JP6347627B2 - Duty ratio control circuit and backlight adjustment circuit - Google Patents

Description

  The present invention relates to an image display apparatus having a panel self-refresh (PSR) function, a duty ratio control circuit for controlling a duty ratio of a brightness control signal for controlling the brightness of a backlight of the display panel, and a duty The present invention relates to a backlight adjustment circuit that controls the luminance of a backlight using a luminance control signal whose duty ratio is controlled by a ratio control circuit.

  In order to reduce the power consumption of an image display device equipped with a display panel such as a liquid crystal panel, an image display device employing an image interface standard such as a display port (DisplayPort) displays a still image whose screen display does not change. Further, image data for one screen (one frame) of the still image is stored in a memory circuit inside the image display device, and the image data of the still image stored in the memory circuit is read to refresh the screen display. Panel self-refresh function has been put to practical use.

  FIG. 7 is a circuit diagram illustrating an example of a configuration of a conventional image display apparatus. The image display device 40 shown in the figure has a panel self-refresh function, and includes a serial transfer circuit 12, a memory circuit 14, a controller 16, a selector 18, a backlight 22, and a display panel 24. ing.

In the image display device 40, the serial transfer circuit 12 receives serial data and auxiliary data transferred via a display port from a personal computer (PC) or the like.
In the case of a display port, the serial data includes data instructing validity and invalidity of the panel self-refresh function in addition to image data. Further, the auxiliary data includes data for instructing the serial transfer circuit 12 to restart from the hibernation state and return to the operation state.
The auxiliary data is data that can be received even when the serial transfer circuit 12 is in a dormant state. The serial transfer circuit 12 includes a portion that performs high-speed serial transfer of image data and a portion that performs low-speed serial transfer of auxiliary data. In the case of a display port, both signal lines are separate. The serial transfer circuit 12 is put in a pause state mainly for high-speed serial transfer.

  When the controller 16 receives data instructing the validity of the panel self-refresh function from the serial transfer circuit 12 in the first display mode, the controller 16 subsequently receives still images for one screen sequentially received by the serial transfer circuit 12. After the image data is sequentially written in the memory circuit 14 in the image display device 40, the serial transfer circuit 12 is put into a sleep state, and a switching instruction signal for instructing the second display mode is output.

The second display mode is a display mode in which a still image corresponding to image data stored in the memory circuit 14 (hereinafter also referred to as image data of the memory circuit 14) is displayed on the display panel 24 by the panel self-refresh function.
In the second display mode, the selector 18 outputs the still image data read from the memory circuit 14 by the controller 16 in response to the switching instruction signal to output image data (for example, the image data B0, FIG. B1) is output. On the display panel 24, a still image corresponding to the image data of the memory circuit 14 is displayed with the luminance illuminated from the back side by the backlight 22 at the timing read from the memory circuit 14.

  Subsequently, when receiving data from the serial transfer circuit 12 that instructs the serial transfer circuit 12 to return from the sleep state to the operating state, the controller 16 restarts the serial transfer circuit 12 to put it in the operating state. Thereafter, upon receiving data instructing invalidation of the panel self-refresh function from the serial transfer circuit 12, a switching instruction signal instructing the first display mode is output.

In the first display mode, images (still images and moving images) corresponding to image data (hereinafter also referred to as image data of the serial transfer circuit) included in the serial data input from the outside and received by the serial transfer circuit 12 are displayed. This is a display mode displayed on the panel 24.
In the first display mode, the selector 18 outputs the image data of the serial transfer circuit 12 as output image data (for example, A2 and A3 in FIG. 8) in response to the switching instruction signal. On the display panel 24, an image corresponding to the image data of the serial transfer circuit 12 is displayed with the brightness illuminated from the back side by the backlight 22 at the timing when the image data is received by the serial transfer circuit 12.

  In this case, in order to switch the images smoothly, as shown in FIG. 8, the V (vertical) blanking period of the output timing of the image data of the memory circuit 14 and the output timing of the image data of the serial transfer circuit 12 It is necessary to switch together with the V blanking period. In order to match both timings, reading of the image data from the memory circuit 14 is stopped, and the V blanking period of the image data from the serial transfer circuit 12 is waited.

  As described above, when reading of the image data of the memory circuit 14 is stopped and the V blanking period of the image data of the serial transfer circuit 12 is waited, the V blanking period is temporarily changed depending on the switching timing as shown in FIG. May increase. This can be considered as a state in which the refresh rate is temporarily changed. A temporary increase in the V blanking period may appear as flickering of an image displayed on the display panel 24 such as a liquid crystal panel.

  On the other hand, when switching from the second display mode to the first display mode, the V blanking is performed by waiting for a plurality of frames until the V blanking periods of the two coincide with each other without stopping the reading of the image data of the memory circuit 14. It is conceivable to suppress an increase in the ranking period. However, in this method, since it may take time to switch from the second display mode to the first display mode, there is a possibility that images cannot be switched smoothly.

