JPH0451290A - Driving circuit for liquid crystal display device - Google Patents

Abstract

PURPOSE:To drastically decrease the number of switches for selecting liquid crystal driving voltages by level shifting the square wave voltage varying in level with every integer times of a frame period or every integer times of a line period and generating the plural liquid crystal driving voltages corresponding to respective display regions. CONSTITUTION:A digital image signal DS is subjected to series/parallel conversion by a shift clock signal CPH and a horizontal start signal STH and forms the 3-bit display data corresponding to the number of the signal electrodes 3 of the liquid crystal display device 1. This data is introduced to a control circuit 115. The 3-bit display data led to a decoder 121 is decoded by a control circuit 115 to make on-off control of 3 pieces of switches Si(i=1, 2,..., 8) 133 in a voltage selecting circuit 131 to alternately select the positive liquid crystal driving voltage ViP higher than a common electrode voltage Vsc or the negative liquid crystal driving voltage ViN lower than the common electrode voltage Vsc. The liquid crystal driving voltage Vi is impressed to respective signal electrodes 3 via an output terminal 135.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a digital drive circuit for a liquid crystal display device capable of displaying multiple gradations.

(Conventional technology) Liquid crystal display devices take advantage of their light weight and low power consumption.
2. Description of the Related Art Liquid crystal display devices have come to be used in various fields, and among them, liquid crystal display devices capable of displaying multiple gradations are attracting attention as displays for televisions, personal computers, and the like.

For example, active matrix liquid crystal display devices, in which each pixel is equipped with a switching element such as a thin film transistor, have been developed in recent years because they are capable of displaying images with a large number of scanning lines without crosstalk between adjacent electrodes. It has started to attract attention.

Taking this active matrix type liquid crystal display device as an example, a first electrode substrate has a plurality of signal electrodes and scanning electrodes arranged in a matrix, and a switching element connected to a pixel electrode at each intersection. , a liquid crystal cell in which a liquid crystal composition is sandwiched by a second electrode substrate on which a common electrode is installed, and a drive circuit section for applying a drive voltage to each electrode of the liquid crystal cell.

This drive circuit section includes a signal electrode drive circuit connected to a plurality of signal electrodes, a scan electrode drive circuit connected to a plurality of scan electrodes, and a common electrode drive circuit connected to a common electrode.

The liquid crystal driving voltage is supplied to each signal electrode using an analog method, in which an analog image signal is input and the parallel image signals for one horizontal line are obtained by sequentially sampling and holding the signals, and a digital image signal is input. There is a digital method in which parallel image signals for one horizontal line are obtained by processing this digital image signal.

Therefore, a signal electrode drive circuit for an active matrix liquid crystal display device capable of multi-gradation digital display will be described with reference to FIG.

This signal electrode drive circuit (501) is a serial/parallel conversion circuit (511) mainly composed of a shift register, a latch, etc.
), n decoders (521), and n voltage selection circuits (531).

A multi-gradation digital image signal DS consisting of m bits, a shift clock signal CPH, and a horizontal start signal STH are input to the serial/parallel conversion circuit (511).

This multi-gradation digital image signal DS is serial-parallel converted using a shift clock signal CPH and a horizontal start signal STH so that it is simultaneously output to each decoder (521).
It becomes bit display data and is led to a decoder (521).

Further, each voltage selection circuit (531) is provided with each liquid crystal drive voltage Vl, V2 . ..., V2k is supplied.

This is because liquid crystal display devices generally need to be driven with alternating current to prevent deterioration of the liquid crystal composition. For example, 3
Considering the case of bit (8 gradations), the liquid crystal drive voltage V1 has 8 levels (V IP
-V 8P, V IN -V 8N), a total of 16 levels are required.

In addition, the common electrode voltage VSC is determined by the m-bit display data.
A 1-bit signal is added to the m-bit display data from the frequency control signal input terminal DF so that a higher level liquid crystal drive voltage VIP or a lower level liquid crystal drive voltage ViN can be selected, and is decoded by a decoder (521). be converted into This causes the switches (531) in the voltage selection circuit (531) to turn on at twice the display frequency.
The liquid crystal driving voltages Vl, V2 . ..., V2
One of them is selected.

