JP2005156711A - Light source device and its driving method, and video display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light source device which can simply and linearly adjust the brightness of a light source irrespective of a modulation system of a spatial light modulator. <P>SOLUTION: The light source device is turned on with a fixed cycle or always turned on and has a plurality of light emitting elements 1101 to 1108, to which fixed power is supplied and a light source drive circuit 12 which selectively drives the light-emitting elements and makes the fixed number of light-emitting elements emit light for a period of lighting. The light source driving circuit 12 performs PWM drive of the light-emitting elements 1101 to 1108, respectively and makes the fixed number of light-emitting elements emit light. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light source device, and more particularly to a light source device for illuminating a spatial light modulator and a driving method thereof. The present invention also relates to a video display device including such a light source device.

  In video display devices such as a projection video display device, a direct view liquid crystal display device, and an HMD (Head Mounted Display), light from a light source is modulated by a spatial light modulator to display an image. Examples of the spatial light modulator include a TN (Twisted Nematic) liquid crystal device, a ferroelectric liquid crystal device, and a DMD (Digital Micromirror Device).

  The TN liquid crystal device uses properties such as optical rotation and birefringence to change the brightness of light passing therethrough by controlling the degree of polarization according to the magnitude of the applied voltage. Since the light transmission rate (transmittance or reflectance) can be controlled continuously, gradation expression can be performed by AM (Amplitude Modulation) driving.

  A ferroelectric liquid crystal device uses birefringence to switch between two polarization states according to the polarity of an applied voltage. The light transmittance (transmittance or reflectance) is discrete and has only two states, an ON state and an OFF state. For this reason, the brightness of the passing light is controlled by PWM (Pulse Width Modulation) driving. That is, gradation is expressed by controlling the time ratio between the ON state and the OFF state. This is a gradation expression method using a phenomenon in which the human eye has an integration effect, and if the blinking cycle of light is short, humans perceive the average brightness without recognizing the blinking.

  The DMD has as many micromirrors as the number of pixels, and switches the tilt of the micromirrors according to the polarity of the applied voltage. There are only two states (ON state and OFF state) of the micro mirror to be controlled. For this reason, the brightness of the passing light is controlled by PWM drive.

  As described above, there are spatial light modulators that perform gradation expression by AM driving and those that perform gradation expression by PWM driving. Here, the gradation expression method by PWM drive will be specifically described. When the gradation is expressed with 8-bit precision, the time allocated to bit 0 is referred to as one slot, and the times allocated to bits 1, 2, 3, 4, 5, 6, 7 are respectively 2, 4, 8, It is assumed that there are 16, 32, 64, and 128 slots. That is, 255 slots are provided for each image update cycle, a predetermined bit is assigned to each slot, and ON / OFF control is performed for each bit. For example, in order to obtain a brightness of level 133 (= 128 + 0 + 0 + 0 + 0 + 4 + 0 + 1) with respect to the maximum value 255, the states in the slots corresponding to bits 7, 6, 5, 4, 3, 2, 1, 0 are respectively turned on and off. , OFF, OFF, OFF, ON, OFF, ON.

  Next, a light source that illuminates the spatial light modulator will be described. As this type of light source, a discharge lamp is generally used, but recently, a light source using a light emitting element such as an LED (Light Emitting Diode), an LD (Laser Diode), or an EL (Electroluminescence) element has been proposed. Yes. For example, Patent Document 1 describes a projection display apparatus using a large number of LEDs as light sources. Light emitting elements such as LED, LD, and EL elements (1) do not contain heat rays and ultraviolet components, and can emit single colors such as red, green, and blue, and (2) simple lighting control. (3) There is an advantage that the response speed is fast, and (4) it does not burst. However, there is a drawback that a single luminous flux is small.

  In the case of using a light emitting element such as an LED, LD, or EL element as the light source, there are two methods for adjusting the brightness of the light source: control of the luminous flux and control of the light emission time.

  First, a method for adjusting the brightness of the light source by controlling the luminous flux will be described. In a light emitting element such as an LED, LD, or EL element, the luminous flux can be increased by increasing the drive current. That is, the brightness of these light emitting elements can be controlled by AM driving. However, when the brightness is adjusted by the AM drive, the luminous flux-drive current characteristic is not linear. In addition, depending on the light emitting element, a phenomenon in which the emission color is shifted by a drive current, that is, a so-called blue shift or red shift may occur. Therefore, the brightness of the light source cannot be accurately adjusted unless the light emission characteristics are grasped. In particular, in the case of using a plurality of light emitting elements, if the color balance of each light emitting element is deviated, the chromaticity of the combined light deviates from a desired value.

  Next, a method for adjusting the brightness of the light source by controlling the light emission time, that is, an adjustment method by PWM drive will be described. For example, Patent Document 2 describes a method of adjusting the brightness of an LED by PWM driving. In the adjustment method by PWM drive, the light source is periodically turned on and off, and the brightness is adjusted by changing the time ratio of turning on and off. As described above, since the human eye has an integral effect, when the light blinks at a short cycle of a certain degree or less, the brightness of the light feels equal to the brightness when continuously lit at the average value in the cycle. In other words, it feels bright when the ratio of the lighting time is large and dark when it is small. In the case of the adjustment method using PWM drive, if the response speed of the light source is sufficiently high, the brightness is determined by the ratio of the lighting time, and therefore the brightness can be adjusted accurately. However, when the blinking cycle is long and fluctuations in brightness are recognized by human eyes, a problem called flicker occurs.