  Also, when displaying a still image with the panel self-refresh function, the refresh rate is intentionally set to be lower than when displaying an image corresponding to the image data of the serial transfer circuit 12 in order to reduce the power consumption of the display panel. May drop. Also in this case, the brightness when displaying a still image by the panel self-refresh function may appear to change as compared with the case where an image corresponding to the image data of the serial transfer circuit 12 is displayed.

Here, there is Patent Document 1 as a prior art document relevant to the present invention.
Patent Document 1 relates to a gray insertion method for a liquid crystal display. In this document, it is determined whether a frame displayed on a liquid crystal display is a dynamic frame or a static frame. By increasing the insertion level and synchronously increasing the duty cycle of the pulse width modulation signal, and in static frames, decreasing the gray insertion level and synchronously decreasing the duty cycle of the pulse width modulation signal, A method of making improvements and improving flicker is disclosed.

JP 2010-250277 A

The first object of the present invention is to eliminate the above-mentioned problems of the prior art and to reduce the flicker that occurs when the V blanking period increases when switching from the second display mode to the first display mode. A ratio control circuit and a backlight adjustment circuit are provided.
In addition to the first object, a second object of the present invention is to reduce a change in luminance that occurs when the refresh rate for intentionally displaying a still image is lowered in the second display mode. It is an object of the present invention to provide a duty ratio control circuit and a backlight adjustment circuit.

In order to achieve the above object, the present invention provides an image stored in an internal memory circuit by a first display mode for displaying an image corresponding to image data input from the outside on a display panel and a panel self-refresh function. A duty ratio control circuit for controlling a duty ratio of a brightness control signal for controlling a brightness of a backlight of the display panel in an image display device having a second display mode for displaying a still image corresponding to data on the display panel; There,
Based on a switching instruction signal for instructing switching between the first display mode and the second display mode, and an image timing signal representing a V blanking period of an image displayed on the display panel, the second display mode A V blanking detection unit that outputs a V blanking detection signal that detects a V blanking period immediately after the second display mode when switching from the first display mode to the first display mode;
An elapsed time counter that counts an elapsed time from the start of the V blanking period immediately after the second display mode when switching from the second display mode to the first display mode based on the V blanking detection signal;
A first offset amount for changing a duty ratio of the luminance control signal by a constant value only in a V blanking period immediately after the second display mode when switching from the second display mode to the first display mode; Specifies the amount of change for changing the duty ratio by a constant value per unit time, the limit amount for setting the upper limit of the time for changing the duty ratio of the luminance control signal, and the polarity of the first offset amount and the amount of change A setting register that holds the polarity of the control direction to be
Based on the duty ratio of the luminance control signal in the first display mode, the V blanking detection signal, the elapsed time, and the first offset amount, the change amount, the limit amount, and the polarity of the control direction, The duty ratio control signal for controlling the duty ratio of the luminance control signal only in the V blanking period immediately after the second display mode when switching from the second display mode to the first display mode is calculated by the following equation (1). A duty ratio control unit,
A luminance control signal generation unit that generates a luminance control signal having a duty ratio controlled by the duty ratio control signal;
The duty ratio control unit uses the duty ratio of the luminance control signal in the first display mode, included in the auxiliary data transferred from the outside via the serial transfer port, from the second display mode. Controlling the duty ratio of the luminance control signal only in the V blanking period immediately after the second display mode when switching to the first display mode;
The duty ratio of the luminance control signal only in the V blanking period immediately after the second display mode when switching from the second display mode to the first display mode = the duty ratio of the luminance control signal in the first display mode ± (The first offset amount ± the change amount × the elapsed time) Formula (1)
Here, when switching from the second display mode to the first display mode, it is detected by the V blanking detection signal, the elapsed time <the limit amount, and the two positive polarities of the above formula (1) Provides a duty ratio control circuit that is set according to the polarity in the control direction.
The present invention also provides a still image corresponding to image data stored in an internal memory circuit by a first display mode for displaying an image corresponding to image data input from the outside on the display panel and a panel self-refresh function. In the image display device having the second display mode for displaying on the display panel, a duty ratio control circuit for controlling a duty ratio of a luminance control signal for controlling the luminance of the backlight of the display panel,
Based on a switching instruction signal for instructing switching between the first display mode and the second display mode, and an image timing signal representing a V blanking period of an image displayed on the display panel, the second display mode A V blanking detection unit that outputs a V blanking detection signal that detects a V blanking period immediately after the second display mode when switching from the first display mode to the first display mode;
An elapsed time counter that counts an elapsed time from the start of the V blanking period immediately after the second display mode when switching from the second display mode to the first display mode based on the V blanking detection signal;
A first offset amount for changing a duty ratio of the luminance control signal by a constant value only in a V blanking period immediately after the second display mode when switching from the second display mode to the first display mode; Specifies the amount of change for changing the duty ratio by a constant value per unit time, the limit for setting the upper limit of the time for changing the duty ratio of the luminance control signal, and the polarity of the first offset amount and the amount of change A setting register that holds the polarity of the control direction to be
Based on the duty ratio of the luminance control signal in the first display mode, the V blanking detection signal, the elapsed time, and the first offset amount, the change amount, the limit amount, and the polarity of the control direction, The duty ratio control signal for controlling the duty ratio of the luminance control signal only in the V blanking period immediately after the second display mode when switching from the second display mode to the first display mode is calculated by the following equation (1). A duty ratio control unit,
A luminance control signal generating unit that generates a luminance control signal having a duty ratio controlled by the duty ratio control signal;
A reference duty ratio input unit that receives the duty ratio of the luminance control signal in the first display mode, input from the outside,
The duty ratio control unit switches from the second display mode to the first display mode using a duty ratio of a luminance control signal in the first display mode, which is input from the reference duty ratio input unit. Controlling the duty ratio of the luminance control signal only in the V blanking period immediately after the second display mode at the time,
The duty ratio of the luminance control signal only in the V blanking period immediately after the second display mode when switching from the second display mode to the first display mode = the duty ratio of the luminance control signal in the first display mode ± (The first offset amount ± the change amount × the elapsed time) Formula (1)
Here, when switching from the second display mode to the first display mode, it is detected by the V blanking detection signal, the elapsed time <the limit amount, and the two positive polarities of the above formula (1) Provides a duty ratio control circuit that is set according to the polarity in the control direction.

