JP2010008599A - Liquid crystal display and control method of liquid crystal display - Google Patents

Abstract

Provided is a technique for maintaining a high quality image of a liquid crystal display device when performing backlight blinking.
A color sensor detects each detection signal corresponding to each light quantity of red, green, and blue of a light beam applied to the back surface of an LCD panel. Further, the current-voltage conversion and integration circuit 121 integrates each detection signal. Further, the median filter circuit 33 detects the maximum value and the minimum value for each period of the signal obtained from the integration circuit, and obtains the median data signal that is the average value thereof. Further, the luminance / chromaticity automatic control circuit 34 obtains a feedback data signal from the median data signal and the target value signal. Further, the backlight blinking control circuit 35 generates a blinking signal for controlling blinking of the light source. The light source driver 140 generates a drive signal for driving the light source from the feedback data signal and the blinking signal. In this way, the amount of light from the light source can be accurately controlled even when the light source is blinking.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal display device and a method for controlling the liquid crystal display device.

  In recent years, liquid crystal display devices using liquid crystals have been widely used in various industrial fields. Such a liquid crystal display device includes an LCD panel (liquid crystal panel) and a backlight (light source) as optical members. In addition, the liquid crystal display device includes a backlight control circuit for controlling a backlight and an LCD driver as a circuit unit (see Patent Document 1).

For example, in the invention described in Patent Document 1, each of the luminances of a light source divided into a plurality of parts is detected and controlled by a single photosensor. Here, the light source blinks.
JP-A-2005-208486

  When improvement in image quality (definition) of images displayed on a liquid crystal display device is required, and controlling a plurality of light sources with a single photosensor cannot improve image quality and ensure sufficient definition Has arisen. For example, the amount of light in the area at the edge of the screen and the amount of light in the area surrounded by the light source are greatly different from each other because the influences from the periphery are greatly different. As a result, there is a concern that feedback cannot be correctly applied with one photosensor. In addition, when detecting the amount of light with a single photosensor, there is a concern that the amount of light actually visible is not measured and feedback is not applied. For example, with feedback that keeps the difference in the amount of light measured by one sensor constant, the amount of light actually visible and the amount of light detected in this way differ when the light source is blinking. There may be cases.

  In recent years, backlight blinking that periodically blinks the backlight tends to be frequently used as a light source control method. Furthermore, pulse width control (PWM control) using a pulse width modulation signal (PWM signal) may be employed. However, there is currently no technology for controlling the amount of light from a light source with high accuracy when performing backlight blinking.

  In view of the above-described problems, the present invention provides a technique for maintaining the image quality of a liquid crystal display device at a high quality when performing backlight blinking.

  The liquid crystal display device of the present invention includes a liquid crystal panel having red, green, and blue color filters, each light source that emits red, green, and blue light beams to the back surface of the liquid crystal panel, and the back surface of the liquid crystal panel. Each color sensor that detects each detection signal corresponding to each light quantity of red, green, and blue of the light beam irradiated to each of the above, each integration circuit that integrates each detection signal from each color sensor, and each integration Each median filter circuit for detecting a maximum value and a minimum value for each period of a signal obtained from the circuit and obtaining each median data signal that is an intermediate value between the maximum value and the minimum value; and each median data signal; Each luminance and chromaticity automatic control circuit that obtains each feedback data signal from each target value signal that is a target value for control, and each backlight that generates each blinking signal that controls blinking of each light source Comprising a linking control circuit, and a respective light source driver that generates a drive signal for driving the respective light source from said each feedback data signal said each blinking signal.

  The liquid crystal display device control method of the present invention displays an image by controlling the transmittance of the red, green and blue color filters of the liquid crystal panel, and each light source is red, green and blue with respect to the back surface of the liquid crystal panel. Each color sensor detects each detection signal corresponding to each light quantity of red, green, and blue of the light beam irradiated on the back surface of the liquid crystal panel, and each integration circuit detects from each color sensor. Each of the detection signals of each, and each median filter circuit detects a maximum value and a minimum value for each period of the signal obtained from each of the integration circuits, each of which is an intermediate value between the maximum value and the minimum value Each median data signal is obtained, and each luminance chromaticity automatic control circuit obtains each feedback data signal from each median data signal and each target value signal that is a control target value, and each backlight blinking control circuit Generates the blinking signal for controlling the flashing of the sources, each light source driver generates a driving signal for driving the respective light source from said each feedback data signal said each blinking signal.

  In the technology relating to the liquid crystal display device of the present invention, each color sensor detects the red, green, and blue light amounts of the light beam irradiated on the back surface of the liquid crystal panel. Each integration circuit integrates each detection signal from each color sensor. Each median filter circuit detects a maximum value and a minimum value for each period of a signal obtained from each integration circuit, and obtains each median data signal that is an intermediate value between the maximum value and the minimum value. Each luminance / chromaticity automatic control circuit obtains each feedback data signal from each median data signal and each target value signal. Each backlight blinking control circuit generates each blinking signal for controlling blinking of each light source. Each light source driver generates a drive signal for driving each light source from each feedback data signal and each blinking signal. In this way, the amount of light from each light source can be accurately controlled even if the light sources are blinking.

  According to the technology of the present invention, the amount of light from the light source can be accurately detected even if the light source for the backlight is blinked, so that the image quality of the liquid crystal display device when performing backlight blinking is improved. We can provide technology that keeps quality.

