JP2010113072A - Driving circuit and liquid crystal display device - Google Patents

Abstract

The present invention realizes improvement of moving image characteristics or smoothness of a blurred area during line-of-sight tracking by performing dimming of a backlight of a liquid crystal display device.
A drive circuit for controlling lighting and extinguishing of a backlight, wherein N is an integer of 2 or more, and a cycle for generating a cycle pattern of a backlight lighting period that circulates in N consecutive frame periods Pattern generation means, pulse number setting means for setting the number of lighting pulses in the backlight lighting period, and lighting pulse group for generating and outputting a lighting pulse group based on the set backlight lighting period and lighting pulse number Generating means. When the cyclic frame period is 2, the period pattern of the backlight lighting period is such that the lighting period and extinguishing period of the first frame period and the lighting period and extinguishing period of the second frame period are inverted. The periodic pattern of the backlight lighting period has a relationship in which the lighting period continues as an accumulation of N frame periods.
[Selection] Figure 4

Description

  The present invention relates to a drive circuit and a liquid crystal display device, and more particularly to a technique effective in improving moving image characteristics.

One of the image quality characteristics of liquid crystal display devices is the reproduction characteristics of moving images. The reproduction characteristic of a moving image means how the movement appears on the display screen when a fast moving video signal is displayed. Needless to say, the moving image characteristics of the liquid crystal display device are influenced by the response characteristics of the liquid crystal material, but there are other factors specific to the flat panel.
The following non-patent document 1 (shimodaira) arranges factors that deteriorate the moving image characteristics of a liquid crystal display device, and shows a conventionally proposed improvement method. Among them, hold type display and line-of-sight tracking are explained as factors of image quality deterioration in moving image display. For example, in the case of lighting twice per frame as in a movie, it is shown that a step is seen in an image observed by line-of-sight tracking, resulting in image quality degradation.
The following Patent Document 1 (Kurita) cites the above-mentioned hold type display as the reason why the moving image characteristics of the liquid crystal display device are inferior. Then, the backlight blinks at a duty ratio of 50% while synchronizing with the frame period, so that the display frequency characteristics can be extended to a high frequency range and the moving picture characteristics can be improved as compared with the case of always lighting.
On the other hand, Patent Document 2 below shows a method for improving flicker when performing backlight dimming. The relationship between the display drive frequency (frame frequency) F of the panel and the dimming frequency f of PWM dimming is f = m * F / n (n is an integer greater than 2, m> n and m ≠ 2n) Has been shown to have. And the circuit configuration and operation | movement timing in the case of using a fluorescent lamp as a light source are disclosed.

As prior art documents related to the invention of the present application, there are the following.
Yoshifumi Shimodaira, `` Invited Paper: Fundamental Phenomena Underlying Artifacts Induced by Image Motion and the Solutions for Decreasing the Artifacts on FPDs '', SID2003, pp. 1034-1037 JP-A-9-325715 Japanese Patent No. 3027298

There are the following two main image quality factors for displaying moving images.
(1) The temporal frequency component of the liquid crystal response extends to a high frequency range. (2) The width of the gray blur at the time of line-of-sight tracking is narrow and the change in the gray is smooth. Here, (1) is the hold type. The principle of image quality degradation due to display is represented by frequency components.
The moving image blur of (2) at the time of line-of-sight tracking is a phenomenon explained by the fact that the time response of the liquid crystal of (1) is coordinate-transformed in the two-dimensional direction of the screen by line-of-sight tracking. In addition, the smoothness of the light and shade change during line-of-sight tracking in (2) is the image quality deterioration described in Non-Patent Document 1, and is a deterioration factor that occurs when the backlight blinks.
From the viewpoints of the above (1) and (2), problems of the prior art will be shown.
The above-mentioned Patent Document 1 is a method of blinking a backlight, paying attention to improvement of frequency characteristics. The frequency characteristic of the output signal is improved by providing a backlight turning-on period and a light-off period in the frame period Tf. However, a technique known as the aperture effect of a DA converter that has been conventionally known is merely applied to the display operation.
The liquid crystal display device sequentially writes a display signal based on a video signal to pixels in the screen, and each pixel drives a liquid crystal element based on the written display signal. It is desirable to drive the backlight so that the pixel display timing and the backlight blinking timing are uniform. However, since pixel writing takes time, the display timing varies depending on the position of the pixel in the screen.
When the backlight is lit in a blinking manner, the temporal relationship between the pixel display timing and the backlight blinking timing is not uniform in the screen. As a result, for example, the brightness may be uneven within the screen, or the motion of the moving image may not be displayed correctly. If only the backlight blinks in anticipation of the aperture effect, the above-mentioned timing shift problem occurs, and the improvement of the image quality of the entire screen cannot be expected. Moreover, there is no mention about the image quality at the time of gaze tracking.

Although the above-mentioned patent document 2 has a different purpose, it proposes a method of blinking the backlight as in the above-mentioned patent document 1.
Assuming that a fluorescent lamp is used as the light source, the minimum unit of blinking with respect to the display drive frequency (frame frequency) F for the purpose of eliminating flicker while adjusting the brightness by PWM (pulse width modulation) The driving frequency f of the pulse is f = m × F / n (n is an integer greater than 2, m> n, and m ≠ 2n).
In order to manage the drive frequency, the vertical or horizontal synchronization signal of the display panel is taken in and controlled synchronously.
Here, it is the oscillation signal of the inverter that actually causes the fluorescent lamp to blink. However, the pulse drive frequency f described above is a signal for controlling ON / OFF of the inverter, and does not manage the oscillation signal of the inverter that actually blinks the fluorescent lamp.
An inverter is a conversion device that converts low-voltage DC power into high-frequency (10K to 100 KHz) AC power at a high voltage to generate an applied voltage to a fluorescent lamp. The fluorescent lamp emits light using the oscillation signal of the inverter as discharge energy.
However, as the document itself points out, the time response of the rise and fall of the fluorescent lamp due to inverter oscillation is slow, and the waveform of the light emission output is distorted. Thus, since there is no means for controlling a single light emission pulse that is the minimum unit of light source emission, there is a great difference between the blinking period to be set and the actual light emission period of the fluorescent lamp.