Here, the setting register further holds data for setting a second offset amount for changing the duty ratio of the luminance control signal in the second display mode by a certain value.
The duty ratio control unit further includes the following formula (2) based on the duty ratio of the luminance control signal in the first display mode, the switching control signal, the second offset amount, and the polarity in the control direction. ) To calculate a duty ratio control signal for controlling the duty ratio of the luminance control signal in the second display mode,
Duty ratio of luminance control signal in the second display mode = duty ratio of luminance control signal in the first display mode ± second offset amount Equation (2)
Here, in the second display mode, it is preferably detected by the switching control signal, and the ± polarity of the formula (2) is set by the polarity in the control direction.

  According to another aspect of the present invention, there is provided a backlight adjustment circuit that controls the luminance of the backlight using a luminance control signal whose duty ratio is controlled by the duty ratio control circuit described above. I will provide a.

According to the present invention, it takes a long time to switch from the second display mode to the first display mode by appropriately adjusting the duty ratio of the luminance control signal when switching from the second display mode to the first display mode. In addition, flicker that occurs when the V blanking period increases can be reduced.
Further, according to the present invention, the refresh rate when intentionally displaying a still image is reduced in the second display mode by appropriately adjusting the duty ratio of the luminance control signal in the second display mode. Even in this case, it is possible to reduce the change in luminance after switching from the first display mode to the second display mode and after switching from the second display mode to the first display mode.

It is a circuit diagram of one embodiment showing the composition of the image display device to which the duty ratio control circuit of the present invention is applied. It is a circuit diagram of another embodiment showing the structure of the image display apparatus to which the duty ratio control circuit of the present invention is applied. It is a conceptual diagram of an example showing the transfer timing of serial data and auxiliary data. It is a conceptual diagram showing the change of the duty ratio of the luminance control signal when switching from the second display mode to the first display mode. It is a conceptual diagram showing the change of the duty ratio of the luminance control signal when switching from the second display mode to the first display mode. It is a conceptual diagram showing the change of the duty ratio of the luminance control signal in the second display mode and when switching from the second display mode to the first display mode. It is an example circuit diagram showing the structure of the conventional image display apparatus. It is a conceptual diagram showing the relationship between the V blanking period of the image data of the serial transfer circuit and the V blanking period of the image data of the memory circuit when switching from the second display mode to the first display mode.

  Hereinafter, a duty ratio control circuit and a backlight adjustment circuit of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

  FIG. 1 is a circuit diagram of an embodiment showing a configuration of an image display device to which a duty ratio control circuit of the present invention is applied. The image display apparatus 10 shown in the figure has a panel self-refresh function, and includes a serial transfer circuit 12, a memory circuit 14, a controller 16, a selector 18, a duty ratio control circuit 20 of the present invention, A light 22 and a display panel 24 are provided.

Serial data and auxiliary data are input to the serial transfer circuit 12 from the outside of the image display device 10, for example, from a PC via a serial transfer port such as a display port.
The serial transfer circuit 12 receives serial data and auxiliary data transferred from the outside.