(Liquid Crystal Display Device of Embodiment)
FIG. 1 is a diagram schematically showing a liquid crystal display device 10 of an embodiment in a range necessary for explanation. The liquid crystal display device 10 includes an LCD (Liquid Crystal Display) panel 11 and a backlight unit 12 as main optical members. Further, as the optical member, a diffusion plate (see reference numeral 13 in FIG. 3) is used, but is omitted in FIG. The liquid crystal display device 10 includes a circuit unit 20. The LCD panel 11 is provided with red, green and blue color filters.

  In FIG. 1, only a part of the optical member and the circuit unit 20 is shown, and there is a part where the description is omitted, and the whole is not shown. For example, for the backlight unit, not all of the light sources RGB1 to RGB70 (see FIG. 2), which are a plurality of light sources, are described. Only light source RGB1, light source RGB2, light source RGB3, light source RGB4, light source RGB17, light source RGB18, light source RGB19, light source RGB20, light source RGB46, light source RGB68, and light source RGB70 are described. Similarly, regarding the color sensors S1 to S15 (see FIG. 2), which are a plurality of color sensors, only the color sensor S1 and the color sensor S5 are described.

  As shown in FIG. 1, the circuit unit 20 includes a light amount detection circuit 120, a backlight unit control circuit unit 30, a signal processing circuit unit 36, and a light source driver 140. Here, the light quantity detection circuit 120 is a light quantity detection circuit connected to the color sensor S1, and each of the color sensor S2 to the color sensor S15 is provided with other 14 light quantity detection circuits that are similar. It is omitted in FIG. Similarly, the light source driver 140 is a light source driver for driving the light source RGB1, the light source RGB2, the light source RGB3, and the light source RGB4, and the description of the other 14 light source drivers that drive the light source is omitted in FIG. ing. Further, since the backlight unit control circuit unit 30 is provided for each color sensor, the description of the other 14 backlight unit control circuit units is omitted.

  In the liquid crystal display device 10, only one signal processing circuit unit 36 is provided. The signal processing circuit unit 36 controls each backlight blinking control circuit (for example, the backlight blinking control circuit 35) arranged in each of the 15 backlight unit control circuit units. A detailed description of each backlight blinking control circuit will be described later together with a description of the signal processing circuit unit 36.

  FIG. 2 is a diagram schematically illustrating the relationship between the color sensors S1 to S15 and the light sources RGB1 to RGB70. A sensing range, which is a range in which the amount of light from the light source is controlled by one color sensor, is represented as a portion surrounded by broken lines. The entire surface of the LCD panel 11 is divided into 15 regions so that the amount of light is detected by each color sensor.

  Based on the signals detected by the color sensor S1, the light sources RGB1 to RGB4 are controlled. Further, the light sources RGB5 to RGB8 are controlled based on signals detected by the color sensor S2. Further, the light sources RGB9 to RGB12 are controlled based on signals detected by the color sensor S3. Further, the light sources RGB17 to RGB20 are controlled based on signals detected by the color sensor S5. Further, the light sources RGB21 to RGB26 are controlled based on signals detected by the color sensor S6. Further, the light sources RGB27 to RGB32 are controlled based on the signals detected by the color sensor S7. Further, the light sources RGB33 to RGB38 are controlled based on signals detected by the color sensor S8. Further, the light source RGB39 to the light source RGB44 are controlled based on the signal detected by the color sensor S9. Further, the light source RGB45 to the light source RGB50 are controlled based on the signal detected by the color sensor S10. Further, the light sources RGB51 to RGB54 are controlled based on signals detected by the color sensor S11. Further, the light source RGB55 to the light source RGB58 are controlled based on the signal detected by the color sensor S12. Further, the light sources RGB59 to RGB62 are controlled based on signals detected by the color sensor S13. Further, the light sources RGB63 to RGB66 are controlled based on the signals detected by the color sensor S14. Further, the light sources RGB67 to RGB70 are controlled based on signals detected by the color sensor S15.

  The color sensor S1 can detect each color of red (R), green (G), and blue (B) independently. Similarly, each of the color sensors S2 to S15 can detect red (R), green (G), and blue (B) colors independently.

  The light source RGB1 includes an LED (Light Emitting Diode) that emits each color so that each color of red (R), green (G), and blue (B) can emit light independently. That is, it includes a red (R) LED that emits red light, a green (G) LED that emits green light, and a blue (B) LED that emits blue light. Similarly, each of the light sources RGB2 to RGB70 can emit light of red (R), green (G), and blue (B) independently.

  The correspondence relationship between each of the color sensors S1 to S15 and the light sources RGB1 to RGB70 is as described above. However, since the driving of turning on and off the light sources RGB1 to RGB70 is performed by another combination, this will be described.

  Light source RGB1, light source RGB2, light source RGB5, light source RGB6, light source RGB9, light source RGB10, light source RGB13, light source RGB14, light source RGB17 and light source RGB18 are turned on or off simultaneously. Further, the light source RGB3, the light source RGB4, the light source RGB7, the light source RGB8, the light source RGB11, the light source RGB12, the light source RGB15, the light source RGB16, the light source RGB19, and the light source RGB20 are turned on or off at the same time. Further, the light source RGB21, the light source RGB22, the light source RGB27, the light source RGB28, the light source RGB33, the light source RGB34, the light source RGB39, the light source RGB40, the light source RGB45, and the light source RGB46 are turned on or off at the same time. Further, the light source RGB23, the light source RGB24, the light source RGB29, the light source RGB30, the light source RGB35, the light source RGB36, the light source RGB41, the light source RGB42, the light source RGB47, and the light source RGB48 are turned on or off at the same time. Further, the light source RGB25, the light source RGB26, the light source RGB31, the light source RGB32, the light source RGB37, the light source RGB38, the light source RGB43, the light source RGB44, the light source RGB49, and the light source RGB50 are turned on or off at the same time. Further, the light source RGB51, the light source RGB52, the light source RGB55, the light source RGB56, the light source RGB59, the light source RGB60, the light source RGB63, the light source RGB64, the light source RGB67, and the light source RGB68 are turned on or off at the same time. In addition, the light source RGB 53, the light source RGB 54, the light source RGB 57, the light source RGB 58, the light source RGB 61, the light source RGB 62, the light source RGB 65, the light source RGB 66, the light source RGB 69, and the light source RGB 70 are turned on or off at the same time. That is, the lighting and extinguishing control is performed in units of one row for each of the seven rows.

