Synchronous Backlight Device and Operation Method Thereof

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Reissue Application of U.S. Pat. No. 10,692,443 issued on Jun. 23, 2020. The entirety of the above-mentioned patent is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

Field of the Invention

The invention relates to a display device and more particularly, to a synchronous backlight device and an operation method thereof.

Description of Related Art

FIG. 1 is a schematic waveform diagram of a backlight control signal BL 1 when a backlight device of the related art controls/drives a backlight source in an asynchronous manner. In FIG. 1 , the vertical axis represents the voltage, and the horizontal axis represents the time. In FIG. 1 , Vsync represents a vertical sync signal, and DE represents a data enablement signal. A video processing circuit (not shown) may transmit the vertical sync signal Vsync and the data enablement signal DE to a panel driving circuit (not shown), so as to control the panel driving circuit to drive a liquid crystal display (LCD) panel (not shown). The vertical sync signal Vsync defines a plurality of video frame periods, for example, video frame periods F 1 , F 2 , F 3 and F 4 as illustrated in FIG. 1 . As illustrated in FIG. 1 , the backlight control signal BL 1 of the backlight device of the related art is unrelated to phases (or timings) of the video frame periods F 1 , F 2 , F 3 and F 4 , i.e., the backlight device of the related art controls a backlight source (not shown) in an asynchronous manner. An issue of motion blur may occurs to the LCD panel using the asynchronous backlight.

FIG. 2 A is a schematic waveform diagram of a backlight control signal BL 2 when the backlight device of the related art controls/drives the backlight source in a synchronous manner. In FIG. 2 A , the vertical axis represents the voltage, and the horizontal axis represents the time. In FIG. 2 A , Vsync represents a vertical sync signal, and DE represents a data enablement signal. The vertical sync signal Vsync defines a plurality of video frame periods, for example, video frame periods F 1 , F 2 , F 3 and F 4 as illustrated in FIG. 2 A . As illustrated in FIG. 2 A , a phase (or a timing) of the backlight control signal BL 2 of the backlight device of the related art may be synchronous with the video frame periods F 1 , F 2 , F 3 and F 4 in accordance with the vertical sync signal Vsync, i.e., the backlight device of the related art controls/drives a backlight source (not shown) in a synchronous manner. When the backlight control signal BL 2 is at a high level, the backlight source provides backlight. When the backlight control signal BL 2 is at a low level, the backlight source does not provide backlight. Pulse widths PW 2 of the backlight control signal BL 2 in the video frame periods F 1 , F 2 , F 3 and F 4 are equal to one another, and the pulse widths PW 2 may be modulated according to use requirements.

FIG. 2 B is a schematic waveform diagram of a backlight control signal BL 2 when the backlight device of another related art controls/drives the backlight source in a synchronous manner. In FIG. 2 B , the vertical axis represents the voltage, and the horizontal axis represents the time. The vertical sync signal Vsync and the data enablement signal DE illustrated in FIG. 2 B may be derived with reference to the description related to FIG. 2 A and thus, will not be repeated. As illustrated in FIG. 2 B , a phase (or a timing) of the backlight control signal BL 2 of the backlight device of the related art may be synchronous with the video frame periods F 1 , F 2 , F 3 and F 4 in accordance with the data enablement signal DE, i.e., the backlight device of the related art controls/drives a backlight source (not shown) in a synchronous manner. Pulse widths PW 2 of the backlight control signal BL 2 in the video frame periods F 1 , F 2 , F 3 and F 4 are equal to one another, and the pulse widths PW 2 may be modulated according to use requirements. In any case, in an actual application environment, a period length of the vertical sync signal Vsync (a period length of the data enablement signal DE) may not be fixed, lengths of the video frame periods F 1 , F 2 F 4 and F 4 are different from one another (as illustrated in FIG. 2 A and FIG. 2 B ). For the LCD panel using the synchronous backlight, an issue of backlight flicker may arise to the backlight device of the related art because the period length of the vertical sync signal Vsync is not fixed.