In the case of a display port, serial data includes data for instructing the validity and invalidity of the panel self-refresh function in addition to image data of still images and moving images. The auxiliary data includes data for instructing to restart the serial transfer circuit 12 from the hibernation state to return to the operation state, in the first display mode, that is, an image corresponding to the image data of the serial transfer circuit 12. Includes data of a duty ratio (reference duty ratio) DUTY1 of a reference luminance control signal (PWM (pulse width modulation) signal) when the image is displayed on the display panel 24.
The serial transfer circuit 12 outputs the above-described various data in addition to the image data and the reference duty ratio DUTY1.
The auxiliary data is data that can be received even when the serial transfer circuit 12 is in a dormant state. The serial transfer circuit 12 includes a portion that performs high-speed serial transfer of image data and a portion that performs low-speed serial transfer of auxiliary data. In the case of a display port, both signal lines are separate. The serial transfer circuit 12 is put in a pause state mainly for high-speed serial transfer.

  As shown in FIG. 2, the reference duty ratio DUTY data is further provided with a reference duty ratio input unit 36. The reference duty ratio input unit 36 receives externally input reference duty ratio DUTY1 data. May be used.

Image data of a still image is input to the memory circuit 14 from the controller 16.
The memory circuit 14 is a semiconductor memory such as a DRAM (Dynamic Random Access Memory), and is displayed on the display panel 24 by the panel self-refresh function in the second display mode under the control of the controller 16. The image data of a still image for one screen (one frame) is stored.

The controller 16 receives image data from the serial transfer circuit 12, data instructing the start of the first display mode and the second display mode, data instructing the serial transfer circuit 12 to return from the sleep state to the operating state, and The image data of the still image is input from the memory circuit 14.
The controller 16 controls switching between the first display mode and the second display mode based on data instructing the start of the first display mode and the second display mode.

The controller 16 generates a switching instruction signal instructing switching between the first display mode and the second display mode based on data instructing the start of the first display mode and the second display mode. When receiving data instructing the start of the first display mode, the controller 16 outputs a switching instruction signal instructing the first display mode, and when receiving data instructing the start of the second display mode, the controller 16 A switching instruction signal for instructing is output.
In addition, the controller 16 generates an image timing signal representing an H (horizontal) blanking period and a V (vertical) blanking period of an image displayed on the display panel 24.

The selector 18 receives from the serial transfer circuit 12 the image data of the first display mode (image data of the serial transfer circuit 12), and from the controller 16 the still image data of the second display mode (memory circuit 14). Image data) and a switching instruction signal.
As the output image data, the selector 18 outputs the image data of the serial transfer circuit 12 when the switching instruction signal indicates the first display mode, and when the switching instruction signal indicates the second display mode, the selector 18 Output image data.

  The duty ratio control circuit 20 controls the duty ratio of a brightness control signal for controlling the brightness of the backlight 22, and includes a V blanking detector 26, an elapsed time counter 28, a setting register 30, and a duty ratio control. Unit 32 and a luminance control signal generation unit 34.

A switching instruction signal and an image timing signal are input from the controller 16 to the V blanking detection unit 26.
The V blanking detection unit 26 outputs a V blanking detection signal that detects a V blanking period when switching from the second display mode to the first display mode based on the switching instruction signal and the image timing signal. .

The elapsed time counter 28 receives a V blanking detection signal from the V blanking detection unit 26.
The elapsed time counter 28 counts an elapsed time TIME from the start of the V blanking period when switching from the second display mode to the first display mode based on the V blanking detection signal.

  The setting register 30 holds and outputs setting values of the first offset amount OFFSET1, the second offset amount OFFSET2, the change amount VALUE, the limit amount LIMIT, and the polarity in the control direction.

The first offset amount OFFSET1 is used to change (increase or decrease) the duty ratio of the luminance control signal when switching from the second display mode to the first display mode by a certain value.
The second offset amount OFFSET2 is used to change (increase or decrease) the duty ratio of the luminance control signal in the second display mode by a certain value.
The change amount VALUE is used to change (increase or decrease) the duty ratio of the luminance control signal when switching from the second display mode to the first display mode by a constant value per unit time.
The limit amount LIMIT is used to set an upper limit value of the time (elapsed time TIME) for changing (increasing or decreasing) the duty ratio of the luminance control signal when switching from the second display mode to the first display mode. .
The control direction is used to specify the polarity (positive / negative) of the first offset amount OFFSET1, the second offset amount OFFSET2, and the change amount VALUE.

