JP6769154B2 - Head-up display - Google Patents

Description

The present invention relates to a method of driving a transmissive display device and a light emitting device.

As a transmissive display device, Patent Document 1 discloses a head-up display device (hereinafter referred to as a HUD device). This HUD device projects the display image of the liquid crystal display unit onto the windshield by the light from the light emitting device (backlight), and superimposes the virtual image of the display image and the landscape seen through the transparent plate.

Japanese Unexamined Patent Publication No. 2013-228442

The HUD device disclosed in Patent Document 1 transmits the light emitted from the light emitting device to the liquid crystal display unit, then projects the light onto the windshield of the vehicle, and finally allows the virtual image to be visually recognized through the windshield. In this configuration, assuming that the light emitted from the light emitting device is 100, the light transmitted through the liquid crystal display unit is attenuated to 6 to 7, and the light reaching the driver as a virtual image is attenuated to 1 to 2. Therefore, if the display brightness of the virtual image is desired to be 10,000 to 15,000 candelas, the light emitting device must emit as much as 1 million candelas of light. Therefore, the current flowing through the light emitting device becomes large, and a large amount of electric power is required.

On the other hand, the HUD device is generally configured so that the brightness of the virtual image to be displayed can be adjusted according to the driver's preference and the like. The conventional HUD device can adjust the emission intensity and the display brightness of a virtual image by controlling the power supplied to the light emitting device by PWM (Pulse Width Modulation) according to the operation of the driver. ..

However, when the driver sets the display brightness of the virtual image to high brightness, there is a problem that the radiation noise becomes large because the large current is repeatedly turned on / off.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for driving a transmissive display device and a light emitting device, which have a large display luminance but a small radiation noise.

In order to achieve the above object, the head-up display according to the first aspect of the present invention is
A light emitting part that emits light when a drive current flows,
A control unit that causes the drive current to flow through the light emitting unit and emits light by PWM control.
A head-up display including a display unit that displays an image and is illuminated by light from the light emitting unit, and allows a virtual image of the light emitted by the display unit to be visually recognized.
When a display brightness larger than the reference brightness is set, the control unit fixes the duty ratio of the drive current flowing through the light emitting unit to 100%, and increases or decreases the drive current according to the display brightness, thereby causing the light emitting unit. When the display brightness is set to be less than the reference brightness, the emission intensity of the light emitting unit is controlled by increasing or decreasing the duty ratio of the drive current according to the set display brightness .
The control unit includes a control means and a drive means.
The control means obtains the current value and the duty ratio of the drive current flowing through the light emitting unit according to the display brightness, and obtains a first PWM signal indicating the obtained current value and a second PWM signal indicating the obtained duty ratio. And output,
The control unit includes smoothing means for smoothing the first PWM signal.
The drive means uses the drive current obtained by switching the current of the value indicated by the first PWM signal smoothed by the smoothing means at the duty ratio indicated by the second PWM signal as the light emitting unit. Supply to.

For example, when the display brightness lower than the reference brightness is set, the control unit fixes the current value of the drive current to the reference current value.

The control unit may change the current value represented by the first PWM signal or the duty ratio indicated by the second PWM signal non-linearly with respect to the display brightness in consideration of the γ characteristic of the display unit. ..

The transmissive display device of the present invention has a duty ratio of 100% and does not switch current when the display luminance is larger than the reference luminance. Therefore, the radiation noise can be suppressed to a small value.

It is a schematic diagram of the vehicle equipped with the HUD device which concerns on one Embodiment of this invention. It is the schematic which shows the structure of the HUD apparatus which concerns on one Embodiment of this invention. It is a simplified circuit diagram which shows the structure of the control part which concerns on one Embodiment of this invention. An example of the display brightness-drive current table of the HUD device according to the embodiment of the present invention is shown, (a) the relationship between the display brightness of the virtual image and the current value of the drive current flowing through the light emitting unit, and (b) the display of the virtual image. It is a figure which shows the relationship between the luminance and the duty ratio of a drive current. It is a timing chart which shows the waveform example of the drive current according to the display luminance-drive current table shown in FIG. It is a flowchart of the light emission intensity control process executed by the CPU shown in FIG.

A method of driving the transmissive display device and the light emitting device according to the present invention will be described with reference to the drawings with reference to an embodiment embodied in a vehicle head-up display.

