Display control device and display control method

Abstract

To provide a display control device and display control method capable of easily suppressing the occurrence of luminance unevenness.SOLUTION: A display control device 1 includes: a switching (SW) frequency variation unit 10 which randomly varies a reference frequency being a reference for determining the frequency such that a time integral average of the frequency of an input signal becomes a target frequency; a voltage signal generation unit 20 which generates the input signal at the frequency varied by the SW frequency variation unit; and a drive control unit 40 which controls the luminance of a display screen for each scanning-line on the basis of the input signal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a display control device and a display control method.

Background Art

[0002] Conventionally, in order to achieve high-quality display on a display screen, a technique for controlling a DC / DC converter is known. For example, in Patent Document 1, an input signal to a timing control circuit is input to a phase synchronization circuit, and the switching frequency of the DC / DC converter is determined by controlling the DC / DC converter based on the output of the phase synchronization circuit, and a liquid crystal display device that synchronizes the phases of a switching signal and a control signal is described.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the liquid crystal display device described in Patent Document 1, if the switching frequency of the DC / DC converter deviates from the target value even slightly due to a control error of the phase synchronization circuit or ambient noise, the phases of the switching signal and the control signal deviate. As a result, stripe-like brightness unevenness may occur on the display screen. In addition, in order to control the switching frequency of the DC / DC converter so as not to deviate from the target value, very high control accuracy is required, making circuit design difficult.

[0005] The present disclosure has been made in view of the above problems. An object of the present disclosure is to provide a display control device and a display control method capable of easily suppressing the occurrence of brightness unevenness.

Means for Solving the Problems

[0006] A display control device according to an aspect of the present disclosure includes a frequency variation unit that randomly varies a reference frequency serving as a reference for determining the frequency so that a time-integrated average of the frequency of an input signal becomes a target frequency, a signal generation unit that generates the input signal at the frequency varied by the frequency variation unit, and a drive control unit that controls the luminance of a display screen for each scanning line based on the input signal.

[0007] A display control method according to an aspect of the present disclosure is a display control method executed by a display control device. The method randomly varies a reference frequency serving as a reference for determining the frequency so that a time-integrated average of the frequency of an input signal becomes a target frequency, generates the input signal at the varied frequency, and controls the luminance of a display screen for each scanning line based on the input signal.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide a display control device and a display control method that can easily suppress the occurrence of luminance unevenness.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 4C

Figure 4D

Figure 4E

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9A

Figure 9B

Figure 10

Figure 11

Figure 12

Figure 13

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or equivalent components are denoted by the same reference numerals, and descriptions of the same or equivalent components will be omitted as appropriate.

[0011] <First Embodiment> FIG. 1 is a functional block diagram showing a schematic configuration of a display control device 1 according to the first embodiment. The display control device 1 controls the display on a display device capable of displaying an image. That is, the display device displays an image based on a signal from the display control device 1 in the present disclosure.

[0012] In the present embodiment, the display control device 1 generates an input signal and inputs the generated input signal to the display device. The display device includes a display screen and displays an image on the display screen based on the input input signal. Specifically, the display control device 1 includes a converter circuit that creates a constant voltage by a periodic switching operation, and the converter circuit generates a backlight voltage. Examples of the converter circuit include a DC / DC converter circuit and an AC / DC converter circuit. In the present embodiment, the converter circuit is a DC / DC converter circuit, and the following description will be made. However, the converter circuit is not limited to the DC / DC converter circuit, and any type of circuit can be used as long as it can create a constant voltage by a periodic switching operation. The DC / DC converter circuit includes a switching element that can switch on and off. Examples of the switching element include semiconductor elements such as transistors or MOSFETs (metal-oxide-semiconductor field-effect transistors).

[0013] The display device is a device that displays an image. The display device may be configured by a well-known display (display screen) such as a liquid crystal display (LCD), an organic EL display (OELD), or an inorganic EL display (IELD). However, the display device is not limited to the examples shown here, and the present disclosure can be applied to all display devices in which luminance unevenness may occur due to switching noise.

[0014] The display of the display device includes, for example, a large number of pixels arranged in a matrix vertically and horizontally. Each pixel is provided with a switching element such as a thin film transistor, and a pixel electrode is connected to the switching element. Further, the display includes a plurality of scanning lines, and a predetermined number of pixels are connected to each scanning line. When a drive signal is input to the scanning line, the pixels connected to the scanning line emit light with a luminance corresponding to the drive signal, thereby displaying an image.

[0015] The input signal is a signal line on which switching noise is superimposed (that is, affected by switching noise). In the present embodiment, the signal line is assumed to be a backlight voltage and will be described below. That is, in the present embodiment, it will be described that the DC / DC converter circuit generates a backlight voltage as an input signal. However, the signal line is not limited to the backlight voltage, and may be any signal on which the switching noise of the converter circuit is superimposed and which can affect the luminance of the display screen. Specifically, examples of the signal line include, in addition to the backlight voltage, a backlight control signal, a liquid crystal scanning voltage, a liquid crystal scanning signal, and the like.

[0016] As shown in FIG. 1, the display control device 1 according to the present embodiment includes, as functional blocks, a switching (SW) frequency fluctuation unit 10, a voltage signal generation unit 20, a control signal generation unit 30, and a drive control unit 40. In the present embodiment, the voltage signal generation unit 20 is configured to include the above-described DC / DC converter circuit.