  FIG. 9 is a block diagram showing a circuit configuration of a conventional PWM drive system light source device. This light source device includes a plurality of light emitting elements C1101 to C1108, a light source control unit C121, a power source C122, and a switch circuit C123. The power source C122 supplies current in common to the light emitting elements C1101 to C1108 via the switch circuit C123. The switch circuit C123 is ON / OFF controlled by a control signal from the light source control unit C121. When the switch circuit C123 is turned on, all the light emitting elements C1101 to C1108 are turned on. On the other hand, when the switch circuit C123 is turned off, all the light emitting elements C1101 to C1108 are turned off.

  FIG. 10 is a timing chart showing an operation of the conventional PWM driving type light source device shown in FIG. This example shows the operation when the light source device is turned on periodically. It is assumed that the switch circuit C123 is turned on when the control signal supplied from the light source controller C121 is at a high level. The switch circuit C123 is turned on only for a period of 6/8 of the light source lighting period. The average luminous flux in the lighting period in this case is 6/8 luminous flux when all the light emitting elements are lit for the lighting period. Thus, by controlling the lighting time ratio, the luminous flux ratio with respect to the maximum luminous flux can be adjusted.

The purpose of adjusting the brightness of the light source in the video display device is as follows: (1) a function of dimming to reduce power consumption, and (2) a plurality of light sources that emit light of different colors. The function of dimming the light source of each color to adjust the chromaticity of the combined light as desired, (3) desired spatial light by combining the modulation with the light source and the modulation for each pixel with the spatial light modulator The purpose is to provide a function to perform modulation. As an example of providing the function of (3), in Patent Document 3, in a direct-view type liquid crystal display device, the light source is AM driven according to the video signal, and the gradation control of the liquid crystal device is changed correspondingly, A method for improving image quality is described. Patent Document 4 describes a method of reducing the PWM control speed for DMD by modulating illumination light using a dynamically changing density filter together with a discharge lamp in a projection display apparatus using DMD. Has been.
JP 2000-56410 A JP 2001-272938 JP-A-6-102484 JP-A-9-149350

  As described above, dimming for adjusting the brightness of the light source includes AM driving and PWM driving. However, dimming by these AM drive and PWM drive has the following problems.

  In the dimming by AM driving, it is not possible to adjust the brightness linearly because the luminous flux-driving current characteristics are not linear, and depending on the light emitting elements, the emission color is shifted due to the driving current. Have difficulty.

  In dimming by PWM driving, brightness can be controlled more easily and linearly than in AM driving, but gradation is expressed by PWM driving, such as a ferroelectric liquid crystal device or DMD. Application to a light source that illuminates a spatial light modulator for performing the above has been difficult for the following reasons.

  As described above, the spatial light modulator includes a gray scale expression by AM driving such as a TN liquid crystal device and a gray scale expression by PWM driving such as a ferroelectric liquid crystal device and DMD. . As a method of dimming a light source that illuminates a spatial light modulator that expresses gradation by AM driving, either AM driving or PWM driving can be applied. However, as a method of dimming a light source that illuminates a spatial light modulator that expresses gradation by PWM driving, AM driving is good, but PWM driving is inappropriate. The reason is that the spatial light modulator needs to be illuminated with a constant light flux during the PWM drive period. That is, in the light control by PWM driving, light is not emitted during a certain period of the lighting period (in the example of FIG. 10, 2/8 of the lighting period), and thus the spatial light modulator is illuminated during this period. Therefore, even if the spatial light modulator is PWM-driven, gradation expression cannot be performed.

  In addition to the above problem, in the dimming by PWM driving, a blinking operation is performed such that light is emitted during a certain period of the lighting period (in the example of FIG. 10, a period of 6/8 of the lighting period). There is also a problem that flicker occurs depending on the length.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a light source device and a driving method capable of easily and linearly adjusting the brightness of the light source regardless of the modulation scheme of the spatial light modulator, and an image using the same. It is to provide a display device.

  In order to achieve the above object, the light source device and the driving method of the present invention are characterized by selectively driving a plurality of light emitting elements each emitting a constant luminous flux to emit a certain number of light emitting elements over a lighting period. There is to make it.

  According to the above feature, the brightness of the light source is indicated by the relative luminous flux, which is the ratio of the luminous flux when a certain number of light emitting elements emit light to the total luminous flux when all the light emitting elements emit light. Since the number of driven light emitting elements is constant at any point in the lighting period, the relative luminous flux during the lighting period is constant. As described above, unlike the conventional blinking operation in which light emission is performed in a certain period of the lighting period, a constant relative light flux is always obtained over the lighting period, and thus flicker does not occur.

  In addition, constant power is supplied to the plurality of light emitting elements, and the current and voltage for driving the light emitting elements do not increase or decrease. That is, in the present invention, the brightness of the light emitting element is not adjusted by the current or voltage for driving the light emitting element, but is adjusted by the number of light emitting elements that are driven simultaneously. Therefore, there is no problem that the brightness cannot be adjusted linearly because the luminous flux-driving current characteristic of the light emitting element is non-linear. In addition, when a light-emitting element whose emission color changes depending on the driving current or voltage is used, the emission color does not shift even if the brightness is adjusted.

  In the above-described light source device and driving method of the present invention, the plurality of light emitting elements may be driven by pulse width modulation (PWM) to emit a certain number of light emitting elements. With this configuration, it is possible to provide a light source device that can be applied to a spatial light modulator that is PWM-driven and that is dimmed by PWM driving. In addition, since a plurality of light emitting elements are uniformly selected during the lighting period, light emission characteristics are averaged when there are individual differences in the light emission characteristics of the respective light emitting elements.