When switching from the second display mode to the first display mode, when reading of the image data of the memory circuit 14 is stopped and the V blanking period of the image data of the serial transfer circuit 12 is waited, the increase amount of the V blanking period is It changes depending on the switching timing. Further, how the luminance changes when the V blanking period increases is determined by the characteristics of the display panel 24.
In the second display mode, the amount of change in luminance when the refresh rate is intentionally lowered varies depending on the refresh rate and the characteristics of the display panel 24.
Therefore, the image display device 10 can reduce the occurrence of flicker and the change in luminance according to the increase amount of the V blanking period, the amount of change in luminance, the refresh rate, the characteristics of the display panel 24, and the like. Each set value of the first offset amount OFFSET1, the second offset amount OFFSET2, the change amount VALUE and the limit amount LIMIT, and the polarity in the control direction are determined and set in the setting register 30.

Subsequently, the duty ratio control unit 32 receives the reference duty ratio DUTY1 from the serial transfer circuit 12, the V blanking detection signal from the V blanking detection unit 26, the elapsed time TIME from the elapsed time counter 28, and the first from the setting register 30. Each set value of the offset amount OFFSET1, the second offset amount OFFSET2, the change amount VALUE, the limit amount LIMIT, and the polarity in the control direction are input.
The duty ratio control unit 32 includes reference duty ratio DUTY1, V blanking detection signal, elapsed time TIME, first offset amount OFFSET1, second offset amount OFFSET2, change value VALUE and limit amount LIMIT set values and control directions. The duty ratio control signal (control amount) for controlling the duty ratio of the luminance control signal is calculated based on the polarity of the brightness control signal.

  The duty ratio control unit 32 outputs a duty ratio control signal for controlling the duty ratio of the luminance control signal to be the reference duty ratio DUTY1 in the first control mode.

  Further, when the duty ratio control unit 32 switches from the second display mode to the first display mode, the reference duty ratio DUTY1, V blanking detection signal, elapsed time TIME, first offset amount OFFSET1, change amount VALUE, and limit amount LIMIT Based on each set value and the polarity in the control direction, a duty ratio control signal for controlling the luminance control signal so that the duty ratio of the luminance control signal becomes the duty ratio DUTY2 is calculated by the equation (1).

Duty ratio DUTY2 = Reference duty ratio DUTY1 ± (First offset amount OFFSET1 ± Change amount VALUE × Elapsed time TIME) Expression (1)
Here, when switching from the second display mode to the first display mode, it is detected by the V blanking detection signal, the elapsed time TIME <the limit amount LIMIT, and the two '±' polarities in the equation (1) are It is set according to the polarity of the control direction.

The duty ratio control unit 32 outputs a duty ratio control signal for performing control so that the duty ratio of the luminance control signal becomes the reference duty ratio DUTY1 in the second display mode.
Further, when the refresh rate when intentionally displaying a still image is lowered in the second display mode, the duty ratio control unit 32 sets the reference duty ratio DUTY1, the switching control signal, and the second offset amount OFFSET2 set value. Based on the polarity in the control direction, a duty ratio control signal for controlling the luminance control signal so that the duty ratio of the luminance control signal becomes the duty ratio DUTY3 is calculated by Expression (2).

Duty ratio DUTY3 = Reference duty ratio DUTY1 ± 2nd offset amount OFFSET2 Equation (2)
Here, in the second display mode, it is detected by a switching control signal, and the polarity of “±” in Expression (2) is set by the polarity in the control direction.

  The duty ratio control unit 32 determines the duty ratio DUTY2 and the duty ratio DUTY2 so that the duty ratios DUTY2 and DUTY3 calculated by the expressions (1) and (2) do not fall below 0% and do not exceed 100%. It is desirable to normalize DUTY3.

Subsequently, the duty ratio control signal is input from the duty ratio control section 32 to the luminance control signal generation section 34.
The luminance control signal generator 34 generates a luminance control signal having a duty ratio controlled by the duty ratio control signal. As the duty ratio of the luminance control signal increases, the luminance of the backlight 22 increases.

A luminance control signal is input from the luminance control signal generator 34 to the backlight 22.
The backlight 22 illuminates the display panel from the back side with a luminance corresponding to the luminance control signal.
The duty ratio control circuit 20 and the backlight 22 constitute a backlight adjustment circuit of the present invention. The backlight adjustment circuit controls the luminance of the backlight 22 using the luminance control signal whose duty ratio is controlled by the duty ratio control circuit 20.

Output image data is input from the selector 18 to the display panel 24.
The display panel 24, like a liquid crystal panel, displays an image corresponding to the output image data with luminance illuminated from the back side by the backlight 22.

  Next, the operation of the image display device 10 will be described.

The basic operation of the image display apparatus 10 other than the control of the duty ratio of the luminance control signal is the same as that of the conventional image display apparatus 40.
In the image display device 10, serial data and auxiliary data transferred from a PC or the like via a display port are received by the serial transfer circuit 12.