[0017] The SW frequency variation unit 10 randomly varies the reference frequency that serves as a reference for determining the frequency of the input signal (the backlight voltage in this embodiment). In this embodiment, the reference frequency is the switching frequency of the switching signal that switches the on / off of the switching element included in the voltage signal generation unit 20 (that is, the DC / DC converter circuit). Specifically, the SW frequency variation unit 10 varies the switching frequency so that the time integral average of the frequency of the input signal becomes the target frequency. The target frequency is determined as appropriate. The target frequency may be determined, for example, so that the emission luminance on the display screen becomes the target luminance.

[0018] The voltage signal generation unit 20 functions as the signal generation unit in the present disclosure. The voltage signal generation unit 20 generates an input signal at the frequency varied by the SW frequency variation unit 10. The voltage signal generation unit 20 inputs the generated input signal to the drive control unit 40.

[0019] FIG. 2 is a diagram showing a specific configuration of the SW frequency variation unit 10 and the voltage signal generation unit 20 in the first embodiment. As shown in FIG. 2, the voltage signal generation unit 20 is provided with a frequency setting terminal 21, and the SW frequency variation unit 10 is connected to the frequency setting terminal 21.

[0020] In this embodiment, the SW frequency variation unit 10 is constituted by an analog circuit. That is, as shown in FIG. 2, the SW frequency variation unit 10 includes a first resistor 11, a second resistor 12, and a thermistor 13. Specifically, one end of the first resistor 11 is grounded, and the other end is connected in parallel to one ends of the second resistor 12 and the thermistor 13, respectively. Also, the other ends of the second resistor 12 and the thermistor 13 are connected to the frequency setting terminal 21 of the voltage signal generation unit 20, respectively.

[0021] The resistance values of the first resistor 11 and the second resistor 12 are appropriately determined according to the target frequency, the specifications of the voltage signal generation unit 20, and the like. The thermistor 13 is an example of a circuit element whose parameters change according to environmental noise. Specifically, the thermistor 13 is a circuit element in which the resistance value TH as a parameter changes according to the temperature as environmental noise. As the thermistor 13, a PTC thermistor in which the resistance value TH is higher when the temperature is higher or an NTC thermistor in which the resistance value TH is lower when the temperature is higher can be used. In this embodiment, it is assumed that a PTC thermistor is used as the thermistor 13.

[0022] By including the thermistor 13, the SW frequency variation unit 10 has a resistance value that changes according to the temperature as environmental noise. That is, when the temperature of the thermistor 13 is high, the resistance value becomes higher compared to when the temperature of the thermistor 13 is low. Therefore, according to the change in the resistance value based on the temperature change of the thermistor 13, the resistance value of the entire SW frequency variation unit 10 varies between, for example, the resistance value R1 of the first resistor 11 and R1 + R2 which is the sum of the resistance value R1 of the first resistor 11 and the resistance value R2 of the second resistor 12.

[0023] The voltage signal generation unit 20 generates a voltage signal by switching on and off the switching element based on the switching frequency varied by the SW frequency variation unit 10 as an input signal. In this embodiment, the voltage signal generation unit 20 includes a DC / DC converter circuit capable of determining the switching frequency based on the resistance value of the circuit element connected to the frequency setting terminal 21. That is, the DC / DC converter circuit varies the switching frequency according to the variation in the resistance value of the SW frequency variation unit 10 connected to the frequency setting terminal 21, and the voltage signal generation unit 20 generates a backlight voltage as a voltage signal based on the varied switching frequency.

[0024] FIG. 3 is a graph showing the relationship between the resistance value of the circuit element connected to the frequency setting terminal 21 and the switching frequency. The graph of FIG. 3 shows the characteristics of the DC / DC converter circuit. In the graph of FIG. 3, the horizontal axis represents the resistance value of the circuit element connected to the frequency setting terminal 21, and the vertical axis represents the switching frequency. The DC / DC converter circuit determines the switching frequency based on the resistance value of the circuit element connected to the frequency setting terminal 21.

[0025] For example, in the present embodiment, as shown in FIG. 3, the DC / DC converter circuit has a characteristic that the higher the resistance value of the circuit element connected to the frequency setting terminal 21, the lower the switching frequency. As described above, the SW frequency variation unit 10 connected to the frequency setting terminal 21 includes the thermistor 13, and its resistance value varies between R1 and R1 + R2. The DC / DC converter circuit determines the switching frequency according to the variation of the resistance value of the SW frequency variation unit 10, for example, based on the characteristics shown in the graph of FIG. 3. In the present embodiment, in this way, as the DC / DC converter circuit, a converter circuit capable of varying the switching frequency based on the change in the parameter of the circuit element (here, the resistance value of the thermistor 13) according to the environmental noise is used.

[0026] The voltage signal generation unit 20 generates a voltage signal based on the determined switching frequency. For example, the voltage signal generation unit 20 generates a backlight voltage having a frequency synchronized with the switching frequency. Here, since the switching frequency randomly varies with time according to the resistance value of the SW frequency variation unit 10 based on the resistance value of the thermistor, the frequency of the backlight voltage generated by the voltage signal generation unit 20 also randomly varies with time according to the time variation of the switching frequency. The voltage signal generation unit 20 inputs the generated backlight voltage to the drive control unit 40.

