WO2017068738A1 - Light source driving device and image display device - Google Patents

Light source driving device and image display device Download PDF

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Publication number
WO2017068738A1
WO2017068738A1 PCT/JP2016/003032 JP2016003032W WO2017068738A1 WO 2017068738 A1 WO2017068738 A1 WO 2017068738A1 JP 2016003032 W JP2016003032 W JP 2016003032W WO 2017068738 A1 WO2017068738 A1 WO 2017068738A1
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signal
light source
pixel
pixel signal
laser
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PCT/JP2016/003032
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French (fr)
Japanese (ja)
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吉昭 我妻
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株式会社Ｊｖｃケンウッド
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/10—Scanning systems
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/02—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes by tracing or scanning a light beam on a screen
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/068—Stabilisation of laser output parameters

Definitions

  • the present invention relates to a light source driving device for driving a semiconductor laser and an image display device using the light source driving device.
  • a scanning-type image display device that emits laser light intensity-modulated according to an image signal from a semiconductor laser (LD: Laser Diode) and scans the laser light in a horizontal direction and a vertical direction to display an image on a projection target.
  • a semiconductor laser there is a relationship referred to as an IL characteristic between the drive current value of an input pixel signal and the laser output power (intensity) of emitted laser light.
  • the laser output power increases linearly when the drive current value is increased.
  • Some semiconductor lasers have a kink region where the IL characteristic abruptly changes and the linearity is lost in a region where the drive current value is small.
  • a semiconductor laser having a kink region may not be able to accurately display a low gradation level.
  • the frequency of the pixel signal is equal to or greater than the reciprocal of the generation period of the pixel signal, and the amplitude (current amplitude) is equal to or greater than the width of the kink region.
  • a high frequency signal is superimposed.
  • a semiconductor laser having a kink region when a pixel signal to which a gradation level is assigned on the assumption that the IL characteristic is linear is input to the semiconductor laser, gradation collapse may occur at a low gradation level.
  • a high frequency signal having an amplitude equal to or larger than the width of the kink region is superimposed on the pixel signal as in Patent Document 1, the laser output power varies according to a change in the amplitude of the superimposed high frequency signal.
  • the brightness of the pixel is the brightness corresponding to the laser output power obtained by averaging the fluctuating laser output power.
  • the relationship between the drive current value of the pixel signal and the average laser output power is made closer to linear, and the IL characteristic in the kink region is apparently made closer to linear, thereby suppressing occurrence of gradation collapse at a low gradation level. be able to.
  • the laser output power of the laser beam exceeds the rated laser output power when a high frequency signal having an amplitude equal to or larger than the width of the kink region is superimposed on the pixel signal at a high gradation level. May end up.
  • the life of the laser is remarkably shortened.
  • the present embodiment has been made in view of the above background, and can display a low gradation level with high accuracy without causing the laser output power of the laser light to exceed the rated laser output power at a high gradation level.
  • An object is to provide a light source driving device and an image display device.
  • the light source driving device includes a signal generation unit that generates a pixel signal corresponding to a gradation level of a pixel constituting an image for each pixel, and a semiconductor that emits laser light having an intensity corresponding to the pixel signal.
  • a laser and a signal superimposing unit that superimposes a high-frequency signal on the pixel signal input to the semiconductor laser, wherein the high-frequency signal has a frequency and a reciprocal of a generation cycle in which the signal generation unit generates the pixel signal.
  • the current amplitude is the width of the drive current value of the pixel signal in a region where LED light emission and LD light emission are mixed in the IL characteristic of the semiconductor laser, and the drive current value of the pixel signal is at least When in the mixed region, the signal superimposing unit superimposes the high frequency signal on the pixel signal.
  • an image display apparatus includes the above-described light source driving apparatus and an optical deflector that displays an image by deflecting laser light emitted from the semiconductor laser in a horizontal direction and a vertical direction. .
  • FIG. 2 shows IL characteristics of a semiconductor laser that is one of an R light source, a G light source, and a B light source used in the image display apparatus according to the present embodiment. It is a figure which shows typically the state which superimposed the high frequency signal on the pixel signal, when the drive current value of a pixel signal exists in a threshold current. It is a figure which shows typically the state which superimposed the high frequency signal on the pixel signal when the target laser output power is near rated laser output power.
  • FIG. 1 is a block diagram showing a schematic configuration of an image display apparatus 500 according to the present embodiment.
  • the image display device 500 includes a light source driving device 250 and an optical deflector 100.
  • the light source driving device 250 includes a signal generation unit 40, a laser light generation unit 50, and a control unit 200.
  • the signal generation unit 40 includes an R light source signal generation unit 40r, a G light source signal generation unit 40g, and a B light source signal generation unit 40b that generate a pixel signal that is a pixel unit signal of each of the three primary colors.
  • the R light source signal generation unit 40r sequentially generates a pixel signal having a drive current value corresponding to the gradation level of the red component of each pixel, and inputs the pixel signal to the R light source 51r.
  • the G light source signal generation unit 40g sequentially generates a pixel signal having a drive current value corresponding to the gradation level of the green component of each pixel for each pixel, and inputs the pixel signal to the G light source 51g.
  • the B light source signal generation unit 40b sequentially generates a pixel signal having a driving current value corresponding to the gradation level of the blue component of each pixel for each pixel, and inputs the pixel signal to the B light source 51b.
  • the laser light generator 50 includes a light source 51 as a semiconductor laser, prisms 52 to 54, a mirror 55, and a lens 56.
  • the light source 51 is an R light source 51r that emits red (R) laser light, a G light source 51g that emits green (G) laser light, and B that emits blue (B) laser light, which are semiconductor lasers. And a light source 51b.
  • R red
  • G green
  • B blue
  • the R light source 51r sequentially emits red laser light whose intensity is modulated according to the gradation level of the red component of each pixel in units of pixels.
  • the G light source 51g sequentially emits green laser light whose intensity is modulated according to the gradation level of the green component of each pixel in units of pixels.
  • the B light source 51b sequentially emits blue laser light whose intensity is modulated according to the gray level of the blue component of each pixel in units of pixels.
