JPH0627902A - Circuit for driving display device - Google Patents

Abstract

PURPOSE:To obtain the driving circuit of a display device capable of preventing orientation inversion phenomenon in liquid crystal molecules by preventing an unstable display signal from being held between a pixel electrode and a counter electrode after the power source is turned ON. CONSTITUTION:Plural pixel electrodes 12 arranged in matrix, plural switching elements 13, plural column electrodes 14, and plural row electrodes 15 are provided on the surface of a light-translucent substrate 11 constituting the display device. Once a control circuit 18 outputs pulses as the signal Lout for a specific time after the power source is turned ON, D-type flip-flops D1-Dn of a row electrode driving circuit 17 are set and H signals are outputted as scanning signals G1-Gn to the respective row electrodes to turn ON the respective switching elements 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit of a display device using a material such as liquid crystal whose optical properties are changed by applying a voltage.

[0002]

2. Description of the Related Art A display device using liquid crystal is shown in FIG.
As shown in the cross-sectional view of FIG. 1, the translucent substrate 61 on which electrodes such as picture element electrodes 62, column electrodes 63, row electrodes (not shown) and an alignment film 64 arranged in a matrix are formed on the surface.
And a translucent substrate 66 having a counter electrode 67 and an alignment film 68 formed on the surface thereof face each other at regular intervals, and a liquid crystal 65 is sealed between them by a sealing member 69.

FIG. 6 is a block diagram showing an example of a drive circuit of a conventional display device. A plurality of picture element electrodes 62 arranged in a matrix and a plurality of switching elements such as thin film transistors (TFTs) for controlling a voltage applied to the picture element electrodes 62 are provided on a surface of a transparent substrate 61 which constitutes a display device. 70, a plurality of column electrodes 63 for transmitting a display signal to the switching element 70, and a plurality of row electrodes 71 for transmitting a scanning signal for selectively driving the switching element 70. The column electrode drive circuit 73 uses the synchronization signal SYN.
It is controlled by a control circuit 74 that operates in synchronization with C and the like, and is mainly composed of a shift register circuit, a sample hold circuit, etc., and connected to each column electrode 63. The row electrode drive circuit 72 is similarly controlled by the control circuit 74 and is mainly composed of a shift register circuit or the like,
It is connected to each row electrode 71.

The matrix driving operation of the pixel electrodes 62 will be described below with reference to the timing chart shown in FIG. First, in the period A1, the row electrode drive circuit 72 outputs the pulsed scanning signal G1 to the first row electrode 7
1 (scan signal becomes high level) and the column electrode drive circuit 73 causes the display signal Sx (x is 1 to n).
Up to a natural number. Note that n is a natural number. (Hereinafter the same) is output to each column electrode 63, each switching element 7 in the first row is output.
0 becomes conductive, and the display signal Sx is applied to each pixel electrode 62 in the first row. Then, in FIG. 5, the first
The voltages v1 to vn according to the display signal Sx are applied to the liquid crystal 65 existing between each pixel electrode 62 in the row and the counter electrode 67, and the image on the scanning line in the first row is displayed.

Next, in the period A2, the row electrode drive circuit 72 outputs the pulsed scanning signal G2 to the second row electrode 71.
And the column electrode drive circuit 73 outputs to each column electrode 6
When the display signal Sx is output to 3, the switching elements 70 in the second row are rendered conductive, and the display signal Sx is applied to the pixel electrodes 62 in the second row. Then, in FIG. 5, the voltage v1 corresponding to the display signal Sx is applied to the liquid crystal 65 existing between each pixel electrode 62 on the second row and the counter electrode 67.
vn is applied, and the image on the scanning line in the second row is displayed.

Thereafter, by performing the same operation as that described above from the period A3 to the period An, the image from the scanning line of the third row to the scanning line of the nth row is displayed, and the first vertical scanning ends. .

Next, in the period B1, the above-mentioned period A
Similarly to the operation in 1, the row electrode drive circuit 72 outputs the pulsed scanning signal G1 to the first row electrode 71, and the column electrode drive circuit 73 responds to the display signal in the first vertical scanning. When the display signal Sx having the opposite polarity is output to each column electrode 63, each switching element 70 of the first row is output.
Becomes conductive and the display signal Sx is applied to each pixel electrode 62 in the first row. Then, in FIG. 5, the voltages −v1 to −vn corresponding to the display signal Sx are applied to the liquid crystal 65 existing between each pixel electrode 62 on the first row and the counter electrode 67, and the liquid crystal 65 on the first row is applied. The image on the scan line is displayed.

