JPH0619419A - Driving voltage supply circuit - Google Patents

Abstract

PURPOSE:To prevent an output waveform from being distorted by a simple means when an internal driving voltage is used. CONSTITUTION:In an integrated circuit 5 which has an internal driving voltage generating circuit 4 and selectively outputs the internal driving voltage or an external driving voltage according to a selection of input terminals 6, 8a, 8b... for the internal driving voltage and external driving voltage, external capacitors 17a, 17b... are connected to the input terminals 8a, 8b... for the external driving voltage. Thus, the external capacitors 17a, 17b... are connected to the input terminals 8a, 8b... for the external driving voltage, so when the internal driving voltage is used, the external capacitors 17a, 17b... speedily absorb the distortion of output waveforms appearing at output terminals 7a, 7b... even if the output waveforms are distorted at the time of the switching of the internal driving voltage, outputted from an internal driving voltage generating circuit 4, to a desired output level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive voltage supply circuit, and more particularly, to a drive IC used in a driver IC for driving a display device such as a liquid crystal display panel and selectively supplying an internal drive voltage and an external drive voltage. It relates to a voltage supply circuit.

[0002]

2. Description of the Related Art For example, in a driver IC for driving a display device such as a liquid crystal display panel, a drive voltage supply circuit capable of selectively supplying an internal drive voltage and an external drive voltage is used.

As shown in FIG. 3, this type of drive voltage supply circuit includes a plurality of voltage dividing resistors (1a) (1b) ...
Integrated circuit (5) containing internal drive voltage generation circuit (4) consisting of a) (2b) ... and changeover switches (3a) (3b).
Composed of. Specifically, a plurality of voltage dividing resistors (1a) (1b) are connected in series to an input terminal (6) for internal drive voltage (hereinafter referred to as the first input terminal) to which a predetermined power supply voltage is input. Then, a series circuit of operational amplifiers (2a) (2b) ... And changeover switches (3a) (3b) ... is connected to each voltage dividing point to derive a plurality of output terminals (7a) (7b). Each output terminal (7
a) (7b) ... have input terminals (8) for multiple external drive voltages.
a) (8b) ... [hereinafter referred to as a second input terminal] are connected in correspondence with each other. Further, each of the changeover switches (3a) (3b) ... Is ON-OFF controlled based on a control signal inputted from the switch control terminals (9) (10). In the figure, (11) is an output terminal that is connected to the first input terminal (6) and outputs the power supply voltage as it is.

This drive voltage supply circuit is built in the driver IC (12) as shown in FIG.
1) (7a) (7b) ... is connected to a switching circuit (13), and a driver IC (12) derived from the switching circuit (13)
The output terminals (14), (14), ... Are connected to the respective pixels (16), (16), ... Of the liquid crystal display (15) as a capacitive load.

In the above drive voltage supply circuit, first, when the internal drive voltage is used, a predetermined power supply voltage is input from the first input terminal (6) and the voltage dividing resistors (1a) (1b). Internal drive voltage is generated by operational amplifiers (2a) (2b) .... Then, the changeover switches (3a) (3b) ... are turned on based on the control signals from the switch control terminals (9) (10), and the output resistors (7a) (7b). 1
b) ... and the operational amplifiers (2a) (2b) ... can obtain the internal driving voltage of the output level. At this time, the second
The input terminals (8a), (8b), ... Of are unused and are in an open state. Then, the internal drive voltage of each of these output levels is sent to the switching circuit (13), and the switching circuit (13).
The internal drive voltage of the desired output level selected by the switching control at the output terminal (14) of the driver IC (12)
It is applied to each pixel (16) (16) via (14) and drives the liquid crystal display panel (15).

When an external drive voltage is used, the second
After connecting an external power supply (not shown) to the input terminals (8a) (8b) of the switch, the changeover switches (3a) (3b) ... OFF
Then, the external drive voltage from the external power source is sent as it is to the output terminals (7a) (7b). And like above
The external drive voltage of each output level is sent to the switching circuit (13), and the external drive voltage of the desired output level selected by the switching control of the switching circuit (13) is output to the output terminal of the driver IC (12). (14) (14) ... is applied to each pixel (16) (16).
5) drive.

[0007]

By the way, as described above, when the internal drive voltage is used, if an external power source is connected to the second input terminals (8a) (8b) ... Output voltage (7a) (7b) without changing drive voltage
The second input terminal (8a) as it is sent to ...
(8b) ... is normally open.

However, the liquid crystal display panel (1) is provided between the output terminals (14) (14) of the driver IC (12).
Since the capacitive loads composing the pixels (16) (16) of 5) are connected, the internal drive voltage appearing at the output terminals (7a) (7b) ... is switched to a desired output level by a switching circuit ( 13)
When switching by, the operational amplifiers (2a) (2) of the internal drive voltage generation circuit (4) corresponding to the output level to be switched
Between b) ..., one output is pulled to the other output, and the output waveform appearing at the output terminals (7a) (7b) ... is distorted. There is a problem in that the display image quality of the liquid crystal display panel is affected by such distortion of the output waveform.