  • the prism 52 bends the optical path of the R laser beam emitted from the R light source 51r by 90 degrees.
  • the prism 53 bends the optical path of the G laser light emitted from the G light source 51g by 90 degrees and synthesizes the R laser light with the G laser light.
  • the prism 54 bends the optical path of the B laser light emitted from the B light source 51b by 90 degrees, and combines the R laser light and the G laser light with the B laser light.
  • the mirror 55 reflects the combined light obtained by combining the R, G, and B laser beams output from the prism 54.
  • the lens 56 collects the combined light from the mirror 55 and makes it incident on the mirror 12.
  • the signal superimposing unit 60 superimposes the high frequency signal on the pixel signal generated by the signal generating unit 40.
  • the R light source signal superimposing unit 60r, the G light source signal superimposing unit 60g, and the B light source signal superimposing unit 60b are generated by the R light source signal generating unit 40r, the G light source signal generating unit 40g, and the B light source signal generating unit 40b.
  • a high frequency signal is superimposed on each pixel signal. Details of the high frequency signal will be described later.
  • the optical deflector 100 includes a mirror 12, a horizontal drive unit 11H, and a vertical drive unit 11V.
  • the mirror 12 is a MEMS (Micro Electro Mechanical System) mirror, for example, and the angle changes according to the drive signal.
  • the mirror 12 is oscillated so that the laser beam is scanned in the horizontal direction of the screen 70 by the horizontal driving unit 11H, and is oscillated so that the laser beam is scanned in the vertical direction of the screen 70 by the vertical driving unit 11V.
  • An image based on the image signal is displayed on the screen 70 by scanning the laser beam in the horizontal direction and the vertical direction by the optical deflector 100.
  • the control unit 200 includes an APC (Auto Power Control) circuit, and controls the drive current value of the pixel signal input to the semiconductor laser so that laser light having a desired laser output power (intensity) is emitted (APC). control). Specifically, the control unit 200 drives the R light source 51r, the G light source 51g, and the B light source 51b according to the respective pixel values in the input image signal, and the drive current value of the pixel signal corresponding to the desired laser output power. R light source signal generation unit 40r, G light source signal generation unit 40g, and B light source signal generation unit 40b are controlled.
  • APC Auto Power Control
  • a pixel signal corresponding to a desired laser output power is not input based on the IL characteristic of the semiconductor laser to be used, instead of inputting a pixel signal assigned a gradation level on the premise of linearity to the semiconductor laser. Since the signal is generated and input to the semiconductor laser, the IL characteristic does not need to be linear, unlike the technique described in Patent Document 1.
  • the control unit 200 generates a horizontal drive signal based on the input horizontal synchronization signal and supplies it to the horizontal drive unit 11H.
  • the horizontal drive unit 11H swings the optical deflector 100 in the horizontal direction based on the horizontal drive signal.
  • the control unit 200 generates a vertical drive signal based on the input vertical synchronization signal and supplies the vertical drive signal to the vertical drive unit 11V.
  • the vertical drive unit 11V swings the optical deflector 100 in the vertical direction based on the vertical drive signal.
  • FIG. 2 shows an example of the IL characteristic of the semiconductor laser that is one of the R light source 51r, the G light source 51g, and the B light source 51b.
  • the IL characteristic changes sharply and the linearity is lost (the laser output power increases linearly with respect to the drive current value of the pixel signal).
  • a kink region is not included.
  • the kink region further includes a transition region in which LD light emission (laser light emission) and LED light emission (natural light emission) coexist (laser output power is around 1 mW).
  • the drive current value of the pixel signal in this transition region is the threshold current Ith.
  • the threshold current Ith has a certain width (threshold current width ⁇ I).
  • the minimum value of the threshold current Ith is 84.4 mA, and the maximum value is 84.84 mA. Therefore, the threshold current width ⁇ I is 0.44 mA.
  • the rated laser output power is around 5 mW.
  • the threshold current width ⁇ I is very small compared to the drive current width Ic in a region (kink region) where the IL characteristic changes sharply and becomes nonlinear. This threshold current width ⁇ I is substantially constant even when various conditions such as temperature change, and is uniquely determined by the type of laser.
  • the high frequency signal superimposed on the pixel signal will be described below.
  • the semiconductor laser goes back and forth between the LED emission region and the LD emission region, so that the laser output power becomes unstable and the target laser output I can't get power.
  • the drive current is within the threshold current Ith in at least one of the R light source 51r, the G light source 51g, and the B light source 51b, the target laser output power cannot be obtained with the light source whose drive current is within the threshold current Ith. Therefore, a color shift different from the color originally intended to occur occurs.
  • FIG. 3 is a diagram schematically showing a state in which a high-frequency signal is superimposed on the pixel signal when the drive current value of the pixel signal is within the threshold current Ith.
  • the pixel signal is indicated by a one-dot chain line, and the high-frequency signal is indicated by a solid line.
  • the pixel signal is a pulse wave, and the generation cycle is T. Further, it is assumed that the drive current value of the pixel signal corresponding to the target laser output power is the drive current value Ip within the threshold current Ith.
  • the frequency of the high frequency signal superimposed on the pixel signal is equal to or greater than the reciprocal (1 / T) of the pixel signal generation period T.
  • the current amplitude of the high frequency signal is a threshold current width ⁇ I.
  • the high frequency signal in a figure is a sine wave, it is not restricted to this, For example, a pulse wave and a triangular wave may be sufficient.
  • the laser output power of the highest gradation is set slightly lower than the rated laser output power in order to achieve both high brightness of the highest gradation and long life of the semiconductor laser.
  • FIG. 4 is a diagram schematically showing a state in which a high frequency signal is superimposed on a pixel signal when the target laser output power is near the rated laser output power.
  • the pixel signal is indicated by a one-dot chain line
  • the high-frequency signal is indicated by a solid line.
  • the current amplitude of the high frequency signal superimposed on the pixel signal is very small with respect to the drive current value of the pixel signal, and therefore corresponds to the peak of the drive current value in the signal after the high frequency signal is superimposed.
  • the laser output power will not exceed the rated laser output power. For this reason, the lifetime of the semiconductor laser is not significantly shortened compared with the case where no high-frequency signal is superimposed.
