JPH01136483A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To eliminate noise component and to display a still picture with high picture quality by reading a voltage of a video signal before one display period stored in each electrode capacitance of each picture element of each line on a display panel in the case of displaying of still picture by a capacitor at the input side of an inverting amplifier, inverting the polarity and applying it to a liquid crystal element through amplification. CONSTITUTION:In the case of still picture display, gate signals X1-Xn outputted from an X driver circuit go sequentially to a high level at an interval of a short period taub for refresh signal at an input terminal 29. Moreover, the refresh signal at the input terminal 29 goes to a high level at each period taub. Just before picture elements 12a, 12b of each line are scanned, the video signal of one preceding line picture element is resident as noise component in capacitors 30, 30'. Thus, the contact 20b of the switch 20 is switched for period taub only based on the high level of the refresh signal. In this case, the discharge path of the capacitors 30, 30' is formed by the switch 20 and the resident signal component in the capacitors 30, 30' is completely discharged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device having a still image display function.

[Conventional technology]

Conventionally, a color liquid crystal television receiver, which is an example of a liquid crystal display device, is often configured as shown in Fig. 4 using a twisted nematic (CTN type) liquid crystal display panel, and an antenna (1). The received signal is input to the tuner (2), and the video intermediate frequency signal of the desired channel is output from the tuner (2) to the video detection circuit (4) via the video intermediate frequency amplification circuit (3).

Then, the video intermediate frequency signal is detected as a video signal by the detection circuit (4), and the video @ signal is output from the detection circuit (4) to the color demodulation circuit (5) and the sync separation circuit (6), and the detection circuit The audio signal included in the detection signal (4) is transmitted to the speaker (8) via the audio detection amplification circuit (7).
).

Furthermore, the demodulation circuit (5) converts the input video signal into three primary color signals, and the demodulation circuit (5) converts the input video signal into three primary color signals.
The primary color signal is sent to the color switching circuit αG via the polarity inversion circuit (9).
is input.

In addition, the synchronization separation circuit (6) separates and extracts the same signal of the input video signal, and the synchronization separation circuit (6) separates and extracts the same signal of the input video signal.
The synchronizing signal of 6) is supplied to the control signal generation circuit Ql),
The generation circuit 0υ generates various timing control signals for timing control of the polarity inversion circuit (9), the one-color switching circuit α0, and the x and Y driver circuits described later.

Then, based on the control signal from the generating circuit αυ, the operation of the vertical X driver 48 circuit head and the horizontal Y driver circuit a4, which drive the color display liquid crystal display panel (2), is controlled, and the driver circuit (to) is controlled. From display spring/1/(to)
Display spring iv a is connected to the gate signal terminal for each line of
Gate signal X+ to drive each horizontal line of 'a line-sequentially
,..., Xn is output, and the driver circuit σ
From →, the three primary color signals are sequentially output as display video signals Y+, .

By the way, as shown in FIG. 5, each pixel in a matrix array of display spring/I/Q 211 in. One end of the liquid crystal element Q4 is connected to the source (S) of the transistor αG, and the other end is connected to the common electrode terminal of all pixels (
C).

Further, the transistor αe has a gate signal Xi (, i=o, . . . , n
), that is, the input terminal of the video signal Yj (j=1. terminal, that is, the video input terminal (yj).

In addition, in order to drive the three primary colors, the liquid crystal element α of each pixel is actually divided into three parts according to the color scheme of the three primary colors, and each divided area is divided into three parts. The kings are applied sequentially.

The timing control signal output from the generation circuit αυ to the driver circuit (to) consists of a horizontal synchronization signal for the clock and a vertical synchronization signal for reset, and the driver circuit α1 receives the horizontal synchronization signal for the clock and the reset vertical synchronization signal. The driver circuit C13 is a shift register operated by a vertical timing signal for the video signal.
Gate signal x1 for each line period (hereinafter referred to as lH)
.about.Xn are sequentially output, and transistors IrJ of n pixels of each horizontal fin are turned on at once by IH.

Further, the timing control signal output from the generation circuit aυ to the driver circuit 0.0 is a horizontal synchronization signal for resetting,
A shift register consisting of a clock signal for the display interval of each pixel in the horizontal direction and a control signal for still image display described later, and in which the driver circuit αΦ is operated by the horizontal synchronization signal for resetting and a clock signal for the display interval of each pixel. , m sample-and-hold circuits that sample and hold the output signal of the switching circuit QO using each successive pit of the shift register, and m sample-and-hold circuits that amplify and output the output signal of each sample-and-hold circuit as a video signal Y+-Ym, respectively. and a drive circuit, and sequentially outputs each video signal Y1 to Ym at the display interval.