FIG. 3 is a conceptual diagram of an example showing the transfer timing of serial data and auxiliary data. As shown in the figure, image data for one screen is transferred to the image display device 10 for each frame from a PC or the like. One frame includes an image display period during which an image is displayed and a blanking period during which no image is displayed. Serial data including image data for one screen is sequentially transferred during the image display period.
The blanking period includes an H (horizontal) blanking period and a V (vertical) blanking period. A blanking start signal (BS) is transferred at the start timing of each blanking period, and a blanking end signal (BE) is transferred at the end timing of blanking.
Serial data including data instructing validity and invalidity of the panel self-refresh function is transferred during the blanking period. Data instructing to return the serial transfer circuit 12 from the hibernation state to the operation state is transferred during a period in which the serial transfer circuit 12 is in the hibernation state. The auxiliary data including the reference duty ratio DUTY1 is transferred at an arbitrary timing.

  When the controller 16 receives data (PSR function valid instruction) for instructing the validity of the panel self-refresh function from the serial transfer circuit 12 in the first display mode, the controller 16 sequentially receives 1 After sequentially writing still image data (still image data) for the screen into the memory circuit 14 inside the image display device 10, the serial transfer circuit 12 is put into a sleep state, and a switching instruction signal for instructing the second display mode is issued. Output.

  In the second display mode, the selector 18 outputs the still image data read from the memory circuit 14 by the controller 16 in response to the switching instruction signal to output image data (for example, the image data B0, FIG. B1) is output. On the display panel 24, a still image corresponding to the image data of the memory circuit 14 is displayed with the luminance illuminated from the back side by the backlight 22 at the timing read from the memory circuit 14.

  Subsequently, when the controller 16 receives from the serial transfer circuit 12 data (serial transfer circuit restart instruction) instructing to restart the serial transfer circuit 12 from the paused state and return to the operating state, the serial transfer circuit 12 is restarted to the operating state. Thereafter, upon receiving data (PSR function invalid instruction) for instructing invalidation of the panel self-refresh function from the serial transfer circuit 12, a switching instruction signal for instructing the first display mode is output.

When switching from the second display mode to the first display mode, first, the V blanking detection unit 26 performs V blanking when switching from the second display mode to the first display mode based on the switching instruction signal and the image timing signal. A V blanking detection signal for detecting the period is output.
For example, as shown in FIG. 8, the V blanking detection unit 26 changes based on the image timing signal so that the switching instruction signal indicates the first display mode from the second display mode. A V blanking increase period immediately after stopping the image data is detected.

  Subsequently, the elapsed time counter 28 counts the elapsed time TIME from the start of the V blanking period when switching from the second display mode to the first display mode based on the V blanking detection signal.

  Subsequently, the duty ratio control unit 32 changes the reference duty ratio DUTY1, V blanking detection signal, elapsed time TIME, first offset amount OFFSET1, change value VALUE, limit value LIMIT, and control direction polarity. Based on the equation (1), a duty ratio control signal for controlling the duty ratio of the luminance control signal to be equal to the duty ratio DUTY2 of the luminance control signal when switching from the second display mode to the first display mode is calculated. The

  Subsequently, the luminance control signal generator 34 generates a luminance control signal having a duty ratio controlled by the duty ratio control signal.

  In the first display mode, the selector 18 outputs the image data of the serial transfer circuit 12 as output image data (for example, A2 and A3 in FIG. 8) in response to the switching instruction signal. On the display panel 24, an image corresponding to the image data of the serial transfer circuit 12 is displayed with the brightness illuminated from the back side by the backlight 22 at the timing when the image data is received by the serial transfer circuit 12.

For example, when the two “±” polarities of equation (1) are both set to “+”, the duty ratio of the luminance control signal in the second display mode is set to the reference duty ratio DUTY1 as shown in FIG. Assuming that, the duty ratio DUTY2 of the luminance control signal when switching from the second display mode to the first display mode becomes the reference duty ratio DUTY1 + the first offset amount OFFSET1 at the start timing of the V blanking period, and then elapses Until the time TIME reaches the limit value LIMIT setting value, the amount of change VALUE increases every unit time, and when the elapsed time TIME reaches the limit value LIMIT setting value, the elapsed time TIME becomes the limit amount LIMIT The duty ratio when the set value is reached is maintained.
Thereafter, when the first display mode is entered, the duty ratio of the luminance control signal returns from the duty ratio DUTY2 to the reference duty ratio DUTY1.

In addition, when the polarity of “±” on the front side of the expression (1) is set to “−” and the polarity of “±” on the back side is set to “+”, as shown in FIG. If the duty ratio of the luminance control signal at the time is the reference duty ratio DUTY1, the duty ratio DUTY2 of the luminance control signal when switching from the second display mode to the first display mode is the reference at the start timing of the V blanking period. The duty ratio becomes DUTY1 – 1st offset amount OFFSET1, and then the change value VALUE decreases every unit time until the elapsed time TIME reaches the limit value LIMIT setting value, and the elapsed time TIME becomes the limit amount LIMIT When the set value is reached, the duty ratio when the elapsed time TIME reaches the set value of the limit amount LIMIT is maintained.
Thereafter, when the first display mode is entered, the duty ratio of the luminance control signal returns from the duty ratio DUTY2 to the reference duty ratio DUTY1.