  • the high-frequency signal can be superimposed on the pixel signal without significantly shortening the life of the semiconductor laser. That is, a high-frequency signal having a constant current amplitude can be superimposed on pixel signals corresponding to laser output power at all gradation levels.
  • the high-frequency signal is changed depending on the magnitude of the gradation level when changing the gradation level. There is no need to perform complicated processing such as determining whether to superimpose or changing the current amplitude of the superimposed high-frequency signal.
  • the above-described high-frequency signal is superimposed on the pixel signal.
  • the laser output power can be prevented from becoming unstable at a low gradation level, and the low gradation level can be accurately displayed. Further, even if the above-described high-frequency signal is superimposed on the pixel signal at a high gradation level, the laser output power of the laser light does not exceed the rated laser output power.
  • the light source driving device and the image display device according to the present embodiment can be used as, for example, a light source driving device mounted on a passenger car or an image display device implemented on a passenger car.

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  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
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Abstract

A light source driving device (250) is provided with: a signal generation unit (40) which generates a pixel signal corresponding to the grayscale level of pixels constituting an image, on a pixel by pixel unit basis; a light source (51) which emits laser light of an intensity corresponding to the pixel signal; and a signal superimposition unit (60) which superimposes a high frequency signal on a pixel signal input to the light source (51). The high frequency signal has a frequency which is not less than the inverse of a generation period for generation of the pixel signal by the signal generation unit (40), and has a current amplitude equal to the width of a pixel signal drive current value in a region of the I-L characteristic of the light source (51) in which LED emitted light and LD emitted light are mixed. The signal superimposition unit (60) superimposes the high frequency signal on the pixel signal at least when the pixel signal drive current value is in the abovementioned region.

Description

光源駆動装置及び画像表示装置Light source driving device and image display device
　本発明は、半導体レーザを駆動する光源駆動装置、及び、光源駆動装置を用いた画像表示装置に関する。 The present invention relates to a light source driving device for driving a semiconductor laser and an image display device using the light source driving device.
　画像信号に応じて強度変調したレーザ光を半導体レーザ（ＬＤ：Ｌａｓｅｒ　Ｄｉｏｄｅ）から出射し、このレーザ光を水平方向及び垂直方向に走査させて投射対象に画像を表示させる走査型の画像表示装置が知られている。半導体レーザにおいて、入力される画素信号の駆動電流値と出射されるレーザ光のレーザ出力パワー（強度）との間にＩ－Ｌ特性と称される関係がある。Ｉ－Ｌ特性によれば、駆動電流値を増大させるとレーザ出力パワーは線形的に増大する。半導体レーザの中には、駆動電流値が小さい領域において、そのＩ－Ｌ特性が急峻に変化して線形性が崩れるキンク領域を有するものがある。 A scanning-type image display device that emits laser light intensity-modulated according to an image signal from a semiconductor laser (LD: Laser Diode) and scans the laser light in a horizontal direction and a vertical direction to display an image on a projection target. Are known. In a semiconductor laser, there is a relationship referred to as an IL characteristic between the drive current value of an input pixel signal and the laser output power (intensity) of emitted laser light. According to the IL characteristic, the laser output power increases linearly when the drive current value is increased. Some semiconductor lasers have a kink region where the IL characteristic abruptly changes and the linearity is lost in a region where the drive current value is small.
　キンク領域を有する半導体レーザでは、低い階調レベルを精度よく表示できない場合がある。特許文献１では、このような低い階調レベルを精度よく表示するため、画素信号に対し、周波数が画素信号の生成周期の逆数以上であり、かつ、振幅（電流振幅）がキンク領域の幅以上である高周波信号を重畳している。 A semiconductor laser having a kink region may not be able to accurately display a low gradation level. In Patent Document 1, in order to accurately display such a low gradation level, the frequency of the pixel signal is equal to or greater than the reciprocal of the generation period of the pixel signal, and the amplitude (current amplitude) is equal to or greater than the width of the kink region. A high frequency signal is superimposed.
特開２０１１－０７５９５７号公報JP 2011-079557 A
　キンク領域を有する半導体レーザでは、Ｉ－Ｌ特性が線形であることを前提に階調レベルを割り当てた画素信号を半導体レーザに入力すると、低い階調レベルにおいて階調つぶれが発生する場合がある。特許文献１のようの画素信号にキンク領域の幅以上の振幅を有する高周波信号を重畳する場合、レーザ出力パワーは重畳する高周波信号の振幅の変化に応じて変動するが、ユーザに視認される各画素の明るさは変動するレーザ出力パワーを平均したレーザ出力パワーに対応する明るさとなる。画素信号の駆動電流値と平均したレーザ出力パワーとの関係を線形に近づけて、キンク領域におけるＩ－Ｌ特性を見かけ上線形に近づけることで、低い階調レベルにおける階調つぶれの発生を抑制することができる。 In a semiconductor laser having a kink region, when a pixel signal to which a gradation level is assigned on the assumption that the IL characteristic is linear is input to the semiconductor laser, gradation collapse may occur at a low gradation level. When a high frequency signal having an amplitude equal to or larger than the width of the kink region is superimposed on the pixel signal as in Patent Document 1, the laser output power varies according to a change in the amplitude of the superimposed high frequency signal. The brightness of the pixel is the brightness corresponding to the laser output power obtained by averaging the fluctuating laser output power. The relationship between the drive current value of the pixel signal and the average laser output power is made closer to linear, and the IL characteristic in the kink region is apparently made closer to linear, thereby suppressing occurrence of gradation collapse at a low gradation level. be able to.
　しかしながら、特許文献１に記載の技術では、高い階調レベルにおいて、画素信号にキンク領域の幅以上の振幅を有する高周波信号を重畳したときにレーザ光のレーザ出力パワーが定格レーザ出力パワーを超えてしまう場合がある。レーザ光のレーザ出力パワーが定格レーザ出力パワーを超えるとレーザの寿命は著しく短縮される。 However, in the technique described in Patent Document 1, the laser output power of the laser beam exceeds the rated laser output power when a high frequency signal having an amplitude equal to or larger than the width of the kink region is superimposed on the pixel signal at a high gradation level. May end up. When the laser output power of the laser light exceeds the rated laser output power, the life of the laser is remarkably shortened.