As shown in FIG. 1, the head-up display device (HUD device) 1 according to the present embodiment is installed on the dashboard of the vehicle 2, generates a display light L representing a display image, and generates the generated display light L. It emits light toward the windshield 3. The display light L reaches the viewer 4 (mainly the driver of the vehicle 2) after being reflected by the windshield 3. As a result, the viewer 4 can visually recognize the virtual image V of the image formed in front of the windshield 3. The image includes, for example, information about the vehicle 2 (eg, engine speed, navigation information, etc.).

As shown in FIG. 2, the HUD device 1 includes a control unit 100, a light emitting unit 20, a liquid crystal display unit 30, a reflecting mirror 41, a reflecting mirror 42, a housing 50, and a translucent unit 51. Be prepared.

The housing 50 is formed in a box shape by a light-shielding material. Each configuration of the HUD device 1 such as the control unit 100 and the light emitting unit 20 is housed in the housing 50. The housing 50 is formed with an opening 50a through which the display light L passes.

The translucent portion 51 is made of a translucent resin such as acrylic, and is provided so as to close the opening 50a of the housing 50. The light transmitting portion 51 is formed in, for example, a curved shape in order to prevent the reached external light from being reflected toward the viewer 4.

The control unit 100 has an image display control function and a backlight power supply function, and is communicably connected to the vehicle-mounted LAN (Local Area Network) 70. The control unit 100 receives the image data of the display image via the vehicle-mounted LAN 70, supplies a display control signal for displaying the image defined by the image data to the liquid crystal display unit 30, and controls the liquid crystal display unit 30. And drive. Further, the control unit 100 mounts display brightness information indicating the brightness of the display image of the HUD device 1 set by the viewer 4 or the like (hereinafter, simply referred to as display brightness), that is, the display brightness Ls of the recognized virtual image. The drive current received via the LAN 70 and passed through the light emitting unit 20 is PWM-controlled to control the brightness of the light emitting unit 20, that is, the light emitting intensity.

The light emitting unit 20 is composed of a light emitting device, and emits light with a brightness controlled by the control unit 100. The light emitting unit 20 emits the emitted light BL toward the liquid crystal display unit 30 as illumination light BL. In other words, the light emitting unit 20 functions as a backlight and illuminates the liquid crystal display unit 30 from behind.

The liquid crystal display unit 30 is composed of, for example, a transmissive TFT display panel or the like, and displays an image defined by image data according to a display control signal supplied from the control unit 100. When the illumination light BL passes through the liquid crystal display unit 30, it is modulated by the display image to become the display light L.

The reflecting mirror 41 reflects the display light L from the liquid crystal display unit 30 toward the reflecting mirror 42. The reflecting mirror 42 reflects the display light L from the reflecting mirror 41 toward the windshield 3. The display light L reaches the windshield 3 after passing through the translucent portion 51. As a result, the virtual image V to be imaged is magnified more than the image displayed on the liquid crystal display unit 30.

Next, the internal structures of the control unit 100 and the light emitting unit 20 will be described with reference to FIG.

The light emitting unit 20 includes an LED (Light Emitting Diode) 21. A drive current ID is passed through the LED 21 from the control unit 100. The drive current ID is a current signal controlled by PWM (Pulse Width Modulation) by the control unit 100. By PWM controlling the drive current ID, the emission intensity of the LED 21 changes.

The control unit 100 includes a microcontroller (hereinafter referred to as a microcomputer) 110 and an LED driver IC (Integrated Circuit) 120, and displays the display of the liquid crystal display unit 30 and the current value of the drive current ID flowing through the LED 21 of the light emitting unit 20. And the duty ratio, and control.

The microcomputer 110 includes a CPU (Central Processing Unit) 111, a ROM (Read Only Memory) 112, and a RAM (Random Access Memory) 113.

The CPU 111 controls the LED driver IC 120 and the liquid crystal display unit 30 by executing a control program stored in the ROM 112. Further, the CPU 111 is communicably connected to the control unit of the vehicle body via the vehicle-mounted LAN 70.

The ROM 112 stores a control program executed by the CPU 111. The control program includes an operation control program for controlling the liquid crystal display unit 30 based on the image data, and an operation control program for controlling the LED driver IC 120 to control the drive current ID flowing through the LED 21. The ROM 112 also stores a display luminance-drive current table showing the relationship between the display luminance Ls, the value of the drive current ID flowing through the LED 21, and the duty ratio thereof. Details of the display luminance-drive current table will be described later with reference to FIG. The RAM 113 functions as a work memory of the CPU 111.