  More specifically, each light source RGB is driven as follows. The red (R) LED of the light source RGB1 and the red (R) LED of the light source RGB2 are connected to each other and are driven by a red driver (not shown) of the light source driver 140. . The green (G) LED of the light source RGB1 and the green (G) LED of the light source RGB2 are connected to each other and are driven by a green driver (not shown) of the light source driver 140. ing. The blue (B) LED of the light source RGB1 and the blue (B) LED of the light source RGB2 are connected to each other and driven by a blue driver (not shown) of the light source driver 140. ing.

  Similarly, all the LEDs emitting the same color of the respective light sources belonging to the same row in the region surrounded by the broken lines shown in FIG. 2 are connected to each other, and similarly, for each LED of each color by a light source driver (not shown). To be controlled. That is, each of the 35 light source drivers has an independent driver for each color for driving three LEDs of red, green, and blue.

  FIG. 3 is a schematic diagram showing the relationship among the LCD panel 11, the diffusion plate 13, and the backlight unit 12 by a cross-sectional view. FIG. 3 is a cross-sectional view of FIG. 1 viewed from the right side surface, and includes the light source RGB18, the light source RGB20, the light source RGB46, the light source RGB48, the light source RGB50, the light source RGB68, the light source RGB70, and the color sensor S1. Color sensor S15 is shown. The color sensor S10 is disposed on the back surface of the light source RGB50 and is not visible from the right side surface, but is illustrated in FIG. 3 in order to clarify the positional relationship.

  As shown in FIG. 3, the light emitted from each light source is scattered by the diffusion plate 13 and transmitted through the diffusion plate 13 to irradiate the LCD panel 11. By transmitting through the diffusion plate 13, the light intensity becomes uniform, and red, green, and blue are also mixed uniformly. At this time, the light emitted from each light source and scattered is detected by each color sensor. For example, the amount of light detected by the color sensor S5 is mostly light from the light source RGB17, the light source RGB18, the light source RGB19, and the light source RGB20. However, the color sensor S5 also detects the light amounts from the light source RGB45, the light source RGB46, the light source RGB47, the light source RGB48, the light source RGB49, and the light source RGB50. The color sensor S5 also detects the amount of light from the light source RGB67, the light source RGB68, the light source RGB69, and the light source RGB70. The correspondence with each light source is the same for the amount of light detected by other color sensors. By adopting such a light quantity detection method, the light quantity detected by each color sensor is equivalent to the light quantity that is actually visually recognized.

  Each part of the circuit unit 20 will be described. First, the light amount detection circuit 120 will be described. The red color detection signal from the color sensor S 1 sensor that detects red color is input to the current-voltage converter and the integration circuit 121. In addition, a green color detection signal from the color sensor S 1 that detects green color is input to the current-voltage converter and the integration circuit 122. Further, the blue color detection signal from the color sensor S 1 that detects blue color is input to the current-voltage converter and the integration circuit 123.

  Each of the current-voltage converter and integration circuit 121, the current-voltage converter and integration circuit 122, and the current-voltage converter and integration circuit 123 converts current into voltage and integrates it. That is, by performing an integration operation on the time axis, it functions as a low-pass filter on the frequency axis.

  FIG. 4 is a diagram illustrating a waveform of a voltage output from the current-voltage converter and the integration circuit (for example, the current-voltage converter and the integration circuit 121). The horizontal axis in FIG. 4 is time t, and the vertical axis in FIG. 4 is amplitude. Time T1 indicates one cycle time. The reciprocal of time T1 is the repetition frequency. The frequency of the voltage output from the current-voltage converter and the integration circuit 121 varies depending on the vertical synchronization frequency and blinking method described later. For example, in Japan, the vertical synchronization frequency is generally 60 Hz (Hertz). Then, it is set to 120 Hz in a video signal conversion circuit described later. If the blinking method described later is used, the frequency of the signal output from the integrating circuit 121 is 60 Hz.

  The waveform of the voltage output from the current-voltage converter and the integration circuit is obtained by superimposing a DC component on a 60 Hz sine waveform. Here, the reason for using the current-voltage converter and the integration circuit (for example, the current-voltage converter and the integration circuit 121) is as follows. The current / voltage converter is used because the output from the color sensor is obtained as a current output, and the DAY conversion circuit (A / D conversion circuit) 31 of the backlight unit control circuit unit 30 corresponds to the analog voltage. This is because a digital value is output. There are two reasons for using the integration circuit. First, since the stepwise backlight blinking repeated at the period T1 is adopted as the driving method of the light source driver, the signal obtained from the color sensor is also stepped. An integrating circuit is used to smooth the stepped signal as much as possible. In addition, the reason for using the integration circuit is that, in the embodiment, since the pulse width modulation method is used as the light source driver light amount control method, it is desired to cut the fluctuation of the pulse modulation by passing through the integration circuit. .