[0027] Figures 4A to 4E are schematic graphs for explaining the process of generating an input signal according to environmental noise. With reference to Figures 4A to 4E, the process of generating an input signal according to environmental noise will be described.

[0028] Figure 4A is a graph showing the temperature change of the thermistor 13 over time. In the graph shown in Figure 4A, the horizontal axis represents time and the vertical axis represents the temperature of the thermistor 13. As shown in the graph of Figure 4A, due to random temperature changes as environmental noise over time, the temperature of the thermistor 13 also fluctuates randomly. In the example shown in Figure 4A, the temperature of the thermistor 13 fluctuates between a first temperature T1 and a second temperature T2 (T1 < T2). The amplitude TW of the temperature change indicated by the difference between the first temperature T1 and the second temperature T2 is determined according to parameters such as, for example, the heat capacity of the thermistor 13, the proximity from the thermistor 13 to the heat source, and the temperature of the heat source.

[0029] Figure 4B is a graph showing the relationship between the temperature of the thermistor 13 and the resistance value of the circuit element (here, the SW frequency fluctuation unit 10) connected to the frequency setting terminal 21. In the graph shown in Figure 4B, the horizontal axis represents the temperature of the thermistor 13 and the vertical axis represents the resistance value of the circuit element connected to the frequency setting terminal 21. As shown in the graph of Figure 4B, in the present embodiment, the higher the temperature of the thermistor 13, the higher the resistance value of the circuit element connected to the frequency setting terminal 21.

[0030] Figure 4C is a graph showing the change in the resistance value of the circuit element connected to the frequency setting terminal 21 over time. In the graph shown in Figure 4C, the horizontal axis represents time and the vertical axis represents the resistance value of the circuit element connected to the frequency setting terminal 21. As shown in the graph of Figure 4A, since the temperature of the thermistor 13 fluctuates between the first temperature T1 and the second temperature T2, as shown in the graph of Figure 4B, the resistance value of the circuit element connected to the frequency setting terminal 21 fluctuates between R1 and R1 + R2. That is, when the temperature of the thermistor 13 fluctuates randomly as shown in the graph of Figure 4A, the resistance value of the circuit element connected to the frequency setting terminal 21 also fluctuates randomly as shown in the graph of Figure 4C in response to the fluctuation of the temperature of the thermistor 13.

[0031] Figure 4D is a graph showing the relationship between the resistance value of the circuit element connected to the frequency setting terminal 21 and the switching frequency. That is, the graph shown in Figure 4D is the same as the graph in Figure 3. In the graph shown in Figure 4D, the horizontal axis is the resistance value of the circuit element connected to the frequency setting terminal 21, and the vertical axis is the switching frequency. When the resistance value of the circuit element connected to the frequency setting terminal 21 is R1, the DC / DC converter circuit determines the switching frequency to be fmax. When the resistance value of the circuit element connected to the frequency setting terminal 21 is R1 + R2, the DC / DC converter circuit determines the switching frequency to be fmin. Therefore, the switching frequency varies between fmax and fmin.

[0032] Figure 4E is a graph showing the change of the input signal over time. In the graph shown in Figure 4E, the horizontal axis is time, and the vertical axis shows the voltage value of the backlight voltage. As shown in the graph of Figure 4C, as the resistance value of the circuit element connected to the frequency setting terminal 21 varies between R1 and R1 + R2, due to the characteristics shown in the graph of Figure 4D, the switching frequency varies between fmax and fmin. The voltage signal generation unit 20 generates a backlight voltage with a frequency synchronized with the switching frequency as shown in the graph of Figure 4E in response to the variation of the switching frequency. Therefore, as the resistance value of the circuit element connected to the frequency setting terminal 21 varies randomly, the frequency of the backlight voltage also varies randomly.

[0033] Referring to FIG. 1 again, the control signal generation unit 30 generates a control signal for the image to be displayed on the display screen. The control signal generation unit 30 inputs the generated control signal to the drive control unit 40.

[0034] Based on the input signal, the drive control unit 40 controls the brightness of the display screen for each scanning line of the display screen. In this embodiment, since the input signal is the backlight voltage generated by the voltage signal generation unit 20, the drive control unit 40 controls the brightness of the display screen for each scanning line based on the backlight voltage. Specifically, the drive control unit 40 controls the brightness of the display screen for each scanning line based on the voltage signal (backlight voltage) input from the voltage signal generation unit 20 and the control signal input from the control signal generation unit 30.

[0035] Here, with reference to FIG. 5, the details of the control of the brightness of the display screen by the drive control unit 40 will be described. FIG. 5 is a diagram for explaining the control of the brightness of the display screen by the drive control unit 40.

[0036] The backlight voltage is shown in the upper part of FIG. 5. The backlight voltage is the input signal input from the voltage signal generation unit 20 to the drive control unit 40. As described above, the frequency of the backlight voltage varies randomly by the SW frequency variation unit 10. Therefore, as shown in FIG. 5, the period of the backlight voltage is not constant but random.