The microcomputer 110 having such a configuration receives image data defining an image to be displayed from an operation unit (not shown) via the vehicle-mounted LAN 70. The microcomputer 110 generates a display control signal of the liquid crystal display unit 30 from the image data and transmits it to the liquid crystal display unit 30.

Further, the microcomputer 110 receives, for example, display luminance information indicating the display luminance of the virtual image V set by the driver by operating the operation unit from the vehicle-mounted LAN 70.

The microcomputer 110 obtains the current value of the drive current ID to be passed through the LED 21 in order to obtain the display luminance Ls indicated by the display luminance information, generates a PWM1 signal having a duty ratio corresponding to this current value, and outputs the PWM1 signal to the LED driver IC 120. To do.

Further, the microcomputer 110 obtains the duty ratio of the drive current ID to be passed through the LED 21 in order to obtain the display luminance Ls indicated by the display luminance information, generates a PWM2 signal having this duty ratio, and outputs the PWM2 signal to the LED driver IC 120.

Here, the operation of the control unit 100 to obtain the current value of the drive current ID to be passed through the light emitting unit 20 and its duty ratio will be described with reference to FIG.

The ROM 112 contains information that defines a correspondence relationship (a) between the display luminance Ls of the virtual image V and the current value of the drive current ID flowing through the LED 21, and a correspondence relationship (b) between the display luminance Ls and the duty ratio of the drive current ID. However, for example, it is stored in advance in the form of a table.

As shown in FIG. 4A, when the display brightness Ls is equal to or less than the reference brightness Lc, the current value of the drive current ID is fixed to the reference current value Ic, and when the display brightness Ls is larger than the reference brightness Lc, the drive current ID The current value of is set to increase from the reference current value Ic to the maximum current value Im as the display brightness Ls increases.

Further, as shown in FIG. 4B, when the display luminance Ls is smaller than the reference luminance Lc, the duty ratio of the drive current ID increases as the display luminance Ls increases, and becomes 100% at the reference luminance Lc. Further, when the display luminance Ls is larger than the reference luminance Lc, the duty ratio of the drive current ID is fixed at 100%.

Assuming that the display luminance Ls gradually increases from the minimum luminance to the maximum luminance Lm according to the setting of the display luminance-drive current table shown in FIG. 4, (1) the display luminance Ls is as schematically shown in FIG. Until the reference brightness Lc is reached, the current value is fixed at the reference current value Ic and the duty ratio gradually increases. (2) When the display brightness Ls becomes larger than the reference brightness Lc, the duty ratio is fixed at 100%. , The drive current ID becomes a continuous current, and the current value gradually increases from the reference current value Ic to the maximum current value Im.

Similarly, assuming that the display brightness Ls is gradually reduced from the maximum brightness Lm to the minimum brightness, (1) the duty ratio is fixed at 100% and the drive current ID is continuous while the display brightness Ls is larger than the reference brightness Lc. It becomes a current, and the current value gradually decreases from the maximum current value Im to the reference current value Ic. (2) When the display brightness Ls becomes the reference brightness Lc or less, the current value is fixed to the reference current value Ic and the current is switched. Then, the duty ratio gradually decreases.

In this driving method, when the display luminance Ls is larger than the reference luminance Lc, the duty ratio is 100%, so that the driving current ID is not switched and the driving current ID flows continuously. Therefore, the electromagnetic noise generated by switching the current is not generated. However, the current value of the drive current ID increases or decreases according to the increase or decrease of the display luminance Ls. Therefore, the emission intensity of the LED 21 changes.

On the other hand, when the display luminance is smaller than the reference luminance Lc, the current value of the drive current ID is fixed to the reference current value Ic, but the duty ratio increases or decreases as the display luminance Ls increases or decreases. Therefore, the emission intensity of the LED 21 is substantially changed. In addition, switching of the drive current ID occurs, and electromagnetic noise is generated. However, since the current value is relatively small, the generated electromagnetic noise is small and can be sufficiently absorbed by an electromagnetic shield or the like. Further, although it is difficult to accurately control the current value of a small current, in this setting, the current value is fixed to the reference current value Ic and the drive current ID is controlled by controlling the duty ratio, so that the control can be performed. It's easy. The reference current value Ic is set to the current value that causes the LED 21 to emit light.

