JP2014085463A - Projection type picture display device and multi-vison projection type display device - Google Patents

Abstract

An object of the present invention is to provide a projection display device and a multi-vision projection display device that can further reduce power consumption as compared with a case where a solid state light source is driven by a lower limit current of a light source driving circuit.
A projection display apparatus 100 divides a light source LED 41, 43, 45 and a video signal input from the outside into sub-frames for each of a plurality of color components emitted by the light source LED 41, 43, 45. In addition, signal processing means 9 that generates the light emission timing of the light source LEDs 41, 43, and 45 synchronized with each subframe, and the light source circuit 4 that drives the light source LEDs 41, 43, and 45 to emit light according to the light emission timing are provided. The signal processing unit 3 sets the display resolution of the video signal to n bits during normal operation and limits the display resolution of the video signal to nm bits during power saving operation. The light source circuit 4 is controlled so as to reduce the light emission time of the light source LEDs 41, 43, 45 in accordance with the display resolution.
[Selection] Figure 1

Description

  The present invention relates to a projection-type image display apparatus using a solid-state light source such as a light emitting diode and a spatial light modulator (Spatial-Light-Modulator) such as DMD (Digital-Micro mirror-Device). The present invention relates to control of a solid-state light source for the purpose of reducing power consumption.

  In projection-type image display devices, discharge lamps have been widely used as light sources. However, in recent years, due to technological advances, the output luminance of solid-state light sources such as light-emitting diodes (hereinafter referred to as “LEDs”) and laser diodes can withstand use as light sources for projection display devices. Therefore, solid-state light sources are being used in place of conventional lamp light sources. In particular, a projection-type image display device using a spatial light modulator such as a DMD (Digital-Micro mirror-Device) uses R (red), G (green), and B (blue) solid light sources, and these three colors. The solid-state light source is pulsed in a time-sharing manner and supplied to the spatial light modulator.

  In the display device, an input video signal for one frame is divided into a plurality of subframes, and digital data of R, G, and B color components is applied to the spatial light modulator in each subframe. The light emission periods of the solid light sources of the respective colors are synchronized with the display periods of the respective colors of R, G, and B in each subframe. That is, in each sub-frame in one frame of the input video signal, an image obtained by separating the video signal into R, G, and B color components is projected on the screen or the like in each color, so that it is 1 for human eyes. During the frame period, images of each color of R, G, B in the same frame of the image signal are visually recognized and recognized as a color image by these residual phenomena.

JP-A-10-261080 JP 2006-276642 A

  However, when a solid-state light source is used as a light source for a projection-type image display device, in order to obtain an output luminance equivalent to that of a conventional lamp light source, its power consumption is equal to or higher than that of a discharge lamp. . On the other hand, recently, reduction of power consumption is demanded from the viewpoint of power supply and environmental protection.

  In the multi-vision projection type display device in which the screens of a plurality of projection type video display devices are arranged, there are many cases that are mainly used in monitoring rooms such as roads, traffic, plants, etc. On the other hand, when there is no serious case, the display content is not so noticeable. For this reason, a method of turning off the light source of the projection display apparatus has been proposed as a method for reducing power consumption. However, in this method, no video is displayed when there is a serious incident. You may not notice.

  In a projection-type image display device using a solid-state light source such as an LED, if there is no serious incident, the brightness of the screen can be reduced by reducing the current value flowing to the solid-state light source as a method of reducing power consumption while displaying the image. There is a method of continuing to display what becomes low. That is, the power consumption can be suppressed by setting the drive current value flowing to the solid-state light source that emits pulse light to a low value.

  While the screen brightness is required to be higher during normal operation, it is required to suppress power consumption as much as possible during power saving operation. In the above method, when the screen brightness is increased, the drive current value for the solid light source is high, and when the screen brightness is decreased to reduce power consumption, the drive current value passed through the solid light source must be decreased. However, in order to drive a high drive current value and a low drive current value with the same light source drive circuit, the range of the drive current value is limited.