Therefore, each pixel of display panel α4 has 1
The transistors 06 of m pixels in a line are turned on sequentially, and the transistor αG is connected to the liquid crystal element α of each pixel in one line.
At the same time, for each IH, the transistor α9 of each pixel in the next line is sequentially turned on to turn on the liquid crystal element (
14) Video signals Y+ to Ym via transistor αO
are applied sequentially.

By the way, when a TN type liquid crystal such as the display spring /L/a2 is driven with direct current, the liquid crystal itself undergoes electrolysis, resulting in a significantly shortened lifespan.

Therefore, the TN type liquid crystal is driven with alternating current by changing the polarity of the applied voltage at regular intervals.

In the case of the display panel (6), the inverting circuit (9) changes the polarity of the video signal Y+ -Ym by one field based on the common electrode voltage E (=Earth Rep/L/) as shown in FIG. It is inverted every time and is driven by AC at a display period of one field.

Note that w and w' in FIG. 6 indicate the white level, and B.

B' indicates the black level.

Still, the switching circuitry is the display spring)v (The video signal Y+-Ym of each pixel is divided into three parts and outputted in accordance with the arrangement of the color filter patterns of each of the 12 pixels.

On the other hand, the light transmittance of the liquid crystal element (14) of each pixel changes depending on the potential difference between both ends, and based on the brightness or darkness that occurs at this time, the video signal Y! -Ym screen is displayed.

By the way, in order to display still images in so-called video display devices such as television receivers, it has conventionally been necessary to use a video tape recorder with a still image playback function, or to perform complex still image processing using field memory. It was necessary to add a circuit.

However, in the case of a liquid crystal display device such as the liquid crystal television receiver shown in FIG. 4, for example, each pixel of the display panel 02 has a source (S) of a transistor αG as shown in FIG.
A capacitor αG having a pixel capacitance based on at least the electrode capacitance is present between one end of the liquid crystal element α→ connected to the arc (substrate).

Transistor qO is turned on by IH for each field, and transistor aυ is turned off during the remaining time of each field, so that the converter differential qG charged by turning on transistor αυ is equal to the average of transistor a. Leakage current due to discharge during off-time is extremely small, and during that time, the applied video signal Yj is stored and held, and it operates as a so-called memory.

Therefore, Japanese Patent Publication No. 61-42470 (HO4N5
/66) uses the capacitor OQ to keep the transistor CI5 of each pixel off during the still image display period to prohibit refresh of the liquid crystal element 0, until the charging voltage of the capacitor 06) is discharged and lowered. , display panel αa
It is described that a still image is displayed by driving with a direct current with the charging voltage of a capacitor 0Q, and in this case, a still image can be displayed with a very simple configuration using a capacitor QG.

However, with the method described in the above publication, still images can only be displayed for a relatively short period of several seconds determined by the discharge time of capacitor qQ, and since it is driven by direct current, the lifespan of the display spring /L/(6) is limited. This has the disadvantage that it becomes shorter.

Therefore, Japanese Patent Application Laid-Open No. 58-107782 (HO4N
In 5/66), using the charging voltage of capacitor CLQ, the polarity of the charging voltage of capacitor QQ is reversed and amplified for each field, and then applied again to liquid crystal element 04), and a still image is displayed by AC drive. It describes what to do.

Note that when a still image is displayed and the electrode capacity is insufficient, a capacitor is attached as a capacitor OQ.

[Problem that the invention seeks to solve]

By the way, in the case of still image display described in JP-A-58-107782, immediately before each pixel is scanned, the voltage of the video signal stored in the capacitor ue of each pixel, l field (one display cycle) ago, is During scanning of each pixel, the polarity of the sampled and held voltage is inverted and amplified, and the voltage is applied to the liquid crystal element 04) via the transistor q5 of each pixel.

Since the sample and hold operations are repeated one after another, the voltage of the video signal read out from the capacitor 0Q of the previous pixel remains as a noise component during the sample and hold operation.

Therefore, there is a problem in that the noise component of the video signal applied to the liquid crystal element UΦ of each pixel gradually increases, and still images cannot be displayed with high image quality characteristics.