The microcomputer 110 shown in FIG. 3 receives the display luminance information via the vehicle-mounted LAN 70, applies the display luminance Ls indicated by the received display luminance information to the display luminance-drive current table shown in FIG. 4, and applies the current of the drive current ID. Find the value and duty ratio.

The microcomputer 110 generates a PWM1 signal having a duty ratio corresponding to the obtained current value, and outputs the PWM1 signal to the LED driver IC 120. The PWM1 signal is smoothed by the smoothing circuit shown by the capacitor 131 and supplied to the LED driver IC 120. As a result, abrupt fluctuations in the drive current ID are suppressed, and the generation of electromagnetic noise is suppressed.

Further, the microcomputer 110 generates a PWM2 signal having the obtained duty ratio and outputs the PWM2 signal to the LED driver IC 120.

The LED driver IC 120 is connected to the battery 60 and the anode and cathode of the LED 21, boosts the voltage of the battery 60, generates a drive current ID based on the boosted voltage, and controls the current flowing through the LED 21 by PWM control. It is an element. The LED driver IC 120 includes peripheral elements such as capacitors 132, reactors 141, and 142 for smoothing current, absorbing energy generated by switching, and the like. The illustrated peripheral circuit is an example.

The LED driver IC 120 receives the PWM1 signal smoothed by the capacitor 131, and controls the drive current ID of the current value represented by the voltage to flow. Further, the LED driver IC 120 receives the PWM2 signal and switches the drive current ID in synchronization with this signal. Therefore, if the duty ratio of the PWM2 signal is N%, the duty ratio of the drive current ID is also N%.

Next, the operation of the HUD device 1 will be described with reference to FIGS. 1 to 6.

When the HUD device 1 starts operation, the CPU 111 starts executing the program of the emission intensity control process shown in FIG. 6 stored in the ROM 112.
When the emission intensity control process is started, the CPU 111 reads the set display luminance information via the vehicle-mounted LAN 70 and stores it in the RAM 113 (step S10).

Next, the CPU 111 applies the display luminance Ls indicated by the display luminance information to the display luminance-drive current table stored in the ROM 112, and reads out the current value of the drive current ID to be passed through the LED 21 (step S20).

The CPU 111 further reads the duty ratio corresponding to the display luminance Ls from the display luminance-drive current table (step S30).

Next, the CPU 111 starts outputting a PWM1 signal having a duty ratio corresponding to the current value specified in step S20 and outputting a PWM2 signal having a duty ratio specified in step S30 (step S40), and emits light this time. The strength control process is terminated.

The PWM1 signal output from the microcomputer 110 is smoothed by the capacitor 131 and supplied to the LED driver IC 120, and the PWM2 signal is supplied to the LED driver IC 120 as it is.

The LED driver IC 120 sends a drive current ID to the LED 21 by switching a current having a current value determined by the voltage of the smoothed PWM1 signal according to the PWM2 signal.

This drive current ID is controlled based on the display luminance-drive current table shown in FIG. 4, and when the display luminance Ls is larger than the reference luminance Lc, the duty ratio is 100% and the current value changes. Is controlled by. When the display luminance Ls is equal to or less than the reference luminance Lc, the current value is the reference current value Ic and the duty ratio is controlled to change. Therefore, when the display luminance Ls is larger than the reference luminance Lc, the driving current ID is not switched and electromagnetic noise is not generated. On the other hand, when the display luminance Ls is equal to or lower than the reference luminance Lc, the drive current ID is switched, but since the current value of the switched current is as small as the reference current value Ic, only a small electromagnetic noise is generated.

When the drive current ID flows, the LED 21 emits light, and the light emitting unit 20 emits the illumination light BL toward the liquid crystal display unit 30.

The CPU 111 acquires image data via the vehicle-mounted LAN 70, generates a display control signal for displaying the image defined by the image data, and supplies the display control signal to the liquid crystal display unit 30. The liquid crystal display unit 30 displays an image defined by image data according to a display control signal.

The illumination light BL emitted from the light emitting unit 20 is modulated into the display light L having the strength and color corresponding to the displayed image while passing through the liquid crystal display unit 30, and is sequentially reflected by the reflecting mirrors 41 and 42. Then, the windshield 3 is irradiated through the translucent portion 51.
As a result, the virtual image V is recognized by the viewer 4.

