JPH05181435A - Picture display device and its driving method - Google Patents

Abstract

PURPOSE:To obtain a picture display device with the little unevenness of display by detecting a noise, generating voltage to eliminate the noise and feeding it back. CONSTITUTION:As for the matrix type picture display device, a noise eliminating circuit 50 is interposed between a driving circuit 9 and a reference voltage generator 1 so as to detect the noise on supply voltage signal to a display body at a specified position 10, and the noise is fetched and converted into noise eliminating voltage corresponding to the noise by an integrator 30, then the noise eliminating voltage is impressed on the driving circuit 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device,
In particular, the present invention relates to a matrix type liquid crystal display device which performs multiplex driving and a driving method thereof.

[0002]

2. Description of the Related Art When an image display device represented by a liquid crystal display device has a large number of segments or a large number of pixels, a time-division drive type multiplex drive using matrix electrodes is performed. In the matrix electrode structure, a pair of electrode substrates are arranged to face each other, a plurality of strip-shaped row electrodes (X electrodes) are formed in parallel on one substrate, and a plurality of strip-shaped columns are formed on the other opposing substrate. Electrodes (Y electrodes) are formed in parallel so as to be orthogonal to the row electrodes, and liquid crystal is sealed and sandwiched between both electrode substrates.

In such a matrix type liquid crystal display device, the multiplex drive applies a row electrode waveform consisting of a selection voltage and a non-selection voltage to a row electrode in a predetermined frame period, and in synchronization with this, a column electrode. By applying a column electrode waveform composed of a lighting voltage and a non-lighting voltage to the electrodes, line-sequential scanning is performed to excite the liquid crystal at a desired matrix intersection position (pixel position) for display.

As a method of driving a simple matrix type liquid crystal display device, there is known a method of averaging voltages at half-selected points and non-selected points on a matrix to reduce the influence of cross effects as much as possible. This drive waveform is shown in FIG. 5 and FIG.
Shown in. FIG. 4 shows a display state of the liquid crystal panel to be displayed by these drive waveforms. Although FIG. 4 shows a liquid crystal panel having a 7 × 7 dot structure for the sake of simplicity, the actual number of dots of the liquid crystal panel is much larger than this. The display dots in the shaded area represent the lit state, and the display dots in the white part represent the non-lit state.

Only one row electrode is selected by sequentially applying a selection voltage to each of the row electrodes C1 to C7, and a non-selection voltage is applied during the other non-selected time. Further, a lighting voltage or a non-lighting voltage is simultaneously applied to each of the column electrodes S1 to S7. That is, when the dot at the intersection of a certain row electrode and a certain column electrode is lit, a lighting voltage is applied to the column electrode when the row electrode is in the selected state, and when the dot is not lit, the lighting voltage is not applied in the selected state. A lighting voltage is applied.

Examples of actual drive waveforms are shown in FIGS. 5 and 6. 5A is a drive waveform applied to the row electrode C1, FIG. 5B is a drive waveform applied to the column electrode S2, and FIG.
(C) is a drive waveform applied to the dot at the intersection of the row electrode C1 and the column electrode S2. Further, FIG. 6A shows a row electrode C.
6 is a drive waveform applied to the column electrode S5, and FIG. 6C is a drive waveform applied to the column electrode S5.
5 is a drive waveform applied to the dot at the intersection with 5.

In FIGS. 5 and 6, F1 and F2 are frame periods. In the frame period F1, V
5 = selected voltage, V1 = non-selected voltage, V0 = lighting voltage, V
2 = non-lighting voltage. In the frame period F2, V0 =
Selected voltage, V4 = non-selected voltage, V5 = lighting voltage, V3 =
It is a non-lighting voltage. Here, V5-V4 = V4-V3 =
V2-V1 = V1-V0 = V, V5-V0 = bV (b =
Bias value). In this way, alternating drive is performed by changing the polarities of the frame periods F1 and F2.

As can be seen from the comparison between FIG. 5 and FIG. 6, whether a displayed dot is in a lighting state or a non-lighting state is applied with a selection voltage to a row electrode including the dot. At this time, it depends on whether the lighting voltage is applied to the column electrode or the non-lighting voltage is applied. Such a driving method is a conventionally-known driving method called a voltage averaging method.

