WO2007013251A1 - Light source unit for display device and display device using the light source unit - Google Patents

Abstract

It is possible to provide a light source unit for a display device or a display device not causing interference fringe or waving noise caused by interference between a vertical synchronization signal used for driving a display panel and a flash cycle of the light source. A light source unit for a display device for operating a light source according to a signal in which ON time for turning ON the light source periodically appears includes means for generating a random number and light adjusting means. The light adjusting means thins the ON time from the signal at random according to the brightness adjustment level by the user so that the blanking time when the light source is OFF appears irregularly.

Description

 Specification

 LIGHT UNIT FOR DISPLAY DEVICE AND DISPLAY DEVICE PROVIDED WITH THIS LIGHT UNIT

 TECHNICAL FIELD [0001] The present invention relates to a light source unit for a display device and a display device including the light source unit, and more specifically, for a display device that performs dimming by a pulse width modulation (PWM) method. The present invention relates to a light source unit and a display device including the light source unit.

 Background art

 For example, a display device including a non-self-luminous display panel such as a transmissive liquid crystal display panel generally has a configuration in which a light source unit is disposed on the back side of the display panel. Such a display device is configured such that light emitted from the light source unit is transmitted through the display panel from the back side to the front side, and an image is displayed in a visible state on the front side of the display panel. .

 [0003] As a light control method of such a light source unit for a display device, for example, a light control method using a pulse width modulation method is used. The pulse width modulation method is a method of adjusting the ratio of the light emission time and the non-light emission time within a predetermined short period called a PWM dimming period according to the brightness adjustment level. The dimming method using such a pulse width modulation method has a wider dimming range than the conventional current control method, that is, the dimming method of adjusting the current value flowing through the light source in an analog manner. If you can, you have the advantage. For this reason, it is now widely used.

 On the other hand, in the dimming method based on the pulse width modulation method, the light emission and non-light emission of the light source are alternately repeated in a short cycle, so that the light emission and non-light emission cycle and the vertical synchronization signal of the display panel May interfere. As a result, when horizontal stripe fringes appear on the display panel and flow in the vertical direction, V, V, and so-called wobbling noise may occur.

[0005] Generation of such wobbling noise is preferably suppressed as much as possible because it impairs the display quality of the display device in which the light source unit is incorporated. Various configurations for suppressing this are used. For example, the display panel displays the PWM dimming cycle When the position of the interference fringes appearing on the display panel is fixed by synchronizing with the vertical synchronizing signal of the image to be used, a configuration is used. When the position of the interference fringe is fixed, the interference fringe becomes inconspicuous as compared to the case of flowing in the vertical direction.

 [0006] As prior art documents related to the present invention, JP 2002-287700 A, JP 2002-354823 A, and JP 2004-259510 A are listed.

 Disclosure of the invention

 Problems to be solved by the invention

 [0007] Since this cubbing noise is caused by interference between the PWM dimming period and the vertical synchronizing signal, the frequency of the vertical synchronizing signal changes or the ratio of the light source emission period within the PWM dimming period changes. If this happens, the symptoms that occur will also change. Therefore, no wobbling noise occurs when used with a vertical sync signal at a certain frequency, but it may occur when the frequency is changed to another specific frequency. In addition, when the user adjusts the brightness, the ratio of the light emission time within the PWM dimming cycle changes, so that there is a case where a subtracting noise occurs at a certain brightness.

 There are the following scenes in which vertical synchronization signals having different frequencies are used. First, when using the display panel as a television receiver, etc., the display panel may be configured to support both NTSC and PAL signals, and the user may select and use the signal system. Can be mentioned. Moreover, it is configured to output a plurality of vertical synchronization signals having different frequencies as in a personal computer, and the intermediate user may select or switch between them as appropriate.

 [0009] In a configuration in which a PWM dimming pulse is synchronized with a vertical synchronization signal having a specific frequency, when it is used with a vertical synchronization signal having a frequency different from the frequency, there may be a case where a cubbing noise occurs. Therefore, when both the NTSC system signal and the PAL system signal are used, the PWM dimming pulse cycle is set to a setting suitable for the NTSC system and a setting suitable for the PAL system. An intermediate setting may be used. According to such a configuration, it is difficult to completely eliminate the force that can make the noise noise inconspicuous in any method.