According to the above-mentioned Patent Document 2, for example, when the blinking period is set to blink three or five times in a two-screen display period, the blinking period is overlapped between adjacent frames, and lighting is performed without a gap. Therefore, the change width of the luminance in the display screen is reduced, and flicker can be effectively prevented.
However, in reality, as described above, since it is not a method that can accurately control the rise time of the fluorescent lamp and the fall time of the light extinction, a gap is generated when the light source lighting periods are overlapped between adjacent frames. Become.
Further, since the above-mentioned Patent Document 2 performs backlight dimming using the PWM method, the lighting period is shortened as the light emission is darkened. A gap will occur.
The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to improve the moving image characteristics or to follow the line of sight by adjusting the backlight of the liquid crystal display device. It is an object of the present invention to provide a technique that can realize the smoothness of the blurred area at the time.
The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

Of the inventions disclosed in this application, the outline of typical ones will be briefly described as follows.
In order to solve the above-described problem, the present invention includes means for setting the backlight lighting period so that no gap is generated when the backlight lighting periods are overlapped between adjacent frames. Then, by providing means for interposing a plurality of lighting pulses in the backlight lighting period, the brightness in the lighting period is not biased.
Further, by providing means for propagating the error of the lighting pulse set in a certain lighting period to the next lighting period, a highly accurate lighting pulse is generated. Furthermore, in order to realize the above-described highly accurate control, the backlight is composed of an LED, a combination of an LED and a phosphor, or an OLED.

The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.
According to the present invention, by adjusting the backlight of the liquid crystal display device, it is possible to improve the moving image characteristics or to realize the smoothness of the blurred area at the time of line-of-sight tracking.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In all the drawings for explaining the embodiments, parts having the same functions are given the same reference numerals, and repeated explanation thereof is omitted.
FIG. 17 is a diagram illustrating a basic configuration of a liquid crystal display device. The liquid crystal display device is basically composed of a combination of a liquid crystal display panel 101 and a backlight 100. Here, the liquid crystal display panel 101 forms a screen by arranging a large number of pixels with a small area for controlling the transmittance in a plane and controlling the transmittance of each pixel. A pixel can include R (red), G (green), and B (blue) color filters to display a color image.
The backlight 100 of this embodiment includes a light emitting means such as a light emitting diode (LED), a combination of an LED and a phosphor (for example, a blue excitation white light emitting diode), or an organic light emitting diode (OLED). It is used to emit light so as to illuminate the entire liquid crystal display panel 101.
In order to improve the uniformity of light emission of the backlight 100, a diffusion plate (KB) or the like is disposed between the backlight 100 and the liquid crystal display panel 101 as necessary.
In this way, the light emitted from the backlight 100 is output to the front via the pixels arranged on the liquid crystal display panel 101 described above, and a screen is formed by observing it. For example, to display a screen by inputting a video signal of a television, display with motion by repeating the operation of writing the video signal to the liquid crystal display panel 101 and controlling the transmittance for each pixel at high speed. Is realized.
At this time, the backlight 100 can be driven so as to be constantly lit, or can be driven so as to blink based on some timing. If the property of the displayed screen is measured by a temporal change in the luminance of a certain pixel, the luminance is obtained by combining the temporal change in the transmittance of the liquid crystal display panel 101 and the temporal change in the luminance of the backlight 100. The frequency characteristics of the change will be determined.
Thus, the driving method of the backlight 100 affects the image quality of the display screen.

In general, in a liquid crystal display device, a new video signal is input every frame period, and writing to the liquid crystal display panel 101 is performed based on the content of the signal to perform panel display. The video signal and the scanning method of the liquid crystal display panel 101 include various types such as jumping sequentially, but the present invention does not depend on them, and therefore will not be distinguished below. Further, there are fields, frames, screens, and the like as terms representing the screen configuration. However, the present invention does not depend on them, and therefore will not be distinguished below.
Such an operation of the liquid crystal display panel 101 can be found in a DA converter that converts a digital input signal into an analog output signal with a frame period as a sampling rate. When the response speed of the liquid crystal is sufficiently high, a step-type output is obtained because it immediately follows the change in the input signal. Such a step response can be regarded as a signal obtained by sampling an input signal at a frame period and performing zero-order interpolation (interconnecting frame period intervals with a constant).
However, the actual liquid crystal has a delay, and this response characteristic is approximated by an approximate function (1-EXP (-t)) using an exponential function for each frame period.
By the way, as a method for improving the interpolation accuracy, it is known to shorten the interpolation cycle, increase the sampling rate, or increase the frame frequency.
Increasing the frame frequency shortens the driving period of the liquid crystal and allows the next driving without waiting for settling. Although it is a discrete drive, the output approaches a continuous operation (continuous model).
Increasing the frame frequency in this way has the effect of increasing the accuracy of interpolation. Although not mentioned in the present invention, specifically, the driving frequency of the liquid crystal display panel 101 is converted by converting the input video signal to a high frame frequency using a technique known as a frame interpolation technique, a double speed driving technique, or the like. Can be increased.
As a result, the response characteristic of the liquid crystal display panel 101 is closer to an analog response.

The “hold characteristic” of the liquid crystal display panel 101 described in the prior art refers to the above-described zero-order interpolated output. In other words, it is assumed that the liquid crystal response is sufficiently fast.
By the way, in the analysis of the frequency characteristic of the DA converter, an aperture effect is known in which the reproduction characteristic of the high frequency component is enhanced by inserting a shutter that switches ON and OFF in the output signal path. If the liquid crystal display panel 101 is viewed as a DA converter, blinking the backlight 100 of the liquid crystal display panel 101 is similar to the aperture effect of the DA converter. From this, it can be said that in order to increase the response speed of the liquid crystal display panel 101, it is effective to blink the backlight 100 instead of always lighting.
By the way, the liquid crystal display device sequentially writes display signals based on the video signal to the pixels in the screen, and each pixel drives the liquid crystal element based on the written display signal. It is desirable to drive the backlight 100 so that the pixel display timing and the backlight blinking timing are uniform.
However, since pixel writing takes time, the display timing varies depending on the position of the pixel in the screen. When the backlight 100 is blinked and lit, the temporal relationship between the pixel display timing and the backlight blinking timing becomes non-uniform in the screen.
As a result, for example, the brightness may be uneven within the screen, or the motion of the moving image may not be displayed correctly.
If only the backlight blinks in anticipation of the aperture effect, the above-described timing shift problem occurs, and improvement in image quality cannot be expected.