Next, in the period B2, similarly, the row electrode drive circuit 72 outputs the pulsed scanning signal G2 to the second row electrode 71, and the column electrode drive circuit 73 also performs the first vertical scanning. When a display signal Sx having a polarity opposite to that of the display signal Sx in FIG.
Each of the switching elements 70 in the row becomes conductive, and the display signal Sx is applied to each of the picture element electrodes 62 in the second row.
Then, in FIG. 5, the voltages -v1 to -vn corresponding to the display signal Sx are applied to the liquid crystal 65 existing between each pixel electrode 62 of the second row and the counter electrode 67, and the liquid crystal 65 of the second row is applied. The image on the scan line is displayed.

Thereafter, by performing the same operation as described above from the period B3 to the period Bn, the image on the scanning line from the third scanning line to the nth scanning line is displayed, and the second vertical scanning is completed. .

In this way, by repeating the vertical scanning in which the display signal Sx whose polarity is switched every vertical scanning period is applied to each pixel electrode 62, one image is displayed and
By suppressing the time average value of the display signal Sx near 0 V, deterioration of the liquid crystal due to an electrochemical reaction is prevented.

In such a matrix driving operation, paying attention to the pixel electrodes 62 on the first row, for example, as shown in FIG. 7 (6), the voltage is applied during the period A1 in the first vertical scanning. The voltage v1 changes from the period A2 to the period A
n is held by the electrostatic capacitance formed between the counter electrode 67 and the counter electrode 67, while the voltage −v1 applied during the period B1 in the next second vertical scan is maintained from the period B2 to the period Bn. It is held by the capacitance. Similarly, for the other pixel electrodes 62, the voltage applied during the period in which the row electrodes 71 are selectively driven is held by the capacitance during the rest of the scanning period.

[0012]

However, the operation of the control circuit 74 becomes unstable for a certain period of time after the power is turned on, and at this time, the scanning signal Gy (y is from 1 to n) not planned by the row electrode drive circuit 72. The same may be output to each row electrode 71, and the column electrode drive circuit 73 may output an unstable display signal Sx. Therefore, as compared with the display signal Sx in the normal operation, a voltage in which a DC component whose time average value is not near 0 V is superimposed is applied to each pixel electrode 62, and this DC component is applied to the liquid crystal 65 for a long time, for example, several tens of μsec. When held at, the deterioration due to the electrochemical reaction occurs, and the life of the display device tends to be shortened.

Further, when the column electrode drive circuit 73 outputs an unstable display signal Sx to each column electrode 63 during unstable operation immediately after power-on, a pixel connected to the switching element 70 in the cutoff state. Since a potential difference is generated between the electrodes 62 and the column electrodes 63 and an electric field parallel to the surface of the substrate 61 is applied, the tilt of the liquid crystal molecules in that region becomes uneven in one display pixel. However, there is a problem in that the image quality in that region deteriorates. Once the orientation inversion phenomenon occurs, it cannot be eliminated by applying a voltage that maximizes the inclination of the liquid crystal molecules during normal operation unless the entire inclination is aligned.

In order to solve the above-mentioned problems, an object of the present invention is to prevent an unstable display signal from being held between each pixel electrode and a counter electrode after power is turned on, and to prevent liquid crystal molecules from being held. It is an object of the present invention to provide a drive circuit of a display device capable of preventing the orientation reversal phenomenon.

[0015]

According to the present invention, a plurality of picture element electrodes arranged in a matrix form, a plurality of switching elements for controlling a voltage applied to the picture element electrodes, and a display signal to the switching elements. For a display device having a plurality of column electrodes for transmitting and a plurality of row electrodes for transmitting a scanning signal for selectively driving the switching element, a column electrode drive circuit and a row electrode for sequentially driving the column electrodes In a drive circuit of a display device including a row electrode drive circuit for sequentially driving the display device, the row electrode drive circuit brings the switching element into a conductive state for a predetermined time after power is turned on. Is.

[0016]

According to the present invention, the row electrode drive circuit brings the switching element for controlling the voltage applied to the pixel electrode into a conductive state for a predetermined time after the power is turned on, whereby the pixel electrode and the column electrode are connected. Since the potential difference between them is almost 0 V, an electric field parallel to the substrate surface of the display device is not applied,
It is possible to eliminate the unevenness of the tilt of the liquid crystal molecules.

[0017]

1 is a block diagram showing a drive circuit of a display device according to an embodiment of the present invention. A plurality of picture element electrodes 12 arranged in a matrix and a plurality of switching elements such as thin film transistors (TFTs) for controlling a voltage applied to the picture element electrodes 12 are provided on the surface of a light-transmissive substrate 11 which constitutes a display device. 13, a plurality of column electrodes 14 for transmitting a display signal to the switching element 13, and a plurality of row electrodes 1 for transmitting a scanning signal for selectively driving the switching element 13.
And 5 are provided.

