JP2001042829A - External driving circuit for planar display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to be more versatile without increasing the power consumption and to stabilize the output signals of a D/A converting section and an output circuit section. SOLUTION: By providing a constant voltage output circuit 21 and a constant current output circuit 22, voltages and currents supplied to a D/A converting section 13 and an output circuit section 14 are made constant regardless of the fluctuation of the power supply voltage. Moreover, by providing a control terminal 24, the voltage level of video signals outputted from the section 14 is set by the control voltage from an output control section in accordance with the loading of video bus lines and video signal lines.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a flat display device, and more particularly, to a driving IC for an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art A flat display device represented by a liquid crystal display device is utilized in various fields by utilizing its characteristics of light weight, thinness, and low power consumption. In particular, a liquid crystal display device using a liquid crystal layer as a light modulation layer is widely used as a display device for OA equipment and home electric appliances. Among them, an active matrix type liquid crystal display device using a TFT (thin transistor) as a switching element for each pixel has no crosstalk between adjacent pixels and is suitable for high definition. Attention has been focused on realizing larger, larger, and color images.

In such an active matrix type liquid crystal display device, p-S is used as an element constituting a liquid crystal panel.
A device using an i (polysilicon) TFT is advantageous in narrowing the frame, making it thinner, and improving the definition of a small screen because a driving circuit can be mounted on one of the substrates constituting the liquid crystal panel. ing.

Here, among the scanning line driving circuit and the signal line driving circuit mounted on the same substrate, a circuit configuration of a signal line driving circuit and a driving IC (external driving circuit) will be described.

FIG. 8 is a schematic configuration diagram of a conventional driving IC. The driving IC 1 includes a data control unit 11 for controlling input data sampling and output timing, and a data sampling unit 12 for sampling a digital video signal (RGB data signal) input from the outside.
And a D / A (digital-analog) converter 13 for converting a video signal from digital data to analog data, and an output circuit 14 for outputting an analog video signal to a signal line drive circuit (not shown). .

A clock signal, a synchronizing signal, a data signal, a reference voltage, and the like are supplied from, for example, a PC (Personal Computer) body to each of the above-described units. The necessary power supply voltage (and current) is supplied.

FIG. 9 is a schematic configuration diagram of a signal line drive circuit integrally formed on one substrate, and FIG. 10 is a drive waveform diagram for explaining the operation of the signal line drive circuit.

The signal line driving circuit 2 includes a plurality of shift register circuits 15, a plurality of buffer circuits 16, a plurality of analog switches 17, and a plurality of video bus lines 18. The writing of the analog video signal to the liquid crystal panel 19 is performed by the driving IC 1 and the video bus line 1.
The video signal output to the video signal line 8 is charged by the respective video bus lines 18 and output to the video signal line 20 via the analog switch 17. The video signal line 20 is divided into a plurality of blocks, each of which has a plurality of lines, and each block is connected to the video bus line 18 via the analog switch 17. When a plurality of analog switches 17 corresponding to the block open and close the video signal lines 20 of each block at the same time, a plurality of video signal lines 20 are charged with a video signal voltage at the same time. The video signal is written to the block (block sequential drive). The opening / closing timing of the analog switch 17 is controlled by the shift register circuit 15.

As shown in FIG. 10, a start pulse XST and two types of transfer clocks XCK and / (inverted) XCK having different phases are input to the shift register circuit 15. In the shift register circuit 15, the start pulse XS
T is sequentially transferred in synchronization with the fall of the transfer clock XCK, and is output as shift data. These shift data are input from the buffer circuit 16 to the analog switch 17 as analog switch control signals. The analog switch 17 is opened and closed by the analog switch control signal. Note that the video signal voltage supplied from the driving IC 1 through the video bus line 18 is applied so as to reach a target voltage level when the analog switch 17 is closed.