Of the voltages V0, V1, V2, V3, V4, and V5, V0 and V5 are directly supplied from an external power source or an emitter follower using transistors, and V1 to V5.
4 is supplied directly from the resistance division as shown in the example of FIG. 7A when the display capacitance is relatively small, and after the resistance division as shown in the example of FIG. 7B in other cases. A voltage follower using an operational amplifier is inserted to reduce the impedance, and each is connected to a predetermined terminal of the driver IC. Here, V _adj is a control voltage supplied to adjust the brightness so that the liquid crystal display panel can be viewed easily.

[0010]

However, even in the circuit in which the voltage follower is inserted after the resistance division as shown in FIG. 7 (b), various noises are present here due to the reasons described later, and V1 to V4 However, there is a problem that the effective voltage applied to each display dot is different and the display unevenness occurs.

The present invention has been made in view of the above-mentioned drawbacks of the prior art. A spike-shaped voltage distortion generated in a liquid crystal drive voltage waveform due to noise is generated by a noise removing unit including a switching circuit having a novel structure. It is an object of the present invention to provide a liquid crystal display device having a uniform and easy-to-see screen with less display unevenness.

[0012]

To achieve the above object, in the present invention, an electro-optical medium sandwiched between a pair of electrode substrates forming a matrix electrode and a voltage is selectively applied to the matrix electrode. In an image display device including a drive circuit for driving an electro-optic medium and a reference voltage generator for supplying a predetermined drive voltage to the drive circuit, between the drive circuit and the reference voltage generator. A noise elimination circuit for eliminating noise on the voltage supplied to the electro-optical medium is interposed, and the noise elimination circuit has an integrator, a changeover switch, and an open / close switch, and the changeover switch has an output terminal. Is connected to the input terminal of the drive circuit, one switching terminal A on the input side is connected to the output terminal of the reference voltage generator, and the other switching terminal B on the input side is the integration terminal. Of the integrator, one input terminal of the integrator is connected to a predetermined noise detection position through the open / close switch, and the other input terminal receives a reference voltage generated from the reference voltage generator. Provided is an image display device, which is configured to be supplied as an offset voltage.

In a preferred embodiment, the noise detection position is a supply voltage input section to the liquid crystal drive circuit.

In a further preferred embodiment, a dummy electrode is provided on the electrode substrate and the noise is detected from the dummy electrode.

In the preferred embodiment of the driving method for driving the liquid crystal display device according to the present invention, noise is generated when the changeover switch is connected to the changeover terminal A side and the open / close switch on the noise extraction line is closed. A noise sampling period for sampling and converting to a constant voltage according to the effective value of the noise, and then a hold for supplying the constant voltage to the drive circuit in a state where the open / close switch is opened and the changeover switch is connected to the changeover terminal B side. And a reset period in which the open / close switch is opened and the changeover switch resets the integrator in the state of either the terminal A side or the terminal B side to return to the initial state. And

That is, according to the present invention, in a matrix type image display device, a noise removing circuit is provided between the drive circuit and the reference voltage generator, and the noise removing circuit is provided with noise on the voltage signal supplied to the display body. Is detected at a predetermined position, this noise is taken in by an integrator and converted into a noise removal voltage corresponding to the noise, and this noise removal voltage is applied to the drive circuit.

In the present invention, as a concrete example of the reference voltage generator for outputting the reference voltage used for driving the matrix type display, as for V0 and V5 mentioned above, a direct external power source or an emitter follower using a transistor is used. Is supplied, and regarding V1 to V4,
It is supplied from the resistance division of the external power supply. A noise removing circuit is connected to the output side of the reference voltage generator. The reference voltage includes a selection voltage, a non-selection voltage, a lighting voltage or a non-lighting voltage, and a noise elimination circuit needs to be connected to the output of at least one of the voltages.

[0018]

The action of the present invention concerning the possible cause of noise and noise removal in the present invention will be described below.

One example of possible causes of noise will be described below in the case of a liquid crystal matrix display device.

The liquid crystal panel is one in which a dielectric material called liquid crystal is sandwiched between transparent electrodes and is a capacitive load when viewed from the driver side. Moreover, since the resistance value of the transparent electrode is not zero but has a certain finite value, even if an ideal waveform is applied from the driver IC, the waveform is not distorted in the liquid crystal to some extent and display unevenness occurs. An example of this display unevenness will be described with reference to FIGS. The display is a so-called positive display in which the larger the effective voltage applied to the dot, the blacker the display becomes.