[0037] The control signal is shown in the middle part of FIG. 5. The control signal is the signal input from the control signal generation unit 30 to the drive control unit 40. The control signal is input for each scanning line. In the example shown in FIG. 5, the first control signal for determining the brightness update timing of the first scanning line and the second control signal for determining the brightness update timing of the second scanning line are shown. Actually, the same number of control signals as the number of scanning lines of the display screen are input from the control signal generation unit 30 to the drive control unit 40, but the control signals other than the first control signal and the second control signal are not shown in the figure. That is, when the display screen includes n scanning lines (n is an integer of 1 or more), n control signals from the first control signal to the nth control signal are input to the drive control unit 40.

[0038] The control signal changes in signal intensity at a constant frequency fc. The timings at which the signal intensities of the n control signals change are different from each other. For example, as shown in FIG. 5, the timings at which the signal intensity of the first control signal and the signal intensity of the second control signal change are different. In the example shown in FIG. 5, the first control signal changes (decreases) in signal intensity at times t1, t3, and t5, and the second control signal changes (decreases) in signal intensity at times t2, t4, and t6. The signal intensities of the first control signal and the second control signal change at a constant period (1 / fc). The timing at which the signal intensity changes is the luminance update timing. Therefore, in the example shown in FIG. 5, the luminance update timings of the first scanning line are times t1, t3, and t5, and the luminance update timings of the second scanning line are times t2, t4, and t6.

[0039] FIG. 5 illustrates how the luminance of the entire display screen is updated three times. The first luminance update is the luminance update performed in the time period including times t1 and t2, the second luminance update is the luminance update performed in the time period including times t3 and t4, and the third luminance update is the luminance update performed in the time period including times t5 and t6. In each luminance update of the entire display screen, the n control signals from the first control signal to the nth control signal are each input to the drive control unit 40 once. That is, for the n scanning lines from the first scanning line to the nth scanning line, the luminance is updated once each.

[0040] The lower part of FIG. 5 shows the time change of the luminance of each scanning line. In the example shown in FIG. 5, only the first scanning line and the second scanning line are shown. When m is an integer from 1 to n, the luminance of the mth scanning line is determined based on the signal intensity (backlight voltage) of the input signal at the timing of the luminance update of the mth control signal (that is, the timing at which the signal intensity changes). For example, the luminance of the first scanning line is determined based on the backlight voltage at the timing of the luminance update of the first control signal. That is, the drive control unit 40 inputs a drive signal to each scanning line so that the pixels of the display device emit light with a luminance determined based on the backlight voltage at the timing of the luminance update of the control signal.

[0041] In the time variation of the luminance shown in the lower part of FIG. 5, “Max value” indicates the maximum value of the backlight voltage of the m-th scanning line, “Min value” indicates the minimum value of the backlight voltage of the m-th scanning line, and “target value” indicates the target value of the backlight voltage of the m-th scanning line. When the backlight voltage is the target value, the luminance of the m-th scanning line becomes the target luminance.

[0042] Here, since the control signal changes in signal intensity at a constant frequency fc, the timing of luminance update occurs at a constant period (1 / fc). On the other hand, since the frequency of the backlight voltage is random, the value of the backlight voltage can be different for each timing of luminance update of the m-th scanning line. For example, in the example shown in FIG. 5, the timings of luminance update of the first scanning line are illustrated three times at times t1, t3, and t5, but the value of the backlight voltage is different at each timing. Similarly, the timings of luminance update of the second scanning line are illustrated three times at times t2, t4, and t6, but the value of the backlight voltage is different at each timing. Thus, for each scanning line, since the value of the backlight voltage is different for each timing of luminance update, the luminance of each scanning line can change for each timing of luminance update.

[0043] FIG. 6 is a schematic diagram showing the luminance of the display screen. Specifically, in the upper part of FIG. 6, images of the luminance of each display screen when the first to third startup updates are performed are shown. As shown in the upper part of FIG. 6, the display screen includes a plurality of scanning lines in the vertical direction, and the luminance is controlled for each scanning line. For example, the upper left of FIG. 6 shows the display screen at the first luminance update, the upper center of FIG. 6 shows the display screen at the second luminance update, and the upper right of FIG. 6 shows the display screen at the third luminance update. Since the frequency of the backlight voltage is random and not synchronized with the timing of luminance update, as can be understood from the figure showing the display screen in the upper part of FIG. 6, the luminance varies between scanning lines at each luminance update. Thus, since switching noise is superimposed on the backlight voltage, the luminance of each scanning line instantaneously varies between scanning lines.

[0044] However, since the switching frequency varies randomly with time, the backlight voltage also varies randomly with time. Therefore, as shown in the upper part of FIG. 6, every time the luminance is updated periodically, the luminance of each scanning line changes randomly with time. Note that the period at which the luminance is updated can be determined as appropriate. The period at which the luminance is updated can be a period that cannot be recognized by the human eye, for example, several hundred Hz.

[0045] On the other hand, the human eye cannot capture instantaneous changes in luminance, and the value obtained by integrating the amount of light over a certain period is recognized as the visual brightness. That is, the human eye cannot recognize the change in the luminance of the scanning line for each luminance update as shown in the three upper figures of FIG. 6, and the luminance of the display screen is visually uniformized, and the luminance unevenness on the display screen becomes extremely difficult to recognize. That is, by randomly changing the frequency of the backlight voltage with time, the human eye recognizes the state in which the luminance unevenness for each scanning line and for each time change is suppressed, as shown in the lower part of FIG. 6.