The column electrode drive circuit 16 uses the synchronization signal SYNC.
It is controlled by the control circuit 18 that operates in synchronization with the above, and is mainly composed of a shift register circuit, a sample hold circuit, and the like, and is connected to each column electrode 14. The row electrode drive circuit 17 is also controlled by the control circuit 18, and is mainly configured by a shift register circuit including D-type flip-flops D1 to Dn and buffers C1 to Cn, and connected to each row electrode 15.

The signal CLS from the control circuit 18 is input to the CK terminals of the D-type flip-flops D1 to Dn, the signal Lout is input to the S terminals of the D-type flip-flops D1 to Dn, and the signal SPS is the D-type. Flip-flop D1
Of the D-type flip-flop D1 and the output of the Q-type terminal of the D-type flip-flop D1.
, And the input terminal of the buffer C1, and are sequentially input to the D terminals of the D-type flip-flops D3 to Dn and the input terminals of the buffers C2 to Cn.

The matrix driving operation of each pixel electrode in the normal operation when a long time has passed since the power was turned on is the same as the operation described in FIGS. 5 and 6.
The description is omitted.

Next, the operation from power-on to a predetermined time will be described with reference to the timing chart shown in FIG. From the power supply circuit 30 such as the stabilized power supply circuit to the row electrode drive circuit 17, the column electrode drive circuit 16, the control circuit 18
The supply voltage PS supplied to the voltage rises to a predetermined voltage when the power source is connected to the external power source 40 by the operation of the switch 41. The control circuit 18 outputs the signal Lout for a predetermined time T from the time when the supply voltage PS stabilizes at a predetermined voltage,
For example, by outputting H (high level) for 130 μsec, the D-type flip-flops D1 to Dn of the row electrode driving circuit 17 are set and H is output from the Q terminal, so that the buffers C1 to Cn output to each row electrode 15. The scanning signals G1 to Gn also become H, and each switching element 13
Becomes conductive.

On the other hand, when the column electrode drive circuit 16 outputs the unstable display signals S1 to Sm from the time when the power is turned on to the predetermined time, since the respective switching elements 13 are in the conductive state as described above, the respective picture elements are turned on. Although a constant voltage is applied to the electrode 12, the potential difference between the pixel electrode 12 and the pixel electrode 12 is almost 0 V due to only the voltage drop due to the ON resistance of the switching element 13, which is parallel to the surface of the substrate 11. The electric field is not generated, and it becomes possible to prevent the alignment reversal phenomenon of the liquid crystal molecules.

Next, the control circuit 18 outputs L (low level) after the elapse of a certain time T during which H is output as the signal Lout. The fixed time T is determined in consideration of the time required for the operation of the peripheral circuits of the display device such as the control circuit 18 to shift from the unstable state when the power is turned on to the stable state. It is not limited to.

Next, at time t1, when the signal Lout becomes L, the shift register including the D-type flip-flops D1 to Dn becomes operable, and the start pulse signal SPS is input to the D terminal of the D-type flip-flop D1. The level of the D terminal at the rising edge of the clock signal CLS input to the CK terminal is latched,
To H as a signal G1 through the buffer C1.

When the next clock signal CLS rises t3
Since the start pulse signal SPS is L, the signal G1 is inverted to L. In addition, the next clock signal CLS
At the rising edge t4 of the D-type flip-flop D2,
Since the level of the terminal is L, the terminal Q outputs L as the signal G2 via the buffer C2. Hereinafter, similarly, the scanning signals G3 to Gn are sequentially inverted from H to L in synchronization with the clock signal CLS, and each switching element 13 that has been in a conductive state for a certain period after the power is turned on,
It will be in the shut-off state in sequence.

In this way, after the operation of the peripheral circuits such as the column electrode drive circuit 16 and the row electrode drive circuit 17 shifts to a stable state, a stable regular signal is input to each picture element electrode 12 for normal operation. Will be done. The vertical scanning cycle is about 1/30 seconds or 1/60 seconds, and the polarities of the output signals S1 to Sm of the column electrode drive circuit 16 are inverted every vertical cycle. A voltage with a biased polarity is not retained for a long time, and deterioration due to an electrochemical reaction can be prevented.

