JP3343994B2 - Liquid crystal display - Google Patents

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 suitable for a liquid crystal television receiver using an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal television receiver using an active matrix type liquid crystal display device such as a TFT-LCD (thin film transistor type liquid crystal display device) has been developed. As is well known, the active matrix method directly drives each pixel, and drives a thin film transistor attached to each pixel to apply a voltage to a liquid crystal to form an image.

FIG. 5 is a diagram showing the principle of an active dot matrix type liquid crystal display. As shown in FIG.
The gate lines and the data lines are arranged in a matrix, and each intersection point corresponds to one pixel.

The driving method is to select a gate line corresponding to a scanning line in a line-sequential manner, turn on all the transistors on the selected one gate line, and at the same time, select video data from each data line according to a video signal. Write. This video data is equivalently stored as a charge in the liquid crystal which becomes a capacitor, and continues to drive the liquid crystal until the next signal after one frame comes.

FIG. 6 is a block diagram showing a liquid crystal display device used in a conventional liquid crystal television receiver. In this figure, 1 is a TFT liquid crystal panel, 2a and 2b are source drivers (drivers for driving data lines in the horizontal direction).
The digital video signal corresponding to each pixel of the TFT liquid crystal panel 1 is sampled and output based on the horizontal synchronization signal _HSYNC .

Reference numeral 3 denotes a gate driver for driving the scanning lines, and reference numeral 4 denotes a controller for controlling the source drivers 2a and 2b and the gate driver 3. The controller 4 is supplied with a digital video signal, a clock signal, a horizontal synchronization signal H _SYNC and a vertical synchronization signal V _SYNC . Reference numeral 5 denotes a power supply circuit for supplying power to each unit of the apparatus, and reference numeral 6 denotes a backlight for illuminating the TFT liquid crystal panel.

The controller 4 controls the horizontal synchronizing signal H
_It has a function of generating a horizontal synchronizing signal H _SYNC in a pseudo manner when _SYNC is lost, and compensating for the missing.

[0008]

In the above-described conventional liquid crystal display device, when the horizontal synchronizing signal H _SYNC is lost, the horizontal synchronizing signal H _SYNC is generated in a pseudo manner. In this case, since the video signal is disturbed, there is a problem that a distorted image is displayed on the TFT liquid crystal panel 1.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display device in which an image is not disturbed even if the horizontal synchronizing signal _HSYNC is lost.

[0010]

In order to achieve the above object, a liquid crystal display device according to the present invention is a liquid crystal driving unit which samples a digital video signal corresponding to each pixel of a liquid crystal panel and outputs the sampled video signal based on a horizontal synchronizing signal. In the liquid crystal display device comprising: a detecting means for detecting the state of the horizontal synchronization signal, the liquid crystal drive unit comprises a pair of video data holding unit,
One video data storage unit stores one line every horizontal scanning period.
The operation of sampling and holding video data and the other
One line of video data stored in the video data storage
Output operations are controlled to be executed concurrently.
Is, if the state of the horizontal synchronization signal is detected that not normal by the detecting means, sampling the video data
Output from the video data holding unit on the
One line sampled and held in the image data holding unit
The preceding video data is output.

[0011]

[0012]

According to the present invention, when the state of the horizontal synchronizing signal is not normal (for example, missing or disturbed), the previously sampled video data (for example, one line before) is substituted for the video data obtained by sampling at this time. Video data). Therefore, when the state of the horizontal synchronization signal is not normal, the video data before the normal state is output.
The image is not disturbed by the horizontal synchronization signal.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a television receiver to which the liquid crystal display device according to the present invention is applied. In FIG. 1, reference numeral 10 denotes an antenna, and reference numeral 11 denotes a tuner, which selectively selects a desired one from broadcast signals received via the antenna 10 and outputs the selected signal. Reference numeral 12 denotes an intermediate frequency amplifier circuit that converts a high frequency signal output from the tuner 11 into an intermediate frequency, amplifies and outputs the intermediate frequency signal.

