JP2010054879A - Light source device, image display, and light quantity correcting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology allowing light quantity correction according to the change of light source characteristics. <P>SOLUTION: A measured light quantity P is represented by P=a×D+b (D: a gradation value and a, b: coefficients), and a target light quantity T is represented by T=M×D (M: a constant). A light quantity correcting section sequentially obtains errors δ between the target light quantity T and the measured light quantity P in measuring the light quantity a plurality of times using different gradation values D, and sequentially corrects the coefficients a, b to minimize the errors δ. The light quantity correcting section corrects the light quantity of a light source part by adjusting at least one of the pixel value and the set value of a driving circuit based on the corrected coefficients a, b. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light source device, an image display device, and a light amount correction method.

  2. Description of the Related Art In recent years, a laser scan display that displays an image by raster scanning beam-shaped light such as laser light on a projection surface has attracted attention as one form of an image display device. Since such a laser scan display can express complete black by stopping the supply of laser light, for example, the contrast is very high compared to a projector using a liquid crystal light valve, and the laser light is single. Since the wavelength is high, the color purity is high, and since the coherence is high, the beam is easily shaped (easy to stop). From these characteristics, the laser scan display is expected as a high-quality display that realizes high contrast, high color reproducibility, and high resolution.

  As a laser light source of a laser scan display, a semiconductor laser element such as a laser diode is mainly used. However, the laser characteristics of such a semiconductor laser element change due to a change in temperature, aging, etc. Therefore, it is necessary to correct the laser light quantity so that the image brightness can be obtained.

For example, in Patent Document 1 below, the bias current value of the semiconductor laser element is changed by two or more points, the light emission power of the semiconductor laser element is detected by the received light power detection means, and the threshold current value and quantum efficiency of the semiconductor laser element are detected. By detecting the change, etc., the DC bias current of the semiconductor laser element is set in the bias current control means, and the pulse current corresponding to the change in the quantum efficiency etc. is set in the pulse current control means, so that the laser output level Has been disclosed. Further, in Patent Document 2 below, a relational expression between the detected light amount of the laser light source and the set value of the optical output is automatically calculated, and data of this relational expression is set in the optical recording medium drive device. A technique for adjusting the output level is disclosed.
JP-A-7-147446 JP 2003-91853 A

  In this way, when correcting the amount of laser light in response to changes in laser characteristics due to temperature changes or aging deterioration, in order to increase the correction accuracy, the laser characteristics change in real time while actually operating the device. It is desirable to perform light amount correction according to the above, but no means has been presented in the above prior art.

  Conventionally, no consideration has been given to the light amount correction particularly when the laser is PWM-driven. Such a problem is a common problem even when a light source element other than a laser is used.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a technique capable of performing light amount correction according to a change in light source characteristics.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A light source device,
A light source unit including a light source element;
A PWM signal generator that generates a PWM signal according to the pixel value;
A drive circuit for driving the light source element according to the PWM signal;
A light amount measuring unit for measuring the light amount of the light source unit;
A light amount correction unit that corrects the light amount of the light source unit based on the light amount measured by the light amount measurement unit;
With
When the measured light amount P is expressed as P = a × D + b (D is a gradation value, a and b are coefficients), and the target light amount T is expressed as T = M × D (M is a constant),
The light amount correction unit
An error δ between the target light amount T and the measured light amount P in a plurality of times of light amount measurement using different gradation values D is sequentially obtained, and the coefficients a and b are sequentially corrected so as to minimize the error δ. With
A light source device that corrects the light amount of the light source unit by adjusting at least one of the pixel value and a setting value of the drive circuit based on the corrected coefficients a and b.
According to this light source device, the coefficients a and b are sequentially corrected so as to minimize the error δ between the measured light quantity P and the target light quantity T, and the light quantity correction is performed based on the corrected coefficients a and b. Thus, it is possible to perform light amount correction according to changes in the light source characteristics.

[Application Example 2]
The light source device according to claim 1,
The light amount correction unit
A light source device that sequentially corrects the coefficient a using the accumulated value ΣδD of the product of the error δ and the gradation value D, and sequentially corrects the coefficient b using the accumulated value Σδ of the error δ. .

[Application Example 3]
The light source device according to claim 2,
The light amount correction unit
The current value a _k of the coefficient a is obtained by subtracting a value proportional to the accumulated value ΣδD of the product of the error δ and the gradation value D from the previous value a _{k−1 of the} coefficient a. ,
A light source device that obtains a current value b _k of the coefficient b by subtracting a value proportional to an accumulated value Σδ of the error δ from a previous value b _{k−1 of the} coefficient b.
According to this light source device, the coefficients a and b can be calculated sequentially for each light quantity measurement.

[Application Example 4]
The light source device according to any one of claims 1 to 3,
The light amount correction unit
A correction coefficient calculation unit that calculates first and second correction coefficients for correcting the pixel value according to the coefficients a and b;
Pixel value correction that receives the pixel value as the gradation value D, corrects the pixel value according to the first and second correction coefficients, and supplies the corrected pixel value to the PWM signal generation unit And
A light source device comprising:
According to this light source device, it is possible to achieve the target light amount by correcting the pixel value.

[Application Example 5]
The light source device according to any one of claims 1 to 3,
The light amount correction unit
A correction for calculating a first correction coefficient for adjusting the power supply voltage of the drive circuit according to the coefficient a and a second correction coefficient for correcting the pixel value according to the coefficient b A coefficient calculation unit;
A power supply voltage adjusting unit that adjusts the power supply voltage of the drive circuit according to the first correction coefficient;
A pixel value correction unit that receives the pixel value as the gradation value D, corrects the pixel value according to the second correction coefficient, and supplies the corrected pixel value to the PWM signal generation unit;
A light source device comprising:
According to this light source device, it is possible to achieve the target light amount by adjusting the power supply voltage of the drive circuit and correcting the pixel value.

[Application Example 6]
The light source device according to any one of claims 1 to 3,
The drive circuit is
A first constant current circuit for constantly flowing a first current to the light source element;
A second constant current circuit for flowing a second current to the light source element in addition to the first current;
A switching circuit that performs on / off control of the flow of the second current to the light source element according to the PWM signal;
With
The light amount correction unit
A signal value indicating the value of the second current is used as the gradation value;
The value of the first current of the first constant current circuit is adjusted according to the coefficient b, and the value of the second current of the second constant current circuit is adjusted according to the coefficient a. , Light source device.
According to this light source device, it is possible to achieve the target light amount by adjusting the current values of the first and second constant current circuits.

[Application Example 7]
The light source device according to claim 6,
The light source device, wherein the correction unit adjusts the value of the first current so that the first current becomes equal to a threshold current of the light source element.
According to this light source device, the start and stop of light emission can be quickly switched according to the on / off control of the second current.

[Application Example 8]
The light source device according to any one of claims 1 to 7,
The light source unit has a nonlinear characteristic in which a relationship between the pixel value and the light amount is nonlinear,
The light quantity measuring unit is
An optical sensor for measuring the amount of light emitted from the light source unit;
A converted light quantity calculation unit that calculates a converted light quantity by performing nonlinear conversion that converts the nonlinear characteristic into a linear characteristic with respect to the light quantity measured by the optical sensor, and calculates the converted light quantity as the measured light quantity P;
A light source device comprising:
According to this light source device, it is possible to perform light amount correction according to a change in light source characteristics even when a light source unit having nonlinear characteristics is used.

  The present invention can be realized in various forms, for example, a light source device, a light amount correction method for the light source device, a display device including the light source device, and a computer for realizing the functions of these methods or devices. The present invention can be realized in the form of a program, a recording medium on which the computer program is recorded, and the like.