FIG. 3 is a circuit diagram showing an example of the pulse generation circuit 20 of the control circuit 18 shown in FIG. 1, which outputs the signal Lout having the pulse width T from the time when the power is turned on. The pulse generation circuit 20 is a two-stage shift register.
Two D-type flip-flops 22 and 23, latch circuits 24 and 25 connected to the / Q terminal of the D-type flip-flop 23 (hereinafter, "/" indicates negative logic), and buffers 21 and 26. , The oscillation circuit 33 uses the synchronization signal SYN.
The clock signal FR synchronized with C is output and input to the CK terminal of the D-type flip-flop 22, and the supply voltage PS of the power supply circuit 30 of the display device is passed through the integrating circuit of the resistor 31 and the capacitor 32. , The signal Lin is input to the buffer 21 and binarized, and the / R terminals of the D-type flip-flops 22 and 23 and the latch circuit 2 are inputted.
It is input to one of 4, 4 and 25.

This operation will be described below with reference to the timing chart of FIG. The supply voltage PS is quickly stabilized to a constant voltage when the power is turned on when the switch 41 is turned on to start supplying power from the power supply circuit 30 to the peripheral circuits. During the period W that rises gradually and is lower than the input threshold value of the buffer 21, for example, about 47 msec,
Since the signal L1 is L, the D-type flip-flop 22,
23 is in the reset state, the signals L2 and L3 are H, and the outputs of the latch circuits 24 and 25 are H, and the signal Lout is H.

After the period W when the signal Lin exceeds the input threshold value of the buffer 21, the signal L1 becomes H and the reset state of the D-type flip-flops 22 and 23 is released.

On the other hand, for example, a clock signal FR having a period of 66.6 msec is input to the CK terminal of the D-type flip-flop, and after the lapse of the period W, the first rising time t11.
Then, the output of the / Q terminal, that is, the signal L2 is inverted to L. Next, when the clock signal FR rises for the second time t
In FIG. 12, the signal L2, which is L, is taken in from the D terminal, the signal L2 is inverted to H again, and the signal L2 which has been H until just before D
The output of the / Q terminal of the type flip-flop 23, that is, the signal L3 is taken in from the D terminal, and the signal L3 is inverted to L. When the signal L3 becomes L, the outputs of the latch circuits 24 and 25 are inverted to L, and the signal Lout is output via the buffer 26.
Is output as.

Thus, the resistor 31 and the capacitor 3
The period W determined by the time constant of 2 and the input threshold of the buffer 21,
For example, the level of signal Lout is held at H for a total period of 47 msec and one cycle of clock signal FR, for example, 66.6 msec or more, and the D-type flip-flop forming row electrode drive circuit 17 in FIG. 1 is held. D1-D
It is input to the S terminal of n.

[0032]

As described in detail above, according to the present invention,
When the row electrode drive circuit turns on the switching element that controls the voltage applied to the pixel electrode for a predetermined time after the power is turned on, the potential difference between the pixel electrode and the column electrode becomes approximately 0V, An electric field parallel to the substrate surface of the display device is not applied, so that it is possible to prevent a so-called orientation inversion phenomenon in which the tilt of the liquid crystal molecules becomes nonuniform, and a high quality image can be displayed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a drive circuit of a display device according to an embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of the drive circuit shown in FIG.

3 is a circuit diagram showing an example of a pulse generation circuit 20 in the control circuit 18 shown in FIG.

FIG. 4 is a timing chart showing an operation of the pulse generation circuit 20 shown in FIG.

FIG. 5 is a cross-sectional view showing an example of a display device using liquid crystal.

FIG. 6 is a block diagram showing an example of a drive circuit of a conventional display device.

7 is a timing chart illustrating the operation of the drive circuit of the display device of FIG.

[Explanation of symbols]

 11 translucent substrate 12 picture element electrode 13 switching element 14 row electrode 15 column electrode 16 column electrode drive circuit 17 row electrode drive circuit 18 control circuit 20 pulse generation circuit 21, 26 buffer 22, 23 D-type flip-flop 24, 25 latch Circuit 30 Power supply circuit 31 Resistance 32 Capacitor 33 Oscillation circuit 40 External power supply 41 Switch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshifumi Kawaguchi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Hideki Yakushigawa 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation

Claims (1)

[Claims] 1. A plurality of picture element electrodes arranged in a matrix, a plurality of switching elements for controlling a voltage applied to the picture element electrodes, and a plurality of column electrodes for transmitting a display signal to the switching elements, A column electrode drive circuit for sequentially driving the column electrodes and a row electrode drive circuit for sequentially driving the row electrodes for a display device having a plurality of row electrodes for transmitting scanning signals for selectively driving the switching elements A drive circuit of a display device comprising: a drive circuit of the display device, wherein the row electrode drive circuit brings the switching element into a conductive state for a predetermined time after power is turned on.