　本実施の形態は、以上の背景に鑑みなされたものであり、高い階調レベルにおいてレーザ光のレーザ出力パワーが定格レーザ出力パワーを超えてしまうことなく低い階調レベルを精度よく表示することができる光源駆動装置、及び、画像表示装置を提供することを目的とする。 The present embodiment has been made in view of the above background, and can display a low gradation level with high accuracy without causing the laser output power of the laser light to exceed the rated laser output power at a high gradation level. An object is to provide a light source driving device and an image display device.
　本実施の形態に係る光源駆動装置は、画像を構成する画素の階調レベルに応じた画素信号を画素単位で生成する信号生成部と、前記画素信号に応じた強度のレーザ光を出射する半導体レーザと、前記半導体レーザに入力される前記画素信号に高周波信号を重畳する信号重畳部と、を備え、前記高周波信号は、周波数が、前記信号生成部が前記画素信号を生成する生成周期の逆数以上であり、かつ電流振幅が、前記半導体レーザのＩ－Ｌ特性においてＬＥＤ発光とＬＤ発光とが混在する領域における前記画素信号の駆動電流値の幅であり、前記画素信号の駆動電流値が少なくとも前記混在する領域にあるときに前記信号重畳部が前記画素信号に前記高周波信号を重畳する。 The light source driving device according to the present embodiment includes a signal generation unit that generates a pixel signal corresponding to a gradation level of a pixel constituting an image for each pixel, and a semiconductor that emits laser light having an intensity corresponding to the pixel signal. A laser and a signal superimposing unit that superimposes a high-frequency signal on the pixel signal input to the semiconductor laser, wherein the high-frequency signal has a frequency and a reciprocal of a generation cycle in which the signal generation unit generates the pixel signal. The current amplitude is the width of the drive current value of the pixel signal in a region where LED light emission and LD light emission are mixed in the IL characteristic of the semiconductor laser, and the drive current value of the pixel signal is at least When in the mixed region, the signal superimposing unit superimposes the high frequency signal on the pixel signal.
　さらに、本実施の形態に係る画像表示装置は、上述の光源駆動装置と、前記半導体レーザより発せられたレーザ光を水平方向及び垂直方向に偏向して画像を表示させる光偏向器と、を備える。 Furthermore, an image display apparatus according to the present embodiment includes the above-described light source driving apparatus and an optical deflector that displays an image by deflecting laser light emitted from the semiconductor laser in a horizontal direction and a vertical direction. .
　本実施の形態によれば、高い階調レベルにおいてレーザ光のレーザ出力パワーが定格レーザ出力パワーを超えてしまうことなく低い階調レベルを精度よく表示することができる。 According to this embodiment, it is possible to accurately display a low gradation level without the laser output power of the laser light exceeding the rated laser output power at a high gradation level.
本実施の形態にかかる画像表示装置の概略構成を示すブロック図である。It is a block diagram which shows schematic structure of the image display apparatus concerning this Embodiment. 本実施の形態にかかる画像表示装置で用いる、Ｒ光源、Ｇ光源及びＢ光源のうちのいずれかである半導体レーザが有するＩ－Ｌ特性を示している。2 shows IL characteristics of a semiconductor laser that is one of an R light source, a G light source, and a B light source used in the image display apparatus according to the present embodiment. 画素信号の駆動電流値が閾値電流内にある場合において、画素信号に高周波信号を重畳した状態を模式的に示す図である。It is a figure which shows typically the state which superimposed the high frequency signal on the pixel signal, when the drive current value of a pixel signal exists in a threshold current. 目標のレーザ出力パワーが定格レーザ出力パワー付近である場合に、画素信号に高周波信号を重畳した状態を模式的に示す図である。It is a figure which shows typically the state which superimposed the high frequency signal on the pixel signal when the target laser output power is near rated laser output power.
　以下、図面を参照して本発明の実施の形態について説明する。
　本実施の形態にかかる画像表示装置は、車載用のヘッドアップディスプレイ（ＨＵＤ）などに用いられる。図１は、本実施の形態にかかる画像表示装置５００の概略構成を示すブロック図である。図１に示すように、画像表示装置５００は、光源駆動装置２５０と、光偏向器１００と、を備えている。 Embodiments of the present invention will be described below with reference to the drawings.
The image display apparatus according to the present embodiment is used for an in-vehicle head-up display (HUD) or the like. FIG. 1 is a block diagram showing a schematic configuration of an image display apparatus 500 according to the present embodiment. As shown in FIG. 1, the image display device 500 includes a light source driving device 250 and an optical deflector 100.
　光源駆動装置２５０は、信号生成部４０と、レーザ光発生部５０と、制御部２００と、を有する。信号生成部４０は、三原色の各色の画素単位の信号である画素信号を生成するＲ光源信号生成部４０ｒ、Ｇ光源信号生成部４０ｇ、Ｂ光源信号生成部４０ｂ、を有する。Ｒ光源信号生成部４０ｒは、各画素の赤色成分の階調レベルに応じた駆動電流値の画素信号を画素単位で順次生成し、この画素信号をＲ光源５１ｒに入力する。同様に、Ｇ光源信号生成部４０ｇは、各画素の緑色成分の階調レベルに応じた駆動電流値の画素信号を画素単位で順次生成してＧ光源５１ｇに入力する。また、Ｂ光源信号生成部４０ｂは、各画素の青色成分の階調レベルに応じた駆動電流値の画素信号を画素単位で順次生成してＢ光源５１ｂに入力する。 The light source driving device 250 includes a signal generation unit 40, a laser light generation unit 50, and a control unit 200. The signal generation unit 40 includes an R light source signal generation unit 40r, a G light source signal generation unit 40g, and a B light source signal generation unit 40b that generate a pixel signal that is a pixel unit signal of each of the three primary colors. The R light source signal generation unit 40r sequentially generates a pixel signal having a drive current value corresponding to the gradation level of the red component of each pixel, and inputs the pixel signal to the R light source 51r. Similarly, the G light source signal generation unit 40g sequentially generates a pixel signal having a drive current value corresponding to the gradation level of the green component of each pixel for each pixel, and inputs the pixel signal to the G light source 51g. Further, the B light source signal generation unit 40b sequentially generates a pixel signal having a driving current value corresponding to the gradation level of the blue component of each pixel for each pixel, and inputs the pixel signal to the B light source 51b.