[0046] If an attempt is made to synchronize the phases of the switching signal and the control signal that determine the switching frequency of the DC / DC converter as in the display device described in Patent Document 1, if the phases of these signals are completely synchronized, luminance unevenness will not occur. However, due to control errors in the phase synchronization circuit, ambient noise, etc., if the switching frequency deviates even slightly from the target value, the phases of the switching signal and the control signal will deviate, and luminance unevenness may occur. Moreover, in order to control the switching frequency of the DC / DC converter so as not to deviate from the target value, very high control accuracy is required, making circuit design difficult.

[0047] In contrast, in the display control device 1 according to the present embodiment, the frequency of the backlight voltage changes randomly. As a result, although the brightness of the display screen changes with time for each scanning line, since the human eye recognizes the brightness integrated over a certain period, the visible stripe-like brightness unevenness is suppressed. That is, by controlling the brightness of the display screen using a backlight voltage with a randomly varying frequency, it is possible to easily suppress the occurrence of brightness unevenness. Note that, the faster the variation speed of the switching frequency, the faster the temporal variation of the brightness becomes, so the temporal integration value of the brightness becomes more uniform, and the suppression effect of brightness unevenness is enhanced. Further, by using the thermistor 13 in the SW frequency variation unit 10 as the thermistor 13 such that the temporal integration average of the brightness of the display screen based on the variation of the backlight voltage becomes the target brightness, the brightness visually recognized by the human eye can be controlled to the target brightness.

[0048] In order to make it difficult for people to recognize brightness unevenness, it is preferable to vary the switching frequency so that the positive-direction brightness variation amount and the negative-direction brightness variation amount are about the same when time-integrated with respect to the target brightness. That is, the target frequency of the switching frequency is a frequency such that the positive-direction brightness variation amount and the negative-direction brightness variation amount are about the same when time-integrated with respect to the target brightness. The time integration can be performed within an appropriate range, for example, within a range of 30 milliseconds.

[0049] In the first embodiment described above, the display control device 1 may further include a heat source that generates random environmental noise fluctuations for the thermistor 13. As the heat source, for example, a heater can be used. The heater is arranged, for example, in the vicinity of the thermistor 13. The vicinity of the thermistor 13 is, for example, a range in which the thermistor 13 can be affected by the heat generated by the heater. For example, when the heater generates heat randomly, the resistance value of the thermistor 13 varies randomly due to the influence of the heat generation of the heater. As a result, based on the principle described in the above embodiment, the backlight voltage varies randomly, and the brightness of the display screen varies randomly, thereby suppressing brightness unevenness.

[0050] Alternatively, without separately providing a heat source, the display control device 1 can also use a predetermined circuit element as a heat source. For example, by arranging a switching element such as a MOSFET included in the DC / DC converter circuit of the voltage signal generation unit 20 near the thermistor 13, the MOSFET can be used as a heat source. Alternatively, it is also possible to use a circuit element such as a transformer included in the display control device 1 as a heat source. In this way, by arranging the heat source near the thermistor 13, the variation in the resistance value of the thermistor 13 becomes larger, and as a result, the frequency of the backlight voltage fluctuates more greatly, and it can be expected that the effect of suppressing luminance unevenness will be enhanced.

[0051] Note that if the switching frequency of the voltage signal generation unit 20 becomes too high, the switching loss of the MOSFET, which is a switching element, increases, and as a result, the temperature of the switching element rises too much, and it is assumed that the MOSFET may be damaged. As a countermeasure, it is conceivable to arrange the thermistor 13 near the switching element and use an NTC thermistor as the thermistor 13. In this case, if the temperature of the switching element rises abnormally, the resistance value of the NTC thermistor decreases. As a result, the resistance value of the circuit element (SW frequency variation unit 10) connected to the frequency setting terminal 21 decreases. As a result, since the switching frequency decreases, it becomes easier to prevent the MOSFET from being damaged due to the switching frequency becoming too high.

[0052] In the above first embodiment, the circuit configuration of the SW frequency variation unit 10 is not limited to that shown in FIG. 2. For example, the SW frequency variation unit 10 may be configured only by the thermistor 13 without including the first resistor 11 and the second resistor 12, or may be configured to include other circuit elements. The circuit configuration of the SW frequency variation unit 10 only needs to be such that the resistance value of the SW frequency variation unit 10 varies according to environmental noise.

[0053] In the first embodiment described above, the voltage signal generation unit 20 is described as including a DC / DC converter circuit capable of determining the switching frequency based on the resistance value of the circuit element connected to the frequency setting terminal 21. However, the voltage signal generation unit 20 may include other DC / DC converter circuits. For example, the voltage signal generation unit 20 may be configured to include a DC / DC converter circuit capable of determining the switching frequency based on the voltage of the circuit element connected to the frequency setting terminal 21.

[0054] FIG. 7 is a diagram showing another configuration of the SW frequency variation unit 10 and the voltage signal generation unit 20 in the first embodiment. Specifically, it is a diagram showing a configuration example when the voltage signal generation unit 20 is configured to include a DC / DC converter circuit capable of determining the switching frequency based on the voltage of the circuit element connected to the frequency setting terminal 21.