FIG. 1 shows the relationship between screen display and backlight lighting operation according to the embodiment of the present invention. The screen shown on the left side in the figure is switched in the order of # 1, # 2,... Along the time axis. The backlight 100 has a structure that irradiates the entire liquid crystal screen in a lump. At this time, the operation timing of backlight lighting is represented by a one-dimensional signal along the time axis.
The right side of FIG. 1 shows the backlight lighting signal waveform converted into two-dimensional coordinates of the time axis in the frame and the time axis of frame switching. By this coordinate conversion, it is possible to see the backlight lighting waveform resulting from the accumulation of a plurality of frame periods as well as the backlight lighting waveform within the frame period.
When following the line of sight, the time response of the pixel is observed after being coordinate-transformed as shading in the screen plane. Further, when following the line of sight, the observation is continued while smoothly moving the line of sight in synchronization with the moving object, so that the time responses of the pixels in a plurality of frame periods are observed overlapping.
Here, the time response of the pixel display is obtained by multiplying the backlight lighting within the frame period and the time response of the liquid crystal display panel. When a plurality of frames are overlapped and observed while following the line of sight, if there is a temporal deviation in the blinking of the backlight 100, it will appear as shading unevenness in the planar direction.
In the present embodiment, the backlight 100 is blinked so that the lighting periods overlap without any gap in the accumulation of a plurality of frames, so that it is observed as a smooth time response (that is, a response in the screen plane) similar to the constant lighting. In this way, image quality deterioration in which a step is observed due to blinking of the backlight is avoided.
In this embodiment, the purpose of maintaining the waveform of the lighting period regardless of the brightness adjustment is to aim at preventing image quality deterioration at the time of line-of-sight tracking as a result by overlapping the lighting periods without gaps in the accumulation of a plurality of frames in this way. There is.
On the other hand, as a time response of a single pixel, it goes without saying that there is an effect (aperture effect) that enhances the reproduction characteristics of high-frequency components due to blinking of the backlight. In this way, the present invention can enhance the reproduction characteristics of moving image display and can simultaneously achieve the effect of suppressing image quality deterioration during line-of-sight tracking.

By the way, even if a fluorescent lamp is used, pulsed lighting by inverter oscillation and blinking of the backlight by ON / OFF of the inverter are possible. However, in reality, since it is difficult to control the oscillation frequency of the inverter, the number of lighting pulses and the pulse width cannot be set.
The inverter output is not a square wave, and the light emission output waveform is distorted because there is a time delay in the light emission of the fluorescent lamp. Moreover, since the response speed of ON / OFF of the inverter is slow, the rising and falling of the lighting period cannot be managed with high accuracy. In order to make the brightness variable, the lighting period by the ON and OFF is controlled, but it is difficult to set a high-accuracy brightness for the reasons described above. In the end, the lighting period is changed to adjust the brightness, and as a result, a non-uniform gap occurs in the lighting period as the accumulation between multiple frames. Cannot be realized.
On the other hand, in this embodiment, high-precision control of light emission output is performed by combining an LED having a high-speed time response characteristic, a combination of an LED and a phosphor, or an OLED and a high-speed drive circuit. In addition, it is possible to enhance the reproduction characteristics of moving image display and to achieve both the effects of suppressing image quality deterioration during line-of-sight tracking.

With reference to FIG. 2, moving image blur at the time of line-of-sight tracking, which is one of the image quality deteriorations of the liquid crystal display device, will be described. The principle is described in Non-Patent Document 1 described above, and will be described here using numerical examples.
Here, how the blur of the black and white edge area appears when the white area (numerical value 10) is moving on the screen of the black background (numerical value 0) will be described. The horizontal direction is the arrangement of pixels, the vertical direction is the time elapse of one frame period, and the numbers at each pixel position indicate the display output.
The white area moves a distance of 10 pixels per frame period in the horizontal direction. The left 10 pixels are already white areas, and the signal has been changed. The central 10 pixels have just entered the white region and change to white (10) within one frame period (here, a linear change from 0 to 10). The right 10 pixels are still black.
From this, from the front of the screen, 10 pixels in the central region are seen to change from black (0) to white (10) during the frame period. This is a change of the pixel along the vertical arrow in the figure.
Next, the condition for line-of-sight tracking is added. The line of sight moves in the horizontal direction in synchronization with the movement of the white region (black and white edge). The screen moves discretely in units of 10 pixels and is displayed, but the movement of the following line of sight is assumed to be smooth and continuous. Then, while smoothly moving the line of sight, the user sees a change in black and white while looking at the pixel area around the line of sight. By following the line of sight in this way, the response in the time axis direction of the pixel is observed as shading in the plane direction of the screen. This is a change in pixels along an oblique arrow in the figure.
Next, the condition of backlight blinking is added. All the pixels along the above-mentioned arrow can be observed in the case of always lighting. If the backlight 100 is turned on and off within one frame period, only the pixels corresponding to the lighting period are visually perceived. In this way, the time response obtained by multiplying the pixel and the backlight 100 follows the line of sight, so that the pixel response is felt as shading in the plane direction of the screen.

FIG. 3 is a graph showing the change in shading observed around the black-and-white edge during line-of-sight tracking, obtained by numerical simulation of the above conditions. The horizontal axis is the arrangement of pixels, and the vertical axis is the observed brightness, each corresponding to the previous numerical example.
The observed brightness is calculated by accumulating the display output of the pixel along the oblique arrow in the numerical example. Here, the lighting conditions of the backlight are as follows.
(1) Always on during the frame period (marked with ● in the figure)
(2) Second half lighting during the frame period (marked with ■ in the figure)
(3) Lights blinking within the frame period (▲ in the figure)
As is apparent from the graph of FIG. 3, the backlight 100 is lit in a time-biased manner (while the backlight 100 is lit in the second half of the frame period), whereas the backlight 100 is continuously turned on and off, while it is continuously changing in shades. When doing so, a discontinuous step occurs.
This is because the backlight lighting and extinguishing periods turn on and off the pixel time response (change from black (0) to white (10) in the above example). In any case where the backlight lighting period is the first half, the center, or the second half of the frame period, a discontinuous step is inevitable.
On the other hand, in the case where the backlight 100 is blinked, although the slight difference in level remains, the light and shade change is almost the same as that of the constant lighting. It can be seen that eliminating the time bias by blinking the backlight 100 in this way has an effect of preventing image quality deterioration in the blurred area during line-of-sight tracking.
In this embodiment, the following features are realized by controlling the above-described backlight lighting.
(1) Improvement of video characteristics (extends the frequency component of the display screen to a high frequency range)
(2) Perform backlight dimming (pulse drive of light source) (3) Realize smoothness of blurred area during line-of-sight tracking