Then, selected liquid crystal drive voltages Vl, V are applied to each signal electrode (not shown) connected to the n output terminals (533).
2. ..., one of them is applied to V2.

For example, when a liquid crystal cell provided with red, blue, and green color filters is driven by the above-mentioned drive circuit, the number of colors that can be displayed is expressed by the number of display gradations k being 21 (
2")" color, and when the above-mentioned color liquid crystal cell is driven with a 3-bit (8 gradation) digital image signal DS,
(23,)8 enables display of 512 colors.

(Problems to be Solved by the Invention) The digitally configured signal electrode drive circuit (501
), liquid crystal drive voltages Vl, V2 . ..., it is necessary to select and output one to V2.

Therefore, if an attempt is made to increase the number of display gradations of a liquid crystal display device, a very large number of switches will be required in the voltage selection circuit (531).

Such an increase in the number of switches causes problems such as an increase in chip size and an increase in cost when integrating the drive circuit.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a drive circuit for a liquid crystal display device that is capable of displaying multiple gradations with a simple configuration.

[Structure of the Invention] (Means for Solving the Problems) The drive circuit for a liquid crystal display device of the present invention converts input multi-gradation digital signals into serial-parallel signals line by line to form pixel display data. a conversion circuit; a plurality of decoders that decode pixel display data; a voltage generating circuit that outputs a plurality of liquid crystal driving voltages corresponding to each display gradation by sequentially shifting the level so as to have a second level lower than a predetermined level; The present invention is characterized by comprising a plurality of voltage selection circuits that select and output one voltage for each cycle.

(Function) The driving circuit for a liquid crystal display device of the present invention level-shifts a square wave voltage having a different level every integer multiple of the frame period or every integer multiple of the line period to drive a plurality of liquid crystal display devices corresponding to each display gradation. It generates a driving voltage.

Therefore, a plurality of liquid crystal drive voltages having different levels can be outputted from one output terminal every integer multiple of the frame period or every integer multiple of the line period. As a result, if the number of gradations of the liquid crystal display device is the same as the conventional one, the number of switches for selecting the liquid crystal drive voltage can be significantly reduced.

In addition, by configuring a liquid crystal display device using such a drive circuit, it is possible to realize a liquid crystal display device that is small in size and consumes low power.

(Embodiment) Hereinafter, an active matrix type liquid crystal display device will be described in detail as an embodiment of the liquid crystal display device of the present invention with reference to the drawings.

FIG. 1 shows a schematic configuration diagram of an active matrix type liquid crystal display device (1) capable of 8-gradation digital display as an embodiment of the present invention, and has the following configuration.

That is, n signal electrodes (3) Xp(p
ml+2+...-n) and m scanning electrodes (5) Yq
(q-1°2, . . . 1 rin) are formed in a matrix shape, and pixel electrodes (11) are formed at each intersection of the matrix wiring portions via thin film transistors (7).

The above-described substrate and the other substrate on which the common electrode (21) is formed constitute a liquid crystal cell (41) in which a liquid crystal composition (31) is sandwiched.

In addition, in order to drive this liquid crystal cell (41), a signal electrode drive circuit (Lot) is connected to the signal electrode (3), and a scanning electrode (5) is connected to the signal electrode (3).
), the scanning electrode drive circuit (201>) is connected to the common electrode (21).
A common electrode drive circuit (301) is connected to the active matrix liquid crystal display device (1).

Each pixel electrode (11) has a thin film transistor (
The liquid crystal drive voltage input to the signal electrode (3) is applied according to the selection pulse input to the gate electrode (7), and the potential difference between the common electrode (21) and the pixel electrode (11) is The voltage is applied to the liquid crystal composition (31), and a display operation is performed.