Next, embodiments of the present invention will be described in the following order.
A. First embodiment (light amount correction by correcting pixel values):
B. Second Embodiment (Light quantity correction by correcting the pixel value and the power supply voltage value of the drive circuit):
C. Third Embodiment (Light quantity correction by correcting bias current value and signal current value of drive circuit):
D. Fourth embodiment (light amount correction when a light source having a wavelength conversion element is used):
E. Variation:

A. First embodiment (light amount correction by correcting pixel values):
FIG. 1 is a block diagram showing the configuration of an image display apparatus according to the first embodiment of the present invention. This image display device is a laser scan display that displays an image by scanning laser light on a screen (projected surface) 200. This image display device includes a video signal processing circuit 1010, light source devices 1100R, 1100G, and 1100B for three colors of RGB, a light beam combining optical system 1040, a laser beam scanning unit 1050, a scanning driving unit 1060, and a timing signal generating circuit. 1070 and a pixel synchronous clock generation circuit 1080. A light source device 1100R for red light includes a PWM signal generation circuit 1500, a laser driver 1020, a laser element 1030 for red light emission, a half mirror 1035, a photoelectric conversion element 1090, an I / V converter 1091, an A / V A D converter 1092 and a light amount correction circuit 1200 are included. The configurations of the other color light source devices 1100G and 1100B are the same as the configuration of the red light source device 1100R except for the laser element.

  The video signal processing circuit 1010 receives a video signal and a synchronization signal (vertical synchronization signal and horizontal synchronization signal) transmitted from an external image supply device (not shown) such as a notebook personal computer, for example, and inputs these video signals and Based on the synchronization signal, digital gradation data defining a gradation value corresponding to each pixel of the image to be displayed is generated, and this digital gradation data is stored in the internal memory in units of one frame. At this time, the video signal processing circuit 1010 normally performs inverse γ correction in consideration of the γ characteristic of the image display device on the gradation value of the original video signal. Hereinafter, the gradation data output from the video signal processing circuit 1010 is also referred to as “pixel value D” or “pixel data D”.

  The video signal processing circuit 1010 is synchronized with the frame timing signal Ft and the scanning timing signal St supplied from the timing signal generation circuit 1070 and the pixel synchronization clock signal CL supplied from the pixel synchronization clock generation circuit 1080. Are read out and supplied to the three light source devices 1100R, 1100G, and 1100B. The light source devices 1100R, 1100G, and 1100B drive the laser element 1030 according to the respective pixel data to emit laser light. The three colors of laser light emitted from the light source devices 1100R, 1100G, and 1100B for each color are combined by a light beam combining optical system 1040 and scanned by a laser light scanning unit 1050. As the light combining optical system 1040, a dichroic prism or two dichroic mirrors can be used. The laser beam scanning unit 1050 is, for example, a resonance type MEMS (Micro Electro Mechanical System) scanner having a reflection mirror.

  The laser light of each color is incident on the photoelectric conversion element 1090 through the half mirror 1035. The photoelectric conversion element 1090 generates a light receiving sensor signal Ipd indicating the light amount W of the laser element 1030. Since this light receiving sensor signal Ipd is a current signal, it is converted into a voltage signal VL by the I / V converter 1091, further converted into a digital light quantity signal P by the A / D converter 1092, and supplied to the light quantity correction circuit 1200. The light amount signal P indicates the measured light amount per pixel or the average light amount of one pixel. The light quantity correction circuit 1200 performs light quantity correction by correcting the pixel value based on the light quantity signal P. The content of this light quantity correction will be described later.

  The timing signal generation circuit 1070 has an optical sensor 1070a provided at a predetermined detection position, and a frame timing signal Ft, a scanning timing signal St, and the like are synchronized with the timing at which the optical sensor 1070a detects the laser beam. Is generated. The frame timing signal Ft is a pulse signal that defines the start of one frame. The scanning timing signal St is a pulse signal that defines the start and end of one horizontal scanning period. The pixel synchronization clock generation circuit 1080 generates a pixel synchronization clock CL synchronized with each pixel position in accordance with the scanning timing signal St.

  FIG. 2 is a timing chart showing the operation timing of the image display apparatus. At time t1, the rotation angle θ1 of the reflection mirror of the laser beam scanning unit 1050 coincides with the angle corresponding to the start position of one frame on the screen 200, and at time t2, the rotation angle θ1 of the reflection mirror is on the screen 200. This coincides with the angle corresponding to the start position of one horizontal scanning period. At this time, the frame timing signal Ft is output from the timing signal generation circuit 1070 at time t1, and the scanning timing signal St defining the start of one horizontal scanning period H is output at time t2. Further, at time t3, the rotation angle θ1 of the reflecting mirror coincides with the angle corresponding to the end position of one horizontal scanning period H. At this time, a scanning timing signal St that defines the end of one horizontal scanning period H is output from the timing signal generation circuit 1070 at time t3. The same operation is repeated after time t4.

  The pixel synchronization clock generation circuit 1080 generates a pixel synchronization clock signal CL according to the scanning timing signal St. The pulse interval of the pixel synchronization clock signal CL changes according to the irradiation position of the laser beam, that is, the elapsed time. For example, the pulse interval becomes short near the time t13 to t17 near the center of the screen 200, and the pulse interval becomes long at times t2, t10 to t12, t18 to t20, and t3 near both ends of the screen 200. This is because the changing speed (scanning speed) of the rotation angle θ1 of the reflection mirror of the laser beam scanning unit 1050 changes in a sine wave shape according to the elapsed time.

  As the laser beam scanning unit 1050, a scanning optical system using a polygon mirror and an fθ lens may be used. In this case, the interval of one pixel is constant over the entire scanning range.

  FIG. 3 is an explanatory diagram showing the internal configuration of the PWM signal generation circuit, the laser driver, and the light amount correction circuit. The light amount correction circuit 1200 includes a pixel value correction circuit 1210 and a correction coefficient calculation circuit 1220.

ここで、Ｄｎは予め設定された規格化定数であり、例えばＤｎ＝２５５が利用される。 The pixel value correction circuit 1210 corrects the pixel value D based on the correction coefficients Da and Db supplied from the correction coefficient calculation circuit 1220 and supplies the corrected pixel value Dcr to the PWM signal generation circuit 1500. In the first embodiment, the corrected pixel value Dcr is calculated according to the following equation.

Here, Dn is a preset normalization constant. For example, Dn = 255 is used.

  The PWM signal generation circuit 1500 includes a timing signal generation circuit 1510, a triangular wave signal generation circuit 1520, a comparator 1530, and a pixel value voltage generation circuit 1540. The triangular wave signal generation circuit 1520 has an integration circuit using an operational amplifier 1521 and an integration capacitor 1523. In addition, a switching transistor 1522 is provided in parallel with the integration capacitor 1523. The charging signal Vi is input from the timing signal generation circuit 1510 to the negative input terminal of the operational amplifier 1521. A capacitance reset signal Creset is input from the timing signal generation circuit 1510 to the gate electrode of the switching transistor 1522. The capacitance reset signal Creset is a signal for reliably stopping the generation of the triangular wave signal Tri at the end of one pixel period. As the triangular wave signal generation circuit, various circuits other than the circuit shown in FIG. 3 can be employed. The comparator 1530 compares the triangular wave signal Tri and the pixel value voltage signal Vd to generate the PWM signal Spwm. The pixel value voltage signal Vd is a signal obtained by converting the corrected pixel value Dcr supplied from the light amount correction circuit 1200 according to a predetermined conversion formula (described later). The PWM signal Spwm thus generated is supplied to the laser driver 1020.

  The laser driver 1020 has a series connection of a current limiting resistor 1022 and a driving transistor 1024. The resistor 1022 and the drive transistor 1024 are connected in series with the laser element 1030 between the power supply potential Vlaser and the ground potential. The PWM signal Spwm output from the PWM signal generation circuit 1500 is input to the control terminal of the drive transistor 1024 to control the drive transistor 1024 on / off.

  FIG. 4 is a timing chart showing a state of laser driving using a PWM signal. The pixel value D is supplied to the pixel value voltage generation circuit 1540 in synchronization with the pixel synchronization clock CL, and the pixel value signal Vd is generated accordingly. However, the pixel value signal Vd is a signal having a voltage value corresponding to the pixel value Dcr corrected by the pixel value correction circuit 1210. The charge signal Vi and the capacity reset signal Creset are generated at timings delayed from the pixel synchronization clock signal CL by a predetermined time, respectively. At the beginning of each pixel period, first, the charge signal Vi becomes H level, and the triangular wave signal generation circuit 1520 is charged accordingly, and the voltage value of the triangular wave signal Tri increases. Thereafter, when the charging signal Vi becomes L level, the triangular wave signal generation circuit 1520 is discharged, and the voltage value of the triangular wave signal Tri decreases. The capacitor reset signal Creset has a function of forcibly resetting the triangular wave signal Tri by discharging the integration capacitor 1523 by short-circuiting at the end of one pixel period. The PWM signal Spwm becomes H level when the triangular wave signal Tri is larger than the pixel value signal Vd, and becomes L level when the triangular wave signal Tri is smaller than the pixel value signal Vd. The laser drive current I flows according to the PWM signal Spwm, and the laser element 1030 emits light.