[0010]

Since the loads on the video bus line 18 and the video signal line 20 shown in FIG. 9 differ depending on the size of the liquid crystal panel, one driving IC can be mounted on a plurality of liquid crystal panels having different sizes. When applied, the video signal voltage may not reach the target voltage level within a predetermined time. Therefore, conventionally, it is necessary to prepare a driving IC for each size of the liquid crystal panel, and it has been difficult to generalize the driving IC. In addition, when the driving IC is configured to be applicable to all sizes, the capability becomes excessive as compared with the normal case,
There is a problem that power consumption increases.

Further, the driving IC includes a power supply voltage supply line 10.
When the power supply voltage and the amount of current supplied from the power supply fluctuate, the output signal of the internal D / A converter 13 and the output circuit 14 becomes unstable.

The present invention provides an external drive circuit of a flat panel display device which can be generalized without increasing power consumption and can stabilize output signals of a D / A converter and an output circuit. This is the first object.

A second object of the present invention is to provide an external driving circuit of a flat panel display device which can eliminate the occurrence of ghost when driven sequentially in blocks and can obtain a high-quality display image. I do.

[0014]

In order to achieve the above-mentioned object, according to the present invention, there is provided a data control unit for controlling the timing of sampling and output of an input data signal, and a method for sampling an input digital data signal. And a D / D converter for converting a sampled and output digital data signal into an analog video signal.
A pixel unit including an A conversion unit and an output circuit unit that outputs a converted analog video signal, and a display pixel formed near an intersection of a plurality of scanning lines and a plurality of signal lines arranged in a matrix; For a display panel including a scanning line driving circuit connected to the plurality of scanning lines and a signal line driving circuit connected to the plurality of signal lines, an externally input data signal is output to a video signal for the display panel. A constant-voltage output unit and a constant-current output unit for supplying a driving voltage and a driving current for the D / A conversion unit and the output circuit unit; and the output circuit. And an output voltage control unit for controlling a voltage value of an analog video signal output from the unit.

According to a second aspect of the present invention, in the first aspect, the output voltage control section uses a voltage obtained by dividing a resistance between a power supply potential and a ground potential of the external drive circuit as an output control voltage. It is applied to an output circuit section.

According to a third aspect of the present invention, in the first aspect, a constant voltage output terminal is provided in the constant voltage output section, and a voltage obtained by dividing the voltage between the potential of the constant voltage output terminal and the ground potential is divided by a resistor. It is characterized in that it is applied to the output circuit section as an output control voltage.

According to a fourth aspect of the present invention, in the first aspect, the output voltage control section applies a current extracted from the constant voltage output terminal via a resistor to the output circuit section as an output control current. Features.

According to the above configuration, the driving voltage and the driving current are supplied from the constant voltage output section and the constant current output section to the D / A conversion section and the output circuit section. Even if the amount of current fluctuates, the output signals of the D / A converter and the output circuit do not become unstable.

Since the voltage value of the video signal output from the output circuit is controlled by the output voltage controller, a video signal voltage of an appropriate voltage level is supplied according to the load on the video bus line and the video signal line. It is possible to apply one driving IC to display panels having different sizes. In this case, since the driving IC can be configured with an IC having a smaller capacity as compared with a case where the driving IC is configured to be applicable to all sizes, it can be generalized without increasing power consumption.

Further, in the output voltage control section, the voltage obtained by dividing the potential between the potential of the constant voltage output terminal provided in the constant voltage output section and the ground potential by resistance is used to output the video signal output from the output circuit section. When configured to control the voltage value, the voltage obtained by resistance division can be kept constant regardless of the power supply voltage, so that even if the power supply voltage becomes smaller than the design value, the video signal voltage is reduced. The target voltage level can be reached within a predetermined time.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which an external drive circuit of a flat panel display according to the present invention is applied to a drive IC of a liquid crystal display will be described below.

[First Embodiment] FIG. 1 is a schematic configuration diagram of a driving IC according to a first embodiment, and FIG. 2 is a schematic configuration diagram of an output voltage control unit. The basic configuration of the driving IC 100 shown in FIG. 1 is almost the same as that of the driving IC 1 shown in FIG. 7, and the same parts as those in FIG.