  FIG. 5 is a diagram illustrating a drive signal from the light source driver 140. The horizontal axis in FIG. 5 is time t, and the vertical axis in FIG. 5 is amplitude. FIG. 5A shows that backlight blinking is performed. The time T1 in FIG. 5A is the same time as the time T1 shown in FIG. In this case, time T2 and time T3 are the same time, each of which is time T1 / 2. The light source is turned on at time T2, and the light source is turned off at time T3. For example, if the signal shown in FIG. 5A is a signal for driving the red (R) LEDs of the light sources RGB1 and RGB2, the red (R) LEDs of the light sources RGB1 and RGB2 at time T1. Emits light. At time T2, the red (R) LEDs of the light sources RGB1 and RGB2 are turned off.

  5B and 5C are diagrams in which the time axis of FIG. 5A is enlarged. The waveform shown in FIG. 5B shows, for example, a pulse width modulation signal when the luminance of the red (R) LEDs of the light sources RGB1 and RGB2 is relatively high. The waveform shown in FIG. 5C shows a pulse width modulation signal when the luminance of the red (R) LEDs of the light source RGB1 and the light source RGB2 is relatively low. Here, the upper level of the drawing is the state where the light source is shining. The duty factor (duty ratio) of the waveform shown in FIG. 5B is represented by (T5 / (T4 + T5)). The duty factor of the waveform shown in FIG. 5C is represented by (T6 / (T4 + T6)). The duty factor corresponds to the luminance of light emitted from the light source. In this way, the light quantity from each light source can be controlled by controlling the duty factor, that is, by changing the pulse width. How a drive signal for backlight blinking that has received the pulse width modulation signal is generated will be described later.

  FIG. 6 is a diagram illustrating a waveform of a drive signal of each LED, and a voltage waveform from a current-voltage converter and an integration circuit. The top row shows the waveform of the drive signal from the light source driver 140 that drives the light sources RGB1 and RGB2 (the same waveform as in FIG. 5A). The second row shows the waveform of the drive signal from the light source driver that drives the light sources RGB3 and RGB4. The third row shows the waveform of the drive signal from the light source driver that drives the light source RGB21 and the light source RGB22. The fourth row shows the waveform of the drive signal from the light source driver that drives the light source RGB23 and the light source RGB24. The fifth row shows the waveform of the drive signal from the light source driver that drives the light source RGB25 and the light source RGB26. The sixth row shows the waveforms of drive signals from the light source drivers that drive the light sources RGB51 and RGB52. The sixth row shows the waveforms of drive signals from the light source drivers that drive the light sources RGB51 and RGB52. The seventh row is a waveform of a drive signal from a light source driver that drives the light source RGB 53 and the light source RGB 54. As shown in FIG. 6, with the top waveform as a reference, the second waveform, the third waveform, the fourth waveform, the fifth waveform, the sixth waveform, and the seventh waveform. The phase is delayed in order. This is because each light source RGB in the first row, each light source RGB in the second row, each light source RGB in the third row, each light source RGB in the fourth row, each light source RGB in the fifth row, This is because each light source RGB in the row and each light source RGB in the seventh row are sequentially turned off and turned on.

  The waveform at the eighth stage in FIG. 6 shows the voltage waveform from the current-voltage converter and the integration circuit when the integration time constant of the current-voltage converter and the integration circuit is zero. The waveform at the ninth stage in FIG. 6 is a waveform when the integration time constant is appropriate. This waveform is the same as the waveform shown in FIG. Further, the waveform at the 10th stage in FIG. 6 is a waveform when the time constant of integration is large.

  The integration time constant TI of the current-voltage converter and the integration circuit 121 is represented by TI = 2π × R112 × C111. Here, π is the circular ratio, R112 is the resistance value (Ω (ohms)) of the resistor R112, and C111 is the capacitance value (F (farad)) of the capacitor C111. When the integration time constant TI is very large compared to the time T1 of one cycle, the voltage waveform from the current-voltage converter and the integration circuit 121 is DC (direct current) as shown in the ninth stage of FIG. The waveform is close to. When the integration time constant TI is smaller than the time T1 of one cycle, the voltage waveform from the current-voltage converter and the integration circuit 121 in FIG. 6 is a waveform close to the waveform in the eighth stage in FIG. Become.

  Here, the relationship between the integration time constant TI and the time T4 which is the repetition period of the pulse width modulation signal (see FIGS. 5B and 5C) will be described. The pulse width modulation signal repeated at time T4 includes harmonics of the frequency represented by the reciprocal of time T4 and its sideband components. This component becomes noise and is added to the A / D conversion circuit 31 to cause a conversion error during conversion. Therefore, it is necessary to sufficiently suppress these components. In order to achieve this purpose, it is desirable that the integration time constant TI is at least 50 times the time T4 or more, depending on the duty factor of the pulse width modulation signal.

  Here, if the integration time constant TI is increased too much, the responsiveness of the control system becomes worse. Although it is conceivable to reduce the time T4 without increasing the integration time constant TI, in this case, if the time T4 is too small, the switching loss and unnecessary radiation in the light source driver 140 increase. Therefore, there is an appropriate relationship among these three members as long as the integration time constant TI> time T1> time T4 is satisfied. That is, the time T1 is synchronized with the period (frequency) of the vertical synchronization signal, and for example, the time T1 is 16 msec (milliseconds). In this case, for example, when the time T4 is 1 msec, a signal close to a sine wave can be obtained from the current-voltage converter and the integration circuit by setting the integration time constant TI to 1 msec × 50 = 50 msec or more. Can do.