  For example, there is a synchronous rectification method as a commonly used LED drive circuit method, but when an LED is driven with a low drive current in an LED drive circuit optimized for a high drive current value, it occurs in the drive current. Due to the ripple current, the lighting brightness of the LED is not stabilized, and as a result, the display image quality of the video is affected. Therefore, the drive current has a lower limit. Conversely, when an LED is driven with a high current drive in an LED drive circuit optimized for a low drive current value, the loss due to the circuit increases and heat is generated, so there is an upper limit for the allowable drive current value. is there.

  Therefore, an object of the present invention is to provide a projection display device and a multi-vision projection display device that can further reduce power consumption than when a solid-state light source is driven with a lower limit current of a light source driving circuit.

  A projection display apparatus according to the present invention divides a plurality of solid-state light sources that emit light of different colors and a video signal input from the outside into sub-frames for a plurality of color components that are emitted from the plurality of solid-state light sources. In addition, signal processing means for generating light emission timings of the plurality of solid light sources synchronized with each subframe, and light emission of the plurality of solid light sources according to light emission timings of the plurality of solid light sources generated by the signal processing means Light source driving means for driving, wherein the signal processing means sets the display resolution of the video signal to n bits (n is an integer of 2 or more) during normal operation, and sets the display resolution of the video signal to n− during power saving operation. By limiting to m bits (m is an integer greater than or equal to 1), the light emission times of the plurality of solid state light sources according to the display resolution of the video signal limited to nm bits And it controls the light source driving means so as to reduce.

  The multi-vision projection display device according to the present invention is a multi-vision projection display device configured by combining a plurality of projection-type image display devices, wherein each of the signal processing means emits light from the plurality of solid-state light sources. Each of the light source driving means is controlled so as to decrease the time at the same rate.

  According to the projection type video display apparatus of the present invention, the projection type video display device includes a plurality of solid state light sources, a signal processing unit, and a light source driving unit. By limiting the display resolution of the video signal to nm bits during operation, the light source driving means is configured to reduce the light emission times of the plurality of solid state light sources according to the display resolution of the video signal limited to nm bits. Control.

  Therefore, the power consumption can be suppressed by lowering the driving current value of the solid light source to the lower limit in the power saving mode, and the power consumption can be further suppressed by reducing the light emission time of the solid light source.

  Further, according to the multivision projection display device of the present invention, each signal processing means controls each light source driving means so as to reduce the light emission times of the plurality of solid light sources at the same rate. The relationship between time and luminance is linear, and power consumption can be suppressed without impairing uniformity of luminance and chromaticity among a plurality of screens in a multivision projection display device during power saving operation.

1 is a schematic configuration diagram of a projection display apparatus according to Embodiment 1. FIG. It is a schematic block diagram of a light source circuit. It is a figure which shows the timing of the data processing in a light source lighting timing signal and a spatial light modulator. It is a figure which shows the drive current waveform which flows into R light source lighting timing signal and LED for R light sources. It is a figure which shows the timing of the data processing in a light source lighting timing signal, a spatial light modulator, and the bit pulse of R sub-frame at the time of gradation display being 7-bit display resolution. It is a figure which shows the light source lighting timing signal, the timing of the data processing in a spatial light modulator, and the bit pulse of R sub-frame at the time of gradation representation being 7-bit display resolution and dividing each color sub-frame. FIG. 6 is a schematic configuration diagram of a multivision projection display device according to a second embodiment. It is a figure which shows the characteristic of the electric current and brightness | luminance of LED used for a solid light source.

<Embodiment 1>
Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a projection display apparatus 100 according to Embodiment 1 of the present invention. The projection-type video display device 100 includes a video signal input unit 1, a signal processing unit 9, a light source circuit 4, a light synthesis unit 5, a spatial light modulator 6, a projection lens 7, and a screen 8. . The signal processing means 9 includes an error diffusion circuit 2 and a signal processing unit 3. The light source circuit 4 uses, for example, an LED as a light source, and the light output of the light source circuit 4 is incident on the spatial light modulator 6 via the light combining unit 5 formed of a dichroic mirror.