  FIG. 5 is an explanatory diagram showing the relationship between the PWM signal window assumed in the PWM modulation of this embodiment and the actual PWM signal. The PWM signal window Pwm_Window is a period with a constant width that is delayed by a predetermined period from the rising edge of the pixel synchronization clock signal CL. As described with reference to FIG. 2, one pixel period changes according to the scanning position of the laser beam, but the PWM signal window Pwm_Window is kept at a constant value regardless of the pixel position. The PWM signal Spwm rises to the H level only within this PWM signal window. The duty of the PWM signal Spwm is determined according to the corrected pixel value Dcr (FIG. 3). Here, the duty of the PWM signal Spwm is a value obtained by dividing the pulse width Pwm_Width of the PWM signal Spwm by the PWM signal window Pwm_Window. The larger the duty is, the longer the time during which the laser drive current I flows, so that the laser light amount Wdt further increases. The laser light amount Wdt rises after a slight delay time td from the beginning of the flow of the laser drive current I. This is because the semiconductor laser starts to increase the carrier density of the active region when the current starts to flow, and starts laser emission after the carrier density reaches the threshold value. Therefore, if the duty is not increased to some extent, the laser light quantity becomes zero.

FIG. 6A is a graph showing the relationship between the duty and the light quantity W (average light quantity per pixel). Due to the light emission delay time td described above, the light amount W is zero in a range where the duty is equal to or less than the threshold Duty _th (offset range), and thereafter, the light amount W increases linearly as the duty increases. A range in which the light amount W exceeds 0 can be used as an effective drive range. FIG. 6B is a graph illustrating an example of characteristics of the laser element. The horizontal axis indicates the laser drive current, and the vertical axis indicates the voltage of the laser element and the light amount Wdt per unit time. The light amount Wdt per unit time is substantially zero until the laser drive current I reaches the threshold current Ith, and thereafter increases linearly with the drive current I. The slope η of the drive current I is also called “differential efficiency”. In the PWM modulation of the first embodiment, the laser element is caused to emit light with a drive current value Im sufficiently larger than the threshold current Ith. The average light amount W in the graph of FIG. 6A is a value obtained by averaging the light amount Wdt per unit time over one pixel period (that is, the window Pwm_Window).

ここで、ｆは図６（Ａ）のグラフの傾きである。 The relationship between the duty and the average light amount W shown in FIG. 6A is expressed by the following equation.

Here, f is the slope of the graph of FIG.

ここで、Duty₀は、画素値電圧Ｖｄがゼロの場合のデューティ値であり、これは、デューティの上限値に相当する。Ｋ_dは定数である。また、ＧｐとＶｄ₀は画素値電圧生成回路１５４０（図３）の設定値であり、(1.5)式は画素値電圧生成回路１５４０における変換を表している。(1.4)，(1.5)式から、画素値Ｄが大きいほど画素値電圧Ｖｄが小さくなり、デューティ値が大きくなる（上限値Duty₀に近づく）ことが理解できる。 In the operation of the PWM signal generation circuit 1500 shown in FIG. 4, the duty increases as the pixel value voltage Vd decreases. Accordingly, the pixel value voltage Vd is set so as to decrease as the pixel value D increases. Such a characteristic is expressed by the following equation.

Here, Duty ₀ is a duty value when the pixel value voltage Vd is zero, and this corresponds to an upper limit value of the duty. K _d is a constant. Gp and Vd ₀ are set values of the pixel value voltage generation circuit 1540 (FIG. 3), and equation (1.5) represents conversion in the pixel value voltage generation circuit 1540. From equations (1.4) and (1.5), it can be understood that as the pixel value D increases, the pixel value voltage Vd decreases and the duty value increases (closes to the upper limit value Duty ₀ ).

ここで、Ｗは１画素当たりの平均光量であり、Ｋpd，Ｒ，Ｇadはそれぞれの回路１０９０，１０９１，１０９２における変換係数である。 The light receiving sensor signal Ipd, the voltage signal VL, and the measured light quantity P shown in FIG. 1 are each expressed by the following equations.

Here, W is an average amount of light per pixel, and Kpd, R, and Gad are conversion coefficients in the respective circuits 1090, 1091, and 1092.

When the above equations (1.2) to (1.8) are used, the measurement light quantity P is expressed by the following equation.

  In the above equation (1.9), the measured light quantity P is expressed in the form of a linear function of the pixel value D. The first coefficient a of the linear function is a slope, and the second coefficient b is an intercept. Further, in the equations (1.12) and (1.13), it can be understood that the two correction coefficients Da and Db for the pixel value have only these coefficients a and b as variables.

ここで、係数Ｍは、画素値Ｄがその最大値（例えば２５５）のときに、目標光量Ｔがその最大値となるように予め決定された値である。一方、測定光量Ｐは、上記（1.9)式に示したように、Ｐ＝ａ×Ｄ＋ｂと表される。 The principle of light amount correction in the light amount correction circuit 1200 is as follows. First, it is assumed that the target light amount T is proportional to the pixel value D as in the following equation.

Here, the coefficient M is a value determined in advance so that the target light amount T becomes the maximum value when the pixel value D is the maximum value (for example, 255). On the other hand, the measured light quantity P is expressed as P = a × D + b as shown in the above equation (1.9).

  FIG. 7 is an explanatory diagram for explaining the principle of light quantity correction. As shown in FIG. 7A, if the target light quantity corresponding to a certain gradation value Dk is Tk and the measured light quantity is Pk, the difference between Pk and Tk is represented by a light quantity error δk. The coefficients a and b are sequentially corrected so as to minimize the light quantity error δk, and the correction coefficients Da and Db of the pixel value are corrected according to the corrected coefficients a and b. This is the basic idea.

  In an ideal state, the pixel value correction coefficients Da and Db are set so that the measured light amount P and the target light amount T coincide. However, if the laser characteristics (threshold current Ith and differential efficiency η) shown in FIG. 6B change, an error occurs between the measured light quantity P and the target light quantity T as shown in FIGS. 7B to 7E. The correction coefficients Da and Db of the pixel value are corrected so as to eliminate this error. For example, FIGS. 7B and 7C show the case where the threshold current Ith changes and the coefficient b of the measured light quantity P changes. 7D and 7E show a case where the differential efficiency η is changed and the coefficient a of the measured light quantity P is changed. Since the coefficient a is a variable corresponding to the first correction coefficient Da and the coefficient b is a variable corresponding to the second correction coefficient Db as given by the above equations (1.12) and (1.13), FIG. It can be seen that the first correction coefficient Da is corrected in the cases (D) and (E), and the second correction coefficient Db is corrected in the cases shown in FIGS.

  The pixel value correction coefficients Da and Db are set by sequentially measuring an error δ (= P−T) between a target light amount T and a measured light amount P corresponding to a plurality of pixel values D, and minimizing the error δ. The calculation is performed by obtaining the coefficients a and b and determining the correction coefficients Da and Db of the pixel value based on the coefficients a and b. If the number of measurement of the error δ is small, inaccuracy due to measurement error occurs, so it is desirable to increase the number of measurements and improve the measurement accuracy sequentially. As a method for sequentially obtaining the coefficients a and b so as to minimize the error δ, various numerical optimization methods such as the steepest descent method and the conjugate gradient method can be used. In this embodiment, as will be described below, the steepest descent method is used to sequentially search for the coefficients a and b that minimize the square sum of the light amount error δ.

Here, when the procedure for setting the gradation value D and measuring the measurement light quantity P is repeated from the first to the k-th, the measurement light quantity for the gradation values {D1, D2,..., Di,. Is set to {P1, P,..., Pi,..., Pk}, and the target light quantity is set to {T1, T2,. The evaluation function ε _k is expressed as the sum of squares of the error δ as in the following equation, and coefficients a and b that minimize the evaluation function ε _k are sequentially obtained for the i-th measurement. When the steepest descent method is used in which slopes due to changes in the coefficients a and b are obtained and the coefficients a and b are corrected in the directions, the coefficients ak and bk corrected by the k-th measurement can be expressed by the following equations. . Note that μ _a and μ _b are coefficients.