When the display as shown in FIG. 8A is performed, the display unevenness as shown in FIG. 8B actually occurs. At this time, the voltage waveforms at the dot portions of the row electrode C2 are shown in FIG. 9A, the voltage waveforms at the dot portions of the column electrodes S1 to S6 are shown in FIG. 9B, and the row electrode C2 and the column electrodes S1 to S1. The voltage waveform applied to the dot created by the intersection of S6 is shown in FIG. 9 (c).
Here, as shown in FIG. 9A, spike-like voltage distortion occurs in the non-selected voltage level of the row electrode waveform, and as a result, distortion occurs in the non-selected waveform as shown in FIG. 9C. To do.

The voltage waveform at the dot portion of the row electrode C2 is shown in FIG. 10A, the voltage waveform at the dot portion of the column electrode S7 is shown in FIG. 10B, and the voltage waveform of the row electrode C2 and the column electrode S7 is shown. The voltage waveform applied to the dot formed by the intersection is shown in FIG. Here, as shown in FIG. 10A, spike-like voltage distortion occurs in the non-selected voltage level of the row electrode waveform, and as a result, distortion occurs in the non-selected waveform as shown in FIG. 10C. To do. As can be seen immediately by comparing FIGS. 9C and 10C, the waveform of FIG. 9C has a lower effective value than the ideal waveform, and the waveform of FIG. RMS value is higher than the typical waveform. Therefore, the actual display has display unevenness as shown in FIG.

The mechanism in which spike-like voltage distortion occurs at the non-selected voltage level of the row electrode waveform will be described with reference to FIG. Here, 41 is a row electrode driver IC, 42 is a column electrode driver IC, 43 is a row electrode, 44 is a column electrode, and 45 is a capacitance C of liquid crystal. When the display as shown in FIG. 8 is made while the row electrode waveform is at the non-selection level, the column electrode waveform changes into a rectangular wave shape as shown in FIG. Is differentiated by the resistance value R of the row electrode, and spike-like voltage distortion is superimposed on the non-selected level of the row voltage waveform as shown in FIG. The peak value of this spike noise is attenuated by the output resistance of the row electrode driver IC, the connection resistance between the row electrode and the row electrode driver IC, and the like, and a waveform having distortion as shown in FIG. 11C is a row voltage waveform. Is superimposed on the non-selected level of.

According to the configuration of the present invention, the voltage distortion of the drive waveform generated inside the liquid crystal panel due to the graphic or character displayed on the liquid crystal display device is applied to the driving IC by selecting voltage, non-selecting voltage, lighting voltage or non-lighting. At least one of the voltages is converted into a voltage in which noise superimposed for a certain period of time has been detected, and this voltage is further applied to the driving IC as a correction signal for a certain period of time. By setting the reset period for this, it becomes possible to correct the deviation of the effective voltage applied to each display dot and reduce the display unevenness.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a circuit configuration of essential parts of a liquid crystal display device according to an embodiment of the present invention. In addition, time charts of voltage waveforms when this circuit is operated are shown in FIGS. FIGS. 2B to 2D show the voltage that is displaced from the reference voltage. In FIG. 1, 50 is a noise removal circuit, 1 is a reference voltage generator for generating one of two non-selected voltages, and 9 is a drive IC as a drive circuit. The drive IC 9 is connected to a liquid crystal drive matrix electrode (not shown) and selectively applies a voltage to, for example, the row electrode.

The configuration of the noise removing circuit 50 will be described in detail below. The noise removing circuit 50 mainly includes an integrator 30, a changeover switch 3, and an open / close switch 4.

Regarding the changeover switch 3, the output terminal is connected to the non-selected voltage input terminal 10 of the drive IC 9, one changeover terminal A on the input side is connected to the output terminal of the reference voltage generator 1 and the other on the input side. The switching terminal B of is connected to the output terminal of the integrator 30. The switching terminal A of the change-over switch 3 is connected to the output terminal of the reference voltage generator 1 via a buffer amplifier 2 such as an operational amplifier provided as a voltage follower for lowering the impedance of the reference voltage as shown in FIG. 1, if necessary. It may have been done. By switching the changeover switch 3, the voltage supplied to the drive IC 9 can be switched to either the output voltage of the integrator 30 or the output voltage of the reference voltage generator 1.