This invention has been made with the above-mentioned problems in mind.

[Means for solving problems]

Means for solving the above problems will be explained below.

This invention connects a pixel transistor for a display gate to a liquid crystal element of each pixel arranged in a matrix of a liquid crystal display panel, and sequentially turns on each pixel transistor one horizontal line at a time in each display period, and displays A video signal for display whose polarity is inverted periodically is sequentially applied to each of the liquid crystal elements of one line through each pixel transistor for each scan of one line, and the display panel is driven with alternating current, and when a still image is displayed. In the liquid crystal display device, the voltage of the video signal stored in the electrode capacitance of at least one display period before each display period is read out, the polarity is inverted, the voltage is amplified, and the voltage is re-applied to each of the liquid crystal elements. 1
A gate signal terminal for each line of a gate signal that is turned on sequentially with a constant refresh period for each line, a common video signal terminal for each of the pixel transistors for one vertical row of the display panel, and one line for each line. Every scanning period, the voltage of the electrode capacitance of each pixel in the same row is written to the input side capacitor via the pixel transistor and the video signal terminal.

an inverting amplifier that inverts the polarity and amplifies the voltage of the capacitor and outputs the amplified voltage; a discharge switch means that discharges and refreshes the capacitance on the input side immediately before scanning each line; and each row of the video signal terminal of each fin. A technical measure is taken to include a signal injection means for injecting the output signal of the inverting amplifier into the video signal terminal at the scanning timing of .

[For production]

Therefore, according to the liquid crystal display device of the present invention, when displaying a still image, each pixel in one row of the display panel has 4!
The voltage of the video signal stored in the j capacity before the I display period is
After being read out to the capacitor on the input side of the inverting amplifier, the polarity is inverted and amplified when each pixel is scanned, and the signal is applied to the liquid crystal element of each pixel, and a still image is displayed on the display panel by AC drive. Moreover, since the capacitance on the input side is discharged and refreshed immediately before reading out the video signal of each pixel, the video signal applied to each pixel contains noise components such as the video signal of the previous line or pixel. Therefore, high-quality still images can be displayed, and the technical problem is solved.

〔Example〕

Next, the present invention will be explained in detail with reference to FIGS. 1 to 3 showing one embodiment thereof.

In Figure 1, (12a), < 12b) is the fourth
Figure display spring/l/(2) (vertical, horizontal) = (i, j
), (i+t.

These are the pixels of the i and i+x lines of the j-th row provided at the j)-th position, each consisting of a liquid crystal element a, a 1-pixel transistor (to) and a capacitor α forming a pixel capacitor, and the pixel (121) is Transistor Q sieve goo) C
G) is connected to the input terminal of the gate signal Xi from the X driver circuit similar to the driver circuit (to) in FIG.
The gate (G) of the transistor α$ in b) is X.

αη is a Y driver circuit corresponding to the Y driver circuit σ in FIG. The discharge changeover switch (1) has 9 inverting amplifiers Qυ, and the switching piece of the switch handle and the input terminal of the amplifier Qυ are connected to the video signal terminal (y
j).

@, (2), (Foundation) is the sampling switch provided in the pull-hold circuit (G), the normal/static changeover switch, and the sample-hold capacitor, and (C) is the three primary colors from the switching circuit αQ in Figure 4. A video input terminal into which a signal is input as a video signal for display; (E) is a switch 121)
Sampling pulse input terminal for on/off control of
The wire is the input terminal for the display control signal that switches the switch wire to the contacts (23a) and (23b) depending on the normal reception image display and still image display.The wire is the input terminal for the on/off control signal of the amplifier Ql. Amplify the switch wire for each line scan α
From the contact (20a) connected to 9 to the grounded contact (20a)
20b) is an input terminal for a refresh signal that is instantaneously switched.

(1) is a capacitor of parasitic capacitance that occurs between the input side of the amplifier Q]) and the ground, and (to)' is the capacitor for reading that is provided between the input terminal of the amplifier Qv and the ground. Together with the capacitor (to), it forms the input side capacitance of the amplifier.

In addition, in Fig. 1, the display panel (2) in the driver circuit αη
) is shown for each vertical row of the display spring /L/(6).

C]), switch 4, etc. are similarly provided.

Further, the capacitor (to)' is provided only when the capacitance of the capacitor is insufficient.

Sarani, amplifier (I9. switch wire, capacitor (c)
This forms a signal injection means.