  In the above case, the blinking cycle of each of the plurality of light emitting elements may be the same as or different from the lighting cycle. When the blinking period is different from the lighting period, the light emission timings of the respective light emitting elements are different between the front and rear lighting, and the light emitting elements are caused to uniformly emit light in all phases of the lighting period. Therefore, when the spatial light modulator driven by PWM is illuminated, there is no bias in the light emitting elements that emit light in the slot corresponding to a specific bit, so even if there are individual differences in the light emission characteristics of each light emitting element, spatial light modulation The linearity of the gradation expression in the container is maintained.

  In the light source device and driving method of the present invention described above, a certain number of light emitting elements may be selected from the plurality of light emitting elements to emit light. In this case, the combination of the light emitting elements selected as the certain number of light emitting elements may be the same or different in front and rear lighting. When the combination of the light emitting elements is the same for the front and rear lighting, the light emitting element to be selected is uniquely determined, so that the configuration of the light source driving circuit is simplified. When the combination of light emitting elements differs between front and rear lighting, the light emitting elements are uniformly selected over a plurality of lighting periods to emit light. Therefore, the variation in the light emission characteristics when the light emission characteristics of each light emitting element have individual differences is averaged.

  In the light source device and driving method of the present invention described above, at least one other light emitting element may emit light over the lighting period. According to this configuration, the brightness adjustment range of the light source is shifted by the amount that the other light emitting elements emit light.

  In the above case, the power supplied to the other light emitting elements may be adjusted. According to this configuration, it is possible to continuously adjust the luminous flux of the other light emitting elements, and the adjustment of the luminous flux is reflected in the brightness of the light source. Therefore, it is possible to continuously adjust the brightness of the light source.

  Further, power supplied to at least one of the plurality of light emitting elements may be adjusted. According to this configuration, individual differences in the light emission characteristics of the light emitting elements can be corrected. In addition, when a light emitting element whose chromaticity changes depending on a driving current or a driving voltage is used, the chromaticity of each light emitting element can be adjusted to be uniform.

  The video display device of the present invention includes any one of the light source devices described above and a spatial light modulator that is illuminated with light emitted from the light source device. According to this configuration, since the light source device having the above-described features is used, the brightness of the display image can be adjusted easily and linearly, and the occurrence of flicker and the emission color can be adjusted. Misalignment is also suppressed.

  As described above, according to the light source device and the driving method of the present invention, the brightness of the light source can be easily and linearly adjusted regardless of the luminous flux-driving current characteristics of the light emitting element, and the flicker can be adjusted. It is possible to prevent the occurrence of the light emission and the emission color shift.

  In the present invention, in the case where PWM driving is performed, in addition to the above effect, an AM driving spatial light modulator such as a TN liquid crystal device and a PWM driving spatial light modulation such as a DMD or a ferroelectric liquid crystal device. There is an effect that it can be used as a light source in any of the vessels.

  In the present invention, when light emitting elements are selected uniformly, in addition to the above effects, even if there are individual differences in the light emitting characteristics of the light emitting elements, the effect can be reduced.

  Among the present inventions, the light emitting elements that uniformly emit light in all phases of the lighting cycle, even when there is an individual difference in the light emission characteristics of the light emitting elements when illuminating the PWM driven spatial light modulator, The effect is that the linearity of the expression is maintained.

  According to the video display device of the present invention, it is possible to realize a video display device with excellent display image quality by including the light source device that achieves the above-described effects.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration example of a video display device including the light source device of the present invention. The video display device includes light source devices 1R, 1G, and 1B, an illumination optical system 2, a spatial light modulator 3, a projection optical system 4, and a signal processing circuit 5.

  The light source devices 1R, 1G, and 1B are light source devices according to the present invention, and emit red, green, and blue light, respectively. The light source device 1R includes a light emitting element array 11R composed of a plurality of light emitting elements that emit red light, and a light source driving circuit 12R that drives the light emitting element array 11R. The light source device 1G includes a light emitting element array 11G including a plurality of light emitting elements that emit green light, and a light source driving circuit 12G that drives the light emitting element array 11G. The light source device 1B includes a light emitting element array 11B composed of a plurality of light emitting elements that emit blue light, and a light source driving circuit 12B that drives the light emitting element array 11B. As a light emitting element used for each light emitting element array 11R, 11G, and 11B, LED is desirable. This is because the LED can (1) emit light of a single color such as red, green, and blue, (2) can control light emission electrically, and (3) has a response time of about several microseconds or less. This is because the control described later is possible because the period is sufficiently small with respect to the period in which flicker is felt or the image update period. As light emitting elements having such characteristics, there are LD and EL elements in addition to LEDs.

  Light emitted from each of the light source devices 1R, 1G, and 1B is efficiently and uniformly illuminated on the spatial light modulator 3 by the illumination optical system 2. The illumination optical system 2 includes a color synthesis optical system 21 and an integrator optical system 22. In the color synthesis optical system 21, light from each of the light source devices 1R, 1G, and 1B is incident through different paths, and the incident light is emitted on the same path. As the color synthesis optical system 21, a dichroic prism, a dichroic mirror, a fly-eye lens, or the like is used. The integrator optical system 22 makes the illuminance distribution of the light from the color synthesis optical system 21 uniform on the spatial light modulator 3. As the integrator optical system 22, a fly-eye lens, a rod lens, a light pipe, or the like is used.