In FIG. 4, the structural example of the backlight lighting period of a present Example is shown.
In the present embodiment, the backlight lighting period is continuous in the accumulation of a plurality of frames. FIG. 4 shows three types of square waves (1), (2), and (3) as examples that satisfy the conditions.
(1) includes a lighting period and a light-off period in which one frame period is divided into two, and both are inverted and arranged in adjacent frames.
(2) includes a lighting period and a light extinguishing period obtained by dividing one frame period into three, and both are inverted and arranged in adjacent frames.
(3) includes a lighting period and a light-off period in which one frame period is divided into five, and both are inverted and arranged in adjacent frames.
In summary, the lighting period set in a certain frame period is inverted in the next frame period. In other words, a periodic pattern of lighting and extinguishing is formed so that there is no gap as an accumulation when N frame periods are combined, and the periodic pattern is circulated and used as the number of frames progresses. .
Here, an example of two (N = 2) frame periods is shown, but a plurality of frame periods of three or more (N ≧ 3) can be established. In this embodiment, waveforms other than those shown in the figure can be used as long as the same conditions as described above are satisfied.
Note that the lighting period (4) in FIG. 4 is a configuration of the conventional method (Patent Document 1) shown for comparison, but the backlight lighting period is discontinuous even if a plurality of frames are accumulated. It is clear that the same effect as the embodiment cannot be obtained. Although not shown in the figure, if the backlight lighting period is variably set, there is a gap in the accumulated result, and it is apparent that the same effect as this embodiment cannot be obtained.

In this embodiment, while maintaining the waveform of the lighting period, the lighting pulses generated based on the brightness setting are distributed and arranged inside the lighting period. Of course, it is possible to change the period pattern of the lighting period from (1) to (2), (2) to (3), etc. at any time with some control signal, but the waveform of the lighting period itself is PWM modulated. It is not intended to be controlled by, for example.
In the figure, for the sake of easy understanding, the backlight lighting period and the start position of the frame period are shown in synchronization.
However, this embodiment does not necessarily require that the backlight lighting period and the start position of the frame period be synchronized. In the first place, the writing timing of the display signal to the pixels of the liquid crystal display panel 101 is shifted depending on the screen position. Therefore, even if the phase is adjusted in the pixel at the specific position, the phase is shifted in the pixel at the other position.
Therefore, when the backlight lighting period and the phase of the frame period are fixed as in the waveform (4) according to the prior art shown in the figure, the pixel display condition is fixed depending on the screen position, and a bright screen area, a dark screen An area appears and image quality deteriorates.
In this embodiment, in order to eliminate the image quality degradation due to such a phase shift depending on the screen position, the condition of pixel display is averaged by inverting the backlight lighting period and the extinguishing period in the adjacent frame period. It is characterized by doing. Further, as described above, such blinking of the backlight 100 is also effective in improving the image quality when following the line of sight.
In general, the frame period is set to about 30 frames / second to 240 frames / second. For example, if the lighting period is half of one frame, it takes about 2 ms to 16 ms. The brightness is variable by adjusting the number and width of the lighting pulses arranged in the lighting period. Accordingly, the lighting pulse has a relatively high frequency component, and the lighting pulse itself does not cause visual flicker. Therefore, the arrangement of the lighting pulse has a relatively high degree of freedom, and the method of generating the lighting pulse does not have to be limited to a specific method. Next, a configuration example of the lighting pulse within the lighting period is shown.

FIG. 5 shows a configuration example of lighting pulses arranged in the lighting period of the present embodiment. The horizontal axis is the time axis, and the vertical axis indicates the signal amplitude. A lighting pulse and a lighting period are shown on the time axis.
The lighting pulse is the minimum unit of backlight lighting, and the pulse width and the pulse interval can be variably set as control targets. The signal amplitude of the pulse may be variable, but here the signal amplitude is a binary level of 0 and 1 for simplicity.
A plurality of lighting pulses are arranged inside the lighting period. A combination of lighting pulses within the lighting period is referred to as a lighting pulse group. The time that is not the lighting period is inevitably a light-off period (not shown). Thus, the backlight lighting has two properties, that is, the frequency component of the lighting period and the frequency component of the lighting pulse.
If the lighting pulse is arranged without a gap in the lighting period at the maximum brightness setting, the frequency component depends only on the cycle of the lighting period. If only one lighting pulse is arranged in the lighting period at the lowest brightness setting, the frequency component depends only on the period of the lighting period.
Under the above intermediate condition, the frequency component of the lighting pulse appears. However, since it is a higher frequency component than the lighting period, it is not visually detected. That is, the lighting pulse is used as a means for adjusting the brightness and has little influence on the image quality.
On the other hand, the lighting period has an effect on image quality because the frequency component is close to the frame period. For example, there is an effect of improving the moving image reproduction characteristic by the aperture effect described above. The present invention is characterized by controlling different roles and properties of the lighting period and the lighting pulse.

In this embodiment, brightness adjustment is realized by variably controlling the condition of the lighting pulse in the lighting period while maintaining the waveform of the lighting period.
FIG. 5 shows pulse width modulation (PWM) and pulse frequency modulation (PFM) as a method of controlling the lighting pulse within the lighting period. In the pulse width modulation, a plurality of lighting pulses are arranged in the lighting period, and the time width of each pulse is controlled. If the brightness is set to the minimum, the pulse width is narrow, and if the brightness is set to the maximum, the pulse width is controlled so that all pulses continue without a gap. The number of pulses arranged here may be fixed or variable.
In the pulse frequency modulation, the number of lighting pulses arranged in the lighting period is variably controlled. If the brightness is set to the minimum, the number of pulses is small. If the brightness is set to the maximum, the number of pulses is controlled so that all the pulses are continuous without a gap. Each pulse width may be fixed and variable.
In the method of generating the lighting pulse, the PWM method can have the characteristics of PFM by variably setting the number of pulses. In the PFM method, PWM characteristics can be obtained by variably setting the pulse width. By adopting a control method that combines the features of both methods, there is an effect of increasing the degree of freedom of control. Moreover, you may arrange | position a lighting pulse at random in a lighting period by a certain method. It goes without saying that the signal amplitude of the pulse can be controlled as a method for further increasing the degree of freedom.