The integrator 30 is composed of an operational amplifier 5, a capacitor 7 and a discharge switch 6 connected in parallel with the operational amplifier 5 in this embodiment. Therefore, when the discharge switch 6 is opened, the integrator 30 functions, and when the discharge switch 6 is closed, the integrator 30 is discharged and reset.

The input terminal 10 of the driving IC 9 is further connected to the negative input terminal 32 of the operational amplifier 5 via the open / close switch 4. That is, when the open / close switch 4 is closed while the discharge switch 6 is open, the noise voltage signal whose polarity is inverted is integrated by the integrator 30. The positive input terminal 8 of the operational amplifier 5 is connected to a predetermined output terminal of the reference voltage generator 1 and receives a reference voltage for offset adjustment.

The operation of the circuit of this embodiment will be described below.

When the liquid crystal panel has the display pattern as shown in FIG. 8, the column electrode waveform becomes the waveform shown in FIG. 2 (a).
At this time, the non-selection voltage input terminal 10 of the drive IC 9 is connected to FIG.
As in (b), spike-like voltage distortion (noise) occurs.

First, for only t ₁ hours (noise sampling period), the changeover switch 3 with the discharge switch 6 kept open.
To the A side to connect and close the open / close switch 4. At this time, the non-selection voltage input terminal 10 of the drive IC 9 is connected to FIG.
Although the spike-like voltage distortion as shown in (b) is generated, the waveform as shown in FIG. 2 (c) is output to the output of the integrator 30, and the voltage of the opposite polarity corresponding to the magnitude of noise is generated. Occurs.

Next, when the open / close switch 4 is opened and the changeover switch 3 is tilted to the B side only for t ₂ hours (hold period), the output of the integrator 30 is held and the non-selection voltage input of the drive IC 9 is input. A waveform as shown in FIG. 2C is output to the terminal 10 for t ₂ time.

This is the voltage for correcting the reference voltage fluctuation due to the spike noise shown in FIG. 2 (b). That is, it is a voltage for removing this noise corresponding to the noise detected at the input terminal 10. This noise removal voltage has a polarity opposite to that of spike noise, and the voltage is adjusted while observing the display so as to eliminate display unevenness. This voltage is variable by changing the input resistance of the integrator 30, but an amplifier may be provided after this to change its gain. Further, when there is no linearity between the spike noise and the correction voltage, it is possible to make the amplifier have the opposite non-linearity for the correction.

Next, during the time t ₃ (reset period), the discharge switch 6 is closed and the integrator 30 is reset to the initial state. At this time, the open / close switch 4 may be in the open state, and the changeover switch 3 may be tilted to either the A side or the B side.

The above sequence is summarized in Table 1.

[0037]

[Table 1]

In FIG. 2D, the changeover switch 3 is t
₂ shows voltage waveforms at the non-selected voltage input terminal 10 when connected to the B side for ₂ and t ₃ hours. By thus feeding back the noise voltage and applying it to the drive IC 9, spike noise is removed and a stable drive voltage is supplied on average.

When two circuits of this kind were made to correct the distortion of two non-selected voltages, the effect of correcting the voltage distortion was exhibited and the display unevenness was reduced. Almost the same effect was obtained by making one of the circuits correspond to one of the two non-selection voltages.

In a more preferable driving method according to the present invention,
A standby period t ₄ is provided after the reset period t ₃ so that a sequence including a noise sampling period, a hold period, a reset period, and a standby period is repeated. During the standby period, the changeover switch 3 is connected to A. Further, the open / close switch 4 is preferably opened, and in this case, the discharge switch 6 may be open or closed.

By providing such a standby period, even if the frame frequency differs depending on the model of the display body, it is possible to respond by changing only the value of t ₄ . That is, even if the frame frequency changes, the noise removal effect does not change, and a stable noise removal effect can be obtained.