  The spatial light modulator 3 spatially modulates the light from the illumination optical system 2. The modulated light enters the projection optical system 4 as a light beam (image light beam) that forms an image. The projection optical system 4 projects the image light beam from the spatial light modulator 3 onto a screen (not shown).

  The signal processing circuit 5 drives the spatial light modulator 3 based on the video signal S1 supplied from the outside. When driving the spatial light modulator 3, the signal processing circuit 5 performs signal processing such as synchronization detection, color space conversion, and degamma correction on the video signal S1. The signal processing circuit 5 controls the light source devices 1R, 1G, and 1B in synchronization with an image update timing (for example, a frame switching timing) obtained from the video signal S1. In this control, switching of the light source devices 1R, 1G, and 1B (switching of emission color), adjustment of the brightness and chromaticity of an image light beam (synthetic light) projected onto the screen, and the like are performed.

  In the above-described video display device, R (red) light, G (green) light, and B (blue) light are sequentially emitted from the light source devices 1R, 1G, and 1B and applied to the spatial light modulator 3. In the spatial light modulator 3, gradation representation is performed by PWM driving or AM driving, and image light beams of R (red) light, G (green) light, and B (blue) light are formed. The image light beams of R (red) light, G (green) light, and B (blue) thus formed are sequentially projected onto a screen (not shown) by the projection optical system 4 so that color display is performed.

  Next, the light source device of the present invention used as the light source devices 1R, 1G, and 1B will be specifically described. Since the circuit configurations of the light source devices 1R, 1G, and 1B are basically the same, they will be described without distinction here.

  FIG. 2 shows an example of a circuit configuration of a light source device according to an embodiment of the present invention. The light source device includes a light emitting element array 11 including a plurality of light emitting elements 1101 to 1108 and a light source driving circuit 12 that drives the light emitting element array 11. The light source drive circuit 12 includes a light source control unit 121, a power source 122, and a plurality of switch circuits 1231 to 1238.

  One electrode of each of the light emitting elements 1101 to 1108 is commonly connected to one electrode of the power source 122, and the other electrode is commonly connected to the other electrode of the power source 122 via the switch circuits 1231 to 1238, respectively. . The power source 122 supplies power to the light emitting elements 1101 to 1108 in common. The switch circuits 1231 to 1238 are for ON / OFF control of power supply to the light emitting elements 1101 to 1108, respectively. In the example of FIG. 2, the light emitting element 1101 is connected to the power source 122 with a polarity that emits light when the switch circuit 1231 is ON. Similarly, the other light emitting elements 1102 to 1108 are also connected to the power source 122 with such a polarity that light is emitted when the switch circuits 1232 to 1238 are ON, respectively. The light source control unit 121 performs ON / OFF control of the switch circuits 1231 to 1238 based on the light source control signal S2 supplied from the signal processing circuit 5 shown in FIG.

  There are several modes of operation for light source lighting control and light beam adjustment in the above light source device. Hereinafter, the operation examples 1 to 4 will be given to specifically describe the characteristics of each operation.

(Operation example 1)
FIG. 3 is a timing chart showing a first operation example of the light source device shown in FIG. This example is an operation when the light source device is periodically turned on in synchronization with the image update period in the spatial light modulator. The switch circuits 1231 to 1238 are turned on when the control signal supplied from the light source control unit 121 is at a high level. The lower side in FIG. 3 shows the relative luminous flux of the luminous flux emitted from the light source device with reference to the luminous flux when the light emitting elements are all turned on, as the brightness of the light source. In the following description, it is assumed that the lighting period is divided into periods P1 to P8.

  All of the switch circuits 1231 to 1238 are controlled so that 7/8 of the lighting periods are turned on. Specifically, in the switch circuit 1231, the period P1 is turned off and the periods P2 to P8 are turned on. In the switch circuit 1232, the period P2 is turned off, and the periods P1, P3 to P8 are turned on. In the switch circuit 1233, the period P3 is turned off, and the periods P1, P2, and P4 to P8 are turned on. In the switch circuit 1234, the period P4 is turned off, and the periods P1 to P3 and P5 to P8 are turned on. In the switch circuit 1235, the period P5 is turned off, and the periods P1 to P4 and P6 to P8 are turned on. In the switch circuit 1236, the period P6 is turned off, and the periods P1 to P5, P7, and P8 are turned on. In the switch circuit 1237, the period P7 is turned off, and the periods P1 to P6 and P8 are turned on. In the switch circuit 1238, the period P8 is turned off and the periods P1 to P7 are turned on.

  As described above, each of the switch circuits 1231 to 1238 is in the OFF state during one-eighth of the lighting period, and any period of the periods P1 to P8 can be obtained by shifting the timing of the OFF state from each other. In FIG. 5, seven of the switch circuits 1231 to 1238 are controlled to be in an ON state. Therefore, at any point in the lighting period, a relative light flux (7/8) with respect to the total light flux when all the light emitting elements 1101 to 1108 are turned on is emitted from the light source device.

  In this operation example, the light source can be dimmed by changing the ratio of the period in which the switch circuits 1231 to 1238 are turned on with respect to the lighting period, and the adjustment range is 0 / It is in the range of 8-8 / 8.

