JP7565333B2 - Semiconductor laser driver - Google Patents

Description

This technology relates to a semiconductor laser driving device. More specifically, it relates to a semiconductor laser driving device that includes a substrate with a built-in laser driver and a semiconductor laser.

Conventionally, electronic devices with distance measurement functions often use a distance measurement method called ToF (Time of Flight). In ToF, a light emitting unit irradiates an object with sine wave or rectangular wave light, a light receiving unit receives the reflected light from the object, and a distance measurement calculation unit measures the distance from the phase difference between the irradiated light and the reflected light. To achieve such distance measurement functions, optical modules are known that house a light emitting element and an electronic semiconductor chip that drives the light emitting element in a case and integrate them. For example, an optical module has been proposed that includes a laser diode array aligned and mounted on an electrode pattern of a substrate, and a driver IC electrically connected to the laser diode array (see, for example, Patent Document 1).

JP 2009-170675 A

The above-mentioned conventional technology employs a structure that encourages heat generation by constructing a cover that covers the entire component, including the electronic elements, from a thermally conductive material. However, this conventional technology has the problem that even if there is a bias in the distribution of heat, the entire component is treated evenly, resulting in reduced heat generation efficiency.

This technology was developed in light of these circumstances, and its purpose is to arrange components taking into account the heat distribution of the laser driver that drives the semiconductor laser.

The present technology has been made to solve the above-mentioned problems, and a first aspect of the technology is a semiconductor laser driving device that includes a semiconductor laser and a laser driver that is arranged so that at least a portion of the semiconductor laser overlaps with the semiconductor laser, and the heat generating portion of the laser driver and the semiconductor laser are arranged without overlapping. This has the effect of suppressing the effect of the heat generated from the heat generating portion of the laser driver on the semiconductor laser.

In addition, in this first aspect, it is desirable that the distance between the heat generating portion of the laser driver and the semiconductor laser is 1 mm or less. This has the effect of suppressing the effect of the parasitic inductor on the waveform of the light.

In addition, in the first aspect, the laser driver may be built into a substrate on which the semiconductor laser is mounted. This provides the effect of reducing the height of the semiconductor laser driving device.

In addition, in this first aspect, the heat generating portion may be assumed to be a circuit that drives the semiconductor laser. In addition, in this first aspect, the semiconductor laser may include a plurality of laser diodes, and the heat generating portion may be a plurality of transistors that drive corresponding laser diodes among the plurality of laser diodes.

In addition, in this first aspect, the heat generating portion may be disposed at one predetermined location of the laser driver, or may be distributed at a plurality of predetermined locations of the laser driver. Also, the heat generating portion may be disposed in a predetermined shape around the semiconductor laser.

1 is a diagram showing an example of a top view of a semiconductor laser driving device 10 according to an embodiment of the present technology; 1 is a diagram showing an example of a cross-sectional view of a semiconductor laser driving device 10 according to an embodiment of the present technology; 2 is a diagram showing an example of a circuit configuration of a laser driver 200 according to an embodiment of the present technology. 2 is a diagram showing an example of a circuit configuration of a drive unit 210 according to the embodiment of the present technology. FIG. 2 is a diagram showing a first example of an arrangement of a laser driver 200 and a semiconductor laser 300 according to an embodiment of the present technology. FIG. 11 is a diagram showing a second example of an arrangement of the laser driver 200 and the semiconductor laser 300 according to the embodiment of the present technology. FIG. 11 is a diagram showing a third example of an arrangement of the laser driver 200 and the semiconductor laser 300 according to the embodiment of the present technology. FIG. 11 is a diagram showing a fourth example of an arrangement of the laser driver 200 and the semiconductor laser 300 according to the embodiment of the present technology. FIG. 11 is a diagram showing a fifth example of an arrangement of a laser driver 200 and a semiconductor laser 300 according to an embodiment of the present technology. FIG. FIG. 8 is a diagram showing an example of a system configuration of an electronic device 800 which is an application example of an embodiment of the present technology. 8 is a diagram showing an example of the external configuration of an electronic device 800 which is an application example of an embodiment of the present technology.

Hereinafter, modes for carrying out the present technology (hereinafter, referred to as embodiments) will be described in the following order.
1. Embodiment 2. Application Example

1. Preferred embodiment
[Semiconductor laser driving device]
FIG. 1 is a diagram showing an example of a top view of a semiconductor laser driving device 10 according to an embodiment of the present technology.

This semiconductor laser driving device 10 is designed to measure distances using ToF. ToF has the advantage that it has high depth accuracy, although not as high as structured light, and can operate without problems even in dark environments. In addition, it is thought to have many advantages over other methods such as structured light and stereo cameras in terms of simplicity of device configuration and cost.

In this semiconductor laser driving device 10, a semiconductor laser 300, a photodiode 400, and a passive component 500 are electrically connected by wire bonding and mounted on the surface of a substrate 100 that incorporates a laser driver 200. The substrate 100 is assumed to be a printed wiring board.