  On the other hand, the video signal is input to the video signal input unit 1 from the outside, and is input to the signal processing unit 3 through the error diffusion circuit 2. The signal processing unit 3 converts (divides) the frame of the video signal into subframes of pulse width modulation digital display data of each color component of R (red), G (green), and B (blue), and spatial light modulation To the device 6. Further, the signal processing unit 3 generates a light source lighting timing signal for causing each of the R, G, and B LEDs synchronized with each subframe to emit light, and outputs the light source lighting timing signal to the light source circuit 4.

  The spatial light modulator 6 is composed of, for example, a DMD (Digital-Micromirror-Device), and is based on pulse width modulation digital display data of R, G, and B color components input from the signal processing unit 3. The intensity of the emitted light of the three colors from the circuit 4 is modulated and projected onto the screen 8 via the projection lens 7, whereby an image is displayed on the screen 8.

  Here, when the spatial light modulator 6 is configured by DMD, the display resolution is limited to about n bits (n bits is an integer of 2 or more) from the reaction speed of the movable micromirror. For this reason, human visual sensitivity is increased on the low luminance side, and a difference of one gradation can be recognized. A so-called false contour is easily perceived, but in order to solve the problem of false contour, a video signal obtained by raising an n-bit video signal to n bits or more by gamma conversion is input to the video signal input unit 1. However, since the spatial light modulator 6 is limited to about n bits, a video signal of n bits or more must be converted to about n bits. In such a case, an error diffusion method is effective in which quantization is performed by an error diffusion method and a gray scale of n bits or more can be expressed in a pseudo manner. The error diffusion method is known (for example, Patent Documents 1 and 2).

  That is, the error diffusion circuit 2 sets the display resolution of the video signal of n bits or more input from the video signal input unit 1 to n bits during normal operation, and outputs the video signal to the signal processing unit 3. On the other hand, at the time of power saving operation, the signal processing unit 3 limits the display resolution of the video signal, and the error diffusion circuit 2 performs the operation of the video signal limited by the signal processing unit 3 in addition to the operation at the time of normal operation. Correct the display resolution. Details of operations of the error diffusion circuit 2 and the signal processing unit 3 during power saving operation will be described later.

  Here, the pulse width of the minimum bit when performing the pulse width intensity modulation in the spatial light modulator 6 is determined by the reaction speed of the spatial light modulator 6. When gradation is expressed by pulse width intensity modulation, n bits (n is an integer of 2 or more) requires a period twice as long as n-1 bits. Therefore, when the pulse width time of the minimum bit is a, The subframe period expressing the display resolution n bits can be expressed as the following equation (1).

  As described above, the display resolution of the gradation expression is determined in the subframe period. Therefore, in order to express as many gradations as possible, normally, as many subframes as possible are used in the frame period of the video signal. FIG. 3 is a diagram showing a timing chart of the light source lighting timing signal and the data processing in the spatial light modulator 6, and the bit pulse width of the R subframe when the video signal is displayed with gradation representation of display resolution of 8 bits. Is shown. Although not shown in FIG. 3, the bit pulse width of the G subframe and the B subframe is the same as that of the R subframe.

  Next, details of the light source circuit 4 will be described with reference to FIG. FIG. 2 is a schematic configuration diagram of the light source circuit 4. The light source circuit 4 includes an R light source LED 41 that emits red (R) light, an R light source drive circuit 40, a G light source LED 43 that emits green (G) light, a G light source drive circuit 42, and a blue (B ) A B light source LED 45 that emits light and a B light source drive circuit 44 are provided. The drive current value of the R light source LED 41 is controlled by pulse driving from the R light source drive circuit 40, and the R light source LED 41 is turned on according to the light source lighting timing from the signal processing unit 3.

  Similarly, the G light source LED 43 is driven by the G light source drive circuit 42 by a pulse drive, and the driving current value is controlled according to the light source lighting timing from the signal processing unit 3, and the B light source LED 45 is driven for the B light source. The drive current value is controlled by pulse drive from the circuit 44, and the lighting operation is performed according to the light source lighting timing from the signal processing unit 3. The R, G, B light source LEDs 41, 43, 45 correspond to solid light sources, and the R, G, B light source drive circuits 40, 42, 44 correspond to light source driving means.