The CPU 111 executes the light emission intensity control process shown in FIG. 6 in synchronization with a relatively long cycle, for example, the vertical synchronization period of the liquid crystal display unit 30, and adjusts the light emission intensity of the LED 21 of the light emitting unit 20.

Here, it is assumed that the viewer 4 or the like operates the operation unit to set a new display luminance Ls. After that, when the CPU 111 executes the emission intensity control process, the CPU 111 takes in the newly set display luminance Ls via the vehicle-mounted LAN 70 and stores it in the RAM 113 (step S10).

Next, the CPU 111 applies the display luminance Ls to the display luminance-drive current table, and reads out the current value and the duty ratio of the drive current ID flowing through the LED 21 (steps S20 and S30).

Next, the CPU 111 starts outputting a PWM1 signal having a duty ratio corresponding to the specified current value and outputting a PWM2 signal having the specified duty ratio (step S40). The LED driver IC 120 PWM-controls the drive current ID to be passed through the LED 21 by switching the current ID having a current value determined by the voltage of the PWM1 signal smoothed by the capacitor 131 according to the PWM2 signal.

As a result, the emission intensity of the LED 21 changes, and a virtual image V having a desired display brightness Ls is displayed.

As described above, according to the HUD device 1 according to the embodiment of the present invention, when the emission intensity of the LED 21 is high, the duty ratio of the drive current ID flowing through the LED 21 is fixed at 100%. Therefore, the drive current ID is not interrupted. Therefore, radiation noise is not generated due to switching, and radiation noise can be suppressed.

(Modification example)
The invention of the present application is not limited to the above embodiment, and can be appropriately modified.

For example, in the above embodiment, when the display luminance Ls is equal to or less than the reference luminance Lc, electromagnetic noise is generated due to the switching of the drive current ID. In order to prevent the leakage of the electromagnetic noise, the non-light emitting surface of the light emitting unit 20 may be covered with an electromagnetic shield, and the electromagnetic shield may be arranged on a part or all of the inner surface and the outer surface of the housing 50. Further, the housing 50 may be composed of a conductor.

In the above embodiment, the control unit 100 is composed of the microcomputer 110 and the LED driver IC 120, but may be composed of one IC. Further, two or more ICs may be configured by arbitrary division of roles.

In the above embodiment, information is transmitted from the microcomputer 110 to the LED driver IC 120 by the duty ratio of the PWM1 signal and the PWM2 signal. This is effective for reducing the number of IC terminals. However, the present invention is not limited to this, and for example, the current value and the duty ratio may be transmitted by an analog signal (for example, a voltage signal), or may be transmitted by serial digital data or parallel digital data.

In the above embodiment, as shown in FIG. 4, in the range where the display luminance Ls is equal to or less than the reference luminance Lc, the current value is fixed, the duty ratio changes linearly, and the display luminance Ls is larger than the reference luminance Lc. An example is shown in which the duty ratio is fixed at 100% and the current value changes linearly. The present invention is not limited to this. How to set the current value or the duty ratio with respect to the display luminance Ls is arbitrary. For example, at least one of the current value and the duty ratio may be changed non-linearly with respect to the display luminance Ls in consideration of the γ characteristic of the entire HUD device 1 or the liquid crystal display unit 30.

Further, in the above embodiment, the current value of the drive current ID is fixed to the reference current value Ic in the range where the display luminance Ls is equal to or less than the reference luminance Lc, but the current value may be changed. For example, as the display luminance Ls becomes smaller, both the current value and the duty ratio may be gradually reduced.

Further, in the above embodiment, the lowest current value when the viewer 4 or the like sets the display brightness of the virtual image V to a value larger than the reference brightness Lc is set as the reference current value Ic, but the reference current value Ic is set to another value. It may be a current value.

In the above embodiment, the display luminance-drive current characteristic is stored in the ROM 112 in the form of a table, but the present invention is not limited to this. The method is arbitrary as long as the drive current ID corresponding to the display luminance can be obtained. For example, the display luminance-drive current characteristic may be stored in the ROM 112 in the form of a function of current value = f1 (Ls) and duty ratio = f2 (Ls). In this case, in step S20, the CPU 111 may apply the display luminance Ls to the function f1 (Ls) to obtain the current value, and in step S30, apply the display luminance Ls to the function f2 (Ls) to obtain the duty ratio. .. Further, an arithmetic expression for obtaining the current value and the duty ratio may be incorporated in the program.