Above (1.17), (1.18) where the partial differential term ∂ε _k / ∂a, the ∂ε _k / ∂ _b is expressed by the following equation.

Therefore, the following equation is derived from the equations (1.17) to (1.20).

Furthermore, when it deform | transforms so that it can calculate sequentially, following Formula is obtained.

When the coefficients a and b are sequentially calculated in this way, the correction coefficients Da and Db of the pixel value can be obtained according to the above equations (1.12) and (1.13) according to the coefficients a and b. Note that arbitrary values can be set as the initial values a ₀ and b ₀ of the coefficients a and b.

  If such sequential light quantity correction proceeds well, the coefficient a converges to the coefficient (target inclination) M in the target light quantity T equation T = M × D, and the coefficient b converges to zero. Therefore, the measured light quantity P is proportional to the pixel value D.

  FIG. 8 is a block diagram showing the function of the light amount correction circuit in the first embodiment. The control target 1400 represents the operations of the PWM signal generation circuit 1500, the laser driver 1020, the laser element 1030, and the light detection circuits 1090 to 1092. The function of the correction coefficient calculation circuit 1220 (FIG. 3) is represented by nine calculation blocks 1401 to 1409 in FIG. The computations of these computation blocks 1401 to 1409 are in accordance with the above formulas (1.15), (1.23) to (1.27) and (1.12) to (1.13).

FIG. 9 shows a configuration example when the operation blocks 1407 to 1409 for obtaining the second correction coefficient Db in FIG. 8 are realized by a specific circuit. In FIG. 9A, an error integration element 1407, a correction element 1408, and a variable conversion element 1409 are connected in series. FIG. 9B is a block diagram expressing these using delay elements 1410 and 1411 and a gain element. The delay element 1410 performs error accumulation, and the delay element 1411 sequentially corrects the parameter b. In order to simplify this block diagram, the above equation (1.26) is transformed into the following equation (1.28).

The expression (1.30) can be expressed in a block diagram as shown in FIG. 9C, and the output of the delay element 1410 is multiplied by μ _b / K by the gain element 1413 and sent to the delay element 1412. It can be understood that the operation is equivalent to.

Now, in order to realize the delay element with a flip-flop, it is preferable to prevent the operation from being lost. For this purpose, if an arithmetic unit for gain adjustment is inserted in each place and the delay elements are replaced by flip-flops 1414 and 1415, FIG. 9D is obtained. In order for FIG. 9C and FIG. 9D to perform an equivalent operation, each gain only needs to satisfy the relationship of the following equation.

FIG. 10 shows a configuration example when the operation blocks 1404 to 1406 for obtaining the first correction coefficient Da in FIG. 8 are realized by a specific circuit. In FIG. 10A, an error integration element 1404, a correction element 1405, and a variable conversion element 1406 are connected in series. FIG. 10B is a block diagram representing these operations using delay elements 1423 and 1421 and gain elements 1420 and 1422. Referring to this figure, even if two gain elements 1420 and 1422 are combined into one gain element 1424 as shown in FIG. 10 (c) and the output is sent to the delay element 1425, the operation between the input and output is as follows. You can see that it does n’t change. This corresponds to the transformation of the above equation (1.24) as follows.

Similarly to FIG. 9D, when a gain is appropriately inserted and the delay elements 1424 and 1425 are replaced with flip-flops 1427 and 1428, FIG. 10D is obtained. Here, the gain element 1426 is inserted for gain adjustment for circuit commonality. If each gain satisfies the following equation, FIG. 10 (c) and FIG. 10 (d) are equivalent operations.

  As described above, in the first embodiment, the coefficients a and b for minimizing the error δ related to the pixel value D with respect to the measured light amount P (P = a × D + b) and the target light amount T (T = M × D) are set. The light quantity is corrected by sequentially obtaining and correcting the pixel value D according to these coefficients a and b. As a result, it is possible to realize light amount correction so that a target light amount T proportional to the pixel value D can be obtained even if the characteristics of the light emitting element change.

  The light amount correction in the first embodiment is preferably performed periodically during the operation of the image display apparatus. The light amount correction can be executed at an arbitrary timing regardless of whether the image is being displayed. For example, the light amount correction may be performed during image display, or the light amount correction may be performed during the blanking period. When light amount correction is performed during image non-display (for example, during a blanking period), it is preferable to provide a mechanism for changing the angle of the half mirror 1035 (FIG. 1). Then, using this mechanism, the angle at which the laser beam is reflected toward the photoelectric conversion element 1090 is set only during execution of the light amount correction, and the angle at which the optical path of the laser beam is not obstructed when the light amount correction is not performed. It is preferable. In this way, it is possible to perform light amount correction without reducing the luminance during image display. In addition, when using the mechanism which changes the angle of a mirror in this way, you may use all the mirrors instead of a half mirror.

B. Second Embodiment (Light quantity correction by correcting the pixel value and the power supply voltage value of the drive circuit):
FIG. 11 is an explanatory diagram showing the internal configuration of the PWM signal generation circuit, the laser driver, and the light amount correction circuit in the second embodiment, and corresponds to FIG. 3 of the first embodiment. In the second embodiment, the light amount correction circuit 1200a corrects the pixel value D and corrects the power supply voltage Vlaser of the laser driver 1020, thereby realizing light amount correction. The correction coefficient calculation circuit 1220a calculates a correction coefficient Db for pixel values and a correction coefficient Dvlaser for power supply voltage. The latter is also referred to as “power supply voltage command value Dvlaser”. The pixel value correction circuit 1210a corrects the pixel value D according to the following equation in accordance with the pixel value correction coefficient Db.

  The power supply control circuit 1120 sets the power supply voltage Vlaser of the laser driver 1020 according to the correction coefficient Dvlaser for the power supply voltage. This correction coefficient Dvlaser is, for example, a digital value indicating the value of the power supply voltage Vlaser. The configurations of the PWM signal generation circuit 1500 and the laser driver 1020 are the same as those in the first embodiment.

FIG. 12 is a graph showing an example of a change in the amount of emitted light when the power supply voltage Vlaser is changed. When the power supply voltage Vlaser increases, the gradient f of the average light amount W per pixel increases, and the duty threshold Duty _th decreases.

平均光量Ｗの傾きｆ（図１２）は、以下で表される。

ここで、Ｋ_f，ｆ₀は定数である。 The relationship between the duty and the average light quantity W in the second embodiment is expressed by the following equation.

The gradient f (FIG. 12) of the average light quantity W is expressed as follows.

Here, K _f and f ₀ are constants.

  Note that the IV characteristic of the laser element is non-linear as shown in FIG. However, since the IV characteristic is almost linear in the vicinity of the drive current Im used in PWM modulation, the slope f of the average light quantity W is expressed by a linear function of the correction coefficient Dvlaser for the power supply voltage as described in (2.4) above. But there is no practical problem.

Similar to the expressions (1.4) and (1.5) in the first embodiment, the duty and the pixel value voltage Vd are expressed by the following expressions.

Similarly to the equations (1.6) to (1.8) in the first embodiment, the light receiving sensor signal Ipd, its voltage signal VL, and the measured light amount P are expressed by the following equations, respectively.

When the above equations (2.2) to (2.9) are used, the measured light quantity P is expressed by the following equation.

  As shown in the formula (2.10), also in the second embodiment, the measured light quantity P is written in the form of P = a × D + b. If the above equations (2.10) to (2.15) are compared with the equations (1.9) to (1.14) of the first embodiment, the correction coefficient Dvlaser for the power supply voltage is the first correction of the first embodiment. It can be understood that this corresponds to the coefficient Da. The second correction coefficient Db in the second embodiment and the second correction coefficient Db in the first embodiment are also in a correspondence relationship, but the specific contents are slightly different. In the second embodiment, if the pixel value is corrected according to the above formula (1.1) as in the first embodiment, the correction coefficient Da, Db for the pixel value and the correction coefficient Dvlaser for the power supply voltage are used. Therefore, these three variables Da, Db, Dlaser cannot be determined from the two coefficients a, b. Therefore, in the second embodiment, correction using only one correction coefficient Db is executed in the pixel value correction circuit 1210a (FIG. 11), and the correction coefficient Db and the correction value Dvlaser for the power supply voltage are expressed as coefficients a, It is devised so that it can be determined from b.