FIG. 6 shows a basic configuration example of a lighting pulse generation circuit that is a feature of the present embodiment.
With the backlight light quantity setting value 112 that indicates the brightness of the backlight 100 as an input, the lighting pulse condition setting means 124 calculates a lighting pulse condition signal 114 that indicates a generation condition of a lighting pulse that is arranged within the backlight lighting period. . In response to the result, the lighting pulse group generation / output unit 125 generates and outputs a lighting pulse group signal 115 composed of a plurality of lighting pulses.
The backlight lighting period is arranged so as to repeat over the backlight extinguishing period. The brightness setting value is reflected in the lighting pulse generation condition and does not change the lighting period. If the lighting pulse in the backlight lighting period is set to one and the pulse width is variably set according to the brightness setting value, this is the same operation as the conventional PWM method.
In this embodiment, the number of pulses is variably set according to the brightness setting value. Alternatively, a plurality of lighting pulses are arranged, and the pulse width is variably set according to the brightness setting value. In this way, pulses are arranged as evenly as possible within the backlight lighting period.
While the conventional PWM method changes the ratio between the lighting period and the extinguishing period, the present invention is characterized in that the ratio between the backlight lighting period and the extinguishing period is kept constant. Then, the brightness is adjusted by changing the number and width of lighting pulses within the backlight lighting period. Even when the brightness is set to the minimum, since the lowest brightness setting is practically no light (zero), a lighting pulse having a width in the backlight lighting period can be arranged.

If the writing time of the liquid crystal display panel 101 is taken into consideration, the display timing differs depending on the position of the pixel in the screen. The phase relationship between the operation timings of the backlight 100 and the liquid crystal display panel 101 is not constant over the entire screen.
Therefore, in this embodiment, it is not important to synchronize the synchronization signal included in the video signal with the backlight lighting. Specifically, it is possible to use an independent oscillation circuit without using the synchronization signal extracted by the synchronization signal separation circuit. However, as a matter of course, the synchronization signal extracted by the synchronization signal separation circuit can also be used.
As described above, the operation of the present embodiment can be realized without managing the phase relationship between the two if the accuracy of both the frame period and the backlight lighting period is high. Extremely, if it is assumed that the time response of the liquid crystal display panel 101 is analog (not discrete but continuous), the frame period need not be considered.
For the above reasons, the backlight lighting operation of the present embodiment can be realized without strictly defining a quantitative relationship with a synchronizing signal (in other words, a frame period, a frame frequency, etc.) of a video signal. In this embodiment, the degree of freedom of timing control is high.

FIG. 7 shows a basic configuration example from the input of the video signal to the display in the present embodiment.
The video signal 110 is a signal including a synchronization signal based on some standard. Here, the synchronizing signal extraction and distribution circuit is not shown, but is used as appropriate.
The backlight light quantity setting means 123 inputs the video signal 110 and the brightness of the external environment (not shown) as necessary, and sets the light emission amount of the backlight 100 based on the signal. For example, the maximum value of the video signal in the screen can be detected with reference to the video signal 110, and the maximum value can be used as the backlight light quantity.
If the amplitude range of the video signal is 0 to 255 and the detected maximum value is 100, the amount of backlight light is set to (100/255). At this time, in order to make the maximum value displayed on the liquid crystal display panel 101 coincide with the maximum value 100 of the video signal, the display signal 111 of the liquid crystal display panel 101 is obtained by multiplying the video signal by (255/100). It ’s fine.
In this way, the display signal 111 is corrected and calculated based on the backlight light amount setting value 113 using the display signal processing unit 121. The above calculation method is an example, and other conditions can be added. For example, although not shown in the figure, a means for inputting the brightness of the surrounding environment by a sensor is prepared, and the backlight light amount is set so that the screen is brightened if the surrounding environment is bright, and conversely the screen is darkened if it is dark. You can also.
The lighting pulse condition setting unit 124 receives the backlight light amount setting value 112 and calculates a lighting pulse condition signal 114 indicating a generation condition of the lighting pulse.
The lighting pulse group generation output means 125 generates and outputs a lighting pulse group signal 115 composed of a plurality of lighting pulses based on the lighting pulse generation signal 114. The backlight 100 receives the lighting pulse group signal 115 and emits light. Thus, a display screen is formed by the combination of the backlight 100 and the liquid crystal display panel 101.

FIG. 8 shows an example of a circuit configuration when the backlight 100 is divided into a plurality of parts and driven with a time difference in this embodiment.
For example, the backlight 100 is divided into horizontal stripe regions, and the backlight 100 is turned on based on the writing timing of the liquid crystal display panel 101 in the corresponding region, thereby matching the pixel response with the timing of lighting the backlight. be able to.
For this purpose, a region 122 is divided as an optical / mechanical structure of the backlight 100, and means 122 for detecting the display timing for each divided region of the liquid crystal display panel 101 is prepared in the backlight lighting circuit. Using the detected display timing signal 116, the backlight 100 in the corresponding area is turned on. The dividing method of the backlight 100 is arbitrary and is not limited.

FIG. 9 is a diagram illustrating a configuration example of signals when the backlight 100 is turned on in synchronization with the video signal in the present embodiment.
The video signal transmits data for one screen repeatedly at a frame period (or frame period). FIG. 9 shows an example in which one screen repeats white and black.
The liquid crystal display panel 101 repeatedly displays white and black based on the video signal, but the response speed of the liquid crystal element for each pixel is finite and does not rise or fall immediately. In FIG. 9, the liquid crystal response is approximately shown using an EXP function. However, if the response is sufficiently fast, it approaches a step function. The backlight lighting period is set synchronously or asynchronously with the frame period. Here, for the sake of easy understanding, it is shown in a synchronized manner, but the intended effect can be obtained even if it is not strictly synchronized.
In the first frame, three backlight lighting periods are arranged, and lighting and extinguishing are reversed in the next frame. The time relationship between lighting and extinguishing can be rephrased as a lighting cycle.
The lighting period is configured by arranging lighting pulses as shown in the lower part of FIG. The lighting pulse refers to a pulse signal of the minimum unit for lighting the backlight 100 within the backlight lighting period. The lighting pulse group refers to a set of lighting pulses for lighting the backlight 100 within the backlight lighting period.
The present embodiment is characterized in that the number and shape of pulses arranged in the lighting pulse period are variable while maintaining the waveform of the lighting pulse period. Brightness is controlled by the variable setting of the lighting pulse.
In this way, in this embodiment, (1) improvement of moving image characteristics (extending the frequency component of the display screen to a high frequency), (2) backlight 100 light control (pulse driving of the light source), (3) The effect of realizing the smoothness of the blurred area at the time of line-of-sight tracking can be obtained.