　レーザ光発生部５０は、半導体レーザとしての光源５１と、プリズム５２～５４と、ミラー５５と、レンズ５６と、を有する。光源５１は、半導体レーザである、赤（Ｒ）のレーザ光を射出するＲ光源５１ｒと、緑（Ｇ）のレーザ光を射出するＧ光源５１ｇと、青（Ｂ）のレーザ光を射出するＢ光源５１ｂと、を有する。Ｒ光源５１ｒは、Ｒ光源信号生成部４０ｒから画素信号が入力されると、各画素の赤色成分の階調レベルに応じて強度変調された赤色のレーザ光を画素単位で順次出射する。同様に、Ｇ光源５１ｇは、Ｇ光源信号生成部４０ｇから画素信号が入力されると、各画素の緑色成分の階調レベルに応じて強度変調された緑色のレーザ光を画素単位で順次出射する。また、Ｂ光源５１ｂは、Ｂ光源信号生成部４０ｂから画素信号が入力されると、各画素の青色成分の階調レベルに応じて強度変調された青色のレーザ光を画素単位で順次出射する。 The laser light generator 50 includes a light source 51 as a semiconductor laser, prisms 52 to 54, a mirror 55, and a lens 56. The light source 51 is an R light source 51r that emits red (R) laser light, a G light source 51g that emits green (G) laser light, and B that emits blue (B) laser light, which are semiconductor lasers. And a light source 51b. When a pixel signal is input from the R light source signal generation unit 40r, the R light source 51r sequentially emits red laser light whose intensity is modulated according to the gradation level of the red component of each pixel in units of pixels. Similarly, when a pixel signal is input from the G light source signal generation unit 40g, the G light source 51g sequentially emits green laser light whose intensity is modulated according to the gradation level of the green component of each pixel in units of pixels. . Further, when a pixel signal is input from the B light source signal generation unit 40b, the B light source 51b sequentially emits blue laser light whose intensity is modulated according to the gray level of the blue component of each pixel in units of pixels.
　プリズム５２は、Ｒ光源５１ｒより発せられたＲのレーザ光の光路を９０度折り曲げる。プリズム５３は、Ｇ光源５１ｇより発せられたＧのレーザ光の光路を９０度折り曲げるとともに、Ｇのレーザ光にＲのレーザ光を合成する。プリズム５４は、Ｂ光源５１ｂより発せられたＢのレーザ光の光路を９０度折り曲げるとともに、Ｂのレーザ光にＲのレーザ光及びＧのレーザ光を合成する。ミラー５５は、プリズム５４より出力されたＲ，Ｇ，Ｂのレーザ光が合成された合成光を反射する。レンズ５６は、ミラー５５からの合成光を集光してミラー１２へと入射させる。 The prism 52 bends the optical path of the R laser beam emitted from the R light source 51r by 90 degrees. The prism 53 bends the optical path of the G laser light emitted from the G light source 51g by 90 degrees and synthesizes the R laser light with the G laser light. The prism 54 bends the optical path of the B laser light emitted from the B light source 51b by 90 degrees, and combines the R laser light and the G laser light with the B laser light. The mirror 55 reflects the combined light obtained by combining the R, G, and B laser beams output from the prism 54. The lens 56 collects the combined light from the mirror 55 and makes it incident on the mirror 12.
　信号重畳部６０は、信号生成部４０が生成した画素信号に高周波信号を重畳する。具体的には、Ｒ光源信号重畳部６０ｒ、Ｇ光源信号重畳部６０ｇ及びＢ光源信号重畳部６０ｂが、Ｒ光源信号生成部４０ｒ、Ｇ光源信号生成部４０ｇ及びＢ光源信号生成部４０ｂの生成した画素信号に、それぞれ高周波信号を重畳する。なお、高周波信号の詳細については後述する。 The signal superimposing unit 60 superimposes the high frequency signal on the pixel signal generated by the signal generating unit 40. Specifically, the R light source signal superimposing unit 60r, the G light source signal superimposing unit 60g, and the B light source signal superimposing unit 60b are generated by the R light source signal generating unit 40r, the G light source signal generating unit 40g, and the B light source signal generating unit 40b. A high frequency signal is superimposed on each pixel signal. Details of the high frequency signal will be described later.
　光偏向器１００は、ミラー１２と、水平駆動部１１Ｈと、垂直駆動部１１Ｖと、を有する。ミラー１２は、例えばＭＥＭＳ（Ｍｉｃｒｏ　Ｅｌｅｃｔｒｏ　Ｍｅｃｈａｎｉｃａｌ　Ｓｙｓｔｅｍ）ミラーであり、駆動信号に応じて角度が変わる。ミラー１２は、水平駆動部１１Ｈによってレーザ光をスクリーン７０の水平方向に走査させるよう揺動され、垂直駆動部１１Ｖによってレーザ光をスクリーン７０の垂直方向に走査させるよう揺動される。光偏向器１００によるレーザ光の水平方向及び垂直方向の走査によって、スクリーン７０には画像信号に基づく画像が表示される。 The optical deflector 100 includes a mirror 12, a horizontal drive unit 11H, and a vertical drive unit 11V. The mirror 12 is a MEMS (Micro Electro Mechanical System) mirror, for example, and the angle changes according to the drive signal. The mirror 12 is oscillated so that the laser beam is scanned in the horizontal direction of the screen 70 by the horizontal driving unit 11H, and is oscillated so that the laser beam is scanned in the vertical direction of the screen 70 by the vertical driving unit 11V. An image based on the image signal is displayed on the screen 70 by scanning the laser beam in the horizontal direction and the vertical direction by the optical deflector 100.