  Also in the second embodiment, as in the first embodiment, an error δ (δ = P−T) between the target light amount T (T = M × D) corresponding to a plurality of pixel values D and the measured light amount P is calculated. Measurement is performed to obtain coefficients a and b that minimize the error δ, and correction coefficients Dvlaser and Db are determined based on these coefficients a and b. In the steepest descent method for obtaining the coefficients a and b, the expressions (1.16) to (1.27) described in the first embodiment can be used as they are, so that the description is omitted here.

  FIG. 13 is a block diagram illustrating functions of the light amount correction circuit according to the second embodiment. The function of the correction coefficient calculation circuit 1220a (FIG. 11) is represented by nine arithmetic blocks 1401 to 1409a in FIG. The difference from FIG. 8 is only the calculation contents of the two calculation blocks 1406a and 1409a of the correction coefficient calculation circuit 1220a and the pixel value correction circuit 1210a. The operations of the operation blocks 1406a and 1409a correspond to the above equations (2.13) and (2.14).

ここでは、画素値用の補正係数Ｄｂが、係数ａに依存せず、係数ｂのみから算出されている。 FIG. 14 is an explanatory diagram showing details of the calculation blocks 1403 to 1409a of the correction coefficient calculation circuit 1220a, and corresponds to FIGS. 9 and 10 of the first embodiment. The operation blocks 1403 to 1409a in FIG. 14A are the same as those in FIG. When this is decomposed into unit operations and expressed, FIG. 14B is obtained. Here, since the arithmetic circuit for obtaining b _k / _ak is division, the circuit configuration is complicated. Therefore, the circuit may be changed as follows. If the control loop operates well, the coefficient a _k approaches the constant M in the target light quantity T equation T = M × D. Therefore, when the coefficient a _k is replaced with the constant M in the calculation block for obtaining the coefficient b _k in FIG. 14B, FIGS. 14C and 14D are obtained. By this approximation, the sequence for obtaining the coefficient a _k and the sequence for obtaining the coefficient b _k can be separated, so that the circuit configuration can be simplified as shown in FIG. In the circuit configurations of FIGS. 14C and 14D, it can be understood that the above equation (2.14) is replaced by the following equation (2.14a).

Here, the correction coefficient Db for the pixel value is calculated from only the coefficient b without depending on the coefficient a.

  As described above, in the second embodiment, the coefficients a and b for minimizing the error δ related to the pixel value D with respect to the measured light amount P (P = a × D + b) and the target light amount T (T = M × D). Are sequentially obtained, and the light quantity is corrected by correcting the pixel value D and the driving voltage Vlaser of the laser driver accordingly. As a result, it is possible to realize light amount correction so that a target light amount T proportional to the pixel value D can be obtained even if the characteristics of the light emitting element change. Note that the light amount correction in the second embodiment can be performed at an arbitrary timing regardless of whether an image is being displayed.

C. Third Embodiment (Light quantity correction by correcting bias current value and signal current value of drive circuit):
FIG. 15 is a diagram showing a circuit configuration of a laser driver 1020b used in the third embodiment. The laser driver 1020b includes two constant current circuits 1610 and 1620 and a switching circuit 1630. The first constant current circuit 1610 includes an operational amplifier 1612, a current generation transistor 1614, and a resistor 1616. Similarly, the second constant current circuit 1620 includes an operational amplifier 1622, a current generating transistor 1624, and a resistor 1626. The first constant current circuit 1610 is a circuit for constantly supplying a constant bias current Ibias to the laser element 1030. The second constant current circuit 1620 is a circuit for adding a constant signal current Isig during a period when the PWM signal Spwm is at the H level. The signal current Isig is also referred to as “light emission current Isig”.

  The switching circuit 1630 is a circuit that switches whether or not to allow the signal current Isig to flow through the laser element 1030 in accordance with the PWM signal Spwm. The switching circuit 1630 includes two switching transistors 1632 and 1634, an inverter 1636, and a resistor 1638. The resistor 1638 and the first switching transistor 1632 are connected in series, and these are inserted between the power supply Vlaser and the second constant current circuit 1620. The second switching transistor 1634 is interposed between the laser element 1030 and the second constant current circuit 1620. Here, PMOS transistors are used as the switching transistors 1632 and 1634. The PWM signal Spwm is supplied to the control terminal of the first switching transistor 1632 and is also supplied to the control terminal of the second switching transistor 1634 via the inverter 1636. During the period in which the PWM signal Spwm is at the H level, the first switching transistor 1632 is turned off and the second switching transistor 1634 is turned on. Therefore, a current obtained by adding the bias current Ibias and the signal current Isig flows through the laser element 1030. On the other hand, during the period when the PWM signal Spwm is at the L level, the first switching transistor 1632 is turned on and the second switching transistor 1634 is turned off. Accordingly, only the bias current Ibias flows through the laser element 1030. Note that the first switching transistor 1632 and the resistor 1638 may be omitted, and the signal current Isig may be on / off controlled using only the second switching transistor 1634.

  FIG. 16 is a timing chart showing the operation of the laser driver 1020b. A bias current Ibias always flows through the laser element 1030, and a current obtained by adding the bias current Ibias and the signal current Isig flows during a period in which the PWM signal Spwm is at the H level. Therefore, light emission starts immediately in response to the rise of the PWM signal Spwm.

  The value of the bias current Ibias is adjusted according to the bias command voltage Vapc1 input to the operational amplifier 1612 of the first constant current circuit 1610. The value of the signal current Isig is adjusted according to the signal current command voltage Vapc2 input to the operational amplifier 1622 of the second constant current circuit 1620. The constant current circuits 1610 and 1620 may be constant current circuits that can change the current values according to command values Vapc1 and Vapc2 given from the outside, and have various circuit configurations other than those shown in FIG. It can be adopted.

  FIG. 17 is a block diagram illustrating an internal configuration of the light source device according to the third embodiment. The light source device 1700R is a circuit portion corresponding to the light source device 1100R for red light in FIG. The parts other than the light source device are the same as those in FIG. The light source device 1700R includes a PWM signal generation circuit 1500, a laser driver 1020b, a red laser element 1030, a photoelectric conversion element 1090, an I / V converter 1091, an A / D converter 1092, and a light amount correction. Circuit 1200b. The light amount correction circuit 1200b includes a correction coefficient calculation circuit 1220b and a pseudo pixel value application circuit 1230. The pseudo pixel value application circuit 1230 includes a pseudo pixel value generation circuit 1232, a constant multiplication circuit (gain element) 1234, a multiplication circuit 1236, and a selection circuit 1238. The light source device 1700R further includes an adjustment fixed pixel value register 1710, a selection circuit 1720, and two D / A converters 1770 and 1780. In this light source device 1700R, two correction coefficients Dapc1 and Dapc2 are adjusted by light amount correction, these are DA-converted, and supplied to the laser driver 1020b as a bias command voltage Vapc1 and a signal current command voltage Vapc2. Details of the operation of these circuits will be described later. The correction coefficients Dapc1 and Dapc2 are also referred to as “voltage command values Dapc1 and Dapc2”.

  FIG. 18 is a graph showing the relationship between the duty and the average light quantity W when the laser driver 1020b of FIG. 15 is used. In the third embodiment, the graph of the average light amount W with respect to the duty of the PWM signal shows a characteristic with almost no offset. The condition that the offset becomes zero is that the bias current Ibias matches the threshold current Ith (FIG. 6B). Further, the slope f of the graph of FIG. 18 changes depending on the signal current Isig. As will be described in detail later, in the third embodiment, in order to adjust the bias current Ibias and the signal current Isig, the duty of the PWM signal is fixed during the blanking period of the screen drawing, and the pseudo pixel value Dq ( The light quantity correction is executed using (to be described later).