FIG. 3 shows a circuit configuration of a liquid crystal display device according to another embodiment of the present invention. The output side of the drive IC 9 is connected to each row electrode terminal of the liquid crystal panel 11, and the output side of the column electrode driving IC 12 is connected to each column electrode terminal of the liquid crystal panel 11. The negative input terminal of the operational amplifier 5 in the integrator 30 is connected to the dummy electrode for detecting spike noise through the buffer amplifier 14 and the open / close switch 4.

The circuit of this embodiment is different from the embodiment of FIG. 1 only in the method of detecting spike noise (detection position), and other configurations and operations are similar to those of the embodiment of FIG. The same reference numerals are given and the description of the operation is omitted. The buffer amplifier 14 may be omitted.

[0044]

As described above, according to the present invention, noise superimposed on the reference voltage supplied to the liquid crystal drive IC is detected, and a voltage for eliminating the noise is created and fed back to eliminate the noise. As a result, distortion of the reference voltage is eliminated and a stable drive voltage is supplied, whereby display unevenness of the liquid crystal panel can be reduced and display quality of the liquid crystal display device can be improved. Moreover, since the circuit structure is simple, the display quality can be improved at low cost.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a main part of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of voltage waveforms driving the liquid crystal display device of FIG.

FIG. 3 is a circuit diagram of a main part of a liquid crystal display device according to another embodiment of the present invention.

FIG. 4 is a plan view showing a display state of a liquid crystal display panel.

5 is an explanatory diagram of drive voltage waveforms in one row and one column of the liquid crystal display panel in the display state of FIG.

6 is an explanatory diagram of drive voltage waveforms in different rows and columns of the liquid crystal display panel in the display state of FIG.

7A and 7B are circuit diagrams showing different examples of the reference voltage generating circuit.

FIG. 8 is an explanatory diagram of display unevenness on the liquid crystal display panel.

9 is an explanatory diagram of actual driving voltage waveforms in one row and one column of the liquid crystal display panel in the display state of FIG.

10 is an explanatory diagram of an actual drive voltage waveform of another column of the liquid crystal display panel in the display state of FIG.

FIG. 11 is an explanatory diagram for explaining the reason why spike-like voltage distortion occurs at a non-selected level of a row electrode waveform.

[Explanation of symbols] 1 reference voltage generator 3 changeover switch 4 open / close switch 5 operational amplifier 6 discharge switch 7 capacitor 8 input terminal 9 liquid crystal drive IC 10 input terminal 30 integrator 50 noise elimination circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Hasebe 1150 Hazawa-machi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Asahi Glass Co., Ltd. Central Research Laboratory

Claims (4)

[Claims] 1. An electro-optical medium sandwiched between a pair of electrode substrates forming a matrix electrode, a drive circuit for selectively applying a voltage to the matrix electrode to drive the electro-optical medium, and the drive circuit. An image display device including a reference voltage generator for supplying a predetermined drive voltage to a device, wherein noise removal for removing noise on a voltage supplied to an electro-optic medium between the drive circuit and the reference voltage generator. A circuit is interposed, and the noise removal circuit has an integrator, a changeover switch, and an open / close switch. Regarding the changeover switch, the output terminal is connected to the input terminal of the drive circuit, and one of the input side The switching terminal A of is connected to the output terminal of the reference voltage generator, the other switching terminal B on the input side is connected to the output terminal of the integrator, and one of the integrators is The input terminal of is connected to a predetermined noise detection position through the open / close switch, and the other input terminals are configured to be supplied with a reference voltage generated from the reference voltage generator as an offset voltage. An image display device characterized by. 2. The image display device according to claim 1, wherein the noise detection position is a supply voltage input portion to the drive circuit. 3. The image display device according to claim 1, wherein a dummy electrode is provided on the electrode substrate, and the noise is detected from the dummy electrode. 4. A method for driving the image display device according to claim 1, wherein noise is sampled with the changeover switch connected to the changeover terminal A side and the open / close switch closed. A noise sampling period for converting to a constant voltage according to the effective value of the noise, and then a hold period for supplying the constant voltage to the drive circuit with the open / close switch opened and the changeover switch connected to the changeover terminal B side; Then, the opening / closing switch is opened, and the reset switch performs a reset period in which the integrator is reset in either state of the terminal A side or the terminal B side to return to the initial state, and a sequence is repeated. Driving method of display device.