The driving IC 100 according to the first embodiment includes a constant voltage output circuit 21 and a constant current output circuit 22 connected to the power supply voltage supply line 10. The constant voltage output circuit 21 and the constant current output circuit 22 receive the supply of the power supply voltage from the power supply voltage supply line 10 and supply the D / A converter 13 and the output unit 14 with the constant voltage and the constant current power supply voltage, respectively. are doing.

The output circuit section 14 has a control terminal 24 for inputting an output control voltage from an output control section 30 described later.
Is provided. In the output circuit section 14, the output control section 3
The voltage / current level of the video signal to be output is determined according to the output control voltage input from 0.

As shown in FIG. 2, the output control section 30 is a circuit for inputting a predetermined voltage to the control terminal 24 by dividing the voltage between the power supply voltage of the driving IC 100 and GND (ground) by resistance. , A resistance element whose resistance value can be adjusted or changed. The voltage level of the output control voltage can be arbitrarily set by changing the resistance value of the resistance element.

In the above configuration, the D / A converter 13 and the output unit 14 are supplied with the constant voltage and the constant current from the constant voltage output circuit 21 and the constant current output circuit 22, respectively. Even if the supplied power supply voltage or its current amount fluctuates, the internal D / A converter 13 and output circuit 14
Output signal does not become unstable, and stable operation can always be performed.

The output control unit 30 sets the voltage level of the output control voltage so that the video signal voltage output from the output circuit unit 14 reaches the target voltage level within a predetermined time, thereby enabling video output. A video signal voltage having an appropriate voltage and current level can be supplied according to the load on the bus line 18 and the video signal line 20. According to this, it is not necessary to prepare a driving IC for each size of the liquid crystal panel,
One driving IC can be applied to liquid crystal panels having different sizes. In addition, since the driving IC can be configured with an IC having a smaller capacity as compared with a case where the driving IC can be applied to all sizes, the generalization of the driving IC can be realized without increasing the power consumption. be able to.

[Second Embodiment] In a second embodiment, in addition to the features of the first embodiment, a driving IC capable of stably outputting a video signal voltage with respect to a variation in a power supply voltage will be described. I do.

Normally, the power supply voltage used for the driving IC is generated by, for example, a DC / DC converter. However, due to individual differences between DC / DC converters, even if the same voltage is set, a slight variation occurs in the output voltage. If the power supply voltage varies as described above, the control voltage supplied from the output control unit 30 to the control terminal 24 in the first embodiment also varies, which affects the video signal voltage output from the output circuit unit 14. Will be.

FIG. 3 is a voltage waveform diagram of the video signal voltage output from the output circuit unit 14. In FIG. 3, (a)
Indicates that the power supply voltage is as designed (hereinafter, the voltage as designed is V
1), (b) is a state in which the power supply voltage is higher than the design value (hereinafter, the voltage in this state is V2), and (c) is a state in which the power supply voltage is lower than the design value (hereinafter, the voltage in this state is V2). V3).

Here, assuming that the input voltage of the control terminal 24 required for the video signal voltage to reach the target voltage level within a predetermined time is VA1, the input voltage becomes VA1 at the power supply voltage V1. FIG. 3A shows a voltage waveform when the resistance value is determined and the resistance is divided. In this case, the video signal voltage reaches a target voltage level within a predetermined time. Next, when looking at the power supply voltage V2, the resistance value that determines the voltage level of the input voltage to the control terminal 24 is set to be optimal when the power supply voltage V1 is used. When the voltage changes from V1 to V2, the voltage level of the input voltage to the control terminal 24 also changes (hereinafter, this voltage is referred to as VA2). In this case, since the relationship of VA1 <VA2 is satisfied, the capability of the driving IC is improved. As a result, as shown in FIG. 3B, the voltage waveform reaches the target voltage level earlier than at the time of the power supply voltage V1. On the other hand, when the power supply voltage is V3, the voltage level of the input voltage to the control terminal 24 decreases (hereinafter, this voltage is referred to as VA3), and the relationship of VA3 <VA1 holds.
As a result, the performance of the driving IC decreases, and reaches the target voltage level later than at the time of the power supply voltage V1. In this case, as shown in FIG. 3C, the voltage may not reach the target voltage level.