　制御部２００は、ＡＰＣ（Ａｕｔｏ　Ｐｏｗｅｒ　Ｃｏｎｔｒｏｌ）回路を有し、所望のレーザ出力パワー（強度）のレーザ光が出射されるように、半導体レーザに入力する画素信号の駆動電流値を制御する（ＡＰＣ制御）。具体的には、制御部２００は、入力された画像信号におけるそれぞれの画素値に応じてＲ光源５１ｒ、Ｇ光源５１ｇ及びＢ光源５１ｂにそれぞれ所望のレーザ出力パワーに対応する画素信号の駆動電流値が入力されるよう、Ｒ光源信号生成部４０ｒ、Ｇ光源信号生成部４０ｇ及びＢ光源信号生成部４０ｂを制御する。なお、ＡＰＣ制御では、線形性を前提として階調レベルを割り当てた画素信号を半導体レーザに入力するのではなく、使用する半導体レーザのＩ－Ｌ特性に基づいて所望のレーザ出力パワーに対応する画素信号を発生させ半導体レーザに入力するので、特許文献１に記載された技術と異なり、Ｉ－Ｌ特性が線形である必要はない。 The control unit 200 includes an APC (Auto Power Control) circuit, and controls the drive current value of the pixel signal input to the semiconductor laser so that laser light having a desired laser output power (intensity) is emitted (APC). control). Specifically, the control unit 200 drives the R light source 51r, the G light source 51g, and the B light source 51b according to the respective pixel values in the input image signal, and the drive current value of the pixel signal corresponding to the desired laser output power. R light source signal generation unit 40r, G light source signal generation unit 40g, and B light source signal generation unit 40b are controlled. In the APC control, a pixel signal corresponding to a desired laser output power is not input based on the IL characteristic of the semiconductor laser to be used, instead of inputting a pixel signal assigned a gradation level on the premise of linearity to the semiconductor laser. Since the signal is generated and input to the semiconductor laser, the IL characteristic does not need to be linear, unlike the technique described in Patent Document 1.
　制御部２００は、入力された水平同期信号に基づいて水平駆動信号を生成し水平駆動部１１Ｈに供給する。水平駆動部１１Ｈは、この水平駆動信号に基づいて光偏向器１００を水平方向に揺動させる。また、制御部２００は、入力された垂直同期信号に基づいて垂直駆動信号を生成し垂直駆動部１１Ｖに供給する。垂直駆動部１１Ｖは、この垂直駆動信号に基づいて光偏向器１００を垂直方向に揺動させる。 The control unit 200 generates a horizontal drive signal based on the input horizontal synchronization signal and supplies it to the horizontal drive unit 11H. The horizontal drive unit 11H swings the optical deflector 100 in the horizontal direction based on the horizontal drive signal. Further, the control unit 200 generates a vertical drive signal based on the input vertical synchronization signal and supplies the vertical drive signal to the vertical drive unit 11V. The vertical drive unit 11V swings the optical deflector 100 in the vertical direction based on the vertical drive signal.
　図２は、Ｒ光源５１ｒ、Ｇ光源５１ｇ及びＢ光源５１ｂのうちのいずれかである半導体レーザが有するＩ－Ｌ特性の一例を示している。図２に示すように、画素信号の駆動電流値が小さい領域には、Ｉ－Ｌ特性が急峻に変化して線形性が崩れる（画素信号の駆動電流値に対してレーザ出力パワーがリニアに増大しない）領域であるキンク領域が存在する。キンク領域にはさらに、ＬＤ発光（レーザ発光）とＬＥＤ発光（自然発光）が混在する遷移領域が存在する（レーザ出力パワーが１ｍＷ付近）。この遷移領域における画素信号の駆動電流値が閾値電流Ｉｔｈである。閾値電流Ｉｔｈは一定の幅（閾値電流の幅ΔＩ）を持つ。なお、図２に例として示した半導体レーザにおいて、閾値電流Ｉｔｈの最小値は８４．４ｍＡ、最大値は８４．８４ｍＡである。よって、閾値電流の幅ΔＩは０．４４ｍＡである。また、定格レーザ出力パワーは５ｍＷ付近である。 FIG. 2 shows an example of the IL characteristic of the semiconductor laser that is one of the R light source 51r, the G light source 51g, and the B light source 51b. As shown in FIG. 2, in the region where the drive current value of the pixel signal is small, the IL characteristic changes sharply and the linearity is lost (the laser output power increases linearly with respect to the drive current value of the pixel signal). Not) is a kink region. The kink region further includes a transition region in which LD light emission (laser light emission) and LED light emission (natural light emission) coexist (laser output power is around 1 mW). The drive current value of the pixel signal in this transition region is the threshold current Ith. The threshold current Ith has a certain width (threshold current width ΔI). In the semiconductor laser shown as an example in FIG. 2, the minimum value of the threshold current Ith is 84.4 mA, and the maximum value is 84.84 mA. Therefore, the threshold current width ΔI is 0.44 mA. The rated laser output power is around 5 mW.
　画素信号の駆動電流値が閾値電流Ｉｔｈ内にある場合、半導体レーザはＬＥＤ発光域とＬＤ発光域との間を行き来するため、レーザ出力パワーが不安定になる。閾値電流の幅ΔＩは、Ｉ－Ｌ特性が急峻に変化して非線形となる領域（キンク領域）の駆動電流の幅Ｉｃと比べて非常に微小である。この閾値電流の幅ΔＩは、温度などの諸条件が変化してもほぼ一定であり、レーザの種類によって一意に定まる。 When the drive current value of the pixel signal is within the threshold current Ith, the laser output power becomes unstable because the semiconductor laser moves between the LED emission region and the LD emission region. The threshold current width ΔI is very small compared to the drive current width Ic in a region (kink region) where the IL characteristic changes sharply and becomes nonlinear. This threshold current width ΔI is substantially constant even when various conditions such as temperature change, and is uniquely determined by the type of laser.