  The response speeds of the light sources RGB1 to RGB70 and the color sensors S1 to S15 are fast, and when there is no integration action of the current-voltage converter and the integration circuit, a signal corresponding to the luminance cannot be detected by the noise component. . As described above, this is the reason why the current-voltage converter and integration circuit 121 to the current-voltage converter and integration circuit 123 are provided. A circuit similar to the light quantity detection circuit 120 described above is provided for each of the color sensors S2 to S15, and 15 light quantity detection circuits are provided in the circuit unit 20 as a whole.

  The backlight unit control circuit unit 30 will be described. The backlight unit control circuit unit 30 includes an A / D conversion circuit 31, a data ram (data RAM) 32, a median filter circuit 33, a luminance / chromaticity automatic control circuit 34, and a backlight blinking control circuit 35. The backlight unit control circuit unit 30 is a backlight unit control circuit unit provided corresponding to the light amount detection circuit 120. Similarly, 14 backlight unit control circuit units corresponding to each of the other 14 light quantity detection circuits are provided, and 15 backlight unit control circuit units are provided in the circuit unit 20 as a whole. Yes.

  Hereinafter, the backlight unit control circuit unit 30 will be described as a representative, but the same applies to the other backlight unit control circuit units. As described above, the three digital data corresponding to red, green, and blue A / D converted by the A / D conversion circuit 31 are sequentially stored in the data RAM 32 as digital sensor data signals. Here, the sample timing signal of the A / D conversion circuit 31 is supplied from the backlight blinking control circuit 35. A memory access signal for specifying the address of the data RAM 32 is supplied from the luminance / chromaticity automatic control circuit 34. Here, the frequency of the sample timing signal is a signal having such a frequency that the point P1 (maximum level point) and the point P2 (minimum level point) shown in FIG. 4 can be detected with high accuracy, for example, as shown in FIG. When the frequency of the sine wave is 60 Hz, although it depends on the performance of the A / D conversion circuit, the frequency is approximately 100 times that of 6 KHz. Further, the frequency of generation of the memory access signal is the same frequency, and different addresses are generated for each cycle.

  A sample data signal is output from the data ram 32 to the median filter circuit 33. The sample data signal includes a maximum value level (amplitude at a point marked with a symbol P1 in FIG. 4) and a minimum value level (amplitude at a point marked with a symbol P1 in FIG. 4), and has five maximum values. The level and the five minimum value levels are output to the median filter circuit 33. In the median filter circuit 33, the maximum and minimum third values are acquired. Then, ½ of the sum of the selected middle values of the maximum and minimum is an intermediate value (amplitude at the level of a thick solid line between the points P1 and P2 in FIG. 4). As a result, the noise component is further suppressed, and a more correct amount of light is detected. Here, this median data signal corresponds to the luminance and chromaticity actually observed with the naked eye.

  Here, how to obtain the maximum value level and the minimum value level will be described. First, the first method will be described. Since the length of time T1 (time of one cycle) is known, the maximum value level can be detected by detecting the maximum value during each time interval of time T1. Similarly, the minimum value level can be detected by detecting the minimum value between the time intervals of time T1.

  Next, the second method will be described. The phase of the phase of the sine wave shown in FIG. 4 is synchronized with the waveform of the drive signal shown in FIG. That is, the phase relationship between the two changes according to the integration time constant TI, but when the integration time constant TI is determined, the phase relationship between the two becomes constant. Therefore, a time (first predetermined time) between the rising point of the time T2 shown in FIG. 5A and the point P1 shown in FIG. 4 is obtained in advance. Then, when the first predetermined time has elapsed from the rising point of time T2, the maximum value level is obtained by sampling the sine wave signal. Similarly, a time (second predetermined time) between the rising point of time T2 shown in FIG. 5A and point P2 shown in FIG. 4 is obtained in advance. When the second predetermined time has elapsed from the rising point of time T2, the sine wave signal is sampled to obtain the minimum value level.

  In the luminance chromaticity automatic control circuit 34, desirable red LED luminance (referred to as a red target value) and green LED luminance (referred to as a green target value) based on the target luminance and the target chromaticity. ), And each of the luminances of blue LEDs (referred to as blue target values). Then, the target value is compared with the current median data signal of each color to output a feedback signal. If the current median data signal is smaller than the target value, the duty factor of the pulse width modulation signal is increased. If the current median data signal is small, a feedback signal to be increased is output. More specifically, as follows. The red target value is compared with the current median data signal of red, and if the target value is smaller, a feedback signal that increases the duty factor of the pulse width modulation signal that drives the red LED is output. . If the target value is larger, a feedback signal is output that reduces the duty factor of the pulse width modulation signal that drives the red LED.

  Similarly, the green target value is compared with the current median data signal of green, and if the target value is smaller, the duty factor of the pulse width modulation signal is increased, and if the target value is larger. , Output a feedback signal to control the green LED to reduce the duty factor. Similarly, the blue target value is compared with the current median data signal of blue, and if the target value is smaller, the duty factor of the pulse width modulation signal is increased, and if the target value is larger. The feedback signal for controlling the blue LED for decreasing the duty factor is output.

  In color adjustment, a so-called target white balance and luminance are generally obtained, and then the ratio of R, G, and B is generally adjusted. A description will be given of how to obtain each of the red target value, the green target value, and the blue target value from the target luminance and the target chromaticity in the luminance chromaticity automatic control circuit 34. First, a relational expression between X, Y, and Z in the CIE color system, the target luminance (Y), and the target chromaticity (x, y) is obtained by Expressions 1 to 3.

  Using Equations 1 to 3, X, Y, and Z can be obtained from Y, x, and y. Further, when X, Y, and Z are given, each of the red target value Rt, the green target value Gt, and the blue target value Bt is expressed by the following equation 4 according to the CIE1931 color system generally used in industrial applications. Given in.