In the above embodiment, the display brightness Ls is set by the viewer 4 or the like by operating the operation unit, but the present invention is not limited to this, and other users may set the display brightness Ls. Further, an illuminance sensor for acquiring the external light intensity is installed in the HUD device 1 or the vehicle 2, and the display brightness Ls is set by the signal from the illuminance sensor, or the display control program sets the display brightness. May be good.

In the above embodiment, the liquid crystal display unit 30 is illustrated as an image display element through which the illumination light BL passes, but any display panel can be used as long as an arbitrary image can be displayed and the illumination light BL can pass through. Further, the display device is not limited to the transmissive type and may be a reflective type display device.

In the above embodiment, an example is shown in which the emission intensity control process is executed in each vertical synchronization period of the liquid crystal display unit 30. Assuming that the display of the liquid crystal display unit 30 is 30 frames / second, the light emission intensity of the light emitting unit 20 is changed approximately every 33 ms. The present invention is not limited to this, and for example, the light emission driving process may be executed every 50 ms to 500 ms. In the embodiment, the light emitting intensity is controlled by the light emitting unit 20 which is substantially a backlight, and it is desirable that the light emitting unit is updated in a period of one display frame or more.

In the above embodiment, the control mode is switched depending on whether the display luminance Ls is equal to or less than the reference luminance Lc or larger than the reference luminance Lc, but is controlled depending on whether the display luminance Ls is less than the reference luminance Lc or greater than or equal to the reference luminance Lc. The mode may be switched.

In the above embodiment, the transmissive display device according to the present invention is applied to the in-vehicle HUD device 1, but it may be applied not only to the in-vehicle HUD device but also to the HUD device mounted on a vehicle such as an airplane or a ship. Further, although the display light L from the HUD device 1 is projected on the windshield 3, it may be projected on the combiner. Further, the display device according to the present invention may be applied to a display device such as a projector used indoors or outdoors instead of the HUD device.

1 ... HUD device 2 ... Vehicle 3 ... Windshield 4 ... Viewer 20 ... Light emitting unit (light emitting device)
21 ... LED
30 ... Liquid crystal display 41 ... Reflector 42 ... Reflector 50 ... Housing 50a ... Opening 51 ... Translucent 60 ... Battery 70 ... In-vehicle LAN
100 ... Control unit 110 ... Microcontroller 111 ... CPU
112 ... ROM
113 ... RAM
120 ... LED driver IC
131 ... Capacitor 132 ... Capacitor 141 ... Reactor 142 ... Reactor

Claims (3)

A light emitting part that emits light when a drive current flows,
A control unit that emits light by passing a drive current through the light emitting unit and controlling PWM (Pulse Width Modulation).
A head-up display including a display unit that displays an image and is illuminated by the light from the light emitting unit, and visually recognizes a virtual image of the light emitted by the display unit.
When a display brightness larger than the reference brightness is set, the control unit fixes the duty ratio of the drive current flowing through the light emitting unit to 100%, and increases or decreases the drive current according to the display brightness, thereby causing the light emitting unit. When the display brightness is set to be less than the reference brightness, the emission intensity of the light emitting unit is controlled by increasing or decreasing the duty ratio of the drive current according to the set display brightness .
The control unit includes a control means and a drive means.
The control means obtains the current value and the duty ratio of the drive current flowing through the light emitting unit according to the display brightness, and obtains a first PWM signal indicating the obtained current value and a second PWM signal indicating the obtained duty ratio. And output,
The control unit includes smoothing means for smoothing the first PWM signal.
The drive means uses the drive current obtained by switching the current of the value indicated by the first PWM signal smoothed by the smoothing means at the duty ratio indicated by the second PWM signal as the light emitting unit. Supply to
A head-up display that features that. When the display luminance less than the reference luminance is set, the control unit fixes the current value of the drive current to the reference current value.
The head-up display according to claim 1. The control unit changes the current value represented by the first PWM signal or the duty ratio indicated by the second PWM signal non-linearly with respect to the display brightness in consideration of the γ characteristic of the display unit.
The head-up display according to claim 1 or 2, wherein the head-up display is characterized in that.

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