　ここで、画素信号に重畳する高周波信号について以下で説明する。
　上述したように、画素信号の駆動電流値が閾値電流Ｉｔｈ内にあるとき、半導体レーザはＬＥＤ発光域とＬＤ発光域との間を行き来するため、レーザ出力パワーが不安定になり目標のレーザ出力パワーが得られない。Ｒ光源５１ｒ、Ｇ光源５１ｇ及びＢ光源５１ｂの中の少なくとも１つにおいて駆動電流が閾値電流Ｉｔｈ内にある場合、駆動電流が閾値電流Ｉｔｈ内にある光源では目標のレーザ出力パワーが得られないので、本来得ようとした色とは異なる色ずれが発生してしまう。 Here, the high frequency signal superimposed on the pixel signal will be described below.
As described above, when the drive current value of the pixel signal is within the threshold current Ith, the semiconductor laser goes back and forth between the LED emission region and the LD emission region, so that the laser output power becomes unstable and the target laser output I can't get power. When the drive current is within the threshold current Ith in at least one of the R light source 51r, the G light source 51g, and the B light source 51b, the target laser output power cannot be obtained with the light source whose drive current is within the threshold current Ith. Therefore, a color shift different from the color originally intended to occur occurs.
　図３は、画素信号の駆動電流値が閾値電流Ｉｔｈ内にある場合において、画素信号に高周波信号を重畳した状態を模式的に示す図である。図中において画素信号を一点鎖線で示し、高周波信号を実線で示す。図３に示すように、画素信号はパルス波であり、生成周期をＴとする。また、目標のレーザ出力パワーに対応する画素信号の駆動電流値は、閾値電流Ｉｔｈ内の駆動電流値Ｉｐであるとする。 FIG. 3 is a diagram schematically showing a state in which a high-frequency signal is superimposed on the pixel signal when the drive current value of the pixel signal is within the threshold current Ith. In the figure, the pixel signal is indicated by a one-dot chain line, and the high-frequency signal is indicated by a solid line. As shown in FIG. 3, the pixel signal is a pulse wave, and the generation cycle is T. Further, it is assumed that the drive current value of the pixel signal corresponding to the target laser output power is the drive current value Ip within the threshold current Ith.
　画素信号に重畳する高周波信号の周波数は、画素信号の生成周期Ｔの逆数（１／Ｔ）以上である。また、高周波信号の電流振幅は、閾値電流の幅ΔＩである。なお、図中の高周波信号はサイン波であるが、これに限るものではなく、例えばパルス波や三角波であってもよい。画素信号に上述した周波数及び電流振幅を有する高周波信号を重畳した信号を半導体レーザに入力すると、周期的に変動するレーザ出力パワーを平均したレーザ出力パワーが得られる。これにより、画素信号の駆動電流値が閾値電流Ｉｔｈ内にあるときにもレーザ光の出力パワーを安定させることができるので、低い階調レベルを精度よく表示することができる。 The frequency of the high frequency signal superimposed on the pixel signal is equal to or greater than the reciprocal (1 / T) of the pixel signal generation period T. The current amplitude of the high frequency signal is a threshold current width ΔI. In addition, although the high frequency signal in a figure is a sine wave, it is not restricted to this, For example, a pulse wave and a triangular wave may be sufficient. When a signal in which a high-frequency signal having the above-described frequency and current amplitude is superimposed on a pixel signal is input to the semiconductor laser, a laser output power obtained by averaging the laser output power that varies periodically can be obtained. Thereby, even when the drive current value of the pixel signal is within the threshold current Ith, the output power of the laser beam can be stabilized, so that a low gradation level can be accurately displayed.
　半導体レーザは、定格レーザ出力パワーを超えて使用すると寿命が著しく短くなる。このため、画素信号に高周波信号を重畳したときのレーザ出力パワーのピークが定格レーザ出力パワーを超えないようにする必要がある。画像表示装置５００において、最も高い階調の高輝度化と半導体レーザの長寿命化との両立を図るため、最も高い階調のレーザ出力パワーが定格レーザ出力パワーをやや下回るようにする。 ¡Semiconductor lasers have a significantly shorter life when used beyond the rated laser output power. For this reason, it is necessary to prevent the peak of the laser output power when the high frequency signal is superimposed on the pixel signal from exceeding the rated laser output power. In the image display device 500, the laser output power of the highest gradation is set slightly lower than the rated laser output power in order to achieve both high brightness of the highest gradation and long life of the semiconductor laser.
　図４は、目標のレーザ出力パワーが定格レーザ出力パワー付近である場合に、画素信号に高周波信号を重畳した状態を模式的に示す図である。図中において画素信号を一点鎖線で示し、高周波信号を実線で示す。図４に示すように、画素信号の駆動電流値に対して、画素信号に重畳する高周波信号の電流振幅は微小であるため、高周波信号を重畳した後の信号における駆動電流値のピークに対応するレーザ出力パワーが定格レーザ出力パワーを超えることはない。このため、高周波信号を重畳しない場合と比べて半導体レーザの寿命が著しく短くなることはない。 FIG. 4 is a diagram schematically showing a state in which a high frequency signal is superimposed on a pixel signal when the target laser output power is near the rated laser output power. In the figure, the pixel signal is indicated by a one-dot chain line, and the high-frequency signal is indicated by a solid line. As shown in FIG. 4, the current amplitude of the high frequency signal superimposed on the pixel signal is very small with respect to the drive current value of the pixel signal, and therefore corresponds to the peak of the drive current value in the signal after the high frequency signal is superimposed. The laser output power will not exceed the rated laser output power. For this reason, the lifetime of the semiconductor laser is not significantly shortened compared with the case where no high-frequency signal is superimposed.
　上述したように、目標のレーザ出力パワーが定格レーザ出力パワー付近である場合にも、半導体レーザの寿命が著しく短くなることなく画素信号に高周波信号を重畳することができる。つまり、全ての階調レベルのレーザ出力パワーに対応する画素信号において、一定の電流振幅の高周波信号を重畳することができる。このように、全ての階調レベルのレーザ出力パワーに対応する画素信号において一定の電流振幅の高周波信号を重畳する場合、階調レベルを変更する際に、階調レベルの大小により、高周波信号を重畳するかしないかを判断する、重畳する高周波信号の電流振幅を変更する、といった複雑な処理を行う必要がなくなる。 As described above, even when the target laser output power is in the vicinity of the rated laser output power, the high-frequency signal can be superimposed on the pixel signal without significantly shortening the life of the semiconductor laser. That is, a high-frequency signal having a constant current amplitude can be superimposed on pixel signals corresponding to laser output power at all gradation levels. As described above, when superimposing a high-frequency signal having a constant current amplitude in pixel signals corresponding to laser output powers of all gradation levels, the high-frequency signal is changed depending on the magnitude of the gradation level when changing the gradation level. There is no need to perform complicated processing such as determining whether to superimpose or changing the current amplitude of the superimposed high-frequency signal.