Therefore, the present invention has been proposed in view of the above problems, and it is an object of the present invention to prevent the output waveform from being distorted by a simple means when an internal drive voltage is used. It is to provide a drive voltage supply circuit.

[0010]

As a technical means for achieving the above object, the present invention has an internal drive voltage generation circuit, and an internal drive voltage or an internal drive voltage is selected by selecting the first and second input terminals. In an integrated circuit which selectively outputs an external drive voltage, an external capacitor is connected to the second input terminal.

[0011]

In the drive voltage supply circuit according to the present invention, by connecting the external capacitance to the second input terminal, when the internal drive voltage is used, the internal drive voltage output from the internal drive voltage generating circuit is desired. When switching to the output level, even if the output waveform appearing at the output terminal is distorted, the external capacitor quickly absorbs the distortion.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a drive voltage supply circuit according to the present invention will be described with reference to FIGS. The same or corresponding parts as those in FIGS. 3 and 4 are designated by the same reference numerals, and the duplicated description will be omitted.

A feature of the present invention is that when the internal driving voltage is used, the second input terminal (7a) is provided as shown in FIGS.
The external capacitors (17a) (17b) are connected to (7b). Specifically, one ends of the plurality of external capacitors (17a) (17b) ... Are connected to the plurality of second input terminals (8a) (8) of the integrated circuit (5).
b) Connect in correspondence with each of them, and connect the other end to ground.

In the drive voltage supply circuit of the present invention, when the internal drive voltage is used, a predetermined power supply voltage is input from the first input terminal (6) as in the conventional case, so that the internal drive voltage generation circuit (4 ) Generates an internal drive voltage, and when the changeover switches (3a) (3b) ... are turned on based on the control signals from the switch control terminals (9) (10), each output terminal (7a) is turned on.
An internal drive voltage having a predetermined output level is obtained at (7b). Among these internal drive voltages of each output level, the internal drive voltage of a desired output level is selected by the switching control of the switching circuit (13), and the selected internal drive voltage is output to the output terminal of the driver IC (12) ( It is applied to each pixel (16) (16) via 14) (14) to drive the liquid crystal display panel (15).

A capacitive load forming pixels (16) (16) of the liquid crystal display panel (15) is connected between the output terminals (14) (14) of the driver IC (12). Therefore, when the internal drive voltage appearing at the output terminals (7a) (7b) ... Is switched to the desired output level by the switching circuit (13), the internal drive voltage generation circuit (4) corresponding to the switched output level. Operational amplifiers (2a) (2b) ...
In the meantime, one output is pulled to the other output, and the output waveform appearing at the output terminals (7a) (7b) ... tends to be distorted, but in the present invention, the second input terminal (8a) (8b) ...
Since the external capacitors (17a) (17b) ... Are connected to the external capacitors (17a) (17b) ..., the electric charges charged in the external capacitors (17a) (17b) ... Flow into the output terminals (7a) (7b). ) (1
7b) ... The absorption voltage that occurs in the output waveform is quickly absorbed by the charging voltage.

When an external drive voltage is used, the external capacitances (17a) (17b) are connected to the second input terminals (8a) (8b).
If an external power source is connected without connecting ..., it can be used as in the conventional case.

[0017]

According to the drive voltage supply circuit of the present invention, when the internal drive voltage is used, when the internal drive voltage output from the internal drive voltage generation circuit is switched to a desired output level, it is applied to the output terminal. Even if the output waveform that appears appears to be distorted, the external capacitor can quickly absorb the distortion, and the absorption of this distortion improves the display image quality of the liquid crystal display panel, thus significantly improving the reliability. It is possible to improve and provide a high quality drive voltage supply circuit, and its practical value is great.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a drive voltage supply circuit according to the present invention.

FIG. 2 is a driver I incorporating the drive voltage supply circuit of FIG.
Block diagram showing C

FIG. 3 is a circuit diagram showing a conventional example of a drive voltage supply circuit.

4 is a driver I incorporating the drive voltage supply circuit of FIG.
Block diagram showing C

[Explanation of symbols]

 4 Internal drive voltage generation circuit 5 Integrated circuit 6 Internal drive voltage input terminal [first input terminal] 7a, 7b Output terminal 8a, 8b External drive voltage input terminal [second input terminal] 17a, 17b External capacitance

Claims (1)

[Claims] 1. An integrated circuit having an internal drive voltage generation circuit, which selectively outputs an internal drive voltage or an external drive voltage by selecting an input terminal for the internal drive voltage and an external drive voltage. A drive voltage supply circuit characterized in that an external capacitor is connected to a voltage input terminal.