[0055] In this case, as shown in FIG. 7, the SW frequency variation unit 10 includes a DC power supply in addition to the first resistor 11, the second resistor 12, and the thermistor 13. The frequency setting terminal 21 is connected to the SW frequency variation unit 10. The resistance value TH of the thermistor 13, which is a parameter, randomly changes according to the temperature as environmental noise. In response to the change in the resistance value TH of the thermistor 13, the voltage at the frequency setting terminal 21 connected to the SW frequency variation unit 10 varies. The voltage signal generation unit 20 determines the switching frequency based on the voltage at the frequency setting terminal 21. Here, since the voltage at the frequency setting terminal 21 randomly varies according to the change in the resistance value TH of the thermistor 13, the switching frequency determined by the voltage signal generation unit 20 also randomly varies. Thereby, based on the same principle as in the first embodiment, uneven brightness of the display screen can be suppressed.

[0056] In the above-described first embodiment, it was explained that the SW frequency variation unit 10 includes the thermistor 13 as a circuit element whose parameters change according to environmental noise. However, environmental noise is not limited to temperature, and an appropriate circuit element can be used according to the type of environmental noise. For example, if the environmental noise is light, the SW frequency variation unit 10 can include a photosensor as a circuit element whose parameters change according to environmental noise. A photosensor is a circuit element whose resistance value changes according to the intensity of the detected light. By using a photosensor, the resistance value of the SW frequency variation unit 10 varies according to the intensity of the ambient light as environmental noise, and thus, based on the same principle as in the first embodiment, uneven brightness of the display screen can be suppressed.

[0057] Also, when using a photosensor, a light source may be arranged near the photosensor, and the resistance value of the SW frequency variation unit 10 may be randomly varied by randomly emitting the light source. In this case, the brightness visually recognized by the human eye can be controlled to the target brightness by blinking the light source or changing the emission intensity so that the time-integrated average of the brightness of the display screen based on the variation of the backlight voltage becomes the target brightness.

[0058] The environmental noise may be other noise other than temperature and light. By appropriately using a circuit element according to the environmental noise, the display control device 1 can produce the same effect as that described in the first embodiment.

[0059] <Second Embodiment> Next, the second embodiment will be described. The schematic configuration of the display control device 1 according to the second embodiment is the same as the schematic configuration of the display control device 1 according to the first embodiment described with reference to FIG. 1. That is, the display control device 1 according to the second embodiment includes, similarly to the first embodiment, the SW frequency variation unit 10, the voltage signal generation unit 20, the control signal generation unit 30, and the drive control unit 40. Hereinafter, the second embodiment will be described centering on the points different from the first embodiment while appropriately omitting the description of the same points as in the first embodiment.

[0060] FIG. 8 is a diagram showing a specific configuration of the SW frequency variation unit 10 and the voltage signal generation unit 20 in the second embodiment. Similar to the first embodiment, the SW frequency variation unit 10 is connected to the frequency setting terminal 21 of the voltage signal generation unit 20. Also, similar to the first embodiment, the voltage signal generation unit 20 includes a DC / DC converter circuit capable of determining the switching frequency based on the resistance value of the circuit element connected to the frequency setting terminal 21.

[0061] As shown in FIG. 8, the SW frequency variation unit 10 includes a first resistor 11, a second resistor 12, and a switching element 14. That is, in the second embodiment, a switching element 14 is used instead of the thermistor 13 in the first embodiment. The switching element 14 is a circuit element capable of controlling current according to an external signal. As the switching element 14, for example, a transistor, a MOSFET, a photodiode, etc. can be used, but it is not limited thereto.

[0062] In the example shown in FIG. 8, a MOSFET is used as the switching element 14. An external signal is input to the gate of the field effect transistor that is the switching element 14. The external signal is a voltage signal that crosses the gate threshold voltage of the MOSFET. That is, due to the input of the external signal to the gate, a current flows or stops flowing between the source and drain of the MOSFET. As a result, the resistance value of the SW frequency variation unit 10 connected to the frequency setting terminal 21 varies. Based on the variation of the resistance value of the SW frequency variation unit 10, the voltage signal generation unit 20 determines the switching frequency. That is, the switching frequency varies according to the variation of the resistance value of the SW frequency variation unit 10.

[0063] The external signal may be a random signal whose signal strength changes irregularly, or a sweep signal that varies regularly. When the external signal is a random signal, the switching frequency varies randomly, as shown, for example, in FIG. 9A. When the external signal is a sweep signal, the switching frequency varies periodically, as shown, for example, in FIG. 9B. In the present embodiment, it is assumed that the external signal is a random signal for explanation.

[0064] The external signal can be generated by a known circuit. For example, the external signal can be generated by a digital circuit or an oscillation circuit using a comparator. Such a circuit may be provided in the SW frequency variation unit 10, or may be configured as an external circuit not included in the SW frequency variation unit 10.