  Using the red target value Rt thus determined, as described above, the comparison signal of the magnitude of the current median data signal of red, that is, the red feedback data signal which is the difference between the two is used as the luminance chromaticity. It is determined from the automatic control circuit 34. Similarly, a green feedback data signal is obtained from the luminance chromaticity automatic control circuit 34 using the green target value Gt thus obtained. Further, the blue feedback data signal is obtained from the luminance chromaticity automatic control circuit 34 using the blue target value Bt thus obtained.

  Each of the red feedback data signal, the green feedback data signal, and the blue feedback data signal thus obtained is supplied to the light source driver 140. Then, based on the red feedback data signal, the red light source driver included in the light source driver 140 drives the red (R) LEDs of the light sources RGB1 and RGB2 to maintain a desired luminance. Similarly, a green light source driver included in the light source driver 140 based on the green feedback data signal drives the green (G) LEDs of the light sources RGB1 and RGB2 to maintain a desired luminance. Similarly, the blue light source driver included in the light source driver 140 based on the blue feedback data signal drives the blue (B) LEDs of the light sources RGB1 and RGB2 to maintain a desired luminance.

  The target luminance (Y) and target chromaticity (x, y) described above may be fixed, but may be variable according to the preference of the user of the liquid crystal display device. For example, in the following order, it is variable according to the user's preference.

  First, the red (R), green (G), and blue (B) color filters of the LCD panel 11 are controlled to have a transmittance of 100%. This control can be performed by setting the image display signal from the liquid crystal timing controller and liquid crystal driver (LCD timing controller and LCD driver) 39 of the signal processing circuit unit 36 to a value corresponding to 100% transmittance. That is, the image display signal is a signal for controlling the transmittance of the color panel of each color of the LCD panel 11. Here, the state in which each color filter has a transmittance of 100% is a state in which white is displayed on the screen (in a white balance state) when the light amount of the LED of each color is appropriately maintained. When performing this adjustment, the above-described feedback loop including the color sensor and the light source RGB is set in an operating state.

  Next, while visually confirming the LCD panel 11, adjustments are made to achieve the desired brightness and chromaticity. For example, three volumes (not shown) of a red (R) luminance setting volume, a green (G) luminance setting volume, and a blue (B) luminance setting volume are operated. Then, when the desired brightness and chromaticity are obtained, the value of each median data signal from the median filter circuit 33 for each color of red (R), green (G), and blue (B) is a target value. Obtained as Rt, target value Gt, and target value Bt. Then, the target value Rt, the target value Gt, and the target value Bt are stored in the luminance / chromaticity automatic control circuit 34, and the following control is performed using these target values.

  Next, the signal processing circuit unit 36 will be described. The signal processing circuit unit 36 includes a video data conversion circuit 38, an LCD timing controller, and an LCD driver 39. The video data conversion circuit 38 receives a video signal and a synchronization signal from an external signal generator (not shown). The video data conversion circuit 38 outputs a video data signal and a conversion synchronization signal.

  The video signal and the synchronization signal are signals before the double speed, and the synchronization signal includes two types of synchronization signals, a horizontal synchronization signal and a vertical synchronization signal. For example, the frequency of the vertical synchronizing signal, which is a common synchronizing signal in Japan, is 60 Hz. The video data conversion circuit 38 obtains a vertical synchronization signal in which the frequency of the vertical synchronization signal is doubled (doubled) from 60 Hz to 120 Hz in order to improve the accuracy of the image. Further, the video data conversion circuit 38 obtains a horizontal synchronizing signal in which the frequency of the horizontal synchronizing signal is improved by a factor of two (double speed). The conversion synchronization signal includes a doubled vertical synchronization signal and a doubled horizontal synchronization signal. The video data conversion circuit 38 generates a frame discrimination signal. The frame discrimination signal is a signal for discriminating between the first frame and the second frame generated for each doubled vertical synchronizing signal. Here, the contents of the image display signals in the first frame and the second frame are the same. Further, in the first frame, the content of the image signal of the previous second frame changes.

  The conversion synchronization signal and the video data signal are input to the LCD timing controller and the LCD driver 39. Then, an image display signal is output from the LCD timing controller and the LCD driver 39, and the image display signal is input to the LCD panel 11. The conversion synchronization signal and the frame determination signal are input to the backlight blinking control circuit 35.

  The backlight blinking control circuit 35 outputs a drive signal as shown in the first stage drive signal in FIG. 6 (also the signal shown in FIG. 5A) from the light source driver 140 at a high level at time T2. , A circuit for generating a blinking signal that becomes a low level at time T3. Here, time T2 corresponds to the time during which the second frame is displayed on the LCD panel 11, and time T3 corresponds to the time during which the first frame is displayed on the LCD panel 11.

  The operation obtained by supplying the blinking signal to the light source driver 140 will be described. Inside the light source driver 140, pulse width modulation signals as shown in FIGS. 5B and 5C are continuously generated. By obtaining an AND of the pulse width modulation signal and the blinking signal, the drive signal shown in FIG. 5A can be obtained. Further, the second to seventh drive signals in FIG. 6 can be obtained in the same manner.

  The effect obtained by supplying the blinking signal to the light source driver 140 will be described. The response characteristics of the LCD panel 11 are generally slow, while the response of the light source RGB is faster than this. Since the response characteristic of the LCD panel 11 is slow, the effect of increasing the speed for improving the fineness of the image is diminished. In order to improve this, while driving with the drive signal shown in FIG. 5A, the image display signal is changed in synchronization with this drive signal.