[0010] In view of the above situation, the problem to be solved by the present invention is that interference fringes are formed on the display panel. It is possible to provide a light source unit and a display device that do not generate a single buzzing noise, particularly when a vertical synchronization signal used for driving a display panel is used by selecting or switching different frequency forces. Providing a light source unit and display device that do not generate wobbling noise, or when adjusting the brightness, interference fringes do not generate wobbling noise at a specific brightness. A light source unit and a display device are provided.

 Means for solving the problem

 In order to solve such a problem, a light source unit according to the present invention is set by a user in a light source unit for a display device that supplies a light source with a signal in which an on-time for turning on the light source appears periodically. In accordance with the brightness adjustment level, it is configured to include a light control means for generating a light source control signal obtained by thinning the on-time for turning on the light source from this signal at irregular timings.

 [0012] The light source unit for the display device turns on the light source according to a means for generating a random number, a random value generated by the means for generating a random number, and a brightness adjustment level set by the user. The signal power in which the on-time appears periodically may be configured to include a dimming unit that generates a light source control signal by thinning out the on-time at random.

 [0013] Further, a setting for thinning the on-time at irregular timing according to the brightness adjustment level by the user from the means for generating the random number and the signal in which the on-time for turning on the light source appears periodically. A plurality of setting storage means for storing, and a dimming means for extracting a plurality of setting power settings stored by the setting storage means based on the generated random number and generating a light source control signal based on the extracted settings It may be a configuration.

 As the means for generating the random number, a configuration including a voltage value reading circuit that reads the voltage of the power source that drives the light source and a conversion means that converts the read voltage value into a random value can be applied.

[0015] In addition, from the signal in which the on-time for turning on the light source periodically appears, a plurality of settings for randomly setting the on-time according to the brightness adjustment level by the user are stored. The dimming means may be configured to read and use a plurality of settings stored in the setting storage means in order! [0016] A display device according to the present invention has a configuration in which any one of the light source units for the display device is incorporated.

 The invention's effect

 [0017] According to the present invention, the on-time is thinned out at irregular timings, so that the onset timing of the blanking time when the light source is not turned on has no periodicity. Therefore, even if the vertical sync signal power input to the display panel is a certain frequency, or at any brightness, no interference occurs between the occurrence of the blanking time and the vertical sync signal. . As a result, generation of interference fringes on the display panel and occurrence of wobbling noise due to vertical movement of the generated interference fringes can be prevented.

 [0018] By inserting such a lighting unit, it is possible to provide a display device capable of displaying a high-quality image on which no interference fringe noise is generated. Brief Description of Drawings

 FIG. 1 is a block diagram showing a main part of a configuration of a light source unit according to a first embodiment of the present invention and a display device incorporating the light source unit.

 FIG. 2 is a flowchart showing a light source control signal generation method in the light source unit according to the embodiment.

 FIG. 3 is a schematic diagram showing a configuration of a random number generation circuit included in random number generation means of the light source unit according to the embodiment.

 FIG. 4 is a block diagram showing a main part of a configuration of a light source unit according to a second embodiment of the present invention and a display device incorporating the light source unit.

 FIG. 5 is a block diagram showing a main part of a configuration of a light source unit according to a third embodiment of the present invention and a display device incorporating the light source unit.

 BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, a description will be given using a configuration applied as a light source unit for a display device including a transmissive liquid crystal display panel.

First, the light source unit for a display device according to the first embodiment will be described. The concept of the operation of the light source unit for this display device is as follows. Display according to the first embodiment The light source unit for the device alternately turns on and off the light source based on the high-frequency lighting pulse voltage. The lighting pulse voltage is a high-frequency pulse voltage in which an on-time and an off-time alternately appear periodically, and the light source is turned on during the on-time of the lighting pulse voltage and turned off during the off-time. The brightness of the light source is adjusted by setting the timing at which the light source is not turned on by thinning the on-time of the lighting pulse voltage (hereinafter referred to as “blanking time”). This is done by increasing or decreasing the number of occurrences. Then, by causing this blanking time to appear at irregular timings, the operating force periodicity of turning on and off the light source is eliminated.