  Next, the lighting timing of the R, G, B light source LEDs 41, 43, 45 during power saving operation will be described with reference to FIGS. FIG. 4 is a diagram showing an R light source lighting timing signal and a driving current waveform flowing in the R light source LED 41. FIG. 5 is a diagram showing a light source lighting timing signal and a spatial light modulator when the gradation expression is 7-bit display resolution. 6 is a diagram illustrating data processing timing in FIG. 6 and bit pulses of an R subframe.

  The R light source drive circuit 40 supplies current to the R light source LED 41 from the power source stepped down by the synchronous rectification method in accordance with the R light source lighting timing input from the signal processing unit 3. As shown in FIG. 4, a ripple current always flows through the R light source LED 41. The ripple current width is uniquely determined by the circuit. When driving from a high current value to a low current value in the same drive circuit, the ratio of the ripple current value to the drive current value increases at a low current value.

  The change in the current flowing through the R light source LED 41 is a change in the lighting brightness of the R light source LED 41. Therefore, when the ratio of the ripple current value to the drive current value is small, the displayed image is hardly affected. When it becomes larger, the lighting of the R light source LED 41 becomes uneven. As a result, a difference occurs in luminance corresponding to each bit, causing a gradation defect of a projected image. When the drive current value is high, the ripple current value is sufficiently low with respect to the drive current value and does not affect the image. However, when the drive current value is low, a gradation failure of the image is caused. The G light source LED 43 and the B light source LED 45 also have the same problem as the R light source LED 41.

  By reducing the drive current values of the R, G, B light source drive circuits 40, 42, 44, the power consumption of the R, G, B light source LEDs 41, 43, 45 can be reduced. Therefore, there is a limit to lowering the power consumption by reducing the drive current value.

  Therefore, the signal processing unit 3 shortens the period of each subframe when converting the frame of the video signal input from the outside into the subframe of the pulse width modulation digital display data of the R, G, and B color components. Then, a light source lighting timing signal for causing the light source LEDs 41, 43, and 45 of each color of R, G, and B synchronized with each subframe to emit light is generated. A light source lighting timing signal is input to the light source circuit 4, and the R, G, B light source drive circuits 40, 42, 44 reduce the lighting time (light emission time) of the R, G, B light source LEDs 41, 43, 45. Thus, power consumption can be reduced.

The sub-frame period expressing the display resolution n bits is expressed as shown in Equation (1), and is 2 ⁿ −1 times the pulse width of the minimum bit. For example, the display resolution is n bits (n is 2 or more). The subframe period can be reduced to approximately ½ by converting from an n) representation to an n−1 bit representation (more generally, nm, where m is an integer greater than or equal to 1). As a result, the power consumed by the R, G, B light source LEDs 41, 43, 45 can be reduced by about 50%.

  More specifically, by converting the display resolution from the 8-bit representation shown in FIG. 3 to the 7-bit representation shown in FIG. 5, the sub-frame (R sub-frame) period of R pulse width modulation digital display data is reduced to about Therefore, the power consumption of the R light source LED 41 can be reduced by about 50%.

  For this reason, the signal processing unit 3 sets the display resolution of the video signal to n bits during normal operation, and spatially modulates the sub-frames of the n-bit R, G, B color component pulse width modulation digital display data. To the device 6. On the other hand, the signal processing unit 3 limits the display resolution of the video signal to n-1 bits during power saving operation, and outputs n-1 bit R, G, B color component pulse width modulation digital display data. The subframe is output to the spatial light modulator 6, and the light source lighting timing synchronized with each subframe is generated and output to the light source circuit 4. Thereby, the signal processing unit 3 reduces the lighting time of the LEDs 41, 43, and 45 for the R, G, and B light sources in accordance with the display resolution of the video signal limited to n-1 bits during the power saving operation. Thus, the R, G, B light source drive circuits 40, 42, 44 are controlled.

  Here, when the display resolution of the video signal is n bits, and the video signal input unit 1 reduces the D range of the video signal and converts the display resolution to a video signal of n−1 bit representation, for example, the display resolution is When an 8-bit video signal is converted to a 7-bit video signal, the human visual sensitivity is increased on the low luminance side, and image quality degradation such as a so-called false contour is easily perceived.