  Next, a case where a relative light beam (6/8) is obtained as the light beam emitted from the light source device will be described. All of the switch circuits 1231 to 1238 in FIG. 2 are turned ON during a period of 6/8 of the light source lighting period. Further, by shifting the ON timing from each other, control is performed so that six of the eight switch circuits 1231 to 1238 are turned ON at any point in the light source lighting period. By doing so, at any point in the light source lighting period, the luminous flux emitted from the light source device can be reduced to 6/8 of when all the light emitting elements are turned on. FIG. 4 shows an operation example when a relative light beam (6/8) is obtained as a light beam emitted from the light source device.

  In the example illustrated in FIG. 4, the switch circuits 1231 to 1238 are all controlled so that 6/8 of the lighting periods are in the ON state. Specifically, in the switch circuit 1231, the periods P1 and P2 are turned off, and the periods P3 to P8 are turned on. In the switch circuit 1232, the periods P2 and P3 are turned off, and the periods P1 and P4 to P8 are turned on. In the switch circuit 1233, the periods P3 and P4 are turned off, and the periods P1, P2, and P5 to P8 are turned on. In the switch circuit 1234, the periods P4 and P5 are turned off, and the periods P1 to P3 and P6 to P8 are turned on. In the switch circuit 1235, the periods P5 and P6 are turned off, and the periods P1 to P4, P7, and P8 are turned on. In the switch circuit 1236, the periods P6 and P7 are turned off, and the periods P1 to P5 and P8 are turned on. In the switch circuit 1237, the periods P7 and P8 are turned off, and the periods P1 to P6 are turned on. In the switch circuit 1238, the periods P1 and P8 are turned off, and the periods P2 to P7 are turned on.

  As described above, each of the switch circuits 1231 to 1238 is in the OFF state for 2/8 of the lighting periods, and by shifting the timing of the OFF state by a period of 1/8, In any period of the periods P1 to P8, six of the switch circuits 1231 to 1238 are controlled to be in an ON state. For this reason, a relative luminous flux (6/8) is emitted from the light source device at any point in the lighting period.

  As described above, according to this operation example, each light emitting element 1101 to 1108 is PWM-controlled, so that a constant relative luminous flux is always generated during the lighting period regardless of the luminous flux-driving current characteristics. Will be emitted from. Therefore, the present invention can be applied not only to AM driving but also to a spatial light modulator in which gradation expression is performed by PWM driving. On the other hand, in the conventional operation shown in FIG. 10, since all the light emitting elements are turned off in a certain period (period P1, P2) of the lighting period, spatial light in which gradation expression is performed by PWM driving. It could not be applied to the modulator.

  Further, unlike the conventional dimming by AM driving, the driving current supplied to each of the light emitting elements 1101 to 1108 is constant, so that the phenomenon that the emission color shifts (blue shift or red shift) does not occur.

  Further, as in the operation example shown in FIG. 3, the light emitting elements 1102 to 1108 emit light in the period P1, the light emitting elements 1101 and 1103 to 1108 emit light in the period P2, and so on during the lighting period. Since seven light emitting elements are uniformly selected from the light emitting elements 1102 to 1108 to emit light, variations in the light emission characteristics of the respective light emitting elements 1101 to 1108 are averaged. Therefore, when there are individual differences in the light emission characteristics of the light emitting elements 1101 to 1108, the influence can be prevented.

  Further, unlike a conventional blinking operation in which light emission is performed in a certain period of the lighting period, a constant relative luminous flux can be always obtained over the lighting period, so that flicker can be avoided.

(Operation example 2)
In the first operation example described above, light emitting elements are uniformly selected from the light emitting elements 1101 to 1108 to emit light during the lighting period. However, a constant luminous flux can be obtained. Here, an example of such an operation will be described.

  FIG. 5 is a timing chart showing a second operation example of the light source device shown in FIG. This example is also an operation when the light source device is periodically turned on in synchronization with the image update cycle. The switch circuits 1231 to 1238 are turned on when the control signal supplied from the light source control unit 121 is at a high level. The lower side of FIG. 5 shows the relative luminous flux of the luminous flux emitted from the light source device with reference to the luminous flux when the light emitting elements are all turned on, as the brightness of the light source.

  In this operation example, seven switch circuits are selected from the switch circuits 1231 to 1238 for each lighting period, and are turned on during the lighting period. Specifically, in a certain lighting period A, the switch circuit 1231 is turned off and the switch circuits 1232 to 1238 are turned on. In the next lighting period B, the switch circuit 1232 is turned off, and the switch circuits 1231, 1233-1238 are turned on. In the next lighting period C, the switch circuit 1233 is turned off, and the switch circuits 1231, 1232, and 1234 to 1238 are turned on. In the next lighting period D, the switch circuit 1234 is turned off, and the switch circuits 1231 to 1233 and 1235 to 1238 are turned on. In the next lighting period E, the switch circuit 1235 is turned off, and the switch circuits 1231 to 1234 and 1236 to 1238 are turned on. In the next lighting period F, the switch circuit 1236 is turned off, and the switch circuits 1231 to 1235, 1237, and 1238 are turned on. In the next lighting period G, the switch circuit 1237 is turned off and the switch circuits 1231 to 1236 and 1238 are turned on. In the next lighting period H, the switch circuit 1238 is turned off and the switch circuits 1231 to 1237 are turned on.

  As described above, in any of the lighting periods A to H, seven of the switch circuits 1231 to 1238 are controlled to be in an ON state. For this reason, at any time point in any lighting period, a relative luminous flux (7/8) with respect to the total luminous flux when all the light emitting elements 1101 to 1108 are turned on is emitted from the light source device. Note that, when the light flux emitted from the light source device is further reduced, the number of switch circuits that are turned on during the lighting period is reduced to reduce the relative light flux.

