JP4910356B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device such as a liquid crystal television using a liquid crystal panel.

  In recent years, liquid crystal display devices have been recognized for the benefits of improved image quality and thinness, and have been drastically reduced in price, and in addition to PC monitors and commercial display terminals, there is a rapid demand for home television receivers. It is expanding. The liquid crystal panel operates based on various timing pulses for driving generated from a clock signal, a horizontal synchronizing signal, and a vertical synchronizing signal (a signal indicating a video valid period called a DE signal depending on the panel) input to the panel.

  In the liquid crystal panel, video data is normally written to the liquid crystal pixels sequentially scanned downward from the line at the upper end of the screen every horizontal period, and the data is updated every vertical period. Usually, since the clock frequency, the horizontal synchronization frequency, and the vertical synchronization frequency are constant at a predetermined frequency, they are always scanned from top to bottom in the vertical direction of the screen at a constant speed.

  By the way, in recent years, liquid crystal panels have achieved high-speed response, and while moving image display performance has reached a practically acceptable level, it is still far from that of CRT, and realizes display quality with higher image quality. Therefore, the improvement of blurring of moving images is one of the important development issues of liquid crystal display devices. As a cause of such blurring of moving images, there are well-known ones caused by the liquid crystal driving principle of hold-type display and those caused by the response speed of the liquid crystal itself not being sufficiently fast.

  As one of the techniques for improving the blurring of moving images by the former, for example, Patent Document 1 shows a configuration in which a backlight is divided into N blocks in the vertical direction and sequentially turned on and off. On the other hand, in order to improve the blurring of the moving image due to the latter, a so-called overdrive circuit that determines the gradation for actually driving the liquid crystal from the current video signal and the video signal one frame before is generally used. It is equipped.

  Here, especially when watching the movie, if the image quality mode of the liquid crystal display device is set to cinema mode, etc., and the setting is made to suppress the brightness, the other display modes with less heat generation of the backlight and inverter circuit The panel temperature is further reduced. Since the response of the liquid crystal display device is highly dependent on temperature, for example, Patent Document 2 discloses a configuration in which the above-described overdrive LUT is switched based on information from a temperature sensor.

  Further, in general, a liquid crystal display device has a function of adjusting screen brightness by PWM dimming (burst dimming) of a backlight. PWM dimming sometimes generates noise on the display screen and may affect the display quality. Cases in which PWM dimming affects an image include a case in which a signal or circuit outside the panel module is affected, and a case in which the light is affected within the panel module. In the former, for example, noise resulting from PWM dimming is included in an analog video signal input to the display device, and eventually appears on the final display screen. In the latter case, fluctuations in power supply voltage and noise caused by PWM dimming affect the liquid crystal drive circuit in the panel module, and lighting / extinguishing of the lamp itself affects the characteristics of the pixel TFT of the panel and appears on the display screen. is there.

A method of synchronizing the PWM dimming signal with the vertical synchronizing signal is one of effective means for preventing the beat-like interference from being recognized on the screen by affecting the analog video signal input to the display device. However, in terms of noise superposition in the panel module, there are many cases where fixed horizontal stripe noise as shown in FIG. 14 is easily recognized. In such a case, Patent Document 3 discloses a configuration in which the backlight is divided into a plurality of blocks, controlled by different PWM dimming signals, and those dimming signals are switched. By adopting a configuration as shown in Patent Document 3, the noise component on the screen becomes weak and the noise phase is not fixed, so that the noise can be improved.
JP-A-11-202285 Japanese Patent Laid-Open No. 2005-4203 JP 2004-259510 A

  However, the conventional configuration has the following problems. First, the present invention has a problem that when the display performance is improved by dividing the backlight into N blocks in the vertical direction and sequentially turning on and off, there is a large difference in improvement effect depending on the line (position in the vertical direction). Found. For example, FIG. 16 shows the relationship between the light emission area of the backlight divided into four blocks and the liquid crystal panel in the liquid crystal display device configured as shown in FIG. For example, consider the n-k line in the same backlight block as the n-th line near the center of the second backlight block and above the k-th line from the n-th line.