  Specific modes of synchronization are as follows. Light source RGB1, light source RGB2, light source RGB5, light source RGB6, light source RGB9, light source RGB10, light source RGB13, light source RGB14, light source RGB17 and light source RGB18 are controlled by the same blinking signal (first blinking signal). Further, the light source RGB3, the light source RGB4, the light source RGB7, the light source RGB8, the light source RGB11, the light source RGB12, the light source RGB15, the light source RGB16, the light source RGB19, and the light source RGB20 are controlled by the same blinking signal (second blinking signal). Further, the light source RGB21, light source RGB22, light source RGB27, light source RGB28, light source RGB33, light source RGB34, light source RGB39, light source RGB40, light source RGB45, and light source RGB46 are controlled by the same blinking signal (third blinking signal). Further, the light source RGB23, light source RGB24, light source RGB29, light source RGB30, light source RGB35, light source RGB36, light source RGB41, light source RGB42, light source RGB47, and light source RGB48 are controlled by the same blinking signal (fourth blinking signal). Further, the light source RGB25, the light source RGB26, the light source RGB31, the light source RGB32, the light source RGB37, the light source RGB38, the light source RGB43, the light source RGB44, the light source RGB49, and the light source RGB50 are controlled by the same blinking signal (fifth blinking signal). Further, the light source RGB51, the light source RGB52, the light source RGB55, the light source RGB56, the light source RGB59, the light source RGB60, the light source RGB63, the light source RGB64, the light source RGB67, and the light source RGB68 are controlled by the same blinking signal (sixth blinking signal). Further, the light source RGB 53, the light source RGB 54, the light source RGB 57, the light source RGB 58, the light source RGB 61, the light source RGB 62, the light source RGB 65, the light source RGB 66, the light source RGB 69, and the light source RGB 70 are controlled by the same blinking signal (seventh blinking signal).

  The image display signal is updated in synchronization with the vertical synchronization signal and horizontal synchronization signal included in the conversion synchronization signal, and vertical scanning is performed from the upper direction to the lower direction of the LCD panel 11 (see FIG. 1) shown in FIG. Horizontal scanning is performed from the left direction to the right direction of the LCD panel 11. For the first frame, the light source is turned off sequentially as follows. Light source RGB1, light source RGB2, light source RGB5, light source RGB6, light source RGB9, light source RGB10, light source RGB13, light source RGB14, light source RGB17, and light source RGB18 are mainly updated by the content of the image signal of the LCD panel. Simultaneously with the start, the first blinking signal is set to a low level. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned off. Light source RGB3, light source RGB4, light source RGB7, light source RGB8, light source RGB11, light source RGB12, light source RGB15, light source RGB16, light source RGB19, and light source RGB20 are mainly updated by the content of the image signal of the LCD panel. Simultaneously with the start, the second blinking signal is set to a low level. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned off. Light source RGB21, light source RGB22, light source RGB27, light source RGB28, light source RGB33, light source RGB34, light source RGB39, light source RGB40, light source RGB45, and light source RGB46 are used to update the content of the image signal of the LCD panel. Simultaneously with the start, the third blinking signal is set to a low level. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned off. Light source RGB 23, light source RGB 24, light source RGB 29, light source RGB 30, light source RGB 35, light source RGB 36, light source RGB 41, light source RGB 42, light source RGB 47, and light source RGB 48. Simultaneously with the start, the fourth blinking signal is set to a low level. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned off. Light source RGB 25, light source RGB 26, light source RGB 31, light source RGB 32, light source RGB 37, light source RGB 38, light source RGB 43, light source RGB 44, light source RGB 49, and light source RGB 50. Simultaneously with the start, the fifth blinking signal is set to low level. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned off. Time to update the content of the image signal of the LCD panel in the range mainly irradiated by the light source RGB51, light source RGB52, light source RGB55, light source RGB56, light source RGB59, light source RGB60, light source RGB63, light source RGB64, light source RGB67, and light source RGB68 The sixth blinking signal is set to the low level simultaneously with the start of. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned off. Time for updating the content of the image signal of the LCD panel in the range mainly irradiated by the light source RGB53, light source RGB54, light source RGB57, light source RGB58, light source RGB61, light source RGB62, light source RGB65, light source RGB66, light source RGB69, and light source RGB70 The seventh blinking signal is set to the low level simultaneously with the start of. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned off.

  For the second frame, the light source is sequentially turned on as follows. Note that the image display signal is updated in the second frame, but the content is the same as in the first frame. Light source RGB1, light source RGB2, light source RGB5, light source RGB6, light source RGB9, light source RGB10, light source RGB13, light source RGB14, light source RGB17, and light source RGB18 are mainly updated by the content of the image signal of the LCD panel. Simultaneously with the start, the first blinking signal is set to the high level. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned on. Light source RGB3, light source RGB4, light source RGB7, light source RGB8, light source RGB11, light source RGB12, light source RGB15, light source RGB16, light source RGB19, and light source RGB20 are mainly updated by the content of the image signal of the LCD panel. Simultaneously with the start, the second blinking signal is set to the high level. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned on. Light source RGB21, light source RGB22, light source RGB27, light source RGB28, light source RGB33, light source RGB34, light source RGB39, light source RGB40, light source RGB45, and light source RGB46 are used to update the content of the image signal of the LCD panel. Simultaneously with the start, the third blinking signal is set to a high level. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned on. Light source RGB 23, light source RGB 24, light source RGB 29, light source RGB 30, light source RGB 35, light source RGB 36, light source RGB 41, light source RGB 42, light source RGB 47, and light source RGB 48. Simultaneously with the start, the fourth blinking signal is set to the high level. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned on. Light source RGB 25, light source RGB 26, light source RGB 31, light source RGB 32, light source RGB 37, light source RGB 38, light source RGB 43, light source RGB 44, light source RGB 49, and light source RGB 50. Simultaneously with the start, the fifth blinking signal is set to the high level. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned on. Time to update the content of the image signal of the LCD panel in the range mainly irradiated by the light source RGB51, light source RGB52, light source RGB55, light source RGB56, light source RGB59, light source RGB60, light source RGB63, light source RGB64, light source RGB67, and light source RGB68 The sixth blinking signal is set to the high level simultaneously with the start of. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned on. Time for updating the content of the image signal of the LCD panel in the range mainly irradiated by the light source RGB53, light source RGB54, light source RGB57, light source RGB58, light source RGB61, light source RGB62, light source RGB65, light source RGB66, light source RGB69, and light source RGB70 The seventh blinking signal is set to the high level simultaneously with the start of. Thereby, each of the red LED, the green LED, and the blue LED of each light source is turned on.