  In this operation example, as in the first operation example described above, since it is possible to emit a constant relative luminous flux over the lighting period, it can be applied to a spatial light modulator in which gradation expression is performed by PWM driving. is there. In addition, it is possible to prevent the phenomenon of emission color shift (blue shift or red shift), the occurrence of flicker, and the influence of variations in emission characteristics.

(Operation example 3)
In the first and second operation examples described above, the light emitting elements to emit light are switched within the lighting period or for each lighting period. From the viewpoint of obtaining a constant light flux over the lighting period, It is not necessary to switch the light emitting element to emit light. Here, an example of such an operation will be described.

  FIG. 6 is a timing chart showing a third operation example of the light source device shown in FIG. This example is also an operation when the light source device is periodically turned on in synchronization with the image update cycle. The switch circuits 1231 to 1238 are turned on when the control signal supplied from the light source control unit 121 is at a high level. The lower side of FIG. 6 shows the relative luminous flux of the luminous flux emitted from the light source device with reference to the luminous flux when the light emitting elements are all turned on, as the brightness of the light source.

  In this operation example, the switch circuit 1231 is turned off and the switch circuits 1232 to 1238 are turned on during the lighting period. Therefore, at any point in any lighting period, the relative light flux (7/8) with respect to the total light flux when all the light emitting elements 1101 to 1108 are turned on is emitted from the light source device. Note that, when the light flux emitted from the light source device is further reduced, the number of switch circuits that are turned on during the lighting period is reduced to reduce the relative light flux.

  In this operation example, as in the first operation example, since it is possible to emit a constant relative luminous flux over the lighting period, it can be applied to a spatial light modulator in which gradation expression is performed by PWM driving. In addition, it is possible to prevent the phenomenon of emission color shift (blue shift or red shift) and the occurrence of flicker.

  In addition, since the light emitting elements to emit light are uniquely determined without being dynamically switched, the control circuit becomes very simple.

  In this operation example, unlike the first and second operation examples, if there is an individual difference between light emitting elements, the linearity of the total luminous flux-emission number characteristic is distorted, so that the accuracy of the total luminous flux adjustment is deteriorated. The light emitting elements to be driven are biased, and thus there are drawbacks such as a shortened life as a light source device. The first and second operation examples avoid these drawbacks.

(Operation example 4)
In the first operation example described above, the timing for switching the light emitting element to emit light is synchronized with the light source lighting cycle and the image update cycle, and the ON / OFF timing of each of the switch circuits 1231 to 1238 is in each lighting period. Although the same, if the number of light emitting elements that emit light in a predetermined period is constant, the light emitting elements that emit light may be switched at any time. That is, the blinking cycle of each light emitting element may be different from the light source lighting cycle and the image update cycle. Here, an example of such an operation will be described.

  FIG. 7 is a timing chart showing a fourth operation example of the light source device shown in FIG. This example is also an operation when the light source device is periodically turned on in synchronization with the image update cycle. The switch circuits 1231 to 1238 are turned on when the control signal supplied from the light source control unit 121 is at a high level. The lower side of FIG. 7 shows the relative luminous flux of the luminous flux emitted from the light source device with respect to the luminous flux when all the light emitting elements are turned on, as the brightness of the light source. In the following description, timings t0, t1, t2,. . . Assume that timings t0 to t6 exist in the lighting period A, and timings t7 to t12 exist in the lighting period B.

  Now consider signals E, F1-F8. The signal E is set to a high level during the light source lighting period and is set to a low level during the light source extinguishing period. The signal F1 becomes low level at timings t0 to t1, becomes high level at t1 to t8, and thereafter periodically becomes low level for one period and high level for seven periods. The signal F2 becomes low level at timings t1 to t2, becomes high level at t2 to t9, and thereafter periodically becomes low level for one period and high level for seven periods. The signal F3 becomes low level at timings t2 to t3, becomes high level at t3 to t10, and thereafter periodically becomes low level for one period and high level for seven periods. The signal F4 becomes low level at timings t3 to t4, becomes high level at t4 to t11, and thereafter periodically becomes low level for one period and high level for seven periods. The signal F5 becomes low level at timings t4 to t5, becomes high level at t5 to t12, and thereafter periodically becomes low level for one period and high level for seven periods. The signal F6 becomes low level at timings t5 to t6, becomes high level at t6 to t13, and thereafter periodically becomes low level for one period and high level for seven periods. The signal F7 becomes low level at timings t6 to t7, becomes high level at t7 to t14, and thereafter periodically becomes low level for one period and high level for seven periods. The signal F8 becomes low level at timings t7 to t8, becomes high level at t8 to t15, and thereafter periodically becomes low level for one period and high level for seven periods.

  The switch circuit 1231 is turned on only when the signal E = high level and the signal F1 = high level. The switch circuit 1232 is turned on only when the signal E = high level and the signal F2 = high level. The switch circuit 1233 is turned on only when the signal E = high level and the signal F3 = high level. The switch circuit 1234 is turned on only when the signal E = high level and the signal F4 = high level. The switch circuit 1235 is turned on only when the signal E = high level and the signal F5 = high level. The switch circuit 1236 is turned on only when the signal E = high level and the signal F6 = high level. The switch circuit 1237 is turned on only when the signal E = high level and the signal F7 = high level. The switch circuit 1238 is turned on only when the signal E = high level and the signal F8 = high level.