SUMMARY

The invention provides a synchronous backlight device and an operation method thereof for improving the issue backlight flicker.

According to an embodiment of the invention, a synchronous backlight device including a pulse width modulation (PWM) control circuit and a backlight driving circuit is provided. The PWM control circuit is configured to receive video sync information from a video processing circuit and generate a PWM control signal. The video sync information defines a plurality of video frame periods, the PWM control circuit at least divides each of the video frame periods into a first period and a second period, and lengths of the first periods of the video frame periods are equal to one another. A frequency of the PWM control signal in the first periods is different from a frequency of the PWM control signal in the second periods. The backlight driving circuit is coupled to the PWM control circuit to receive the PWM control signal. The backlight driving circuit is configured to drive a backlight source of a display panel according to the PWM control signal.

According to an embodiment of the invention, an operation method of a synchronous backlight device is provided. The operation method includes: receiving video sync information from a video processing circuit, wherein the video sync information defines a plurality of video frame periods; at least dividing each of the video frame periods into a first period and a second period by a PWM control circuit, wherein lengths of the first periods of the video frame periods are equal to one another; generating a PWM control signal by the PWM control circuit, wherein a frequency of the PWM control signal in the first periods is different from a frequency of the PWM control signal in the second periods; and driving a backlight source of a display panel by a backlight driving circuit according to the PWM control signal.

Based on the above, in the synchronous backlight device and the operation method thereof according to the embodiments of the invention, each video frame period is at least divided into the first period and the second period. The lengths of the first periods of various video frame periods are equal to one another. If the length of each video frame period is changed, the lengths of the second periods are changed as well. The frequency of the PWM control signal in the first periods is different from the frequency of the PWM control signal in the second periods. With the backlight source providing compensation light in the second periods, the synchronous backlight device and the operation method thereof can achieve improving the issue of backlight flicker.

In order to make the aforementioned and other features and advantages of the invention more comprehensible, several embodiments accompanied with figures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a schematic waveform diagram of a backlight control signal when a backlight device of the related art controls/drives a backlight source in an asynchronous manner.

FIG. 2 A is a schematic waveform diagram of a backlight control signal when the backlight device of the related art controls/drives the backlight source in a synchronous manner.

FIG. 2 B is a schematic waveform diagram of a backlight control signal BL 2 when the backlight device of another related art controls/drives the backlight source in a synchronous manner.

FIG. 3 is a schematic circuit block diagram illustrating a display device according to an embodiment of the invention.

FIG. 4 is a flowchart illustrating an operation method of a synchronous backlight device according to an embodiment of the invention.

FIG. 5 is a schematic waveform diagram of the phase width modulation (PWM) control signal depicted in FIG. 3 according to an embodiment of the invention.

FIG. 6 is a schematic circuit block diagram illustrating the PWM control circuit depicted in FIG. 3 according to an embodiment of the invention.

FIG. 7 is a schematic waveform diagram of the signals depicted in FIG. 6 according to an embodiment of the invention.

FIG. 8 is a schematic circuit block diagram illustrating the PWM control circuit depicted in FIG. 3 according to another embodiment of the invention.

FIG. 9 is a schematic waveform diagram of the vertical sync signal and the smoothed signal depicted in FIG. 8 according to an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

A term “couple” used in the full text of the disclosure (including the claims) refers to any direct and indirect connections. For instance, if a first device is described to be coupled to a second device, it is interpreted as that the first device is directly coupled to the second device, or the first device is indirectly coupled to the second device through other devices or connection means. Moreover, wherever possible, components/members/steps using the same referral numerals in the drawings and description refer to the same or like parts. Components/members/steps using the same referral numerals or using the same terms in different embodiments may cross-refer related descriptions.