As described above, when the voltage obtained by dividing the voltage between the power supply voltage and GND by resistance is input to the control terminal 24, if the power supply voltage varies, the control terminal 2
4 are different from each other, the video signal voltage may not reach the target voltage level. If the output to the video signal line does not reach the target voltage level when the liquid crystal panel is sequentially driven in blocks, for example, a reflection of a video (hereinafter, referred to as a ghost) to an adjacent block occurs, and a display image is displayed. It will be significantly deteriorated.

In order to suppress such fluctuations in the power supply voltage, D
It is necessary to make the C / DC converter highly accurate, which leads to the use of high precision parts and an increase in the number of parts.
This leads to an increase in the cost and size of the / DC converter.

FIG. 4 is a schematic configuration diagram of a driving IC according to the second embodiment, and FIG. 5 is a schematic configuration diagram of an output control unit. The basic configuration of the driving IC 200 shown in FIG. 4 is also substantially the same as that of the driving IC 1 shown in FIG. 8, and the same parts as those in FIG.

The driving IC 200 according to the second embodiment has a constant voltage output terminal 2 for outputting a voltage from the constant voltage output circuit 21.
5 are provided. Further, as shown in FIG. 5, the output control unit 31 is configured to input a predetermined voltage to the control terminal 24 by dividing the terminal voltage of the constant voltage output terminal 25 and the voltage between GND by resistance. . In the output control unit 31 shown in FIG. 5, the voltage level of the control voltage can be arbitrarily set by changing the resistance value of the resistance element.

FIG. 6 shows the structure of the driving IC 200.
FIG. 4 is a voltage waveform diagram of a video signal voltage output from the output circuit unit 14 when the power supply voltage varies. FIG.
(C) corresponds to FIGS. 3 (a) to 3 (c).

Here, the terminal voltage of the constant voltage output terminal 25 is VT, and the input voltage of the control terminal 24 required for the video signal voltage to reach the target voltage level within a predetermined time is VTA.
And In the driving IC 200 according to the second embodiment, the terminal voltage of the constant voltage output terminal 25 is constant at VT even if the power supply voltage changes as V1 to V3, so that the VTA obtained by resistance division between VT and GND is obtained. Is constant regardless of the power supply voltage. That is, since the performance of the driving IC is constant irrespective of the variation of the power supply voltage, the video signal voltage can always reach the target voltage level within a predetermined time without being affected by the variation of the power supply voltage. Become.

Therefore, even if the power supply voltage becomes lower than the design value, there is no problem that the video signal voltage does not reach the target voltage level as shown in FIG. Occasionally, a ghost does not occur, and a high-quality display image can be obtained. Further, in order to suppress the fluctuation of the power supply voltage, DC / D
It is not necessary to use a high-precision C converter, so that the use of high-precision parts and an increase in the number of parts do not occur, and DC / D
High cost and large size of the C converter can be suppressed.

In the first and second embodiments, the example in which the voltage input to the control terminal 24 is obtained by resistance division has been described.
A bypass capacitor may be inserted between the control terminal 24 and GND.

Further, the input current to the control terminal 24
The same effect can be obtained even when the driving IC is configured to set the voltage level of the video signal. In this case, as shown in FIG. 7, the constant voltage output terminal 25 is connected to the control terminal 24 via a resistor.

[0041]

As described above, in the external drive circuit of the flat panel display according to the present invention, the D / A converter and the output circuit are driven from the constant voltage output section and the constant current output section by the drive voltage. And the driving current is supplied, so that the output signals of the D / A conversion unit and the output circuit unit do not become unstable even if the power supply voltage or the amount of the current fluctuates, and the operation is always stable. It can be carried out.