Next, the second section regarding the configuration of the signal electrode drive circuit (101) will be explained.
This will be explained with reference to the figures.

The signal electrode drive circuit (101) is a serial-to-parallel conversion circuit (111) composed of a shift register, a latch circuit, etc.
, a control circuit (115), a decoder (121), a voltage selection circuit (131), and a voltage generation circuit (141).

Then, a voltage selection circuit (131) selects and outputs the liquid crystal drive voltage V1 from the voltage generation circuit (141) in accordance with the 3-bit display data input to the serial/parallel conversion circuit (111). .

First, the third section regarding the voltage generation circuit (141) of this embodiment.
This will be explained in detail with reference to the drawings.

This drive voltage supply circuit (141) is composed of a square wave voltage generation circuit (151), a level shift circuit (161), and a bias voltage generation circuit (171).

In the figure, A is an operational amplifier (163), R and Ri (1
-1, 2,..., 8) are resistances (165), (167)
, Oi (1-1°2,...,8) is the output terminal (
lEi9), DF is a square wave voltage frequency control signal input terminal (153).

A subtracter is configured by a resistor R (153) and an operational amplifier A (163), and one input terminal receives a bias voltage generated by a bias voltage generating circuit (171) through a voltage dividing resistor R1 (1-1, 2,...,8) (187)
The square wave voltage generated by the square wave voltage generation circuit (151) is input to the other input terminal.

As a result, the square wave voltage is sequentially level-shifted, and the fourth
As shown in the figure, a positive liquid crystal drive voltage VIP higher than the common electrode voltage Vsc and a negative liquid crystal drive voltage ViN lower than the common electrode voltage Vsc are reversed every predetermined period (i=1.2 ..., 8) is connected to each output terminal 0f (
i-1, 2,..., 8) (189). That is, one output terminal Of(i=1.2...,8
) (169) outputs a liquid crystal driving voltage Vi (i=1.2° . . . , 8) having a different level every predetermined period.

The liquid crystal driving voltage Vi (i=1, 2, . . . , 8) outputted from the voltage generating circuit (141) in this manner is selected as follows.

A 3-bit digital image signal DS, a shift clock signal CPH, and a horizontal start signal STH are input to the serial/parallel conversion circuit (111), and the digital image signal DS is converted by the shift clock signal CPH and the horizontal start signal STH. The data is serial-parallel converted into 3-bit display data corresponding to the number of signal electrodes (3) of the liquid crystal display device (1), and is guided to a control circuit (115).

DF is an input terminal of a control bit for AC driving the liquid crystal display device (1), and the liquid crystal drive voltage vto-t,
2. ..., 8) positive liquid crystal drive voltage V IP (1-1,
2°..., 8), "0°" and negative liquid crystal drive voltage ViN (i=1.2.-.
When applying 8>, "1" is input alternately at predetermined intervals.

If "0" is added to the beginning of the display data by the control circuit (115), the 3-bit display data is led as is to the decoder (121), and "1" is added to the beginning of the display data. If so, the 3-bit display data is logically inverted and guided to the decoder (121).

In this way, the 3-bit display data led to the decoder (121) is decoded, and the 8 switches S i (+-1, 2, . . . , 8) (
133), and the positive liquid crystal drive voltage VIP or common electrode voltage VS is higher than the common electrode voltage Vsc.
A negative liquid crystal drive voltage VIN lower than C is alternately selected, and a negative liquid crystal drive voltage v1 is applied to each signal electrode (3) via an output terminal (135).

Table 1 shows an example of the operation of the control circuit (115) and decoder (121) of the liquid crystal display device (1) capable of displaying eight gradations.

For example, if "000°" is input as display data,
As for the display data, "000" and "111" are alternately outputted at a predetermined period by the control bit DF input to the control circuit (115).