FIG. 10 shows a configuration example of the lighting pulse group generation output means. In this embodiment, the lighting pulse is arranged in the lighting period so as to satisfy the set brightness condition while maintaining the lighting period. The number of lighting pulses and the lighting pulse width are input as the set brightness conditions. The brightness within the lighting period is controlled by a value obtained by multiplying both (number of lighting pulses × lighting pulse width).
First, the lighting pulse number setting means 303 divides the lighting period by a predetermined number based on the inputted number of lighting pulses. This division processing can be realized by performing pulse frequency modulation (PFM) based on the number of lighting pulses and dividing the lighting period by the output frequency.
Next, using the lighting pulse generation means 304, a pulse based on the lighting pulse width is generated at each of the divided time intervals. This pulse generation can be realized by performing pulse width modulation (PWM) based on the number of input lighting pulses and arranging output pulses. By combining both, a lighting pulse group that is a set of lighting pulses within the lighting period is generated.
The lighting period is output repeatedly with the extinguishing period interposed therebetween, and the timing control means 302 is a means for managing the interposition of the lighting pulse group and the extinguishing period with these timings. Switch off.
When the brightness setting is the maximum, the lighting period is completely filled with the lighting pulse. When the brightness setting is low, lighting pulses are scattered within the lighting period. Even if the brightness setting is low, the waveform of the lighting period can be maintained if the pulses are scattered within the lighting period. The above configuration example manages both the number and width of the lighting pulses in order to maintain the waveform of the lighting period. Then, the generated lighting pulse group is output.
The above is a configuration in which the number of lighting pulses and the lighting pulse width are controlled simultaneously, or only one of them can be used to generate and output a lighting pulse group.

Another configuration example of a circuit for generating a lighting pulse within a backlight lighting period is shown. Here, simple and highly accurate pulse generation is realized by utilizing the characteristic of the visual characteristic as a characteristic of a low-pass filter.
First, since the lighting pulse is used as a high-frequency component, it is assumed that the flicker does not necessarily occur even if the pulse is not periodically arranged. Further, since the backlight lighting period is periodically repeated at high speed, even if there is a slight error in a single lighting period, if the error is canceled as an accumulation, the image quality does not deteriorate. Based on the above, an error propagation type procedure is shown.
FIG. 11 schematically shows the procedure for calculating the PWM signal. The horizontal axis is an axis indicating the repetition of the lighting period. This lighting period is combined with an appropriate extinguishing period to perform periodic blinking. The reciprocal of this cycle is the lighting frequency. The vertical axis represents the LED light emission amount, and shows the target value and cumulative value of light emission for each lighting period.
The PWM signal Pw is a binary signal that changes in synchronization with the PWM frequency Pf, and its shortest is called a PWM pulse. The minimum unit of the LED light emission amount is the light emission amount during one lighting pulse period of the PWM signal, and this is the characteristic value W of the LED. In FIG. 11, a plurality of PWM pulses in the lighting period are numbered as (1), (2), (3),.
A characteristic value W (LED light emission amount) is accumulated in the vertical axis direction along with the PWM pulse number. Here, if the target value of the light emission amount is Wt, the PWM pulse number Pw for realizing this is an integer value obtained by dividing the target value Wt by the characteristic value W.
Pw = INT (Wt / W)
Here, INT is an integer operation and is rounded up.
The actual light emission amount is a value obtained by multiplying Pw and W, an error occurs with the target value Wt, and the magnitude is Ew = (Pw · W−Wt).
The present embodiment is characterized in that an error Ew generated in a certain lighting period is propagated to the next lighting period. In the figure, the error propagation procedure is indicated by arrows. The error component has already emitted light at the propagation source and does not emit light at the propagation destination, but the magnitude is accumulated at the propagation destination. In the lighting period of the propagation destination, the light emission amount by the actual PWM pulse is accumulated with the propagated error value as an initial value. If the accumulated value exceeds the target value, the error propagation procedure is performed again. By repeating this procedure, the target value can be achieved on average. In the above description, the target value Wt and the characteristic value W have been described as being constant, but it goes without saying that they can be changed at an appropriate timing.

FIG. 12 shows another procedure for generating the lighting pulse. Period 1 is divided into four, a target value of light emission is set for each divided period, and a light emission pulse by error propagation is output for each of the divided target values. In this example, the target value for the entire period 1 has a relationship four times the target value at the time of division. The vertical axis indicates the target value after the division and the cumulative value of the light emission amount. The horizontal axis represents the generation of the lighting pulse and the error propagation procedure for each divided period (here, one backlight lighting period is divided into four).
Since the lighting pulse 1 has an initial value of 0 and exceeds the target value after four light emissions, the error value exceeding the initial value is propagated to the next lighting pulse 2. Since the lighting pulse 2 has the received error value as an initial value and exceeds the target value in four light emission, the error value is propagated to the next lighting pulse 3. The lighting pulse 3 uses the received error value as an initial value and matches the target value in three light emission, so that the error value 0 is propagated to the next lighting pulse 4. The lighting pulse 4 has the received error value (size is 0) as an initial value, and exceeds the target value by four light emission, so that the error value is propagated to the lighting pulse 1 in the next period 2.
By dividing the lighting period 1 into four and arranging the lighting pulses obtained by the above procedure, the target value of the lighting period 1 is realized. The lighting pulses are output side by side on the time axis with a time interval when the target value is set to the maximum. At this time, if the target value is the maximum, each lighting pulse fills the corresponding backlight lighting period without a gap. If the target value is smaller than the maximum value, the lighting pulses are arranged in a distributed manner within the corresponding backlight lighting period with a gap.
The purpose of dividing the target value is to disperse the lighting pulses in this way. And brightness adjustment is realizable, maintaining the waveform of a backlight lighting period.

In the above description, the example in which the backlight lighting period is equally divided into four has been shown, but the number of divisions is arbitrary, and may be an uneven division with weighting. In the example of FIG. 12, since the last light emission of the lighting pulse 4 exceeds the target value, it does not coincide with the target value in the period 1, but the error can be canceled in the period 2. Periodic flashing can be achieved by inserting an appropriate turn-off time (not shown) between the period 1 and the period 2.
FIG. 13 shows the lighting pulses calculated above arranged side by side on the time axis. The lighting pulses 1, 2, 3, and 4 have a ratio of 4, 4, 3, and 4, respectively. Each lighting pulse is arranged at an interval that can accommodate the width when the target value is set to the maximum.
Thus, brightness adjustment can be performed while maintaining the waveform of the lighting period 1. And the period 1 which combined the lighting period and the light extinction period can be maintained.
The error propagation type pulse generation procedure of the present embodiment can simultaneously generate and output pulses. Therefore, if the characteristics of the light source change during the generation procedure, it can be reflected in the generation procedure at any time. Specifically, it is possible to provide an LED temperature measurement sensor, calculate a change in the amount of light emission (or search a table) based on the temperature detection result, and immediately reflect the change in the procedure.