FIG. 3 is a schematic circuit block diagram illustrating a display device 300 according to an embodiment of the invention. The display device 300 includes a video processing circuit, which is, for example, a scaler circuit 310 and/or any other video signal processing circuit. The display device 300 further includes a panel driving circuit 320 , a display panel 330 , a synchronous backlight device 340 and a backlight source 350 . The scalar circuit 310 (i.e., the video processing circuit) may transmit a clock signal, video sync information and video data to the panel driving circuit 320 , so as to control the panel driving circuit to drive the display panel 330 . Based on a design requirement, the video sync information may include a vertical sync signal, a horizontal sync signal, a data enablement signal and/or any other sync signal. The vertical sync signal may define a plurality of video frame periods. Based on a design requirement, the display panel 330 may be a liquid crystal display (LCD) panel or a display panel of any other type. The scalar circuit 310 , the panel driving circuit 320 and the display panel 330 are conventional components and thus, will not be repeatedly described.

In the embodiment illustrated in FIG. 3 , the synchronous backlight device 340 may receive the video sync information from the video processing circuit (e.g., the scalar circuit 310 ). According to the video sync information, the synchronous backlight device 340 may control/drive the backlight source in a synchronous manner. The synchronous backlight device 340 may perform global backlight control or local backlight control on the backlight source 350 . The backlight source 350 may provide backlight 351 to the display panel 330 . Based on a design requirement, the backlight source 350 may be a direct type backlight module or an edge-lighting type backlight module. As the synchronous backlight device 340 controls/drives the backlight source in the synchronous manner, the issue of motion blur may be effectively improved.

In the embodiment illustrated in FIG. 3 , the synchronous backlight device 340 includes a pulse width modulation (PWM) control circuit 341 and a backlight driving circuit 342 . The PWM control circuit 341 is coupled to the video processing circuit (e.g., the scalar circuit 310 ) to receive the video sync information (e.g., the vertical sync signal, the data enablement signal and/or any other sync signal). The PWM control circuit 341 may generate a PWM control signal BL 3 . The backlight driving circuit 342 is coupled to the PWM control circuit 341 to receive the PWM control signal BL 3 . According to the PWM control signal BL 3 , the backlight driving circuit 342 may drive the backlight source 350 of the display panel 330 . The PWM control circuit 341 may perform the global backlight control or the local backlight control on the backlight source 350 .

FIG. 4 is a flowchart illustrating an operation method of a synchronous backlight device according to an embodiment of the invention. Referring to FIG. 3 and FIG. 4 , in step S 410 , the PWM control circuit 341 receives the video sync information (e.g., the vertical sync signal, the data enablement signal and/or any other sync signal) from the video processing circuit (e.g., the scalar circuit 310 ). The video sync information defines a plurality of video frame periods. In step S 420 , the PWM control circuit 341 at least divides each of the video frame periods into a first period and a second period, wherein lengths of the first periods of various video frame periods are equal to one another.

FIG. 5 is a schematic waveform diagram of the PWM control signal BL 3 depicted in FIG. 3 according to an embodiment of the invention. In FIG. 5 , the vertical axis represents the voltage, and the horizontal axis represents the time. In the implementation example illustrated in FIG. 5 , it is assumed that the PWM control circuit 341 receives the vertical sync signal Vsync (i.e., the video sync information) from the video processing circuit (e.g., the scalar circuit 310 ). Referring to FIG. 3 , FIG. 4 and FIG. 5 , the vertical sync signal Vsync (i.e., the video sync information) defines a plurality of video frame periods, for example, video frame periods F 5 , F 6 , F 7 and F 8 as illustrated in FIG. 5 . In another implementation example, the PWM control circuit 341 receives the data enablement signal DE (i.e., the video sync information) from the video processing circuit (e.g., the scalar circuit 310 ). The data enablement signal DE (i.e., the video sync information) also can define a plurality of video frame periods, for example, video frame periods F 5 , F 6 , F 7 and F 8 as illustrated in FIG. 5 .

In step S 420 , the PWM control circuit 341 at least divides each of the video frame periods into a first period and a second period. Based on a design requirement, a first periods includes part or all of a data period of each of the video frame periods, and a second periods includes part or all of a blanking period of each of the video frame periods.