When the output from the control circuit (115) is "000", the switch S1 (133) in the voltage selection circuit (131) is selected and the positive liquid crystal drive voltage V8P (see Figure 4) which is higher than the common electrode voltage Vsc is selected. ) is the signal electrode drive circuit (lot)
is output from the output terminal (135). When the output from the control circuit (115) reaches "111°" after a predetermined period, the switch 58 (1) in the voltage selection circuit (131)
33) is selected, and a negative liquid crystal drive voltage V8N (see Fig. 4) which is lower than the common electrode voltage VSC and has an effective voltage value equal to the positive liquid crystal drive voltage V8P is outputted via the output terminal (135). .

In this way, the voltage selection circuit (131)
By controlling the switch S I (133) in
Positive and negative liquid crystal drive voltages V with different polarities corresponding to display data
AC drive is possible by alternately applying IP and VIN.

Margin Table 1 Below As detailed above, in the liquid crystal display device (1) of this embodiment, one output terminal 01 of the drive voltage supply circuit (141)
(i-1, 2,..., 8) From (169), the positive liquid crystal drive voltage VIP, which is higher than the common electrode voltage VSC, and the negative liquid crystal drive voltage ViN, which is lower than the common electrode voltage Vsc, are alternately changed every predetermined period. can be output to. Therefore,
The number of switches (133) in the voltage selection circuit (131) is
While the conventional liquid crystal display device had 16 devices, the liquid crystal display device (1) of this embodiment had 8 devices, which was half of the conventional number.

This particularly facilitates the integration of the signal electrode drive circuit (101) and provides an inexpensive active matrix liquid crystal display device (1).

Further, according to the driving circuit of the liquid crystal display device of this embodiment, since the liquid crystal driving voltage of a predetermined amplitude is used by sequentially level-shifting, the amplitude of the square wave voltage is changed from V8P to VIN.
This is sufficient, and there is no need to use a square wave voltage with a large amplitude from V8P to V8N, which also has the effect of reducing power consumption.

In the embodiments described above, a liquid crystal display device capable of 8-gradation digital display has been described, but the present invention is not limited thereto, and can be applied to various liquid crystal display devices capable of multi-gradation digital display. In particular, it is possible to easily integrate the drive circuit and reduce power consumption.

[Effects of the Invention] The drive circuit for a liquid crystal display device of the present invention has a simple configuration and can greatly reduce the number of drive voltage selection switches.
This allows the signal electrode drive circuit to be implemented as an LSI at low cost.

Further, it is possible to easily construct a liquid crystal display device that is capable of multi-gradation digital display and has low power consumption.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a liquid crystal display device according to an embodiment of the present invention, FIG. 2 is a schematic configuration diagram of a signal electrode drive circuit section in the liquid crystal display device of FIG. 1, and FIG. FIG. 4 is a schematic diagram of the drive voltage supply circuit; FIG. 4 is a waveform diagram of the liquid crystal drive voltage output from the drive voltage supply circuit in FIG. 3; FIG. 5 is a schematic diagram of the signal electrode drive circuit of a conventional liquid crystal display device. , FIG. 6 is a waveform diagram showing the relationship between the number of display gradations and the drive voltage level in FIG. 5. (1)...Liquid crystal display device (41)...Liquid crystal cell (101)...Signal electrode drive circuit (141)...Drive voltage supply circuit (151)...Square wave voltage generation circuit (161)... )...Level shift circuit (171)...Bias voltage generation circuit (201)...
・Scanning electrode drive circuit (301)...Common electrode drive circuit

Claims (1)

[Scope of Claims] A serial-to-parallel conversion circuit that converts an input multi-gradation digital signal line by line into pixel display data, a plurality of decoders that decode the pixel display data, and a frame period. The level of the square wave voltage is sequentially shifted so that it has a first level higher than a predetermined level and a second level lower than the predetermined level. a voltage generation circuit that outputs a plurality of liquid crystal drive voltages corresponding to each display gradation; and a plurality of voltage selection circuits that select and output one of the liquid crystal drive voltages for each cycle according to the output of the decoder. A driving circuit for a liquid crystal display device, comprising: a circuit for driving a liquid crystal display device;