　以上より、本発明では、少なくとも、画素信号の駆動電流値が半導体レーザのＩ－Ｌ特性においてＬＥＤ発光とＬＤ発光とが混在する領域にあるときに画素信号に上述した高周波信号を重畳すれば、低い階調レベルにおいてレーザ出力パワーが不安定になるのを抑え、低い階調レベルを精度よく表示することができる。また、高い階調レベルにおいて画素信号に上述した高周波信号を重畳してもレーザ光のレーザ出力パワーが定格レーザ出力パワーを超えてしまうこともない。 From the above, in the present invention, at least when the driving current value of the pixel signal is in a region where LED light emission and LD light emission are mixed in the IL characteristic of the semiconductor laser, the above-described high-frequency signal is superimposed on the pixel signal. The laser output power can be prevented from becoming unstable at a low gradation level, and the low gradation level can be accurately displayed. Further, even if the above-described high-frequency signal is superimposed on the pixel signal at a high gradation level, the laser output power of the laser light does not exceed the rated laser output power.
　なお、本発明は上記実施の形態に限られたものではなく、趣旨を逸脱しない範囲で適宜変更することが可能である。 Note that the present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit of the present invention.
　この出願は、２０１５年１０月１９日に出願された日本出願特願２０１５－２０５１６６を基礎とする優先権を主張し、その開示の全てをここに取り込む。 This application claims priority based on Japanese Patent Application No. 2015-205166 filed on October 19, 2015, the entire disclosure of which is incorporated herein.
　以上のように本実施形態に係る光源駆動装置及び画像表示装置は、例えば乗用車に搭載される光源駆動装置、乗用車で実施される画像表示装置として利用可能である。 As described above, the light source driving device and the image display device according to the present embodiment can be used as, for example, a light source driving device mounted on a passenger car or an image display device implemented on a passenger car.
　４０　信号生成部
　４０ｒ　Ｒ光源信号生成部
　４０ｇ　Ｇ光源信号生成部
　４０ｂ　Ｂ光源信号生成部
　５０　レーザ光発生部
　５１　光源
　５１ｒ　Ｒ光源（半導体レーザ）
　５１ｇ　Ｇ光源（半導体レーザ）
　５１ｂ　Ｂ光源（半導体レーザ）
　６０　信号重畳部
　６０ｒ　Ｒ光源信号重畳部
　６０ｇ　Ｇ光源信号重畳部
　６０ｂ　Ｂ光源信号重畳部
　７０　スクリーン
　１００　光偏向器
　２００　制御部
　２５０　光源駆動装置 40 signal generator 40r R light source signal generator 40g G light source signal generator 40b B light source signal generator 50 laser light generator 51 light source 51r R light source (semiconductor laser)
51g G light source (semiconductor laser)
51b B light source (semiconductor laser)
60 signal superimposing unit 60r R light source signal superimposing unit 60g G light source signal superimposing unit 60b B light source signal superimposing unit 70 screen 100 optical deflector 200 control unit 250 light source driving device

Claims (4)

  1. 　画像を構成する画素の階調レベルに応じた画素信号を画素単位で生成する信号生成部と、
    　前記画素信号に応じた強度のレーザ光を出射する半導体レーザと、
    　前記半導体レーザに入力される前記画素信号に高周波信号を重畳する信号重畳部と、を備え、
    　前記信号重畳部が重畳する高周波信号は、周波数が、前記信号生成部が前記画素信号を生成する生成周期の逆数以上であり、かつ電流振幅が、前記半導体レーザのＩ－Ｌ特性においてＬＥＤ発光とＬＤ発光とが混在する領域における前記画素信号の駆動電流値の幅である、光源駆動装置。     A signal generation unit that generates pixel signals corresponding to the gradation levels of the pixels constituting the image in units of pixels;
    A semiconductor laser that emits laser light having an intensity corresponding to the pixel signal;
    A signal superimposing unit that superimposes a high-frequency signal on the pixel signal input to the semiconductor laser,
    The high-frequency signal superimposed by the signal superimposing unit has a frequency equal to or higher than the reciprocal of the generation cycle in which the signal generating unit generates the pixel signal, and the current amplitude is LED emission in the IL characteristic of the semiconductor laser. A light source driving device which is a width of a driving current value of the pixel signal in a region where LD light emission is mixed.
  2. 　前記信号重畳部は、前記画素信号の駆動電流値が少なくとも前記混在する領域にあるときに前記画素信号に前記高周波信号を重畳する、請求項１に記載の光源駆動装置。 The light source driving device according to claim 1, wherein the signal superimposing unit superimposes the high-frequency signal on the pixel signal when the driving current value of the pixel signal is at least in the mixed region.
  3. 　前記信号重畳部は、前記画素信号の駆動電流値が全ての階調レベルにおいて前記画素信号に前記高周波信号を重畳する請求項１に記載の光源駆動装置。 The light source driving device according to claim 1, wherein the signal superimposing unit superimposes the high-frequency signal on the pixel signal at all gradation levels of the driving current value of the pixel signal.
  4. 　請求項１から３のいずれか１項に記載の光源駆動装置と、
    　前記半導体レーザより発せられたレーザ光を水平方向及び垂直方向に偏向して画像を表示させる光偏向器と、を備える画像表示装置。     The light source driving device according to any one of claims 1 to 3,
    An image display device comprising: an optical deflector that displays an image by deflecting laser light emitted from the semiconductor laser in a horizontal direction and a vertical direction.
PCT/JP2016/003032 2015-10-19 2016-06-23 Light source driving device and image display device WO2017068738A1 (en)

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