  When the relationship between the transmittance transition (hereinafter referred to as a response waveform) with respect to the liquid crystal image change in the n-th line and the lighting phase of the lamp is the relationship shown in FIG. 17A, the pixel of the video data in the n-k line. Writing to the flash occurs for k lines earlier than the nth line, but the lamp lighting is the same as that of the nth line. Therefore, as shown in FIG. 17B, the relationship between the liquid crystal response waveform and the lamp lighting phase is Changes, and the effect of improving the video display performance changes.

  As shown in FIG. 18A, the relationship between the vertical screen position and the moving image display performance improvement effect changes corresponding to the divided backlight block, and the improvement effect changes within the screen, so that the improvement is sufficient. An area where the effect cannot be obtained occurs. It is possible to solve this problem by increasing the number of blocks. For example, a normal backlight of 32 inches has about 16 to 20 lamps, but in general, it can be divided equally. If you think about it, the number of divisions will be limited, and there are also examples that use U-shaped lamps, connect the panel on one side of a straight lamp or a panel with half the number of lamps, and use it like a U-shaped lamp. The number of cases where only control equivalent to half the number of lamps can be increased. If the number of divisions is increased before that, there is a problem that the cost of the inverter circuit and the control circuit increases.

  In addition, in order to reduce screen noise by PWM dimming, an inverter circuit and dimming waveform generation circuit are required independently in a configuration in which each divided backlight is driven by PWM dimming signals having different frequencies. The circuit becomes complicated and expensive. Further, since the operation of the inverter circuit becomes asynchronous with respect to the input video signal, there is a possibility that beat disturbance is recognized.

  Furthermore, as another problem, particularly in a large-sized liquid crystal panel, when the temperature difference between the upper side and the lower side of the screen is large, the improvement degree of the moving image display performance is greatly different in the vertical direction of the screen. In addition, in a configuration in which a plurality of overdrive look-up tables are prepared and switched according to temperature in order to improve moving image display performance, circuit costs such as a memory capacity for storing look-up table data and a temperature sensor increase. In particular, over-drive temperature control is harder to introduce in low-inch sets where price competition is severe.

  In order to solve these problems, the first invention is a timing control circuit that receives a horizontal synchronizing signal and a vertical synchronizing signal and generates various timing pulses of a liquid crystal driving circuit synchronized with them, and operates by the timing pulse. And a liquid crystal panel having a gate driver circuit that sequentially drives and drives a plurality of gate wirings connected to the pixel TFT, and is divided into N in the scanning direction of the gate driver, and each performs lighting control independently. In the liquid crystal display device having the backlight device configured as described above and the video signal timing modulation circuit that changes the frequency of the synchronizing signal of the video signal and the phase of the video signal with respect to the synchronizing signal and outputs the same to the liquid crystal panel. The divided backlight devices are sequentially turned on and off in synchronization with the vertical synchronization signal input to the liquid crystal panel. In addition, by modulating the frequency of the horizontal synchronizing signal input to the liquid crystal panel within one frame corresponding to the division of the backlight device, the timing of writing data to the liquid crystal pixels and the backlight device The phase relationship with the timing of turning on / off is made more uniform in the liquid crystal screen.

  As another invention, a horizontal control signal and a vertical synchronization signal are inputted, a timing control circuit for generating various timing pulses of the liquid crystal driving circuit synchronized therewith, and operated by the timing pulse and connected to the pixel TFT. Telecine video detection that detects a telecine video from the regularity of the video signal for each frame and a liquid crystal panel equipped with a gate driver circuit that sequentially scans and drives a plurality of gate wirings, and detects a frame in which the video change occurs In a liquid crystal display device having a circuit and a video signal timing modulation circuit for changing the frequency of the synchronizing signal of the video signal and the phase of the video signal with respect to the synchronizing signal and outputting the same to the liquid crystal panel, the video change obtained from the telecine video detecting circuit The vertical phase of the video signal input to the LCD panel is synchronized with the generated frame. Changes the vertical synchronizing frequency, as the video signal of the next frame is a long time to be written into the liquid crystal pixels, the temperature of the liquid crystal panel to compensate for the lack of overdrive when dropped.