For instance, according to the data enablement signal DE in the video sync information, the video frame period F 5 is at least divided into a first period P 51 and a second period P 52 , the video frame period F 6 is at least divided into a first period P 61 and a second period P 62 , the video frame period F 7 is at least divided into a first period P 71 and a second period P 72 , and the video frame period F 8 is at least divided into a first period P 81 and a second period P 82 . Lengths of the first periods P 51 , P 61 , P 71 and P 81 of the video frame periods F 5 to F 8 are equal to one another. The first period P 51 includes a data period of the video frame period F 5 , and the second period P 52 includes a blanking period of the video frame period F 5 . The first period P 61 includes a data period of the video frame period F 6 , and the second period P 62 includes a blanking period of the video frame period F 6 . The first period P 71 includes a data period of the video frame period F 7 , and the second period P 72 includes a blanking period of the video frame period F 7 . The first period P 81 includes a data period of the video frame period F 8 , and the second period P 82 includes a blanking period of the video frame period F 8 .

In step S 430 , the PWM control circuit 341 generates the PWM control signal BL 3 . A frequency of the PWM control signal BL 3 in the first periods is different from a frequency of the PWM control signal BL 3 in the second periods, but a duty ratio of the PWM control signal BL 3 in the first periods is equal to a duty ratio of the PWM control signal BL 3 in the second periods. For instance, the frequency of the PWM control signal BL 3 in the first period P 51 is different from the frequency of the PWM control signal BL 3 in the second period P 52 , but the duty ratio of the PWM control signal BL 3 in each duty cycle of the first period P 51 is equal to the duty ratio of the PWM control signal BL 3 in each duty cycle of the second period P 52 .

In the embodiment illustrated in FIG. 5 , the frequency of the PWM control signal BL 3 in the first periods is less than the frequency of the PWM control signal BL 3 in the second periods. For instance, the frequency of the PWM control signal BL 3 in the first period P 51 is less than the frequency of the PWM control signal BL 3 in the second period P 52 .

The backlight driving circuit 342 is coupled to the PWM control circuit 341 to receive the PWM control signal BL 3 . In step S 440 , the backlight driving circuit 342 drives the backlight source 350 of the display panel 330 according to the PWM control signal BL 3 , such that the backlight source 350 is driven to provide the backlight 351 to the display panel 330 .

Based on the above, the synchronous backlight device 340 and the operation method thereof provided by the present embodiment, each video frame period is at least divided into the first period and the second period. The lengths of the first periods of various video frame periods are equal to one another. If the length of each video frame period is changed, the lengths of the second periods are changed along therewith, but the lengths of the first periods are not. The frequency of the PWM control signal BL 3 in the first periods is different from the frequency of the PWM control signal BL 3 in the second periods, but the duty ratio of the PWM control signal BL 3 in each first period is equal to the duty ratio of the PWM control signal BL 3 in each second period. Thus, with the backlight source 350 being driven/controlled to provide compensation light (i.e., the backlight 351 ) in the second periods, the average backlight brightness in various video frame periods F 5 to F 8 may tend to be approximately equal to one another. In other words, the synchronous backlight device 340 and the operation method thereof can achieve improving the issue of backlight flicker.

FIG. 6 is a schematic circuit block diagram illustrating the PWM control circuit depicted in FIG. 3 according to an embodiment of the invention. In the embodiment illustrated in FIG. 6 , the PWM control circuit 341 includes a period defining circuit 610 , a first PWM signal generating circuit 620 , a second PWM signal generating circuit 630 and a superimposing circuit 640 . The period defining circuit 610 is coupled to the video processing circuit (e.g., the scalar circuit 310 ) to receive the video sync information (e.g., the vertical sync signal Vsync) from the video processing circuit. According to a timing of the vertical sync signal Vsync (i.e., the video sync information), the period defining circuit 610 may generate a first enablement signal 611 and a second enablement signal 612 . The first enablement signal 611 may define the first periods, and the second enablement signal 612 may define the second periods.