  As described above, each of the first to seventh blinking signals has a duty factor of 50% and changes between a high level and a low level at different phases. By controlling each light source RGB in this way, the deterioration of the image quality due to the slow response speed of the LCD panel 11 is not noticeable, and the image quality is excellent. In other words, during the time when the transient response occurs in the LCD panel 11, the light from the light source RGB is not irradiated so that the image in the state where the transient response is generated cannot be visually recognized. Only a simple screen is visible. In other words, the transient response ends between the first frame and the second frame, and the first frame and the second frame have the same content, so no transient response occurs even when the second frame is updated. .

  The effect of embodiment mentioned above is put together. First, a high-quality image is obtained by backlight blinking employed in the embodiment. Next, when the backlight blinking is employed, the control characteristic of the light amount from the light source employed in the embodiment can provide good control characteristics. That is, a signal corresponding to the amount of light is detected from each of the photosensors arranged vertically and horizontally in synchronization with the blinking timing. In other words, the highest luminance level and the lowest luminance level are detected, and the measurement results for several frames are averaged so that the luminance and chromaticity are the same as those actually seen by the eyes. Therefore, the backlight blinking operation is excellent in that the influence of the non-lighted column does not appear in the detection result of the color sensor. Furthermore, since the integration function is used to detect the highest luminance level and the lowest luminance level, it is good to eliminate the influence of noise components even when the light source is controlled by a pulse width modulation signal. Control characteristics can be obtained.

It is a figure which shows typically the liquid crystal display device of embodiment. It is a figure which shows typically the relationship between a color sensor and a light source. It is a schematic diagram which shows the relationship between a LCD panel, a diffusion plate, and a backlight part with sectional drawing. It is a figure which shows the waveform of the voltage output from a current-voltage converter and an integration circuit. It is a figure which shows the pulse width modulation signal (PWM signal signal) which is a drive signal from a light source driver. It is a figure which shows the waveform of the drive signal of each LED, the voltage waveform from a current-voltage converter and an integration circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device, 11 LCD panel, 12 Backlight part, 13 Diffusing plate, 20 Circuit part, 30 Backlight part control circuit part, 31 A / D conversion circuit, 32 Data ram (data RAM), 33 Median filter circuit, 34 chromaticity automatic control circuit, 35 backlight blinking control circuit, 36 signal processing circuit unit, 38 video data conversion circuit, 39 LCD timing controller and LCD driver, 120 light quantity detection circuit, 121, 122, 123 current voltage conversion and integration circuit 140 Light source driver, RGB1 to RGB70 light source, S1 to S15 color sensor

Claims (5)

A liquid crystal panel with red, green and blue color filters;
Each light source that emits red, green, and blue light beams to the back of the liquid crystal panel;
Each color sensor that detects each detection signal according to each light quantity of red, green, and blue of the light beam irradiated on the back surface of the liquid crystal panel;
Each integrating circuit for integrating each detection signal from each color sensor;
Each median filter circuit that detects a maximum value and a minimum value for each period of the signal obtained from each integration circuit, and obtains each median data signal that is an intermediate value between the maximum value and the minimum value;
Each luminance and chromaticity automatic control circuit that obtains each feedback data signal from each median data signal and each target value signal that is a control target value;
Each backlight blinking control circuit that generates each blinking signal for controlling blinking of each light source;
A liquid crystal display device comprising: each light source driver that generates a drive signal for driving each light source from each feedback data signal and each blinking signal. The light source driver is
The liquid crystal display device according to claim 1, wherein a pulse width modulation signal is generated as the drive signal. Each integrating circuit is
The liquid crystal display device according to claim 1, wherein each of the detection signals has an integration time constant that has a sinusoidal waveform. Each of the backlight blinking control circuits is
The liquid crystal display device according to claim 1, wherein a blinking signal having a duty ratio of 50% is generated. Display the image by controlling the transmittance of red, green and blue color filters on the LCD panel,
Each light source emits red, green and blue light beams to the back of the liquid crystal panel,
Each color sensor detects each detection signal corresponding to each light quantity of red, green, and blue of the light beam irradiated on the back surface of the liquid crystal panel,
Each integration circuit integrates each detection signal from each color sensor,
Each median filter circuit detects a maximum value and a minimum value for each period of the signal obtained from each integration circuit, and obtains each median data signal that is an intermediate value between the maximum value and the minimum value,
Each luminance and chromaticity automatic control circuit obtains each feedback data signal from each median data signal and each target value signal that is a target value for control,
Each backlight blinking control circuit generates each blinking signal for controlling blinking of each light source,
A control method for a liquid crystal display device, wherein each light source driver generates a drive signal for driving each light source from each feedback data signal and each blinking signal.

Images