Further, since the voltage value of the video signal output from the output circuit is controlled by the output controller,
A video signal voltage of an appropriate voltage level can be supplied according to the load on the video bus line or the video signal line. Therefore, it is not necessary to prepare a driving IC for each size of the display panel, and one driving IC can be applied to display panels having different sizes. In this case, the driving IC
Can be configured with an IC having a smaller capacity as compared with the case where the configuration can be applied to all sizes, so that it can be generalized without increasing power consumption.

In particular, in the output control section, the voltage of the video signal output from the output circuit section is obtained by a voltage obtained by dividing the potential between the potential of the constant voltage output terminal provided in the constant voltage output section and the ground potential by resistance. When the value is controlled, the voltage obtained by the resistance division can be constant regardless of the power supply voltage. For this reason, even if the power supply voltage becomes lower than the design value, the video signal voltage can reach the target voltage level within a predetermined time. A high quality display image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a driving IC according to a first embodiment.

FIG. 2 is a schematic configuration diagram of an output control unit.

FIG. 3 is a voltage waveform diagram of a video signal voltage output from an output circuit unit.

FIG. 4 is a schematic configuration diagram of a driving IC according to a second embodiment.

FIG. 5 is a schematic configuration diagram of an output control unit.

FIG. 6 is a voltage waveform diagram of a video signal voltage output from an output circuit unit when a power supply voltage varies.

FIG. 7 is another schematic configuration diagram of an output control unit.

FIG. 8 is a schematic configuration diagram of a general driving IC.

FIG. 9 is a schematic configuration diagram of a signal line driver circuit.

FIG. 10 is a driving waveform chart for explaining the operation of the signal line driving circuit.

[Explanation of symbols]

 1, 100, 200 Drive IC 10 Power supply voltage supply line 11 Data control unit 12 Sampling unit 13 D / A conversion unit 14 Output circuit unit 21 Constant voltage output circuit 22 Constant current output circuit 24 Control terminal 25 Constant voltage output terminal 30, 31 Output control unit

Continued on the front page F term (reference) 2H093 NA16 NC01 NC05 NC34 ND09 ND15 ND39 ND50 5C006 AC02 AC24 AC27 AF82 AF84 BC13 BC16 BC23 BF37 BF43 BF44 FA01 FA22 FA31 FA41 FA47 FA51 5C058 AA09 BA01 BA26 BA33 BB05 BB06 ABB5 DD5 DD30 FF01 FF13 KK01

Claims (4)

[Claims] 1. A data control unit for controlling the timing of sampling and output of an input data signal, a data sampling unit for sampling an input digital data signal, and an analog video signal for sampling and outputting a digital data signal. An external drive circuit for a flat panel display device, comprising: a D / A conversion unit that converts the signal into a signal; and an output circuit unit that outputs the converted analog video signal. A constant voltage output section and a constant current output section for supplying a voltage and a driving current; and an output voltage control section for controlling a voltage value of an analog video signal output from the output circuit section. External drive circuit for flat panel display. 2. The external drive circuit according to claim 1, wherein the output voltage control unit outputs a voltage obtained by dividing a voltage between a power supply potential and a ground potential of the external drive circuit by resistance. An external drive circuit for a flat panel display, wherein the external drive circuit is applied to the output circuit section as a control voltage. 3. The external drive circuit of a flat display device according to claim 1, wherein a constant voltage output terminal is provided in the constant voltage output section, and a resistance between the potential of the constant voltage output terminal and a ground potential is divided. An external drive circuit for a flat panel display device, wherein the obtained voltage is applied to the output circuit section as an output control voltage. 4. The external drive circuit of the flat display device according to claim 1, wherein the output voltage control unit outputs a current extracted from the constant voltage output terminal via a resistor to the output circuit unit as an output control current. An external drive circuit of a flat panel display device, wherein the voltage is applied.