The above-described error propagation type pulse generation procedure has many R (red), G (green), B (blue), or R (red), G (green), B (blue), W (white), etc. It can also be used for lighting control of the backlight 100 combined with a color light source. Here, a procedure for generating a lighting pulse for driving the backlight 100 for controlling the brightness of white light emission using light sources (that is, LEDs) of three colors of R, G, and B will be described.
FIG. 14 is a configuration example of the present embodiment in the case of emitting light by combining three colors of red, green, and blue.
It is known that the emission wavelength distribution can be replaced with tristimulus values X, Y, and Z in consideration of human visual sensitivity. A numerical value obtained by converting the emission wavelength distribution of the light emitting means of three colors of red, green, and blue into X, Y, and Z is set as a calculation target in the generation procedure.
For each of X, Y, and Z, the cumulative value and the target value are compared, and the operation procedure for outputting the drive signal (PWM signal) based on the comparison result is the same as the configuration of the white LED described above. The difference is that X, Y, and Z characteristic values are exchanged between the three colors of red, green, and blue.
Here, the target values are Xt, Yt, and Zt. The characteristic value of the red LED is Xr, Yr, Zr, the characteristic value of the green LED is Xg, Yg, Zg, and the characteristic value of the blue LED is Xb, Yb, Zb.
That means
Red LED = (Xr, Yr, Zr)
Green LED = (Xg, Yg, Zg)
Blue LED = (Xb, Yb, Zb)
If the PWM output signal of the red LED is Pr, the PWM output signal of the green LED is Pg, and the PWM output signal of the blue LED is Pb, the output of the red, green, and blue LEDs is expressed by the following equation (1). Can be expressed by the product of the driving signals of the red, green and blue light emitting means and the XYZ characteristic matrix.

・・・・・・・・・・・・・ （１）
そして、出力の目標値を実現するための発光手段の駆動信号は、下記（２）式に示すように、目標値に特性マトリクスのインバースを掛けることで算出できる。

(1)
The driving signal of the light emitting means for realizing the output target value can be calculated by multiplying the target value by the inverse of the characteristic matrix, as shown in the following equation (2).

・・・・・・・・・・・・・ （２）

(2)

However, the calculation of the matrix inverse is complicated and is not suitable for a simple apparatus configuration. The present embodiment is characterized in that the drive signal is obtained by directly using the components of the characteristic matrix.
The cumulative value of X is Xa, the cumulative value of Y is Ya, and the cumulative value of Y is Ya. The PWM signals Pr, Pg, and Pb are compared with the target values Xt, Yt, and Zt and the magnitudes of the cumulative values Xa, Ya, and Za, and are determined to output a pulse if the cumulative value does not reach the target value.
If you rewrite
IF (Xt> Xa) Pr = 1
ELSE Pr = 0
IF (Yt> Ya) Pg = 1
ELSE Pg = 0
IF (Zt> Za) Pb = 1
ELSE Pb = 0
And
If the PWM signal Pr = 1, Xr is added to the cumulative value Xa, Yr is added to the cumulative value Ya, Zr is added to the cumulative value Za,
If the PWM signal Pg = 1, Xg is added to the accumulated value Xa, Yg is added to the accumulated value Ya, Zg is added to the accumulated value Za,
If the PWM signal Pb = 1, Xb is added to the accumulated value Xa, Yb is added to the accumulated value Ya, and Zb is added to the accumulated value Za.
If you rewrite
IF (Pr == 1) {Xa + = Xr, Ya + = Yr, Za + = Zr}
IF (Pg == 1) {Xa + = Xg, Ya + = Yg, Za + = Zg}
IF (Pb == 1) {Xa + = Xb, Ya + = Yb, Za + = Zb}

By repeating the above, the PWM generation procedure of period 1 is completed. The accumulated value of the result is compared with the target value, and the error is propagated to the next cycle. Error calculation is performed for three colors.
Xe = Xa-Xt
Ye = Ya-Yt
Ze = Za-Zt
These values are used as initial values of accumulated values Xa, Ya, Za of the next period.
In this way, it is possible to realize generation and output of a PWM signal in consideration of the wavelength distribution of the three-color light source. Since the target value can be set in the XYZ format, there is a feature that an arbitrary emission color can be set. Further, when the characteristics of the light source change due to some factor, it is only necessary to change the characteristic value at an arbitrary timing. If the inverse calculation of Expression 2 is used, it has a feature that can be realized extremely easily compared to the case where a huge calculation load is applied to reflect the change in the characteristic value.

As a variation of the above, the present invention can be applied to light emission of four colors obtained by adding white (W) to three colors of red, green, and blue (RGB). W has characteristic values Xw, Yw, and Zw of X, Y, and Z, respectively. The X, Y, and Z target values are compared with the cumulative value, and if all the X, Y, and Z have not reached the target value, W is output as a pulse.
If you rewrite
IF ((Xt> Xa) &(Yt> Ya) &(Zt> Za)) Pw = 1
ELSE Pw = 0
Then, Xw, Yw and Zw are added to the accumulated values Xa, Ya and Za of X, Y and Z in one pulse of the white LED.
If you rewrite
IF (Pw == 1) {Xa + = Xw, Ya + = Yw, Za + = Zw}
In this way, using the RGBW4 colors, a PWM signal for driving the light emitting means to calculate the target value is calculated.
The present embodiment has the effect of providing a simple device configuration without using the characteristic matrix inverse calculation means. In addition, by setting the target value in a divided manner, it is possible to similarly distribute the lighting pulses.
FIG. 15 shows an example of the RGB pulse group generated in the configuration example.
When applying the R (red), G (green), and B (blue) three-color light sources (LEDs) to the backlight 100 that lights independently, it is necessary to set the lighting period in consideration of color reproduction as well as brightness. become.
Here, if the width of the lighting period is variably set using the PWM method, the lighting periods of the three colors R, G, and B may become uneven. Instantaneously, a period during which any one of R, G, and B is lit alone occurs, and depending on the observation conditions, the color image quality deteriorates.
According to the present embodiment, since the lighting period is fixedly set and the lighting pulse arranged inside is controlled, the lighting periods of the three colors R, G, and B can be matched. As a result, it is possible to prevent color image quality deterioration.