  In addition, although explanation is omitted, when both of the two “±” polarities of the formula (1) are set to “−”, or the positive polarity of the “±” on the front side of the formula (1) is “+”, The same applies when the polarity of the rear “±” is set to “−”. Also in this case, it occurs when the V blanking period increases when switching from the second display mode to the first display mode according to the increase amount of the V blanking period, the amount of change in luminance, the characteristics of the display panel 24, and the like. The two “±” polarities of the equation (1) are set so that flickering can be reduced.

  Thus, by appropriately adjusting the duty ratio DUTY2 of the luminance control signal, when switching from the second display mode to the first display mode, a flicker that occurs when the V blanking period increases without taking a long time. Can be reduced.

  Further, when the refresh rate for intentionally displaying a still image is lowered in the second display mode, it is desirable to adjust the duty ratio DUTY3 of the luminance control signal in the second display mode. In this case, based on the reference duty ratio DUTY1, the setting value of the second offset amount OFFSET2, and the polarity in the control direction by the duty ratio control unit 32, the duty ratio of the luminance control signal becomes the duty ratio DUTY3 according to Equation (2). Thus, the duty ratio control signal to be controlled is calculated.

For example, when the polarity of “±” on the front side of Expression (1) is set to “−” and the polarity of “±” on the rear side is set to “+”, and “±” of Expression (2) When the polarity is set to “−”, as shown in FIG. 6, the duty ratio of the luminance control signal in the second display mode is the reference duty ratio DUTY1−the second offset amount OFFSET2. Further, the duty ratio DUTY2 of the luminance control signal when switching from the second display mode to the first display mode becomes the reference duty ratio DUTY1−the first offset amount OFFSET1 at the start timing of the V blanking period, and then the elapsed time TIME Until the limit value reaches the limit value LIMIT, the change value VALUE decreases every unit time, and when the elapsed time TIME reaches the limit value LIMIT, the elapsed time TIME sets the limit value LIMIT. Maintain the duty ratio when the value is reached.
Thereafter, when the first display mode is entered, the duty ratio of the luminance control signal returns from the duty ratio DUTY2 to the reference duty ratio DUTY1.

  Although not described here, the same applies to the case where the polarity of ‘±’ in Expression (2) is set to ‘+’. Also in this case, the polarity of “±” in Expression (2) is set so as to reduce the change in luminance according to the refresh rate, the characteristics of the display panel 24, and the like.

  As described above, by appropriately adjusting the duty ratio DUTY3 of the luminance control signal, even when the refresh rate for intentionally displaying a still image is lowered in the second display mode, the first display mode is set. The change in luminance after switching from the second display mode to the second display mode and after switching from the second display mode to the first display mode can be reduced.

  A specific circuit configuration for realizing the panel self-refresh function is not limited. Further, specific circuits of the V blanking detection unit 26, the elapsed time counter 28, the setting register 30, the duty ratio control unit 32, the luminance control signal generation unit 34, and the reference duty ratio input unit 36 that constitute the duty ratio control circuit 20 The configuration is not limited at all, and any of various configurations of circuits that realize the same function can be used. It is not essential to control the duty ratio of the luminance control signal in the second display mode.

The present invention is basically as described above.
Although the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and it is needless to say that various improvements and modifications may be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10, 40 Image display apparatus 12 Serial transfer circuit 14 Memory circuit 16 Controller 18 Selector 20 Duty ratio control circuit 22 Backlight 24 Display panel 26 V blanking detection part 28 Elapsed time counter 30 Setting register 32 Duty ratio control part 34 Luminance control signal Generation unit 36 Reference duty ratio input unit

Claims (4)