ここで、Ｈ１，Ｈ２は定数である。 FIG. 19 is a graph showing the relationship between the laser drive current I and the average light amount W when the duty of the PWM signal is fixed to a constant value (for example, 50%). The duty and the laser drive current I are expressed by the following equations, respectively.

Here, H1 and H2 are constants.

ここで、Ｆは定数であり、dlyはIsigとIbiasに依存する係数である。係数dlyについては後述する。 The average light quantity W is given by the following equation (the derivation of the equation will be described later).

Here, F is a constant, and dly is a coefficient depending on Isig and Ibias. The coefficient dly will be described later.

この(3.6)式は、バイアス電流Ｉbiasと閾値電流Ｉthの関係に応じて、以下のようにそれぞれ変形できる。 This equation (3.5) is obtained as follows. First, when the instantaneous value of the laser light quantity is represented by w (t), the average light quantity W per pixel is given by the following equation.

Equation (3.6) can be modified as follows according to the relationship between the bias current Ibias and the threshold current Ith.

(3.7)式は、上述した(3.5a)式と同じものである。なお、図２０から理解できるように、遅れ時間tdは信号電流Ｉsigとバイアス電流Ｉbiasに依存する。そこで、(3.9)式では、係数dlyがこれらのパラメータＩsig，Ｉbiasに依存することを示している。 (1) When Ibias <Ith FIG. 20 is a timing chart showing a state of light emission when Ibias <Ith. At this time, the laser emission rises slightly later than the rise of the signal current Isig. Let this delay time be td. When this light emission waveform is approximated by a rectangle, the above equation (3.6) can be modified as follows.

Equation (3.7) is the same as Equation (3.5a) described above. As can be understood from FIG. 20, the delay time td depends on the signal current Isig and the bias current Ibias. Therefore, equation (3.9) shows that the coefficient dly depends on these parameters Isig and Ibias.

ここで、τsはキャリア寿命（数ns）である。 By the way, the delay time td is expressed by the following equation from the laser rate equation.

Here, τs is the carrier lifetime (several ns).

従って、バイアス電流Ｉbiasが閾値電流Ｉthに等しい場合には、１画素当たりの平均光量Ｗはデューティに比例して変化する（図１８参照）。 FIG. 21 is a graph with Ibias / Ith on the horizontal axis and td / τs on the vertical axis. As can be understood from this graph, when the bias current Ibias coincides with the threshold current Ith, the delay time td becomes zero, so the coefficient dly in the above equation (3.9) also becomes zero. As a result, equation (3.7) can be rewritten as

Therefore, when the bias current Ibias is equal to the threshold current Ith, the average amount of light W per pixel changes in proportion to the duty (see FIG. 18).

(3.12)式は、上述した(3.5b)式と同じものである。 (2) When Ibias> Ith FIG. 22 is a timing chart showing the state of light emission when Ibias> Ith. In this case, even when the PWM signal Spwm is at the L level, the laser beam is emitted with a light amount corresponding to the difference between the bias current and the threshold current (Ibias−Ith). When the light emission waveform at the pulse width Pwm_Width is approximated by a rectangle, the above equation (3.6) can be modified as follows.

The formula (3.12) is the same as the formula (3.5b) described above.

ここで、Ｋpd，Ｒ，Ｇad，Ｇdaは変換係数である。 In the circuit shown in FIG. 17, the light receiving sensor signal Ipd, its voltage signal VL, the measured light quantity P, and the adjustment values Vapc1 and Vapc2 for the laser driver are expressed by the following equations, respectively.

Here, Kpd, R, Gad, and Gda are conversion coefficients.

なお、係数Ｋは係数Ｆ１に依存しており、この係数Ｆ１は(3.8)式または(3.13)式に示すようにデューティに依存している。また、係数Ｆ２も、(3.13)式に示すようにデューティに依存している。 Using the above formulas (3.2) to (3.5) and formulas (3.14) to (3.18), the measured light quantity P is expressed by the following formula.

The coefficient K depends on the coefficient F1, and this coefficient F1 depends on the duty as shown in the equation (3.8) or (3.13). The coefficient F2 also depends on the duty as shown in equation (3.13).

  As in the first and second embodiments, the measured light quantity P at the time of correcting the light quantity is preferably expressed as P = a × D + b, which is a form of a linear function of the pixel value D. However, the above formula (3.19) is not in the form of P = a × D + b. More specifically, since the coefficient K and the coefficients F1 and F2 included in the expression (3, 19) depend on the duty, and the duty is proportional to the pixel value D, the measurement light quantity P given by the expression (3.19) is The linear function of the pixel value D cannot be expressed. Therefore, in the third embodiment, at the time of light amount correction, the pixel value D is fixed and the duty is fixed to a predetermined constant value (for example, 50%). Instead, a pseudo pixel value Dq described below is used. Thus, the measurement light quantity P is devised so as to be expressed in the form of P = a × Dq + b.

ここで、Ｄｍは規格化定数であり、例えばＤｍ＝２５５である。 First, in order to introduce the pseudo pixel value Dq into the expression (3.19), as shown in the following expression, the second correction coefficient Dapc2 is changed to a correction coefficient Dapc2 # (hereinafter referred to as “pseudo correction coefficient”) proportional to the pseudo pixel value Dq. It is called “Dapc2 #”.

Here, Dm is a normalization constant, for example, Dm = 255.

When the correction coefficient Dapc2 in the expression (3.19) is replaced with the right side of the expression (3.21), and the coefficients K, F1, and F2 for the fixed duty value are described as K _m , F1 _m , and F2 _m , the following expression is obtained.

  In the above equation (3, 22), the measured light quantity P is represented by a linear function of the pseudo pixel value Dq. Therefore, an error δ (δ = P−T) between the target light amount T (T = M × Dq) corresponding to the plurality of pseudo pixel values Dq and the measured light amount P (P = a × Dq + b) is measured. If the coefficients a and b that minimize the error δ are obtained, the correction coefficients Dapc1 and Dapc2 can be determined based on these coefficients a and b. In the steepest descent method for obtaining the coefficients a and b, the expressions (1.16) to (1.27) described in the first embodiment can be used as they are, so that the description is omitted here.

  FIG. 23 is a block diagram illustrating functions of a light amount correction circuit according to the third embodiment. The function of the correction coefficient calculation circuit 1220b (FIG. 17) is represented by nine calculation blocks 1401 to 1409b in FIG. The operations of the operation blocks 1406a and 1409a correspond to the above equations (3.25) and (3.26). FIG. 23 further illustrates the constant multiplication circuit (gain element) 1234 and the multiplication circuit 1236 shown in FIG. The operations in these circuits 1334 and 1236 correspond to the above equation (3.21). In addition, although the pseudo pixel value Dq is used as the pixel value D in the blocks 1401 to 1404, the symbol D is used here for convenience of illustration.

  In the light source device 1700R shown in FIG. 17, the adjustment fixed pixel value register 1710 stores a fixed pixel value Dconst used at the time of light amount correction. The selection circuit 1720 selects one of the fixed pixel value Dconst and the pixel value D corresponding to the video signal according to the blanking period signal and supplies it to the PWM signal generation circuit 1500. That is, the selection circuit 1720 selects the fixed pixel value Dconst during the blanking period, and selects the pixel value D corresponding to the video signal during the image drawing period. The fixed pixel value Dconst is a value corresponding to a fixed duty value (for example, 50%) assumed at the time of light quantity correction.

  The pseudo pixel value generation circuit 1232 is a circuit that sequentially generates a plurality of different pseudo pixel values Dq during light amount correction. As shown in FIG. 23, the correction coefficient calculation circuit 1220b sequentially calculates two correction coefficients Dapc1 and Dapc2 based on the pseudo pixel value Dq and the measured light quantity P. These correction coefficients Dapc1 and Dapc2 are digital values (voltage command values) respectively indicating the values of the bias command voltage Vapc1 and the signal current command voltage Vapc2 in FIG. The multiplication circuits 1234 and 1236 in FIG. 17 calculate the pseudo correction coefficient Dapc2 # according to the above equation (3.21) based on the pseudo pixel value Dq, the constant Dm, and the second correction coefficient Dapc2. The selection circuit 1238 selects the pseudo correction coefficient Dapc2 # and supplies it to the D / A converter 1770 during the blanking period. The two D / A conversion circuits 1770 and 1780 convert the correction coefficients Dapc1 and Dapc2 into the bias command voltage Vapc1 and the signal current command voltage Vapc2, respectively, and supply them to the laser driver 1020b.