 FIG. 1 is a block diagram showing a main part of the configuration of a light source unit according to the first embodiment of the present invention and a display device including the light source unit.

 The light source unit according to the first embodiment includes a light source, a user interface, PWM dimming means, random number generation means, and light source driving means. As the light source, a conventional general light source such as a fluorescent tube such as a cold cathode tube or a hot cathode tube can be applied. The user interface is operated by the user to adjust the brightness of the light source, and generates a signal corresponding to the operation. The random number generation means has a random number generation circuit therein and generates a random number within a predetermined numerical range. The PWM dimming unit generates a light source control signal based on a signal from the user interface and a random number from the random number generation unit. This light source control signal is a signal that defines the specific number of times and timing of the blanking time. The light source drive means is equipped with an inverter circuit that can generate a high-frequency and high-frequency pulse voltage inside it, and generates a lighting pulse voltage that drives the light source based on the light source control signal from the PWM dimming means and applies it to the light source To do.

 The light source unit according to the first embodiment subdivides the time during which the light source unit is operating into a predetermined short period, generates a light source control signal for each period, and controls the light source for each period. To do. Each subdivided period is referred to as “PWM dimming period” or simply “period”. In the following, “period” refers to PWM dimming period unless otherwise specified.

[0025] In addition to the above-described components, the display device incorporating the light source unit includes a display panel that displays an image and a control signal based on an image signal input from the outside. LCD controller that generates a signal, and a source driver and a gate driver that drive the display panel based on the control signal. The display panel can be a conventional transmissive liquid crystal display panel, and the LCD controller, source driver, and gate driver can be conventional ones. Therefore, these descriptions are omitted.

 Next, the operation of the light source unit having such a configuration will be described.

 FIG. 2 is a flowchart showing a flow of generating a light source control signal in the light source unit according to the first embodiment. The procedure for generating the light source control signal will be described with reference to FIG. When the user operates the user interface, the user interface outputs a signal corresponding to the user's operation, and the dimming ratio D (%) is determined based on this signal (step 1). Based on this dimming ratio D (%), the number M of blanking times within one period is determined (step 2).

[0028] The dimming ratio D (%) refers to the ratio of the actual number of times of light emission of the light source to the number of on-time times of the lighting pulse voltage that can be set to the maximum within one period. The period of the lighting pulse voltage is P,

 I

When the PWM dimming cycle is P, the lighting pulse voltage that can be set to the maximum within one cycle

 P

 The number of on-times N is the PWM dimming period P divided by the lighting pulse voltage period P

 P I

 That is, N = P ZP. And the number of times to thin out the on-time randomly within one cycle,

 p I

 In other words, the number of occurrences of blanking time M is M 2 (P / P) X (100—D) ZlOO

 P I

 Confirmed.

 [0029] When the light source is turned on a predetermined number of times even when the dimming ratio D is 0%, that is, when the light source is not completely turned off, the number of occurrences of blanking time M is M = {(P ZP ) —

 P I

 Z} X (100—D) Determined by ZlOO. Here, Z is the number of times the light source is turned on when the dimming ratio D is 0%. In other words, in this case, the number of times the light source is turned on within one cycle is changed according to the dimming ratio between Z times and N times.

[0030] In this method, for each period, numbers are assigned to the on-time within each period in order of the leading force, and whether or not each on-time is thinned out in order of this number is used as a blanking time. It will be determined whether or not. When generating the light source control signal for each cycle, first, the counter i used for generation and the remaining number L of blanking times are initialized (Step 3 and Step 4). The counter i has the on-time of the starting time of the cycle. This is a variable indicating whether or not the pulling force is being processed. In addition, the number of remaining blanking times M indicates how many times the blanking time must remain within the period.