  As another invention, the horizontal synchronization frequency is modulated so that the time until the video signal of the next frame is written to the liquid crystal pixels in a specific area of the screen is increased in synchronization with the frame where the video change occurs. In addition, the shortage of overdrive in a specific region due to the temperature difference in the vertical direction in the liquid crystal screen is compensated.

  As another invention, a horizontal control signal and a vertical synchronization signal are inputted, a timing control circuit for generating various timing pulses of the liquid crystal driving circuit synchronized therewith, and operated by the timing pulse and connected to the pixel TFT. A liquid crystal panel equipped with a gate driver circuit that scans and drives a plurality of gate wirings sequentially, a backlight device capable of adjusting the brightness by duty control of the pulse signal, and a pulse signal for controlling the backlight In a liquid crystal display device having a backlight control circuit that performs and a video signal timing modulation circuit that changes the frequency of the synchronization signal of the video signal and the phase of the video signal with respect to the synchronization signal and outputs the same to the liquid crystal panel, Is the same as the vertical sync signal of the video signal input to the timing modulation circuit. Is allowed, the video signal input to the panel, by changing the vertical phase for each frame, the phase of the video signal of the write pulse signal for the backlight dimming to the liquid crystal pixel from being fixed.

  According to the present invention, in the liquid crystal display device in which the blur of the moving image due to the divided lighting of the backlight is improved, the improvement effect can be made more uniform in the entire area of the screen, and a higher image quality liquid crystal display device can be provided. . In addition, it is possible to provide a liquid crystal display device with higher image quality in which noise that tends to appear on the liquid crystal display screen is reduced when PWM dimming of the backlight of the liquid crystal display device is performed in synchronization with the vertical synchronization frequency.

  In addition, when watching a movie on a liquid crystal display device, it is possible to provide a high-quality video display device with less blur of moving images without introducing temperature control in the overdrive circuit even in a state where the brightness of the backlight is reduced. . Furthermore, even when the temperature difference in the vertical direction of the screen is large, blurring of moving images can be improved over the entire lower surface.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a liquid crystal display device according to Embodiment 1 of the present invention. As shown in FIG. 1, the liquid crystal display device of the present invention includes a liquid crystal module 10 including a backlight device 11 and a liquid crystal panel 12, a lighting control circuit 17 that controls turning on and off of the backlight device 11, and broadcasting. A signal processing circuit 15 for performing a predetermined process for displaying the video signal extracted from the broadcast signal transmitted from the station on the liquid crystal panel described above, and for outputting the video signal processed by the signal processing circuit to the liquid crystal panel. And a signal modulation circuit 16 for adjusting the timing.

  Here, the liquid crystal panel 12 includes a timing controller and a drive circuit for receiving horizontal synchronization signals and vertical synchronization signals and generating various timing pulses of the liquid crystal drive circuit synchronized with the synchronization signals. . The backlight device 11 includes a fluorescent lamp 13 and an inverter circuit 14 which are arranged on the back surface of the liquid crystal panel 12 and can be controlled by dividing into four in the vertical direction. The signal processing circuit 15 represents various video signal processing circuits necessary for the liquid crystal display device. For example, a color demodulation circuit, a gamma correction circuit, a contrast adjustment circuit, an NR circuit, and an image quality correction circuit. Specifically, the signal modulation circuit 16 changes the frequency of the synchronization signal of the video signal output from the signal processing circuit 15 and the phase of the video signal with respect to the synchronization signal, and outputs the result to the liquid crystal panel 12.

  Here, the vertical synchronization frequency refers to the number of times the display rewrites the screen per second, and refers to the screen drawing speed of the display. The horizontal synchronization frequency is the number of lines (horizontal lines) drawn per second by the display and refers to the screen drawing speed of the display.

  In the above liquid crystal display device, the liquid crystal panel is divided into four in the vertical direction to constitute the fluorescent lamp 13 and the inverter circuit 14, but the present invention is not limited to this, and the size of the liquid crystal panel It is also possible to change according to. In the above liquid crystal display device, a vertical oscillator signal and a horizontal synchronization signal are input, and a reference oscillator (not shown) that generates a reference oscillation clock to generate various timing pulses of the liquid crystal driving circuit synchronized therewith. The lighting control circuit is also controlled based on this clock.