[0065] In response to the input of the external signal, the resistance value of the SW frequency variation unit 10 connected to the frequency setting terminal 21 varies with time. The voltage signal generation unit 20 varies the switching frequency according to the variation of the resistance value of the SW frequency variation unit 10 connected to the frequency setting terminal 21. Then, the voltage signal generation unit 20 generates a backlight voltage having a frequency synchronized with the switching frequency in the same manner as described with reference to the graph of FIG. 4E according to the variation of the switching frequency. When the backlight voltage generated in this way is input from the voltage signal generation unit 20 to the drive control unit 40, the luminance varies with time for each scanning line every time the luminance update is performed, based on the same principle as described in the first embodiment. Since the human eye cannot recognize the change in luminance of each scanning line for each luminance update and the luminance on the display screen is visually uniform, the luminance unevenness in the form of stripes is suppressed. That is, also in the present embodiment, the occurrence of luminance unevenness can be easily suppressed.

[0066] In the second embodiment, the voltage signal generation unit 20 does not necessarily have to be configured to include a DC / DC converter circuit capable of determining the switching frequency based on the resistance value of the circuit element connected to the frequency setting terminal 21. The voltage signal generation unit 20 may be configured to include, for example, a circuit capable of executing the switching of the switching element included in the DC / DC converter circuit based on an external signal.

[0067] In this case, for example, as shown in FIG. 10, the SW frequency variation unit 10 functions as a circuit that generates the external signal and inputs it to the voltage signal generation unit 20. For example, the SW frequency variation unit 10 generates an external signal whose frequency varies randomly, and the voltage signal generation unit 20 generates a backlight voltage whose frequency is synchronized with the external signal based on the external signal received from the SW frequency variation unit 10. As a result, since the voltage signal generation unit 20 inputs a backlight voltage with a random frequency to the drive control unit 40, the luminance of the display screen varies randomly for each scanning line, and thus the occurrence of luminance unevenness can be suppressed.

[0068] In this case, for example, a digital power supply can be used as the SW frequency variation unit 10. The digital power supply includes a power supply unit that supplies power and a power supply control unit that controls the power supply unit. The power supply control unit can be realized by, for example, a microcontroller. A microcontroller is a circuit element that integrates a control unit such as a CPU (Central Processing Unit), RAM (Random Access Memory) and / or ROM (Read Only Memory), and input / output ports, etc. into one integrated circuit. The power supply control unit can function as the SW frequency variation unit 10. For example, a microcontroller in the digital power supply can digitally generate an external signal and supply it to the voltage signal generation unit 20. In this case, since a signal with a randomly varying frequency can be easily generated by the internal operation of the microcontroller, it is not necessary to separately provide a mechanism for generating the external signal. That is, since the processing can be executed only by the operation of the microcontroller, the overall design cost of the device (such as a TV, etc.) equipped with the display control device 1 can be reduced.

[0069] Also, when the voltage signal generation unit 20 drives a DC / DC converter circuit with a microcontroller inside the digital power supply, it is possible to execute a process of varying the frequency of the backlight voltage by the internal operation of the microcontroller. In this case, since the function of the SW frequency variation unit 10 is substantially included in the microcontroller, the display control device 1 can achieve the same effect as in this embodiment without providing the SW frequency variation unit 10.

[0070] <Third Embodiment> Next, a third embodiment will be described. FIG. 11 is a functional block diagram showing a schematic configuration of a display control device 1 according to the third embodiment. As shown in FIG. 11, the display control device 1 according to the third embodiment includes, as functional blocks, a frequency fluctuation unit 50, a voltage signal generation unit 20, a control signal generation unit 30, and a drive control unit 40. That is, the display control device 1 according to the third embodiment includes a frequency fluctuation unit 50 instead of the SW frequency fluctuation unit 10 of the first embodiment.

[0071] The frequency fluctuation unit 50 randomly varies a reference frequency that serves as a reference for determining the frequency of an input signal (a control signal in this embodiment). Specifically, the frequency fluctuation unit 50 varies the reference frequency so that the time integral average of the frequency of the input signal becomes the target frequency.

[0072] The voltage signal generation unit 20 inputs a backlight voltage of a constant frequency to the drive control unit 40.

[0073] In the third embodiment, the control signal generation unit 30 functions as the signal generation unit in the present disclosure. The control signal generation unit 30 generates a control signal for an image to be displayed on the display screen at a frequency varied by the SW frequency fluctuation unit 10 as an input signal. For example, the control signal generation unit 30 generates a generated signal having a randomly varied frequency by the SW frequency fluctuation unit 10. The control signal generation unit 30 inputs the generated control signal to the drive control unit 40.

[0074] The drive control unit 40 controls the luminance of the display screen for each scanning line of the display screen based on the input signal. In this embodiment, since the input signal is the control signal generated by the control signal generation unit 30, the drive control unit 40 controls the luminance of the display screen for each scanning line based on the control signal. Specifically, the drive control unit 40 controls the luminance of the display screen for each scanning line based on the backlight voltage input from the voltage signal generation unit 20 and the control signal input from the control signal generation unit 30.

[0075] Here, while referring to FIG. 12, the details of the control of the luminance of the display screen by the drive control unit 40 will be described. FIG. 12 is a diagram for explaining the control of the luminance of the display screen by the drive control unit 40 in the third embodiment.

[0076] The backlight voltage is shown in the upper part of FIG. 12. In the third embodiment, the frequency of the backlight voltage is constant.