  Accordingly, the switch circuit 1231 is turned on in the light source lighting periods A and B except for the periods t0 to t1 and t8 to t9. The switch circuit 1232 is turned on in the light source lighting periods A and B except for the periods t1 to t2 and t9 to t10. The switch circuit 1233 is turned on in the light source lighting periods A and B except for the periods t2 to t3 and t10 to t11. The switch circuit 1234 is turned on in the light source lighting periods A and B except for the periods t3 to t4 and t11 to t12. The switch circuit 1235 is turned on in the light source lighting periods A and B except for the periods t4 to t5 and t12. The switch circuit 1236 is turned on in the light source lighting periods A and B except for the periods t5 to t6. The switch circuit 1237 is turned on during the light source lighting periods A and B except for the periods t6 to t7. The switch circuit 1238 is turned on in the light source lighting periods A and B except for the periods t7 to t8.

  As described above, at any point in the light source lighting periods A and B, seven switch circuits are selected from the switch circuits 1231 to 1238 and turned on. The blinking period is different from the light source lighting period. That is, in any phase of the lighting cycle, the light emitting elements that emit light are dynamically switched so that the frequency is not biased.

  In this operation example, as in the first operation example described above, since it is possible to emit a constant relative luminous flux over the lighting period, it can be applied to a spatial light modulator in which gradation expression is performed by PWM driving. In addition, it is possible to prevent the phenomenon of emission color shift (blue shift or red shift), the occurrence of flicker and the influence of variations in emission characteristics. In particular, when illuminating a PWM-driven spatial light modulator, it is superior to the first and second operation examples in that the linearity of gradation expression is maintained even if there are individual differences in the light emission characteristics of the light emitting elements. ing. The reason is that light emitting elements are selected evenly in any phase of the image update period and light is emitted, so that the light emitting elements that emit light in slots corresponding to specific bits are not biased.

  Dimming of the light source in this operation example can be performed by adjusting the period in which each switch circuit is turned off and changing the number of switch circuits that are turned on simultaneously during the lighting period. The adjustment range is a relative luminous flux and is a range of 0/8 to 8/8.

(Other embodiments)
FIG. 8 is a block diagram showing a circuit configuration of a light source device according to another embodiment of the present invention. In the light source device, the light emitting element 1109 is added to the light emitting element array 11 and the power adjusting circuit 124 is added to the light source driving circuit 12 in the configuration shown in FIG. Description of parts having the same configuration and operation as those shown in FIG. 2 will be omitted, and only different parts will be described in detail below.

  In the light-emitting element 1109, one electrode is connected to one electrode of the power supply 122, and the other electrode is connected to the other electrode of the power supply 122 through the power adjustment circuit 124. The power adjustment circuit 124 is controlled by the light source control unit 121 and adjusts the current and voltage supplied from the power source 122 to the light emitting element 1109.

  The light source device of the other embodiment can also be applied to the video display device as shown in FIG. 1, and the light source driving circuit 12 is based on the light source control signal S2 supplied from the signal processing circuit 5 as described above. Similarly to the embodiment described above, the switch circuits 1231 to 1238 are turned on / off, and the power adjustment circuit 124 adjusts the luminous flux of the light emitting element 1109. According to this configuration, the brightness of the light source device can be finely adjusted by adjusting the luminous flux of the light emitting element 1109. That is, in the light source device shown in FIG. 2, the brightness is controlled by adjusting the number of light emitting elements to be lit, but in the light source device of the other embodiment, the light emitting elements to be lit are controlled. In addition to the adjustment by the number, the luminous flux of the light emitting element 1109 is continuously adjusted, and thereby the brightness of the light source can be continuously adjusted.

  The light source device of each embodiment described above is an example of the present invention, and the configuration can be appropriately changed without departing from the spirit of the present invention. For example, in the light source device shown in FIG. 2, one light emitting element is provided for one switch circuit, but a configuration in which a plurality of light emitting elements are provided for one switch circuit may be employed. In this case, as compared with the case where the switch circuit and the light emitting element are provided in a one-to-one relationship, even if the control circuit scale is the same, the light source can be brightened or the control circuit scale can be increased even if the brightness is the same. Can be small.

  In the light source device shown in FIG. 2, eight switch circuits are provided, but the number of switch circuits may not be eight. As the number of switch circuits is increased, the light flux can be adjusted more finely, and as the number of switch circuits is decreased, the size of the apparatus can be reduced.

  In the light source device shown in FIGS. 2 and 8, a light emitting element that does not participate in dimming may be added. In this case, since the light beam from the light emitting element that does not participate in light control is added to the light beam from the light emitting element that participates in light control, the adjustment range of the light beam emitted from the light source can be shifted. For example, if there are 8 light emitting elements involved in dimming and 92 light emitting elements not involved in dimming, the light source can be dimmed in the range of relative luminous flux (92/100) to (100/100). It becomes.

  Further, in the light source device shown in FIGS. 2 and 8, the current and voltage for driving part or all of the light emitting elements 1101 to 1108 may be adjusted. In this case, individual differences in the characteristics of the light emitting elements can be corrected, and more accurate light beam adjustment can be performed. In addition, when a light emitting element whose chromaticity changes depending on a driving current or a driving voltage is used, the chromaticity of each light emitting element can be adjusted to be uniform.

  The light source device of the present invention described above is a projection image display device having a projection optical system as shown in FIG. 1, as well as a direct-view image display device having no projection optical system and an HMD that generates a virtual image. It can also be applied to video display devices.