  Next, the processing method of the liquid crystal display device of the present invention will be described with reference to FIGS. First, in the signal processing circuit 15, the above-described color demodulation, gamma correction, contrast adjustment, noise reduction, and image quality correction are performed on the video signal input to the liquid crystal display device. Next, the timing at which the video signal to be displayed on the liquid crystal panel is output is adjusted by changing the frequency of the synchronizing signal of the video signal or the phase of the video signal with respect to the synchronizing signal. On the other hand, the lighting control means 17 receives the control signal and the synchronization signal output from the signal processing circuit, and synchronizes with the synchronization signal to supply power to the lamp 13 connected to the back surface of the liquid crystal panel by the inverter 14. Do through.

  Here, the signal modulation circuit 16 will be described in detail with reference to FIGS. FIG. 2 shows the phase relationship between the lighting and extinguishing of the backlight and the synchronization signal and video signal for each line when the video signal output from the signal processing circuit 15 is output without being processed in the signal modulation circuit 16. It is a thing. Next, FIG. 3 shows the phase relationship between the lighting and extinguishing of the backlight and the synchronizing signal and video signal for each line when the frequency of the synchronizing signal is changed in the signal modulation circuit 16. Furthermore, FIG. 4 shows the phase relationship between the lighting and extinguishing of the backlight and the synchronization signal and the video signal for each line when the phase of the video signal with respect to the synchronization signal is changed in the signal modulation circuit 16. .

  FIG. 2 shows one of the blocks divided into a plurality of blocks (in the case of the present embodiment, as described above, divided into four in the vertical direction). It is composed of k to n + k lines. As described above, in FIG. 2, the phase of the response waveform of the liquid crystal and the lighting phase of the backlight do not match, and the improvement effect of the moving image display performance cannot be made uniform.

  On the other hand, as shown in FIG. 3, in the signal modulation circuit 16, when the synchronization frequency of the video signal is changed, specifically, the frequency of the synchronization signal of n-1 is higher than nk, , N is higher than n−1, n + 1 is higher than n, and n + 1 to n + k lines are further increased in frequency. Further, when this process is viewed in units of one frame, at least one of the vertical video images is divided into a high frequency period and a low frequency period with respect to the average horizontal synchronization frequency of one frame period. There are four times as many as the number of blocks divided within the effective period.

  Thereby, compared with FIG. 2, the phase of the response waveform of the liquid crystal and the phase of the lighting of the backlight are almost the same, and thereby, the improvement effect of the moving image display performance can be made uniform even in line units. Is possible.

  Similarly, as shown in FIG. 4, in the signal modulation circuit 16, when the phase of the video signal with respect to the synchronization signal is changed, specifically, from the synchronization signal of n-1 rather than n, The start timing is lengthened, and further, the start timing of the video signal is lengthened from the synchronization signal of n−k rather than n−1. Next, the start timing of the video signal is shortened from the synchronization signal of n + 1 rather than n, and the start timing of the video signal is shortened from the synchronization signal of n + k than n + 1.

  Thereby, compared with FIG. 2, the phase of the response waveform of the liquid crystal and the phase of the lighting of the backlight are almost the same, and thereby, the improvement effect of the moving image display performance can be made uniform even in line units. Is possible.

  Here, in the liquid crystal display device configured as described above, the video signal output from the signal processing circuit 15 is output at a constant period based on a predetermined horizontal synchronization frequency. An image diagram of this video output is shown in FIG. In this embodiment, the video signal timing modulation circuit 16 is configured to output at least two types of horizontal synchronization frequencies by designating a region, and outputs a video signal near the boundary of the backlight device divided into a plurality of blocks. When this is done, the horizontal synchronization frequency is output lower than the horizontal synchronization frequency (fH1) of the other region (fH2). FIG. 5B shows an image diagram of the video signal and the synchronization signal output seen in the vertical period at this time.