When displaying the normal received image, the input terminal
The display control signal becomes low level and the switch wire is switched to the contact point (23a), and at this time, the input terminal from the color switching circuit α1 shown in FIG. 4 is turned on/off based on the sampling clock of the input terminal wire. The sampled three primary color signals are sampled in synchronization with the scanning of each pixel in each i-th row, and the sampled three primary color signals,
That is, the video signal Yj is held in the capacitor (c) via the switch (a) and the capacitor.

On the other hand, during normal reception image display, the gate signal X+-Xn of the X driver circuit is sequentially applied to the transistor 0 for each IH.
It reaches a high level that turns on 9, &<2 (a),
(b) As shown in each, the i-th of one field,
During the 18 scans of each number i++, the gate signal Xi,
Since X1-z becomes high level, pixel (12a).

The transistor 09 (12b) is turned on at the i-th and iz-th IH.

In addition, as shown in Figure 2 (C), the control signal at the input terminal - is set to a high level that turns on the amplifier 01 only when scanning the j-th pixel of IH when each of the gate signals XI to Xn is at a high level. Become.

Therefore, the video signal Yj held in the capacitor (c) is sent from the amplifier to the switch (7) only when scanning the j-th pixels (121) and (12b).
The video signal Yj of the signal terminal <yj> is supplied to the terminal (yj) through the contact (20a) of the pixel (12a
), (12b) are applied to the liquid crystal element a< through the respective transistors Qi19.

Therefore, the video signal Yj of the signal terminal (yj) is applied to the liquid crystal element α of each pixel in the jth line every jth scan of each line.
4, and a normal reception screen is displayed by AC drive in the same manner as in the conventional case shown in FIG.

Next, when displaying a still image, for example, based on the operation of the still image display command button, the display control signal at the input terminal (A) becomes high level as shown in FIG. 3(a), and the switch (C) is turned on. is switched to the contact (23b), and the amplifier
An output signal of is output from the switch (to).

By the way, when the display is switched to still image display, the video signal of each pixel of the screen of the condenser feed IRED of each pixel of the display spring ρ is accumulated and stored.

On the other hand, when displaying a still image, each gate signal X+-Xn outputted from the X driver circuit sequentially becomes high level ~ at intervals of a short period τb for the refresh signal of the input terminal.

As shown in FIGS. 3(b) and 3(c), when the gate signals Xi and Xi++ are turned on during scanning of the i-th and i++-th IHs of the I field, at this time,
The control signal at the input terminal (c) becomes high level only during the j-th scanning period τa of each line shown in FIG.

Further, the refresh signal at the input terminal - becomes high level in each period τb as shown in FIG. 3(e).

Then, the jvfth pixel (121), (+2
b) Immediately before each scan, a capacitor based on the scan of the jth pixel of the previous line.

In particular, since the video signal of the pixel in the previous line remains as a noise component, the contact (20b) is closed for a period τb based on the high level of the refresh signal.
), and at this time, a discharge path for capacitors (1) and 00' is formed by the switch handle, and the remaining signal components of capacitors ■ and 00' are completely discharged, and capacitors (1) and noodles are The discharge is refreshed.

Then, each line of pixels (12a) and (12b) is scanned, and when the gate signals Xi and Xi++ go to high level, the refresh signal goes to low level, and the switch wire switches to the contact point (20a). Painting! (
+2a) and (12b) each transistor αQ is turned on.

Therefore, when scanning the i-th line of the pixel (12a), the period τcK until the amplifier 0I is turned on shown in FIG. The video signal before the l field is the transistor Q! 19, signal terminal (yj
) through the capacitor (to), and then written to the output.

At this time, the combined capacitance of capacitors (7) and (7)' is C
a, the capacitance of the capacitor Qυ is Ci, and the voltage decreases from Vi due to loss in the capacitor. ``Then, in order to compensate for the loss of the video signals written to the capacitors (7) and (a)' and to invert their polarity, the video signals written to the capacitors (to) and (to)' are , amplifier 621), the polarity is inverted and amplified.

Furthermore, the video signal after polarity inversion outputted from the amplifier Q1) is temporarily held in the capacitor, and at the time of scanning each of the j-th pixels (12a) and (12b), that is, during the period τa Based on the control signal of the input terminal (c), the video signal held in the capacitor (c) is sent to the amplifier α9. Switch ■, signal terminal (yj)
.

Pixel (12a), (12
b) Injection is applied to each liquid crystal element α.