  The correction coefficient Dapc2 # in the above equation (3, 21) indicates the value of the signal current command value Vapc2 in FIG. Therefore, changing the value of the pseudo pixel value Dq means changing the value of the signal current Isig. That is, in the third embodiment, the light amount P is measured while changing the signal current Isig according to the pseudo pixel value Dq. The signal current Isig is a current for causing the laser element 1030 to emit light according to the pixel value D. Therefore, it can be understood that, similarly to the pixel value D, the pseudo pixel value Dq functions as a gradation value indicating the light amount of the laser element 1030.

By the way, when the correction proceeds well so that the measured light amount P (P = a × Dq + b) matches the target light amount T (T = M × Dq), the coefficient a becomes equal to the constant M and the coefficient b converges to zero. . At this time, the following is derived from the above equation (3.24).

  Thus, if the correction converges well, the bias current Ibias of the first constant current circuit 1610 (FIG. 15) becomes equal to the threshold current Ith of the laser element 1030. Therefore, as shown in FIG. 18, desirable characteristics are obtained in which there is no offset and the average light amount W is proportional to the duty. Since the duty is proportional to the pixel value D, the average light quantity W is proportional to the pixel value D.

  FIG. 24 is a timing chart showing how the light amount is corrected in the third embodiment. Here, only changes in the bias current Ibias and the signal current Isig are shown. A period in which “image display is in progress” (a period in which the signal current Isig is constant) means a period in which an actual image is displayed. In addition, a period described as “in adjustment” (a period in which the signal current Isig is changing) means a period in which light amount correction is performed. As can be understood from this figure, when the light amount correction proceeds, the value of the bias current Ibias converges so as to coincide with the value of the threshold current Ith. Further, it can be understood that the light amount correction converges in a very short time (about 0.03 seconds).

  Thus, in the third embodiment, the pseudo pixel value Dq is introduced, and the measured light quantity P is expressed in the form of a linear function P = a × Dq + b of the pseudo pixel value Dq. Then, coefficients a and b that minimize the error δ between the measured light quantity P and the target light quantity T (T = M × Dq) are sequentially obtained, and correction coefficients Dapc1 and Dapc2 are determined according to these coefficients a and b. The amount of light is corrected by correcting. As a result, it is possible to realize light amount correction so that a target light amount T proportional to the pixel value D can be obtained even if the characteristics of the light emitting element change.

  In the first and second embodiments, the target light amount P is expressed as a linear function of the pixel value D, whereas in the third embodiment, a pseudo pixel value Dq of 1 different from the pixel value D is used. It differs in that it is expressed as a next function. However, both the pixel value D and the pseudo pixel value Dq are common in that they are gradation values indicating the amount of light. In the present specification, the “gradation value” is used as a term encompassing both the pixel value D and the pseudo pixel value Dq.

  By the way, in the first embodiment, only the pixel value is corrected, in the second embodiment, the pixel value and the setting value (power supply voltage) of the driving circuit (laser driver) are corrected, and in the third embodiment, the setting of the driving circuit is performed. The values (bias current and signal current) were corrected. As can be understood from these embodiments, the light amount correction can be realized by adjusting at least one of the pixel value and the setting value of the driving circuit.

D. Fourth embodiment (light amount correction when a light source having a wavelength conversion element is used):
FIG. 25 is a block diagram showing the configuration of an image display apparatus according to the fourth embodiment of the present invention. This image display device includes light source devices 1100R, 1100G. The internal configuration of 1100B is different from the apparatus of FIG. 1 only in the following points, and other configurations are the same as those of the first embodiment. That is, in the apparatus of FIG. 25, a characteristic correction circuit 1099 is added between the I / V converter 1091 and the A / D converter 1092. As will be described below, the circuit configuration of the fourth embodiment is a configuration that can be adopted when the light source unit configured by the laser driver 1020 and the laser element 1030 has nonlinear characteristics.

  FIG. 26A shows characteristics of the light source unit in the fourth embodiment. Here, a characteristic G1 in which the average light amount W emitted from the laser element 1030 is nonlinear with respect to the duty is shown. Such a non-linear characteristic G1 is a characteristic that can occur, for example, when the transient response of the drive current of the laser element 1030 is considerably slow with respect to the rise of the PWM pulse. That is, in this case, particularly in a range where the duty is small, the relationship between the increase in the average light quantity W with respect to the increase in duty deviates from the straight line, and a phenomenon that exhibits nonlinear characteristics may occur. The characteristic correction circuit 1099 in FIG. 25 is a circuit that performs nonlinear conversion for converting the nonlinear characteristic G1 in FIG. 26A to the linear characteristic G2 in FIG. That is, the converted light amount Wc obtained by this nonlinear conversion has a linear relationship with the duty. In the circuit of FIG. 25, the characteristic correction circuit 1099 performs non-linear conversion on the input voltage signal VL and outputs the converted signal VLi to the A / D converter 1092. This conversion signal VLi is a signal indicating the converted light amount Wc in FIG.

  In the fourth embodiment, the converted light quantity Wc thus obtained is used as the measured light quantity P, and the light quantity correction is executed so that the measured light quantity P matches the target light quantity T. For this light amount correction, the same method as that described in the first embodiment can be applied. That is, the expressions (1.1) to (1.35) described in the first embodiment can be applied as they are in the fourth embodiment. However, in the fourth embodiment, as the pixel value D input to the light amount correction circuit 1200 (FIG. 3), the original pixel value Dorg is converted back to the non-linear conversion of FIG. 26 (conversion from the non-linear characteristic G2 to the linear characteristic G1). ) Is preferably used. Here, the “original pixel value Dorg” is a value obtained by performing inverse gamma correction on the video signal, and corresponds to the pixel value D in the first embodiment. This inverse conversion operation is executed, for example, by the video signal processing circuit 1010 (FIG. 1). At this time, if the light amount correction is executed so that the target light amount T related to the converted light amount Wc is proportional to the pixel value D input to the light amount correction circuit 1200, the actually measured average light amount W is proportional to the original pixel value Dorg. Linear characteristics can be obtained.

  As described above, also in the fourth embodiment, similarly to the first embodiment, the measurement light quantity P (P = a × D + b) and the coefficients a and b for minimizing the error δ of the target light quantity T are sequentially obtained. The light quantity can be corrected accordingly. As a result, it is possible to realize light amount correction so that a target light amount T proportional to the pixel value D can be obtained even if the characteristics of the light emitting element change.

  It should be noted that the circuit configuration of the fourth embodiment and the calculation of nonlinear conversion can be similarly applied to the second and third embodiments.

E. Variation:
The present invention is not limited to the above-described embodiments and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

E1. Modification 1:
In the above embodiment, the laser scan display that scans the laser beam on the screen 200 and displays an image has been described as an example. However, the present invention is not limited to light generated from other light source units such as LEDs (Light Emitting Diodes). The present invention can also be applied to an image display device that displays an image by scanning. In the above embodiment, a laser scan display using one scanner (laser beam scanning unit 1050) for three color laser light sources has been described as an example. However, a scanner may be provided for each color.

E2. Modification 2:
In the above embodiment, the light quantity measurement unit (half mirror 1035, photoelectric conversion element 1090, I / V converter 1091, and A / D converter 1092) and the light quantity correction unit (light quantity correction circuit 1200) are provided for each color light. However, instead of this, only one set of the light quantity measurement unit and the light quantity correction unit may be provided on the rear side of the light beam synthesis unit 1040. In this case, the light quantity measurement unit and the light quantity correction unit can be operated in a time-sharing manner to perform correction for each color light.