  With such a process, the phase relationship between the video signal writing and the backlight is changed in the nth line near the center of the block shown in FIG. 16 and the nk line above the nth line and the kth line. When considered, the operation of the video signal timing modulation circuit 16 can reduce the difference in phase relationship between the n-th line and the n-k line from the state of FIG. 17 to the state of FIG.

  Depending on the configuration of the video signal timing modulation circuit 16 and the permissible range of the liquid crystal panel 12, as shown in FIG. 5C, a more divided video may be used, or as shown in FIG. 5D. It is also possible to modulate the horizontal synchronization frequency smoothly.

  As described above, by modulating the video signal in accordance with the number of divisions of the backlight, the improvement effect of the moving image display performance having a large variation in the vertical direction of the screen as shown in FIG. 18A is shown in FIG. Thus, it is possible to realize a liquid crystal display device excellent in moving image display performance over the entire screen.

  In the first embodiment, the frequency of the synchronizing signal of the video signal and the phase of the video signal with respect to the synchronizing signal are changed for each line, but the present invention is not limited to this, and for each of a plurality of lines. It is also possible to perform processing for changing the frequency of the synchronizing signal of the video signal and the phase of the video signal relative to the synchronizing signal. As a result, the improvement effect of the moving image display performance can be made uniform, and there is an effect that it is not necessary to perform complicated processing.

(Embodiment 2)
Next, the second embodiment will be described with reference to FIGS. As shown in FIG. 7, in the second embodiment, a telecine video detection circuit 80 is added in addition to the liquid crystal display device described in the first embodiment. The telecine video detection circuit 80 detects a telecine video from the regularity of the video signal for each frame, and detects a frame in which the video change occurs.

  Normally, in a video system with a vertical synchronization frequency of 60 Hz, the same material is output with a periodicity of 2 frames and 3 frames as shown in FIG. (In the interlace method, there are 2 fields and 3 fields, but here, the display on the liquid crystal panel, which is a progressive display, is used as a reference, and one vertical period is one frame.) Therefore, the video changes by 2 frames or 3 frames. Every time.

  The response speed of the liquid crystal changes depending on the temperature. As shown in FIG. 9, when the overdrive process is optimized at the temperature T1, the response is not completed in one frame in the case where the temperature is lower than T0. In the case of high T2, it becomes an excessive response.

  Also, as shown in FIG. 10, since overdrive depends on the liquid crystal writing period (generally, the vertical period), when overdrive is optimized at the vertical synchronization frequency fvs1, the frequency is higher at fvs0 than fvs1. Does not respond in one frame and becomes an excessive response in fvs2 having a low frequency.

  Here, when the user reduces the brightness of the backlight and displays the movie source, the video signal timing modulation circuit 16 shifts the video phase with respect to the vertical synchronization signal at the video change timing obtained from the telecine detection circuit 80. As shown in FIG. 8B, when the image is changed, the writing period to the liquid crystal is set to t2, which is longer than the standard period t1. As shown in FIG. 11, it is possible to compensate for the fact that the temperature falls and does not respond completely by extending the writing cycle, and thus improving the blurring phenomenon of the movie when watching a movie without increasing the number of overdrive LUTs. Can be planned.

  Here, the same effect can be obtained by changing the vertical synchronization frequency so that the vertical period becomes t1 and t2.

  As shown in FIG. 8B, there is a period in which the liquid crystal writing cycle t0 is shorter than the standard t1, but there is no problem with the telecine video because the image does not change.

  Further, FIG. 8C shows an example in which the horizontal synchronization frequency is modulated at the video change timing obtained from the telecine detection 80 and the duty of the video signal is changed with respect to the vertical period.

  Here, the horizontal synchronization frequency is increased by the video signal timing modulation circuit 16 in the video changing frame, and the liquid crystal writing period is maintained at t1 at the upper part of the screen and is increased to t2 at the lower part of the screen. Generally, the liquid crystal panel has a higher temperature at the top of the screen and lower at the bottom of the screen, so the lower the screen, the slower the response of the liquid crystal and the worse the video display performance. It can be mitigated by lengthening the writing cycle.