For instance, FIG. 7 is a schematic waveform diagram of the signals depicted in FIG. 6 according to an embodiment of the invention. In FIG. 7 , the vertical axis represents the voltage, and the horizontal axis represents the time. The vertical sync signal Vsync defines a plurality of video frame periods, for example, video frame periods F 9 and F 10 as illustrated in FIG. 7 . The video frame period F 9 is at least divided into a first period P 91 and a second period P 92 , and the video frame period F 10 is at least divided into a first period P 101 and a second period P 102 . The first enablement signal 611 may define the first periods P 91 and P 101 , and the second enablement signal 612 may define the second periods P 92 and P 102 . Lengths of the first periods P 91 and P 101 are equal to each other. If lengths of the video frame periods are changed, lengths of the second periods P 92 and P 102 are also changed along therewith, but lengths of the first periods P 91 and P 101 are not.

Referring to FIG. 6 and FIG. 7 , the first PWM signal generating circuit 620 is coupled to the period defining circuit 610 to receive the first enablement signal 611 . The first PWM signal generating circuit 620 may generate the first PWM signal 621 according to the first enablement signal 611 in the first periods. The first PWM signal generating circuit 620 may determine a duty ratio of the first PWM signal 621 in each first period according to a duty ratio parameter DR. It is assumed that the duty ratio is 50% in the embodiment illustrated in FIG. 7 , while the duty ratio may be adjusted based on use requirements in other embodiments. The first PWM signal generating circuit 620 may further determine a phase of the first PWM signal 621 in each first period according to the delay parameter DL.

In the embodiment illustrated in FIG. 7 , when the first enablement signal 611 is at a low level, the first PWM signal generating circuit 620 is disabled. When the first enablement signal 611 is at a high level, the first PWM signal generating circuit 620 is enabled. Thus, the first PWM signal generating circuit 620 may generate the first PWM signal 621 in the first periods P 91 and P 101 . The first PWM signal generating circuit 620 may set the duty ratio of the first PWM signal 621 in the first periods P 91 and P 101 to 50% according to the duty ratio parameter DR. The first PWM signal generating circuit 620 may further determine a time of delay TD of a pulse of the first PWM signal 621 in the first periods P 91 and P 101 according to the delay parameter DL, i.e., determine a phase of the first PWM signal 621 in the first periods P 91 and P 101 .

The second PWM signal generating circuit 630 is coupled to the period defining circuit 610 to receive the second enablement signal 612 . The second PWM signal generating circuit 630 may generate the second PWM signal 631 according to the second enablement signal 612 in the second periods. The second PWM signal generating circuit 630 may determine a duty ratio of the second PWM signal 631 in the second periods according to the same duty ratio parameter DR. In the embodiment illustrated in FIG. 7 , when the second enablement signal 612 is at a low level, the second PWM signal generating circuit 630 is disabled. When the second enablement signal 612 is at a high level, the second PWM signal generating circuit 630 is enabled. Thus, the second PWM signal generating circuit 630 may generate the second PWM signal 631 in the second periods P 92 and P 102 . The second PWM signal generating circuit 630 may set the duty ratio of the second PWM signal 631 in the second periods P 92 and P 102 to 50% according to the duty ratio parameter DR. A frequency of the second PWM signal 631 in the second periods P 92 and P 102 is different from a frequency of the first PWM signal 621 in the first periods P 91 and P 101 .

The superimposing circuit 640 is coupled to the first PWM signal generating circuit 620 to receive the first PWM signal 621 . The superimposing circuit 640 is coupled to the second PWM signal generating circuit 630 to receive the second PWM signal 631 . The superimposing circuit 640 may superimpose the first PWM signal 621 and the second PWM signal 631 to obtain the PWM control signal BL 3 , as illustrated in FIG. 7 .