 [0031] Next, a random number R is generated by (Step 5), and it is determined whether or not the generated random number is a specific numerical value (Step 6). If the random number R generated in step 5 is a specific number, the i-th on-time is thinned out to obtain the blanking time (step 7). On the other hand, if the random scale is not a specific value, the i-th on-time is not thinned out (ie, lit) (step 8). In this way, whether or not the generated random number R is a specific numerical power determines whether or not the i-th on-time is thinned out to be the blanking time. The random number generation means and method used here will be described later.

 [0032] There is no particular limitation on what kind of numerical value is a "specific numerical value", but it may be determined by a method in which the i-th on-time is thinned out with a predetermined probability. . For example, if the specified random number X is divisible by the specified number X and the generated random number R is a number that is divisible by the specified number X, the i-th on-time is thinned out and blanked. Time.

 [0033] It is preferable that the probability that the “specific numerical value” appears, in other words, the probability that the i-th on-time is thinned out to be the blanking time varies depending on the dimming ratio D (%). The number of occurrences of blanking time M within one cycle is determined based on the dimming ratio D (%). Therefore, in order to express the number of occurrences M of the determined blanking time without excess or deficiency, the random number R becomes a “specific value” when the dimming ratio D (%) is a large value. Decrease the probability, and if it is a small number, increase the probability. Specifically, for example, when the dimming ratio D is fixed at 80%, the value that is divisible by 8 is set as a “specific value”, and when it is fixed at 40%, the value that is divisible by 4 One way is to do this.

[0034] When the blanking time is obtained by thinning out the i-th on-time, the remaining number L of blanking times is updated (step 9). Specifically, the number of remaining blanking times after subtracting 1 from the number of remaining blanking times L after step 7 is the new number of remaining blanking times. [0035] Then, it is determined whether or not the updated blanking time remaining count L is 0 (step 10). If the number of remaining blanking times L is 0, it means that the number of occurrences of blanking time M determined in step 2 has actually been set, and thereafter it is necessary to develop the blanking time within this period. Disappear. Therefore, all the on-times after the i + 1st are not thinned out (step 11). And it shifts to the next cycle. On the other hand, if the remaining number L of blanking times is 1 or more, it is necessary to express the blanking time within the cycle, so the processing within the cycle is continued.

 [0036] Thereafter, the remaining number of on-times, specifically, the maximum number of on-times within one cycle, N force is also subtracted from the value indicated by counter i, and the numerical value N-i is less than or equal to the remaining number L of blanking times. It is determined whether or not (step 12).

 [0037] In order to secure the number of occurrences M of blanking time determined in step 2, the remaining number of on-time N-i is the blanking time during the light source control signal generation process for the period. The number of remaining times needs to be maintained at a value greater than L. However, if the i-th on-time is determined based on the random number R, whether or not the i-th on-time is to be thinned out may result in continuous occurrence of blanking time. As a result, the remaining number of on-times N-i decreases, while the remaining number of blanking times L does not decrease, so the remaining number of on-times N-i is smaller than the remaining number of blanking times L. Things can happen. If such a situation occurs, it will not be possible to secure the number of occurrences M of the blanking time determined in step 2 in that period. As a result, the brightness of the light source in this period is set to be brighter than the original brightness based on the determined dimming ratio D (%).

[0038] In order to avoid such inconvenience, when the remaining number of on-times N-i is the same as the remaining number of blanking times L, all the on-times after i + 1 and after are the blanking time. (Step 13). The same applies if the remaining number of on-time N−i becomes smaller than the remaining number of blanking times L for some reason. By performing such processing, the original brightness based on the determined dimming ratio D (%) can be set. On the other hand, if the remaining number N-i of on-time is larger than the blanking time L, the processing of the cycle is advanced. [0039] Then, it is determined whether or not the value indicated by the counter i is equal to the on-time number N in one cycle (step 14). If the numerical force indicated by the counter i is smaller than the number of on-times within one cycle, the counter i is updated and the process proceeds to the (i + 1) th on-time processing (step 15). On the other hand, when the value indicated by the counter i becomes equal to the number of on-times N in one cycle, the processing for all the on-times in the cycle has been completed.