  In this case as well, there is a case where t0 is shorter than the standard writing cycle t1, but this is not a problem because the timing is the same as described above and the video does not change.

(Embodiment 3)
Next, a third embodiment of the present invention will be described with reference to FIGS. FIG. 12 is a block diagram of a liquid crystal display device according to Embodiment 3 of the present invention. The video signal timing modulation circuit 16 changes the phase of the video signal output to the liquid crystal panel 12 with respect to the vertical synchronization signal for each frame as shown in FIG. With this configuration, the dimming pulse for the backlight device can be changed only by the writing phase to the liquid crystal pixels while being synchronized with the vertical synchronizing signal input to the display device, without increasing the cost of the backlight device. It is possible to improve screen noise due to dimming.

  In the present invention, a liquid crystal panel that inputs a vertical synchronizing signal and a horizontal synchronizing signal has been described. However, the same effect can be obtained in a liquid crystal panel that inputs a signal indicating a video valid period instead of the synchronizing signal.

  The present invention realizes high-quality display with improved motion blur and screen noise at low cost, and is used for a liquid crystal television and a liquid crystal monitor.

1 is a block diagram illustrating a liquid crystal display device according to a first embodiment of the present invention. The figure which shows the phase relationship of the response waveform of a liquid crystal, and the light control pulse of a backlight in Embodiment 1 of this invention The figure which shows the phase relationship of the response waveform of a liquid crystal, and the light control pulse of a backlight in Embodiment 1 of this invention The figure which shows the phase relationship of the response waveform of a liquid crystal, and the light control pulse of a backlight in Embodiment 1 of this invention The figure which shows the relationship between the vertical synchronizing signal and video signal which are input into the liquid crystal panel in Embodiment 1 of this invention The figure which shows the phase relationship of the response waveform of a liquid crystal, and the light control pulse of a backlight in Embodiment 1 of this invention FIG. 3 is a block diagram showing a liquid crystal display device according to a second embodiment of the present invention. The figure which shows the phase relationship of the telecine image and vertical synchronizing signal which are input into the liquid crystal panel in Embodiment 3 of this invention The figure which shows the relationship between the temperature and response waveform of the liquid crystal display device which has the overdrive circuit The figure which shows the relationship between the frequency of a vertical synchronizing signal, and a response waveform of a liquid crystal display device provided with an overdrive circuit The figure which shows the improvement effect of the response waveform of the liquid crystal in Embodiment 2 of this invention Block diagram showing a liquid crystal display device of Embodiment 3 of the present invention The figure which shows the relationship between the vertical synchronizing signal and video signal in Embodiment 3 of this invention. The figure which shows the example of the screen noise by PWM dimming in a prior art Block diagram showing a liquid crystal display device in the prior art The figure which shows the division | segmentation of the backlight apparatus in a prior art, and the display line of a liquid crystal panel The figure which shows the phase relationship of the response waveform of the liquid crystal and the dimming pulse of the backlight in the prior art The figure which shows the improvement effect of the vertical screen position and animated picture display performance of the liquid crystal panel

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal module 11 Backlight apparatus 12 Liquid crystal panel 13 Fluorescent lamp 14 Inverter circuit 15 Video signal processing circuit 16 Video signal timing modulation circuit 17 Lighting control circuit 80 Telecine video detection circuit

Claims (1)

Signal processing means for outputting a video signal, a horizontal synchronizing signal and a vertical synchronizing signal ;
The backlight device is divided into N blocks in the scanning direction of the output of the gate driver circuit, which will be described later, and the backlight device is synchronized with the vertical synchronization signal which is the output of the signal processing means independently for each block. Lighting control means for sequentially turning on and off ;
A high frequency period and a low frequency period are generated with respect to an average horizontal frequency within one frame period based on a frequency of a horizontal synchronizing signal which is an output of the signal processing means, and the generation of the high frequency period is turned on. Signal modulating means corresponding to the lighting and extinguishing timing for each block of the control means ;
A liquid crystal panel that operates based on the output of the signal modulation means and includes a gate driver circuit that sequentially scans and drives a plurality of gate wirings connected to the pixel TFT ;
A liquid crystal display device.

Images