant current with a pulse width corresponding to the video data from each of the driven transistors 24 to the pixel 13 as a plasma current for display, the plasma display panel can be displayed faithfully to the original video data and without unevenness over its entire surface. It is possible to display a message that does not exist.

The present invention is not limited to the embodiments described above, and can be implemented in various ways. For example, in the embodiments, the display drive circuit is
Although the structure is made of O3I transistors, part or all of them can be replaced with bipolar transistors. Further, although the plasma display panel is designed to display gradation, the present invention can be applied as is even if the brightness of the display is specified instead of specifying the gradation using video data.

〔Effect of the invention〕

As already clear from the above description, according to the present invention,
Pixels arranged in rows and columns within the plane of a plasma display panel are arranged in a predetermined direction and driven by supplying a constant current with a pulse width corresponding to the value of video data to each pixel, which is scanned simultaneously. The display drive circuit of a plasma display panel is made up of multiple switching transistors, one end of which is connected to each pixel and each of which is controlled to open and close with a pulse width according to the value of the video data, and one end that is common to a power supply point of a predetermined voltage. It consists of a plurality of driven transistors, including a reference transistor connected to each other, and the other end of each driven transistor is connected to the other end of a switching transistor, respectively, and a current mirror circuit. Instead, by using the driven transistor of the current mirror circuit as a constant current source to provide a display current to the pixel, a resistor is provided between the display drive circuit and the plasma display panel to limit the current or to equalize the display current. This eliminates the need for connection work when assembling a plasma display panel device, reduces the space for connections, and eliminates unevenness in display, thereby improving 1iii.

[Brief explanation of the drawing]

1 and 2 relate to the present invention, FIG. 1 is a circuit diagram of an embodiment of a display drive circuit for a plasma display panel according to the present invention, and FIG. 2 is a configuration circuit of a plasma display panel device incorporating this display drive circuit. It is a diagram. FIG. 3 is a circuit diagram showing a display drive circuit according to the prior art. In the figure,

Claims (1)

[Claims] Pixels arranged in rows and columns within the plane of a plasma display panel are arranged in a predetermined direction and driven by supplying a constant current with a pulse width corresponding to the value of video data to each pixel, which is scanned simultaneously. a plurality of switching transistors, one end of which is connected to each pixel, each of which is controlled to open and close with a pulse width according to the value of a video signal;
The switching circuit is composed of a reference transistor whose one end is commonly connected to a power supply point of a predetermined voltage, and a plurality of driven transistors, and a current mirror circuit whose other end of each driven transistor is connected to the other end of the switching transistor. When the transistor is turned on, a constant display current corresponding to the current set by the reference transistor of the current mirror circuit is supplied from each driven transistor to each pixel via the corresponding switching transistor. Display drive circuit for plasma display panels.