The semiconductor laser 300 is a semiconductor device that emits laser light by passing a current through a PN junction of a compound semiconductor. This semiconductor laser 300 is composed of multiple laser diodes. Here, examples of compound semiconductors that can be used include aluminum gallium arsenide (AlGaAs), indium gallium arsenide phosphide (InGaAsP), aluminum gallium indium phosphide (AlGaInP), and gallium nitride (GaN).

The laser driver 200 is a driver integrated circuit (IC) for driving the semiconductor laser 300. In this example, the laser driver 200 is built into the substrate 100 in a face-up state.

The photodiode 400 is a diode for detecting light. This photodiode 400 is used for automatic power control (APC) to monitor the light intensity of the semiconductor laser 300 and maintain the output of the semiconductor laser 300 constant.

The passive components 500 are circuit components other than active elements such as capacitors and resistors. The passive components 500 include a decoupling capacitor for driving the semiconductor laser 300.

Figure 2 is a diagram showing an example of a cross-sectional view of a semiconductor laser driving device 10 in an embodiment of the present technology.

As described above, the substrate 100 in this example incorporates the laser driver 200, and the semiconductor laser 300 and other components are mounted on its surface. The semiconductor laser 300 and the laser driver 200 are arranged so that at least a portion of them overlap, and the connection between them is made via a connection via 101. By using this connection via 101, it is possible to shorten the wiring length.

The board 100 also includes thermal vias 102 for heat dissipation. Each component mounted on the board 100 is a heat source, and by using the thermal vias 102, it is possible to dissipate the heat generated in each component from the back surface of the board 100.

The semiconductor laser 300, the photodiode 400, and the passive components 500 mounted on the surface of the substrate 100 are surrounded by a sidewall 600. The material of the sidewall 600 may be, for example, a plastic material or a metal.

The upper surface surrounded by the sidewall 600 is covered by a diffusion plate 700. This diffusion plate 700 is an optical element for diffusing the laser light from the semiconductor laser 300, and is also called a diffuser.

[Laser driver]
FIG. 3 is a diagram showing an example of a circuit configuration of the laser driver 200 according to the embodiment of the present technology.

This laser driver 200 includes a driving unit 210, a pulse data receiving unit 220, an operation mode register 230, a temperature sensor 240, an abnormality detection unit 250, a switch 260, an AD converter 270, a power supply control unit 280, and a constant current generating circuit 290.

The driving unit 210 is a circuit for driving the semiconductor laser 300. As described below, the driving unit 210 is connected to each of the multiple laser diodes of the semiconductor laser 300 and includes multiple transistors that drive the corresponding laser diodes. If the current is increased to light the semiconductor laser 300 brightly, more heat will be generated. Therefore, the driving unit 210 is the main source of heat in the laser driver 200.

The pulse data receiving unit 220 receives pulse data supplied from the outside. This pulse data is a signal that repeatedly turns on and off to cause the semiconductor laser 300 to emit light in the driving unit 210. The pulse data receiving unit 220 receives this pulse data as a differential signal, for example, according to the LVDS (Low Voltage Differential Signaling) standard, converts it into a non-differential signal, and supplies it to the driving unit 210.

The operation mode register 230 is a register for setting the operation mode of the drive unit 210. This operation mode register 230 receives a communication clock, communication data, and a chip enable signal from the outside via an interface such as the SPI (Serial Peripheral Interface) standard, and holds the operation mode.

The temperature sensor 240 is a sensor that detects the temperature inside the laser driver 200. When the temperature detected by the temperature sensor 240 exceeds a predetermined temperature, the emission of the semiconductor laser 300 is stopped by the control described below.

The abnormality detection unit 250 is connected to the photodiode 400 and monitors the light intensity of the semiconductor laser 300 to maintain the output of the semiconductor laser 300 constant and detect the occurrence of an abnormality. For example, when it is detected that the diffusion plate 700 is cracked, the emission of the semiconductor laser 300 is stopped by the control described below.

Switch 260 is a switch that selects signals from the temperature sensor 240 and the photodiode 400 and switches them to the AD converter 270.

The AD converter (Analog-to-Digital Converter) 270 converts analog signals from the temperature sensor 240 and the like, supplied via the switch 260, into digital signals. The converted digital signals are supplied to the power supply control unit 280.

The power supply control unit 280 performs automatic power supply control of the power supply for driving the semiconductor laser 300. This power supply control unit 280 is supplied with signals from the temperature sensor 240 and the photodiode 400, and an abnormality detection signal from the abnormality detection unit 250, and performs power supply control according to the situation.

The constant current generating circuit 290 is a circuit that generates a current set by the power supply control unit 280. This constant current generating circuit 290 is composed of, for example, a DA converter (Digital-to-Analog Converter). The drive unit 210 operates using the current supplied from this constant current generating circuit 290.

Figure 4 shows an example of a circuit configuration of the drive unit 210 in an embodiment of the present technology.

As described above, the semiconductor laser 300 is composed of multiple laser diodes 301, and the driving unit 210 includes a transistor 211 corresponding to each of the laser diodes. In this example, the transistor 211 is assumed to be an nMOS transistor.