[0077] The control signal is shown in the middle part of FIG. 12. In the example shown in FIG. 12, a first control signal for determining the luminance update timing of the first scanning line and a second control signal for determining the luminance update timing of the second scanning line are shown, and the control signals other than the first control signal and the second control signal are not shown. In this embodiment, since the frequency of the control signal fluctuates randomly, the timing at which the luminance update is performed in each scanning line changes randomly every time the luminance is updated.

[0078] For example, in the example shown in FIG. 12, the signal intensity of the first control signal changes (decreases) at times t1, t3, and t5, and the signal intensity of the second control signal changes (decreases) at times t2, t4, and t6. Since the frequencies of the first control signal and the second control signal fluctuate randomly, the interval between time t1 and time t3 and the interval between time t3 and time t5 are different. That is, the timing at which the signal intensity of the first control signal changes can change every time the luminance is updated. The same applies to the second control signal.

[0079] The luminance of each scanning line is shown in the lower part of FIG. 12. In the example shown in FIG. 12, only the first scanning line and the second scanning line are shown. Here, while the backlight voltage has a constant frequency, the frequency of the control signal fluctuates randomly, so the value of the backlight voltage can be different for each luminance update timing of each scanning line every time the luminance is updated. That is, as shown in the lower part of FIG. 12, the luminance of the first scanning line changes every time the luminance is updated. The same applies to the second scanning line.

[0080] FIG. 13 is a schematic diagram showing the luminance of the display screen. Specifically, in the upper part of FIG. 13, images of the luminance of each display screen when the first to third startup updates are performed are shown. Since the frequency of the backlight voltage is not synchronized with the timing of luminance update, as can be understood from the figure showing the display screen in the upper part of FIG. 6, the luminance varies between scanning lines at each luminance update. However, since the timing of luminance update varies, the luminance of each scanning line also changes randomly over time. Thus, based on the same principle as that described in the first embodiment, to the human eye, as shown in the lower part of FIG. 13, the luminance unevenness for each scanning line and over time is recognized in a state where it is suppressed. Therefore, it is possible to easily suppress the stripe-like luminance unevenness that is visually recognized by humans.

[0081] Although the present disclosure has been described based on the drawings and embodiments, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these modifications and corrections are included in the scope of the present disclosure. For example, the functions included in each functional unit or each step, etc. can be rearranged so as not to be logically contradictory, and it is possible to combine or divide a plurality of functional units or steps, etc. into one.

Description of Reference Numerals

[0082] 1 Display control device 10 SW frequency variation unit (frequency variation unit) 11 First resistor 12 Second resistor 13 Thermistor 14 Switching element 20 Voltage signal generation unit 21 Frequency setting terminal 30 Control signal generation unit 40 Drive control unit 50 Frequency variation unit

Claims

1. A frequency variation unit that randomly varies a reference frequency serving as a reference for determining the frequency so that a time integral average of the frequency of the input signal becomes a target frequency; A signal generation unit that generates the input signal at the frequency varied by the frequency variation unit; A drive control unit that controls the luminance of a display screen for each scanning line based on the input signal; A display control device comprising:

2. Further comprising a control signal generation unit that generates a control signal for an image to be displayed on the display screen, The reference frequency is a switching frequency of a switching signal that switches on and off a switching element, The signal generation unit generates a voltage signal by switching on and off the switching element based on the switching frequency varied by the frequency variation unit as the input signal, The drive control unit controls the luminance of the display screen for each scanning line based on the voltage signal and the control signal. The display control device according to claim 1.

3. The frequency variation unit includes a circuit element whose parameter changes according to environmental noise, The switching frequency varies based on the change in the parameter according to the environmental noise. The display control device according to claim 2.

4. The circuit element is a thermistor whose resistance value as the parameter changes according to temperature as the environmental noise. The display control device according to claim 3.

5. The frequency variation unit is connected to a terminal of the signal generation unit, The signal generation unit determines the switching frequency based on the resistance value or voltage of the frequency variation unit connected to the terminal. The display control device according to claim 4.

6. The frequency variation unit is constituted by a circuit including a circuit element capable of controlling current according to an external signal, The frequency variation unit is connected to a terminal of the signal generation unit, The signal generation unit determines the switching frequency based on the resistance value or voltage of the frequency variation unit connected to the terminal, The display control device according to claim 2.

7. The frequency variation unit generates an external signal whose frequency varies randomly, The signal generation unit generates the input signal whose frequency is synchronized with the external signal, The display control device according to claim 1.

8. A power supply unit that supplies power to the display control device, A power supply control unit that controls the power supply unit, and further includes, The power supply control unit has the frequency variation unit, The display control device according to claim 7.

9. Further includes a voltage signal generation unit that generates a voltage signal of a predetermined frequency, The signal generation unit generates, as the input signal, a control signal for an image to be displayed on the display screen at the frequency varied by the frequency variation unit, The drive control unit controls the luminance of the display screen for each scanning line based on the voltage signal and the control signal, The display control device according to claim 1.

10. A display control method executed by a display control device, Randomly vary a reference frequency serving as a reference for determining the frequency so that a time integral average of the frequency of the input signal becomes a target frequency, Generate the input signal at the varied frequency, Control the luminance of the display screen for each scanning line based on the input signal, Display control method.

Images