FIG. 8 is a schematic circuit block diagram illustrating the PWM control circuit 341 depicted in FIG. 3 according to another embodiment of the invention. In the embodiment illustrated in FIG. 8 , the PWM control circuit 341 includes a low pass filter 710 , a period defining circuit 610 , a first PWM signal generating circuit 620 , a second PWM signal generating circuit 630 and a superimposing circuit 640 . The period defining circuit 610 , the first PWM signal generating circuit 620 , the second PWM signal generating circuit 630 and the superimposing circuit 640 illustrated in FIG. 8 may be inferred with reference to the descriptions related to the embodiment illustrated in FIG. 6 and FIG. 7 and thus, will not be repeated.

In the embodiment illustrated in FIG. 8 , the low pass filter 710 is coupled to the video processing circuit (e.g., the scalar circuit 310 ) to receive the video sync information (e.g., the vertical sync signal Vsync) from the video processing circuit. The low pass filter 710 may output a smoothed signal 711 to the period defining circuit 610 . FIG. 9 is a schematic waveform diagram of the vertical sync signal Vsync and the smoothed signal 711 depicted in FIG. 8 according to an embodiment of the invention. As illustrated in FIG. 9 , the low pass filter 710 may smooth the vertical sync signal Vsync to generate the smoothed signal 711 . The period defining circuit 610 is coupled to the low pass filter 710 to receive the smoothed signal 711 . The period defining circuit 610 may generate the first enablement signal 611 and the second enablement signal 612 according to a timing of the smoothed signal 711 .

It should be noted that in different application scenarios, related functions of the synchronous backlight device 340 , the PWM control circuit 341 and/or the backlight driving circuit 342 may be implemented in a form of software, firmware or hardware by employing general programming languages (e.g., C or C++), hardware description languages (e.g., Verilog HDL or VHDL) or other suitable programming languages. The programming languages capable of executing the related functions may be deployed in any computer-accessible media, such as magnetic tapes, semiconductor memories, magnetic disks or compact disks (e.g., CD-ROM or DVD-ROM) or may be delivered through the Internet, wired communication, wireless communication or other communication media. The programming languages may be stored in the computer-accessible media for a processor of the computer to access/execute the programming codes of the software (or firmware). In the implementation in the hardware form, one or more controllers, the functions of the embodiments of the invention can be implemented or executed by one or more controllers, microcontrollers, microprocessors, application-specific integrated circuits (ASICs), digital signal processors (DSPs), field programmable gate array (FPGAs) and/or other various logical blocks, modules and circuits in other processing units. In addition, the device and the method of the invention can be implemented through a combination of hardware and software.

In light of the foregoing, the synchronous backlight device and the operation method thereof provided by the embodiments of the invention can control/drive the backlight source synchronously, and therefore, the issue of motion blur can be effectively improved. The synchronous backlight device and the operation method thereof can be applied in the backlight control scenarios where the vertical sync signal is variable, or the vertical sync signal is fixed. In the synchronous backlight device and the operation method thereof, each of the video frame periods can be at least divided into the first period and the second period. The lengths of the first periods of various video frame periods are equal to one another. If the lengths of the video frame periods are changed, the lengths of the second periods are also changed along therewith, but the lengths of the first periods are not. The frequency of the PWM control signal BL 3 in the first periods is different from the frequency of the PWM control signal BL 3 in the second periods, but the duty ratio of the PWM control signal BL 3 in the first periods is equal to the duty ratio of the PWM control signal BL 3 in the second periods. Thus, with the backlight source 350 being driven to provide the compensation light (i.e., the backlight 351 ) in the second periods, the average backlight brightness in various video frame periods can tend to be approximately equal to one another. In other words, the synchronous backlight device and the operation method thereof can achieve improving the issue of backlight flicker.

Although the invention has been described with reference to the above embodiments, it will be apparent to one of the ordinary skill in the art that modifications to the described embodiment may be made without departing from the spirit of the invention. Accordingly, the scope of the invention will be defined by the attached claims not by the above detailed descriptions.