A still image corresponding to image data stored in an internal memory circuit is displayed on the display panel by a first display mode in which an image corresponding to image data input from the outside is displayed on the display panel and a panel self-refresh function. In the image display device having the second display mode, a duty ratio control circuit for controlling a duty ratio of a luminance control signal for controlling the luminance of the backlight of the display panel,
Based on a switching instruction signal for instructing switching between the first display mode and the second display mode, and an image timing signal representing a V blanking period of an image displayed on the display panel, the second display mode A V blanking detection unit that outputs a V blanking detection signal that detects a V blanking period immediately after the second display mode when switching from the first display mode to the first display mode;
An elapsed time counter that counts an elapsed time from the start of the V blanking period immediately after the second display mode when switching from the second display mode to the first display mode based on the V blanking detection signal;
A first offset amount for changing a duty ratio of the luminance control signal by a constant value only in a V blanking period immediately after the second display mode when switching from the second display mode to the first display mode; Specifies the amount of change for changing the duty ratio by a constant value per unit time, the limit amount for setting the upper limit of the time for changing the duty ratio of the luminance control signal, and the polarity of the first offset amount and the amount of change A setting register that holds the polarity of the control direction to be
Based on the duty ratio of the luminance control signal in the first display mode, the V blanking detection signal, the elapsed time, and the first offset amount, the change amount, the limit amount, and the polarity of the control direction, The duty ratio control signal for controlling the duty ratio of the luminance control signal only in the V blanking period immediately after the second display mode when switching from the second display mode to the first display mode is calculated by the following equation (1). A duty ratio control unit,
A luminance control signal generation unit that generates a luminance control signal having a duty ratio controlled by the duty ratio control signal;
The duty ratio control unit uses the duty ratio of the luminance control signal in the first display mode, included in the auxiliary data transferred from the outside via the serial transfer port, from the second display mode. Controlling the duty ratio of the luminance control signal only in the V blanking period immediately after the second display mode when switching to the first display mode;
The duty ratio of the luminance control signal only in the V blanking period immediately after the second display mode when switching from the second display mode to the first display mode = the duty ratio of the luminance control signal in the first display mode ± (The first offset amount ± the change amount × the elapsed time) Formula (1)
Here, when switching from the second display mode to the first display mode, it is detected by the V blanking detection signal, the elapsed time <the limit amount, and the two positive polarities of the above formula (1) Is set according to the polarity in the control direction. A still image corresponding to image data stored in an internal memory circuit is displayed on the display panel by a first display mode in which an image corresponding to image data input from the outside is displayed on the display panel and a panel self-refresh function. In the image display device having the second display mode, a duty ratio control circuit for controlling a duty ratio of a luminance control signal for controlling the luminance of the backlight of the display panel,
Based on a switching instruction signal for instructing switching between the first display mode and the second display mode, and an image timing signal representing a V blanking period of an image displayed on the display panel, the second display mode A V blanking detection unit that outputs a V blanking detection signal that detects a V blanking period immediately after the second display mode when switching from the first display mode to the first display mode;
An elapsed time counter that counts an elapsed time from the start of the V blanking period immediately after the second display mode when switching from the second display mode to the first display mode based on the V blanking detection signal;
A first offset amount for changing a duty ratio of the luminance control signal by a constant value only in a V blanking period immediately after the second display mode when switching from the second display mode to the first display mode; Specifies the amount of change for changing the duty ratio by a constant value per unit time, the limit amount for setting the upper limit of the time for changing the duty ratio of the luminance control signal, and the polarity of the first offset amount and the amount of change A setting register that holds the polarity of the control direction to be
Based on the duty ratio of the luminance control signal in the first display mode, the V blanking detection signal, the elapsed time, and the first offset amount, the change amount, the limit amount, and the polarity of the control direction, The duty ratio control signal for controlling the duty ratio of the luminance control signal only in the V blanking period immediately after the second display mode when switching from the second display mode to the first display mode is calculated by the following equation (1). A duty ratio control unit,
A luminance control signal generating unit that generates a luminance control signal having a duty ratio controlled by the duty ratio control signal;
A reference duty ratio input unit that receives the duty ratio of the luminance control signal in the first display mode, input from the outside,
The duty ratio control unit switches from the second display mode to the first display mode using a duty ratio of a luminance control signal in the first display mode, which is input from the reference duty ratio input unit. Controlling the duty ratio of the luminance control signal only in the V blanking period immediately after the second display mode at the time,
The duty ratio of the luminance control signal only in the V blanking period immediately after the second display mode when switching from the second display mode to the first display mode = the duty ratio of the luminance control signal in the first display mode ± (The first offset amount ± the change amount × the elapsed time) Formula (1)
Here, when switching from the second display mode to the first display mode, it is detected by the V blanking detection signal, the elapsed time <the limit amount, and the two positive polarities of the above formula (1) Is set according to the polarity in the control direction. The setting register further holds data for setting a second offset amount for changing a duty ratio of the luminance control signal in the second display mode by a certain value.
The duty ratio control unit further includes the following formula (2) based on the duty ratio of the luminance control signal in the first display mode, the switching control signal, the second offset amount, and the polarity in the control direction. ) To calculate a duty ratio control signal for controlling the duty ratio of the luminance control signal in the second display mode,
Duty ratio of luminance control signal in the second display mode = duty ratio of luminance control signal in the first display mode ± second offset amount Equation (2)
Here, when the second display mode, the detected by the switching control signal, the polarity of the ± of the equation (2) is claimed in claim 1 or 2 in which it is set by the polarity of the control direction Duty ratio control circuit. Backlight adjusting circuit, characterized in that controls the brightness of the backlight using the luminance control signal whose duty ratio is controlled by the duty ratio control circuit according to any one of claims 1 to 3 .

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