13 is a video detection circuit for demodulating a video signal,
14 is an audio detection circuit for demodulating the audio signal, 15 is a volume adjustment circuit for adjusting the level of the audio signal, 16 is an audio amplification circuit for amplifying the audio signal, and 17 is a speaker.
Reference numeral 18 denotes a synchronization signal processing circuit having a built-in PLL circuit.
Synchronizes the phase of the input synchronization signal with the horizontal and vertical drive signals.

Reference numeral 19 denotes a chroma processing circuit, which is a color AP.
It incorporates a C circuit, a color demodulation circuit, an RGB AC video signal forming circuit, and the like. Reference numeral 20 denotes a source driver and a gate driver for driving the TFT liquid crystal panel 21 (the source drivers 2a and 2b and the gate driver 3 shown in FIG. 6).
). The source driver has a sample and hold circuit as in the conventional case.

FIGS. 2 and 3 show the sample and hold circuits 50 and 51 of each pixel in the source driver. In particular, FIG. 2 shows the parallel 2 latch sample and hold circuit 50 and FIG. 1 shows a serial 2 latch sample hold circuit 51.

The operation of these sample-and-hold circuits will be described. First, in the parallel 2-latch sample-and-hold circuit, the switches SW _a and SW _d are turned on and the switch S
By turning off W _b and SW _c , the video data is stored in the capacitor C 1, while the video data of the (n−1) th line before the one stored in the capacitor C 2 is output via the output buffer block 52. You.

[0018]

According to the present invention, when the state of the horizontal synchronizing signal is not normal, the video data is sampled.
Output from the video data holding unit on the
Since the video data of one line before that is sampled and held in the holding unit is output, the image is not disturbed due to the failure of the horizontal synchronization signal.

Next, the serial second latch sample hold circuit 51, when sampling the n-th line, after the switch SW _e is turned on, the switch SWf is sampled each video data in a state of being turned off, n + 1 line until sampling the eye, the switch SW _f is turned on, the image data stored in the capacitor C3 is output at the same time stored in the capacitor C4.

FIG. 4 is a timing chart of control signals for controlling the parallel 2-latch sample-hold circuit 50 and the serial 2-latch sample-hold circuit 51. In particular, signals A, B, C, D, and F are control signals used in parallel 2-latch sample-hold circuit 50, and signals A, B, C, and E are control signals used in serial 2-latch sample-hold circuit 51. Signal.

Parallel 2 latch sample hold circuit 5
Signal used to 0 A, B, C, D, of F, the signal A is a signal for turning on the switch SW _a of the first pixel, the signal B is a signal for turning on the switch SW _a of second pixel, signal C it is a signal for turning on the switch SW _a final th pixel.
Signal D is a signal for turning on the switch SW _d of all the pixels, the signal F is a signal for reversing the switching in the next line.

On the other hand, among the serial 2 signal A to be used for latching the sample hold circuit 51, B, C, E, signals A, B, C is a signal for turning on the switch SW _e for each pixel in the same manner as described above, signal E it is a signal for turning on the switch SW _f of all the pixels.

Referring back to FIG. 1, reference numeral 22 denotes a controller for controlling the apparatus, which includes a CPU, a RAM, and a ROM (not shown). A program for controlling the CPU is written in the ROM. The controller 22
The horizontal synchronizing signal output from the synchronizing signal processing circuit 18 is input, and detection of loss and detection of disturbance are performed.

In this case, when the lack or disturbance of the horizontal synchronizing signal is detected, a control signal is supplied to the liquid crystal drive section 20. Upon input of the control signal from the controller 22, the liquid crystal drive section 20 inhibits the output of the newly sampled video data and outputs the video data sampled one line before. Note that the lack and disturbance of the synchronization signal mainly occur due to a weak electric field, noise, or the like.

Reference numeral 23 denotes a backlight which is turned on by the supply of lamp power and emits light from the back of the TFT liquid crystal panel 21. The liquid crystal drive section 20 and the TFT liquid crystal panel 2
1, the controller 22, and the backlight 23 constitute the liquid crystal display device 100. The controller 22 corresponds to a detecting unit.