1 is a configuration block diagram of an image display device as a first embodiment. It is a timing chart which shows the operation timing of an image display device. It is explanatory drawing which shows the internal structure of the PWM signal generation circuit in 1st Embodiment, a laser driver, and a light quantity correction circuit. It is a timing chart which shows the mode of the laser drive using a PWM signal. It is explanatory drawing which shows the relationship between the PWM signal window assumed in the PWM modulation of embodiment, and an actual PWM signal. It is a graph which shows an example of the relationship between a duty and the average light quantity per pixel, and the characteristic of a laser element. It is explanatory drawing explaining the principle of light quantity correction of 1st Embodiment. It is a block diagram which shows the function of the light quantity correction circuit in 1st Embodiment. It is a block diagram which shows the detail of the calculation block which calculates | requires the 2nd correction coefficient Db. It is explanatory drawing which shows the detail of the calculation block which calculates | requires the 1st correction coefficient Da. It is explanatory drawing which shows the internal structure of the PWM signal generation circuit in 2nd Embodiment, a laser driver, and a light quantity correction circuit. It is a graph which shows an example of the change of the emitted light amount at the time of changing the power supply voltage Vlaser. It is a block diagram which shows the function of the light quantity correction circuit in 2nd Embodiment. It is explanatory drawing which shows the detail of the calculation block of the correction coefficient calculation circuit in 2nd Embodiment. It is a figure which shows the circuit structure of the laser driver used in 3rd Embodiment. It is a timing chart which shows operation | movement of the laser driver in 3rd Embodiment. It is a block diagram which shows the internal structure of the light source device in 3rd Embodiment. It is a graph which shows the relationship between the duty and average light quantity W in 3rd Embodiment. It is a graph which shows the relationship between the laser drive current I and the average light quantity W when the duty of a PWM signal is fixed to a fixed value. It is a timing chart which shows the mode of light emission when bias current Ibias is smaller than threshold current Ith. It is a graph which shows the relationship between Ibias / Ith and td / τs. It is a timing chart which shows the mode of light emission in the case of Ibias> Ith. It is a block diagram which shows the function of the light quantity correction circuit in 3rd Embodiment. It is a timing chart which shows the mode of light quantity correction in a 3rd embodiment. It is a structure block diagram of the image display apparatus as 4th Embodiment. It is explanatory drawing which shows the relationship between the average light quantity in 4th Embodiment, and a conversion light quantity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 200 ... Screen 1010 ... Video signal processing circuit 1020 ... Laser driver 1022 ... Resistance 1024 ... Drive transistor 1030 ... Laser element 1035 ... Half mirror 1040 ... Light beam synthesis optical system 1050 ... Laser beam scanning part 1060 ... Scanning drive part 1070 ... Timing signal generation Circuit 1070a ... Optical sensor 1080 ... Pixel synchronous clock generation circuit 1090 ... Photoelectric conversion element 1091 ... I / V converter 1092 ... A / D converter 1099 ... Characteristic correction circuit (nonlinear conversion circuit)
1100R, 1100G, 1100B ... light source device 1120 ... power supply control circuit 1200 ... light quantity correction circuit 1210 ... pixel value correction circuit 1220 ... correction coefficient calculation circuit 1230 ... pseudo pixel value application circuit 1232 ... pseudo pixel value generation circuit 1234 ... multiplication circuit 1236 ... Multiplier circuit 1238... Select circuit 1400. Capacitor 1530 ... Comparator 1540 ... Voltage generation circuit 1610 ... First constant current circuit 1612 ... Operational amplifier 1614 ... Transistor 1616 ... Resistance 1620 ... Second constant current circuit 1 22 ... operational amplifier 1624 ... transistors 1626 ... resistor 1630 ... switching circuit 1632,1634 ... switching transistor 1636 ... inverter 1638 ... resistance 1700R ... light source apparatus 1710 ... adjustment fixed pixel value register 1720 ... selection circuit 1770,1780 ... D / A conversion circuit

Claims (10)

A light source device,
A light source unit including a light source element;
A PWM signal generator that generates a PWM signal according to the pixel value;
A drive circuit for driving the light source element according to the PWM signal;
A light amount measuring unit for measuring the light amount of the light source unit;
A light amount correction unit that corrects the light amount of the light source unit based on the light amount measured by the light amount measurement unit;
With
When the measured light amount P is expressed as P = a × D + b (D is a gradation value, a and b are coefficients), and the target light amount T is expressed as T = M × D (M is a constant),
The light amount correction unit
An error δ between the target light amount T and the measured light amount P in a plurality of times of light amount measurement using different gradation values D is sequentially obtained, and the coefficients a and b are sequentially corrected so as to minimize the error δ. With
A light source device that corrects the light amount of the light source unit by adjusting at least one of the pixel value and a setting value of the drive circuit based on the corrected coefficients a and b. The light source device according to claim 1,
The light amount correction unit
A light source device that sequentially corrects the coefficient a using the accumulated value ΣδD of the product of the error δ and the gradation value D, and sequentially corrects the coefficient b using the accumulated value Σδ of the error δ. . The light source device according to claim 2,
The light amount correction unit
The current value a _k of the coefficient a is obtained by subtracting a value proportional to the accumulated value ΣδD of the product of the error δ and the gradation value D from the previous value a _{k−1 of the} coefficient a. ,
A light source device that obtains a current value b _k of the coefficient b by subtracting a value proportional to an accumulated value Σδ of the error δ from a previous value b _{k−1 of the} coefficient b. The light source device according to any one of claims 1 to 3,
The light amount correction unit
A correction coefficient calculation unit that calculates first and second correction coefficients for correcting the pixel value according to the coefficients a and b;
Pixel value correction that receives the pixel value as the gradation value D, corrects the pixel value according to the first and second correction coefficients, and supplies the corrected pixel value to the PWM signal generation unit And
A light source device comprising: The light source device according to any one of claims 1 to 3,
The light amount correction unit
A first correction coefficient for adjusting the power supply voltage of the drive circuit is calculated according to the coefficient a, and a second correction coefficient for correcting the pixel value is calculated according to the coefficient b A coefficient calculation unit;
A power supply voltage adjusting unit that adjusts the power supply voltage of the drive circuit according to the first correction coefficient;
A pixel value correction unit that receives the pixel value as the gradation value D, corrects the pixel value according to the second correction coefficient, and supplies the corrected pixel value to the PWM signal generation unit;
A light source device comprising: The light source device according to any one of claims 1 to 3,
The drive circuit is
A first constant current circuit for constantly flowing a first current to the light source element;
A second constant current circuit for flowing a second current to the light source element in addition to the first current;
A switching circuit that performs on / off control of the flow of the second current to the light source element according to the PWM signal;
With
The light amount correction unit
A signal value indicating the value of the second current is used as the gradation value;
The value of the first current of the first constant current circuit is adjusted according to the coefficient b, and the value of the second current of the second constant current circuit is adjusted according to the coefficient a. , Light source device. The light source device according to claim 6,
The light source device, wherein the correction unit adjusts the value of the first current so that the first current becomes equal to a threshold current of the light source element. The light source device according to any one of claims 1 to 7,
The light source unit has a nonlinear characteristic in which a relationship between the pixel value and the light amount is nonlinear,
The light quantity measuring unit is
An optical sensor for measuring the amount of light emitted from the light source unit;
A converted light quantity calculation unit that calculates a converted light quantity by performing nonlinear conversion that converts the nonlinear characteristic into a linear characteristic with respect to the light quantity measured by the optical sensor, and calculates the converted light quantity as the measured light quantity P;
A light source device comprising: An image display device that displays light by scanning light on a projection surface,
A light source device according to any one of claims 1 to 8,
A scanning unit that scans light generated from the light source device onto the projection surface;
A video signal processing unit that generates the pixel value based on a video signal supplied from the outside and outputs the pixel value corresponding to the irradiation position of the light on the projection surface to the PWM signal generation unit; ,
An image display device comprising: A light amount correction method used in a light source device that drives a light source element based on a PWM signal generated according to a pixel value,
(A) measuring a light amount of a light source unit including the light source element;
(B) correcting the light amount of the light source unit based on the measured light amount;
With
When the measured light amount P is expressed as P = a × D + b (D is a gradation value, a and b are coefficients), and the target light amount T is expressed as T = M × D (M is a constant),
The step (b)
An error δ between the target light amount T and the measured light amount P in a plurality of times of light amount measurement using different gradation values D is sequentially obtained, and the coefficients a and b are sequentially corrected so as to minimize the error δ. Process,
Correcting the light amount of the light source unit by adjusting at least one of the pixel value and a setting value of the drive circuit based on the corrected coefficients a and b;
A method for correcting the amount of light.

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