 [0040] In the flowchart shown in Fig. 2, after one cycle of processing is completed, a step for confirming whether or not to continue the processing and shift to the next cycle is inserted (step 16). In principle, the process continues while the light source unit is in operation.

 [0041] Here, the method for generating the random number R in step 5 will be described. The method for generating the random number R is not particularly limited. For example, the following method can be applied. FIG. 3 is a diagram showing an example of the configuration of a random number generation circuit applicable in step 5. This random number generation circuit 1 reads the capacity 3 connected to the wiring 2 to which the power supply voltage for driving the light source is applied (the symbol a reaches the wiring connected to the power supply) and the potential of the capacity 3 Potential reading circuit 4 capable of Although the power supply voltage for driving the light source is preferably maintained at a constant value in nature, in practice, it constantly fluctuates in an analog fashion as time passes. Therefore, the fluctuation of the power supply voltage value is read as a random number. It is not necessary to use the read voltage value as a random number as it is, and rounding off the decimal point for easy handling in later processing, or adding or integrating a predetermined numerical value so that the random number is within a predetermined numerical range Good. According to such a configuration, it is possible to generate a physical random number that is not a pseudo-random number generated by a general random number generation circuit. Therefore, the timing to thin out the on-time can be made more random, and the periodicity can be eliminated.

 [0042] It should be noted that if the display panel is irregular to such an extent that no interference fringes are generated, the blanking time expression timing may be periodic when viewed macroscopically. Therefore, a configuration using a commonly used pseudo-random number generating means may be used.

[0043] In this way, the light source control signal that defines the timing of the occurrence of the blanking time within one cycle is generated. Then, the light source driving means generates a lighting pulse voltage based on the light source control signal thus generated and applies it to the light source. [0044] According to such a configuration, the blanking time appears irregularly, and the light source blinks without periodicity. Therefore, even if the vertical synchronization signal power ^ has a certain frequency or the brightness of the light source is adjusted, no interference occurs between the vertical synchronization signal and the light source control signal. As a result, it is possible to prevent interference fringes and occurrence of wobbling noise due to the interference fringes.

 [0045] Next, a second embodiment of the present invention will be described. The light source unit according to the second embodiment of the present invention includes a setting table in which the number of occurrences and timing of blanking time within one cycle are set. This setting table has a plurality of settings for one type of dimming ratio D (%). A random number is randomly selected from these multiple settings for each cycle.

 FIG. 4 is a block diagram showing a main part of the configuration of the light source unit according to the second embodiment and a display device in which the light source unit is incorporated. The light source unit according to the second embodiment includes a light source, a user interface, PWM dimming means, random number generating means, and storage means. The same light source, user interface, light source driving means, and random number generation means as those of the light source unit according to the first embodiment can be applied. The storage means can store the setting of the timing of the blanking time. In addition, the display device in which the light source unit is incorporated can be applied with the same configuration as the display device according to the first embodiment except for the light source unit.

 [0047] Table 1 below shows an example of a setting table in which the occurrence timing of blanking time within one period is set. This table uses an example in which the maximum number of on-times that can be set within one period is 20. Each number in this table indicates how many on-times the leading force will decimate for the on-time within each cycle. Each dimming ratio D (%) has 5 settings. The dimming ratio D (%) here is 0% for 10 lighting and 100% for 20 lighting all. The number of on-times per cycle is not limited to 20 and can be set as appropriate. Also, the number of settings for each dimming ratio is not limited to five.

[0048] [Table 1]

The operation of the light source unit having such a configuration is as follows. First, based on the user interface operation by the user, the dimming ratio D (%) in a certain period is determined. . A random number is generated by the random number generation means. This random number generating means has the same configuration as that of the light source unit of the first embodiment, and reads the potential value of the capacity connected to the power supply voltage (see FIG. 3). The read potential value also generates a random number. Table 2 below shows an example of a random number generation method by the random number generation means.

[0050] [Table 2]

Table Random number generation table

[0051] For example, if the read potential value is 0.1, 0 is generated as a random number, and if the read potential value is 1.7, 3 is generated as a random number. In this way, the read potential value and this surface force random number are generated.