  Therefore, in the projection display apparatus 100 according to the first embodiment, the error diffusion circuit 2 corrects the display resolution of the video signal using the error diffusion method without reducing the D range of the video signal. More specifically, the error diffusion circuit 2 corrects the display resolution of the video signal limited to n-1 bits by the signal processing unit 3 during power saving operation using the error diffusion method, and the corrected video signal Are output to the spatial light modulator 6 through the signal processing unit 3.

  By the correction by the error diffusion circuit 2, the spatial light modulator 6 can express the display resolution of the video signal limited from n bits to n-1 bits in a pseudo gradation of n bits or more. Thereby, it is possible to minimize image quality degradation that occurs when the display resolution is limited to n-1 bit representation. Note that the error diffusion method is known as described above, and the error diffusion circuit 2 corrects the display resolution of the video signal limited to n−1 bits using such a known method.

  By performing correction by the error diffusion circuit 2, the signal processing unit 3 sets the display resolution of the video signal of n bits or more to n bits during normal operation and the display resolution of the video signal in the power saving mode. By switching so as to limit to n−1 bits, it is possible to minimize image quality degradation due to a decrease in display resolution.

  As described above, in the projection display apparatus 100 according to the first embodiment, the R, G, B light source LEDs 41, 43, 45, the signal processing means 9, and the R, G, B light source drive circuit 40 are used. , 42, 44, and the signal processing unit 3 sets the display resolution of the video signal to n bits during normal operation and limits the display resolution of the video signal to nm bits during power saving operation. The R, G, B light source drive circuits 40, 42, 44 are controlled so as to reduce the lighting time of the R, G, B light source LEDs 41, 43, 45 in accordance with the display resolution of the video signal limited to bits. .

  Accordingly, in the power saving mode, the power consumption can be suppressed by lowering the drive current value of the R, G, B light source LEDs 41, 43, 45 to the lower limit, and further, the R, G, B light source LEDs 41, By reducing the lighting time of 43 and 45, power consumption can be further suppressed. That is, the energy consumption can be reduced.

  Since the signal processing means 9 includes the error diffusion circuit 2 that corrects the display resolution of the video signal limited to nm bits during the power saving operation by the error diffusion method, the gradation expression resolution of the video is reduced. It is possible to suppress power consumption while preventing a false contour from being perceived because the human visual sensitivity is higher.

  In addition, although LED was employ | adopted as a solid light source of the projection type video display apparatus 100, you may employ | adopt the light source which can emit pulses, such as a laser diode, and also in this case, power consumption can be suppressed by said method. .

  The signal processing unit 3 forms a subframe in which all the bit pulses of the same color are continuous, but divides the subframe for each of a plurality of color components into each gradation bit, and arranges them at intervals. Thus, a plurality of subframes may be formed.

  Further, a plurality of subframes may be formed by dividing a subframe for each of a plurality of color components into units based on a specific gradation bit and arranging them at intervals. That is, as shown in FIG. 6, among the bit pulses, for a bit whose bit width is sufficient as compared with the reaction speed of the spatial light modulator 6, the bit pulse is a unit based on a specific gradation bit. It may be divided into subframes and arranged as subframes.

  FIG. 6 shows a gradation expression with a display resolution of 7 bits, and the timing of data processing in the light source lighting timing signal and the spatial light modulator 6 when each color subframe is divided and arranged in units based on 6 bits. FIG. 6 is a diagram illustrating bit pulses of R and R subframes. In FIG. 6, only the R subframe is illustrated, but the G subframe and the B subframe are the same as the R subframe.

  When digital data of each color component is controlled by the spatial light modulator 6 in a time division manner and a color image is synthesized, a phenomenon called color breakup occurs if the repetition of each color is not fast enough. Here, the color breakup is a phenomenon in which a rainbow-like image can be seen instantaneously when the viewer moves the viewpoint rapidly.