  An image display device to which the light source device of the present invention is applied may use an AM drive type spatial light modulator such as a TN liquid crystal device, or a PWM such as a ferroelectric liquid crystal device or DMD. A drive type spatial light modulator may be used. Furthermore, the spatial light modulator may be a transmissive type or a reflective type.

  Furthermore, the video display device to which the light source device of the present invention is applied may be a color display method or a monochrome display method. As a color display system, a single spatial light modulator as shown in FIG. 1 is sequentially irradiated with a plurality of colors, that is, a so-called FSC (Field Sequential Color) system, or a plurality of spatial light modulators. A system that performs color display by optically synthesizing image light after irradiating color light, and a system that performs color display by illuminating white light on a spatial light modulator that has multiple color filters for each pixel. and so on. It is obvious that the light source device and the driving method thereof of the present invention can be applied to a system other than the case where the light source needs to be periodically turned ON / OFF, such as switching the light source color for the FSC system. .

It is a block diagram which shows one structural example of the video display apparatus with which the light source device of this invention is applied. It is a block diagram which shows the circuit structure of the light source device which is one Embodiment of this invention. FIG. 3 is a timing diagram illustrating an operation example of the light source device illustrated in FIG. 2. FIG. 3 is a timing diagram illustrating an operation example of the light source device illustrated in FIG. 2. FIG. 3 is a timing diagram illustrating an operation example of the light source device illustrated in FIG. 2. FIG. 3 is a timing diagram illustrating an operation example of the light source device illustrated in FIG. 2. FIG. 3 is a timing diagram illustrating an operation example of the light source device illustrated in FIG. 2. It is a block diagram which shows the circuit structure of the light source device which is other embodiment of this invention. It is a block diagram which shows the circuit structure of the light source apparatus of the conventional PWM drive. FIG. 10 is a timing diagram illustrating an operation of the light source device illustrated in FIG. 9.

Explanation of symbols

1R, 1G, 1B Light source device 2 Illumination optical system 3 Spatial light modulator 4 Projection optical system 5 Signal processing circuit 11, 11R, 11G, 11B Light emitting element array 12, 12R, 12G, 12B Light source drive circuit 21 Color synthesis optical system 22 Integrator optical system 121, C121 light source control unit 122, C122 power supply 124 power adjustment circuit 1101-1109, C1101-1108 light emitting elements 1231-1238, C123 switch circuit

Claims (22)

A light source device that is constantly lit or constantly lit;
A plurality of light emitting elements each emitting a constant luminous flux;
A light source device comprising: a light source driving circuit that selectively drives the plurality of light emitting elements to emit a certain number of light emitting elements over the lighting period. 2. The light source device according to claim 1, wherein the light source driving circuit drives the plurality of light emitting elements by pulse width modulation to cause the predetermined number of light emitting elements to emit light. The light source device according to claim 2, wherein a blinking cycle in each of the plurality of light emitting elements is different from the lighting cycle. The light source device according to claim 2, wherein a blinking cycle in each of the plurality of light emitting elements is the same as the lighting cycle. The light source device according to claim 1, wherein the light source driving circuit selects the predetermined number of light emitting elements from the plurality of light emitting elements to emit light. The light source device according to claim 5, wherein a combination of light emitting elements selected as the certain number of light emitting elements is different between front and rear lighting. The light source device according to claim 5, wherein a combination of light emitting elements selected as the fixed number of light emitting elements is the same for front and rear lighting. Further comprising at least one other light emitting element;
The light source device according to claim 1, wherein the light source driving circuit causes the other light emitting element to emit light over the lighting period. The light source device according to claim 8, wherein the light source driving circuit includes a power adjustment circuit for adjusting power supplied to the other light emitting elements. The light source device according to claim 1, wherein the light source driving circuit includes a power adjustment circuit that adjusts power supplied to at least one of the plurality of light emitting elements. A light source device according to any one of claims 1 to 10,
An image display device comprising: a spatial light modulator illuminated with light emitted from the light source device. The video display device according to claim 11, wherein the spatial light modulator is driven by pulse width modulation. A driving method of a light source device that is constantly lit or constantly lit,
A first step of selectively driving a plurality of light emitting elements each emitting a constant luminous flux during the lighting period;
And a second step of controlling the number of light emitting elements to be driven so as to be constant over the lighting period. The light source device driving method according to claim 13, wherein the first step is a step of driving the plurality of light emitting elements by pulse width modulation. The driving method of the light source device according to claim 14, wherein a blinking cycle of the light emitting element driven by the pulse width modulation is different from the lighting cycle. The driving method of the light source device according to claim 14, wherein a blinking cycle of the light emitting element driven by the pulse width modulation is the same as the lighting cycle. The method of driving a light source device according to claim 13, wherein the first step is a step of selecting a certain number of light emitting elements from the plurality of light emitting elements to emit light. The driving method of the light source device according to claim 17, wherein a combination of light emitting elements selected as the certain number of light emitting elements is different between front and rear lighting. The light source device driving method according to claim 17, wherein a combination of light emitting elements selected as the certain number of light emitting elements is the same for front and rear lighting. The light source device driving method according to claim 13, further comprising a step of driving at least one other light emitting element during the lighting period. 21. The method of driving a light source device according to claim 20, further comprising a step of adjusting power supplied to the other light emitting element. The method of driving a light source device according to any one of claims 13 to 21, further comprising adjusting power supplied to at least one of the plurality of light emitting elements.

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