Next, the liquid crystal display device 100 having the above configuration will be described.
The operation of will be described. In this case, the sample and hold circuit used for the source driver is the parallel 2-latch sample and hold circuit 50 shown in FIG.

When the controller 22 inputs video data from which the horizontal synchronizing signal H _SYNC of the nth line is missing,
A control signal that determines this lack is supplied to the liquid crystal drive unit 20. In this case, when this control signal is supplied to the liquid crystal driving unit 20, the liquid crystal driving unit 20 has n + 1 lines.
Outputs the video data of the (n-1) th line instead of the video data of the nth line. Specifically, since the signal E is not inverted at the switching of the nth line and the (n + 1) th line, it is inverted at the switching of the next (n + 1) th line and the (n + 2) th line.

Further, the horizontal synchronization signal H is also applied to the (n + 1) th line.
_SYNCIs missing, the signal E is cut off as described above.
The switching is further delayed by one line. After that, the horizontal sync signal
Issue H S_YNCInput until video data that is not missing
The same processing is performed and stored in the capacitor C2 on the (n-1) th line.
Output the obtained normal video data.

When the serial 2-latch sample-and-hold circuit 51 shown in FIG. 3 is used as the sample-and-hold circuit, the signals A, B, and C are not output, and the video data stored in the capacitor C4 one line before. Is output. Therefore, even when the serial 2 latch sample hold circuit 51 is used, a clear image without disturbance is displayed.

If the signal E is not inverted, the direction of the applied voltage applied to the TFT liquid crystal panel 21 is continuous for two lines, but is inverted in the next field. There is no need to worry about deterioration due to the addition.

In the above embodiment, the horizontal synchronizing signal H
_Although the previous normal video data is used when _SYNC is lost, the previous normal video data may be used even when the horizontal synchronization signal H _SYNC is disturbed.

[0032]

According to the present invention, when the state of the horizontal synchronization signal is not normal, the previously sampled normal video data is output instead of the newly sampled video data. With the configuration, the image is not disturbed due to the failure of the horizontal synchronization signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a liquid crystal television receiver to which a liquid crystal display device according to the present invention is applied.

FIG. 2 is a block diagram illustrating an example of a sample and hold circuit used for a source driver of the liquid crystal display device of the embodiment.

FIG. 3 is a block diagram showing another example of the sample and hold circuit used for the source driver of the liquid crystal display device of the embodiment.

FIG. 4 is a timing chart showing an operation of a sample and hold circuit used for a source driver of the liquid crystal display device of the embodiment.

FIG. 5 is a diagram illustrating the principle of an active dot matrix type liquid crystal display.

FIG. 6 is a block diagram showing a conventional liquid crystal display device.

[Explanation of symbols]

 20 LCD drive unit 22 Controller (detection means)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-280674 (JP, A) JP-A-3-244285 (JP, A) JP-A-63-46079 (JP, A) JP-A-6-46079 319097 (JP, A) JP-A-4-51685 (JP, A) JP-A-3-254529 (JP, A) JP-A-3-44379 (JP, A) JP-A-62-110979 (JP, A) (58) Surveyed field (Int.Cl. ⁷ , DB name) G09G 3/00-5/42 H04N 5/66-5/70 G02F 1/133 505-580

Claims (1)

(57) [Claims] 1. A liquid crystal display device comprising a liquid crystal drive section for sampling a digital video signal corresponding to each pixel of a liquid crystal panel and outputting the digital video signal based on a horizontal synchronization signal. The liquid crystal driving unit includes a pair of video data holding units,
One line every horizontal scanning period
The operation of sampling and holding the image data and the other image
Outputs one line of video data held in the image data holding unit.
Are controlled to be performed in parallel.
This is the state of the horizontal synchronization signal is not normal by the detecting means
If the bets is detected, sampling the video data
Output from the video data holding unit on the
A liquid crystal display device for outputting the video data of one line before which is sampled and held in a data holding unit.