FIG. 16 is a block diagram showing a schematic configuration of the liquid crystal display device of the present embodiment.
With reference to FIG. 16, in this embodiment, a signal path from when a video signal is input from the outside to display on the liquid crystal display panel 101 will be described.
The timing generation circuit 501 generates and distributes signals related to various operation timings using the synchronization signal included in the video signal.
The backlight control circuit 502 sets the amount of backlight for each screen by referring to the signal amplitude of the video signal.
The amount of backlight light is transmitted to the backlight 100 to drive the light source means and to the display signal processing circuit 503. Here, if the backlight light amount is suddenly changed in units of screens, there is a possibility that the image quality is deteriorated due to timing deviation from the operation of the liquid crystal display panel 101. Although not shown, by inputting the brightness of the usage environment using a sensor, the amount of backlight light can be varied based on the brightness of the environment.
The display signal processing circuit 503 corrects the video signal based on the backlight light amount set by the backlight control circuit 502 and then transmits a display signal to the source driver 505. Then, by using the source driver 505 and the gate driver 504 to transmit a signal to the wiring of the liquid crystal display panel 101, a display signal for each pixel is written.
Here, the backlight control circuit 502 can be configured by combining the backlight light quantity setting means 123, the lighting pulse condition setting means 124, and the lighting pulse group generation output means 125.
As mentioned above, the invention made by the present inventor has been specifically described based on the above embodiments. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Of course.

It is a figure which shows the relationship between the screen display and the operation | movement of backlight lighting in the liquid crystal display device of the Example of this invention. It is a figure explaining the blurring of the moving image at the time of gaze tracking, which is one of the image quality degradations of the visual liquid crystal display device. It is a graph which shows the shading change observed by the black-and-white edge periphery at the time of a line-of-sight tracking obtained by the numerical simulation on a certain condition. It is a figure which shows the structural example of the backlight lighting period in the liquid crystal display device of the Example of this invention. It is a figure which shows the structural example of the lighting pulse in the liquid crystal display device of the Example of this invention. It is a figure which shows the basic structural example of the lighting pulse generation circuit in the liquid crystal display device of the Example of this invention. In the liquid crystal display device of the Example of this invention, it is a figure which shows the example of a basic structure from the input of a video signal to displaying. In the liquid crystal display device of the Example of this invention, it is a figure which shows the example of a basic composition from the input of a video signal to displaying, when a backlight is divided into two or more. It is a figure which shows the structural example which lights a backlight synchronizing with a video signal in the liquid crystal display device of the Example of this invention. It is a figure which shows the structural example of the lighting pulse group production | generation output means shown in FIG. It is a figure which shows the calculation procedure of the error propagation type PWM signal in the modification of the liquid crystal display device of the Example of this invention. It is a figure which shows the calculation procedure of the error propagation type PWM signal in the modification of the liquid crystal display device of the Example of this invention. In the liquid crystal display device shown in FIG. 12, it is the figure which showed the lighting pulse along with the time-axis. It is a figure which shows the calculation procedure of an error propagation type PWM signal combining three colors of red, green, and blue in the modification of the liquid crystal display device of the Example of this invention. It is a figure which shows the RGB pulse group in the liquid crystal display device shown in FIG. It is a block diagram which shows schematic structure of the liquid crystal display device of the Example of this invention. It is a figure which shows the basic composition of a liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Backlight 101 Liquid crystal display panel 110 Video signal 111 Display signal 112,113 Backlight quantity setting value 114 Lighting pulse condition signal 115 Lighting pulse group signal 116 Display timing signal 121 Display signal processing means 122 Display timing detection means 123 Backlight quantity setting Means 124 Lighting pulse condition setting means 125 Lighting pulse group generation output means 301 Pixel clock generation means 302 Timing control means 303 Lighting pulse number setting means 304 Lighting pulse generation means 305 Lighting pulse output means 306 Switch means 501 Timing generation circuit 502 Backlight control Circuit 503 Display signal processing circuit 504 Gate driver 505 Source driver KB Diffuser

Claims (11)

A drive circuit that controls turning on and off of the backlight,
A periodic pattern generating means for generating a periodic pattern of a backlight lighting period that circulates in consecutive N frame periods, where N is an integer of 2 or more;
Pulse number setting means for setting the number of lighting pulses within the backlight lighting period;
A drive circuit comprising: a lighting pulse group generation unit that generates and outputs a lighting pulse group based on the set backlight lighting period and the number of lighting pulses.   When the cyclic frame period is 2, the period pattern of the backlight lighting period generated by the period pattern generation means includes a lighting period and a lighting period of the first frame period, a lighting period of the second frame period, and The drive circuit according to claim 1, wherein the extinguishing period has a reversal relationship.   2. The drive circuit according to claim 1, wherein the periodic pattern of the backlight lighting period generated by the periodic pattern generation unit has a relationship in which the lighting period continues as an accumulation of N frame periods. With brightness setting means to set the brightness of the backlight,
2. The drive circuit according to claim 1, wherein the number-of-pulses setting unit sets the number of lighting pulses in the lighting period based on the brightness of the backlight set by the brightness setting unit. . With brightness setting means to set the brightness of the backlight,
2. The driving according to claim 1, wherein the pulse number setting unit sets a pulse width of a lighting pulse within the lighting period based on the brightness of the backlight set by the brightness setting unit. circuit.   2. The drive circuit according to claim 1, wherein the lighting pulse group generation means includes means for propagating an error of a lighting pulse set in a certain lighting period in a next lighting period. The lighting pulse group generation means, means for propagating the error of the lighting pulse set in a certain lighting period to the next lighting period;
The drive circuit according to claim 1, further comprising means for receiving an error generated in the previous lighting period and utilizing the error as an initial value. The backlight is composed of light sources of three colors, red, green and blue,
2. The drive circuit according to claim 1, further comprising means for setting the brightness based on the number or width of lighting pulses arranged within each lighting period, and matching the lighting periods of all color light sources. .   The drive circuit according to claim 1, wherein the backlight is an LED, a combination of an LED and a phosphor, or an OLED. A liquid crystal display panel;
With backlight,
A liquid crystal display device comprising a drive circuit for controlling turning on and off of the backlight,
The liquid crystal display device according to claim 1, wherein the drive circuit is the drive circuit according to claim 1.   The liquid crystal display device according to claim 10, wherein the backlight is an LED, a combination of an LED and a phosphor, or an OLED.

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