Then, by repeating the above-described operations, a still image is displayed on the display spring /v<u.

As is clear from the above description, the period τb in FIG. 3 is the discharge refresh period, and the period τC1τa is the application period for one display during the reading period of the signal one field before.

Therefore, in the case of the above embodiment, the gate signals X+ to Xn
Immediately before scanning each line when each becomes high level,
When the switch (7) switches to the contact point (20b), the residual noise components of the capacitors, etc. are completely removed, and the liquid crystal elements (of each pixel of each line) are The video signal of each line one field before can be applied to 141 with its polarity inverted, and by AC driving, a still image of high quality can be displayed on the display panel α.

By the way, when displaying a still image, the display spring/I
/@ need not be AC driven; for example, based on the discharge characteristics of the capacitor a6, the display spring) V(2) may be AC driven with a display period of several fields; in this case, each gate signal It is sufficient to output Xn, etc. at several field cycles.

Also, for example, by the display control signal of the input terminal (a),
Switch (c) is intermittently switched from contact (23a) to (28b
), received images (moving pictures) and still images are displayed alternately, and so-called strobe display can also be performed.

Of course, the present invention can be applied not only to liquid crystal television receivers but also to various liquid crystal display devices, and the liquid crystal display panel may be either color or monochrome.

〔Effect of the invention〕

As described above, according to the liquid crystal display device of the present invention, when displaying a still image using the video signal stored in the interelectrode capacitance of each pixel of the display panel, each pixel in each row of the display panel The voltage of the video signal stored in the electrode capacitance one display cycle before is read out to the capacitance on the input side of the inverting amplifier, and then the polarity is inverted and amplified when each pixel is scanned, and the voltage is applied to the liquid crystal of each pixel. Since the voltage is applied to the element, it is possible to display a still image on the display panel by AC drive.Moreover, since the capacitance on the input side is discharged and refreshed immediately before reading out the video signal of each pixel, the voltage is applied to each pixel. The applied video signal does not contain noise components such as the video signal of the previous line or pixel, and high quality still images can be displayed.

[Brief explanation of the drawing]

1 to 3 show one embodiment of the liquid crystal display device of the present invention, FIG. 1 is a partial block diagram, and FIGS. 2(a) to 3
(C) is a timing chart for explaining the operation of normal received image display, FIGS. 3(a) to (e) are timing charts for explaining the operation of still image display, and FIG. 4 is a timing chart for explaining the operation of displaying a color LCD television. FIG. 5 is an explanatory diagram of the pixels of the liquid crystal display panel of FIG. 4, and FIG. 6 is an explanatory diagram of the AC drive of FIG. 4. α2...Liquid crystal display panel, 04)...Liquid crystal element, α
[Yes]...Pixel transistor, αQ, H, (7),
w'...Capacitor, αη...Y driver 48 circuit, α
~... Sample hold circuit, q9... Buffer amplifier, ■... Discharge selector switch, 621) - Inverting amplifier, (x+) ~ (xn), (xi), (
xi-z) --- Gate signal terminal, (yI) ~ (ym)
, (yj)...Video signal terminal.

Claims (1)

[Claims] (1) A pixel transistor for a display gate is connected to the liquid crystal element of each pixel arranged in a matrix of a liquid crystal display panel,
Each of the pixel transistors is sequentially turned on one line in the horizontal direction in each display period, and a video signal for display whose polarity is inverted in each display period is passed through each of the pixel transistors for one line every scan of one line. The voltage is applied sequentially to each liquid crystal element, the display panel is driven with AC, and when a still image is displayed, the voltage of the video signal accumulated in the electrode capacitance of each liquid crystal element at least one display period before is read out and the polarity is inverted. a gate signal terminal for each line of a gate signal that sequentially turns on each pixel transistor line by line at a constant refresh period; The common video signal terminal of each pixel transistor for one row in the vertical direction of the panel, and the voltage of the electrode capacitance of each pixel in the same row for each scanning period of one line are applied to the pixel transistor and the video signal terminal. an inverting amplifier that inverts the polarity of the voltage written to the input side capacitor via the input side capacitor and outputs the amplified voltage; and a discharge switch means that discharges and refreshes the input side capacitor immediately before each line is scanned. A liquid crystal display device comprising: signal injection means for injecting the output signal of the inverting amplifier into the video signal terminal at the scanning timing of each row of the video signal terminal of each line.