  The signal processing means 9 (more specifically, the signal processing unit 3) divides a subframe for each of a plurality of color components into a plurality of subframes by dividing each subframe for each gradation bit or a unit based on a specific gradation bit. A frame is generated, that is, the signal processing unit 3 arranges the bit pulses at intervals to form subframes, or divides the bit pulses into units based on specific gradation bits. Since a process such as forming a sub-frame with a gap is performed, repetition of lighting of each color can be performed at high speed, and there is an effect of reducing / preventing the color breakup phenomenon.

<Embodiment 2>
Next, the multi-vision projection display device 105 according to the second embodiment will be described. FIG. 7 is a schematic configuration diagram of the multi-vision projection display device 105 according to the second embodiment, and FIG. 8 is a diagram showing the current and luminance characteristics of the LEDs used for the solid-state light source. In the second embodiment, the same components as those described in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The multi-vision projection display device 105 is configured by combining a plurality of projection display devices 101 (100), 102 (100), 103 (100), and 104 (100) to form a larger display screen. The multivision projection display device 105 is configured, for example, by arranging the projection image display devices 100 in a two-stage × two-row arrangement. The projection display devices 101 to 104 adjust the light source driving current of each color in each of the R, G, and B light source driving circuits 40, 42, and 44 so that the luminance and chromaticity between the four screens become uniform. It has been adjusted.

  As shown in FIG. 8, the LED and the laser diode used in the projection display apparatus usually have a linear relationship between current and luminance. Further, there is a difference in characteristics depending on the light source color of the solid light source and individual differences. For this reason, in the multi-vision projection display device 105, when the light source drive current is reduced at a constant rate in order to reduce the power consumption, the uniformity of luminance and chromaticity between the four screens is impaired.

  However, in the projection display devices 101 to 104 constituting the multi-vision projection display device 105, each signal processing unit 3 shortens the period of each subframe as described in the first embodiment, and R, G, When the R, G, and B light source drive circuits 40, 42, and 44 are controlled so as to reduce the lighting time of the B light source LEDs 41, 43, and 45 at the same rate, The relationship between the lighting time of the LEDs 41, 43, and 45 for the G and B light sources and the luminance is linear. Thereby, the power consumption of the multi-vision projection display device 105 can be reduced without impairing the uniformity of luminance and chromaticity between the four screens. In this embodiment, a four-screen multi-vision projection display device has been described as an example, but there is no particular limitation on the number of screens.

  It should be noted that the present invention can be freely combined with each other within the scope of the invention, and each embodiment can be appropriately modified or omitted.

  2 error diffusion circuit, 9 signal processing means, 40 R light source drive circuit, 41 R light source LED, 42 G light source drive circuit, 43 G light source LED, 44 B light source drive circuit, 45 B light source LED, 100 Projection type image display device, 105 multivision projection type display device.

Claims (4)

A plurality of solid state light sources that emit light of different colors;
A signal processing unit that divides a video signal input from the outside into sub-frames for each of a plurality of color components emitted by the plurality of solid-state light sources, and generates emission timings of the plurality of solid-state light sources synchronized with the sub-frames. When,
Light source driving means for driving the plurality of solid light sources to emit light according to light emission timings of the plurality of solid light sources generated by the signal processing means,
The signal processing means sets the display resolution of the video signal to n bits (n is an integer of 2 or more) during normal operation, and sets the display resolution of the video signal to nm bits (m is an integer of 1 or more) during power saving operation. ) To control the light source driving means so as to reduce the light emission time of the plurality of solid-state light sources in accordance with the display resolution of the video signal limited to nm bits. .   The projection type video display according to claim 1, wherein the signal processing means includes error diffusion means for correcting display resolution of the video signal limited to nm bits during the power saving operation by an error diffusion method. apparatus.   The signal processing means generates the plurality of subframes by dividing the subframe for each of the plurality of color components into each gradation bit or a unit based on a specific gradation bit. 2. The projection-type image display device according to 2. A multi-vision projection type display device configured by combining a plurality of projection type image display devices according to any one of claims 1 to 3,
Each said signal processing means is a multivision projection type display apparatus which controls each said light source drive means so that the light emission time of these solid light sources may be decreased at the same rate, respectively.

Images