 [0052] Next, based on the determined dimming ratio D (%) and the generated random number, the setting of the expression of blanking time in a certain period is selected based on the setting table of Table 2. For example, if the determined dimming ratio D is 80% and the generated random power is ^, the setting that thins out the 8th and 10th on-time is used in that period. .

 [0053] In the certain period, the light source is driven by the light source driving unit based on the selected setting, and the setting in the next period is selected. Thereafter, such an operation is repeated. According to such a configuration, the timing of occurrence of the blanking time becomes random and the periodicity is lost. As a result, the same operational effects as those of the first embodiment can be obtained.

Next, a third embodiment of the present invention will be described. The light source unit according to the third embodiment is capable of generating blanking time within one period. One kind of dimming ratio D (% ) A setting table with multiple settings is provided. Then, this setting taper setting is read and used in order for each cycle.

 FIG. 5 is a block diagram showing a main part of the configuration of the light source unit according to the third embodiment and a display device in which the light source unit is incorporated. The light source unit according to the third embodiment includes a light source, a user interface, PWM dimming means, setting storage means, and light source driving means. These can be the same as the light source unit according to the second embodiment. In addition, the same configuration as the display device of the first embodiment or the second embodiment can be applied to the display device in which the light source unit is incorporated, except for the light source unit.

[0056] The setting table has the same structure as that of the light source unit according to the second embodiment. In other words, each has a plurality of settings for one type of dimming ratio D (%).

The operation of the light source unit having such a configuration is as follows. The dimming ratio D (%) is determined based on the operation of the user interface by the user. The setting of the blanking time expression timing corresponding to the determined dimming ratio D (%) is read in order, and the light source driving means drives the light source according to the read setting. Here, the item “random numbers” in Table 1 may be read as “order”. In other words, when the determined dimming ratio D is 80%, in the first cycle, the “order 0” is set, that is, the eighth and tenth on-times are set as blanking times. Using the setting, for the second cycle, use the setting of “Order 1”, that is, the setting with the 7th and 8th on-time as the blanking time. Then, in the sixth cycle, the process returns to “order 0” in the table and proceeds.

[0058] According to such a configuration, although there is periodicity in the expression timing of blanking time macroscopically, the expression timing of blanking time does not have periodicity microscopically. Therefore, the same effect as the first embodiment or the second embodiment can be obtained.

 While various embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

Claims

The scope of the claims  [1] A light source unit for a display device that turns on a light source based on a signal in which an on-time for turning on the light source appears periodically, and the on-time is irregularly determined from the signal according to the brightness adjustment level. A light source unit for a display device, comprising: a light control unit that generates a light source control signal thinned out at various timings.  [2] A light source unit for a display device that turns on a light source based on a signal in which an on-time for turning on the light source appears periodically, a means for generating random numbers, and a random number and brightness generated by the means A light source unit for a display device, comprising: a light control unit that generates a light source control signal obtained by thinning out the on-time with irregular timing according to an adjustment level of the light source.  [3] A light source unit for a display device that turns on a light source based on a signal in which an on-time for turning on the light source appears periodically, and the light source unit generates random numbers, and the light source unit depends on the brightness adjustment level. Signal power A setting that stores a plurality of settings for thinning out the on-time at irregular timings, and a setting storage means power setting based on a random number generated by the random number generating means, and extracting a light source control signal A light source unit for a display device, comprising: a dimming unit that generates the light source unit.  [4] The means for generating the random number includes a voltage value reading circuit for reading a voltage of a power source for driving the light source, and a conversion means for converting the read voltage value into a random number. A light source unit for a display device according to claim 3.  [5] A light source unit for a display device that turns on a light source based on a signal in which an on-time for turning on the light source appears periodically, and the signal power on-time is irregularly adjusted according to the brightness adjustment level. A light source unit for a display device, comprising: a setting storage unit that stores a plurality of settings to be thinned out at various timings; and a dimming unit that extracts a setting in order and generates a light source control signal .  [6] A display device comprising the light source unit for a display device according to any one of claims 1 to 5.