A voltage of 3 to 4 V is applied to the laser diode 301, and a pulse signal from the constant current generating circuit 290 is input as a gate signal for the transistor 211 to control the on/off state of the laser diode 301, thereby causing it to emit light.

As described above, the driving unit 210 is composed of transistors 211 corresponding to the laser diodes 301, and therefore can be distributed and arranged in the laser driver 200. However, depending on the wiring distance, it may become necessary to adjust the delay.

[Circuit Layout]
As described above, the driving section 210 is the main heat source in the laser driver 200. In the following, the driving section 210 will be focused on as a heat generating section, and the relative positional relationship between the heat generating section and the semiconductor laser 300 will be described.

As a thermal countermeasure against the heat generation portion, it is desirable that the heat generation portion and the semiconductor laser 300 do not overlap at the very least. In other words, if the heat generation portion and the semiconductor laser 300 are arranged so as to overlap, the heat from the heat generation portion will directly interfere with the semiconductor laser 300, and there is a risk that the light emission efficiency of the semiconductor laser 300 will decrease. Therefore, when the laser driver 200 and the semiconductor laser 300 are arranged so as to overlap, it is desirable to arrange them so that the heat generation portion does not overlap the semiconductor laser 300.

On the other hand, if the distance between the driving unit 210 and the semiconductor laser 300 is greater than 1 mm, the parasitic inductance due to the wiring will increase, which may distort the light waveform and prevent sharp light rise and fall. Therefore, from the perspective of parasitic inductance, it is desirable to set the distance between the heat generating unit and the semiconductor laser 300 to 1 mm.

Therefore, taking into account both heat generation and parasitic inductance, it is desirable for the distance between the heat generating portion and the semiconductor laser 300 to be within the range of 0 to 1 millimeter.

Figure 5 is a diagram showing a first example of an arrangement of a laser driver 200 and a semiconductor laser 300 in an embodiment of the present technology.

In this first example, the driving unit 210, i.e., the heat generating unit 201, is placed in one location on the laser driver 200. In this case, the distance between the heat generating unit 201 and the semiconductor laser 300 is set to 0 to 1 mm. This allows both heat generation and parasitic inductance conditions to be met.

Figure 6 is a diagram showing a second example of an arrangement of a laser driver 200 and a semiconductor laser 300 in an embodiment of the present technology.

In this second example, the driving unit 210, i.e., the heat generating units 202 and 203, are distributed and placed on both sides of the laser driver 200 in two places. The driving unit 210 is composed of the transistor 211 corresponding to the laser diode 301 as described above, so it is possible to place it in a distributed manner. In this case, the distance between the heat generating units 202 and 203 and the semiconductor laser 300 is 0 to 1 mm in both cases. This makes it possible to achieve both heat generation and parasitic inductance conditions.

Figure 7 is a diagram showing a third example of an arrangement of a laser driver 200 and a semiconductor laser 300 in an embodiment of the present technology.

In this third example, the driving section 210 of the laser driver 200, i.e., the heat generating section 204, is arranged in an L-shape on two sides around the semiconductor laser 300. As described above, the driving section 210 is composed of a transistor 211 corresponding to the laser diode 301, and therefore can be arranged in any shape. In this case, the distance between the heat generating section 204 and the semiconductor laser 300 is 0 to 1 mm on each side. This makes it possible to achieve both heat generation and parasitic inductance conditions.

Figure 8 is a diagram showing a fourth example of an arrangement of a laser driver 200 and a semiconductor laser 300 in an embodiment of the present technology.

In this fourth example, the driving section 210 of the laser driver 200, i.e., the heat generating section 205, is arranged in a U-shape around the three sides of the semiconductor laser 300. As described above, the driving section 210 is composed of the transistor 211 corresponding to the laser diode 301, and therefore can be arranged in any shape. In this case, the distance between the heat generating section 205 and the semiconductor laser 300 is 0 to 1 mm on each side. This makes it possible to achieve both heat generation and parasitic inductance conditions.

Figure 9 is a diagram showing a fifth example of an arrangement of a laser driver 200 and a semiconductor laser 300 in an embodiment of the present technology.

In this fifth example, the driving section 210 of the laser driver 200, i.e., the heat generating section 206, is arranged in a square shape around the four sides of the semiconductor laser 300. As described above, the driving section 210 is composed of the transistor 211 corresponding to the laser diode 301, and therefore can be arranged in any shape. In this case, the distance between the heat generating section 206 and the semiconductor laser 300 is 0 to 1 mm on each side. This makes it possible to achieve both heat generation and parasitic inductance conditions.

Thus, according to the embodiment of the present technology, by arranging the driving unit 210 of the laser driver 200 and the semiconductor laser 300 so that they do not overlap, it is possible to suppress the effect of heat generation in the driving unit 210 on the semiconductor laser 300. Also, by arranging the distance between the driving unit 210 of the laser driver 200 and the semiconductor laser 300 to be 0 to 1 mm, it is possible to suppress the effect of parasitic inductance on the waveform of light.

2. Application Examples
[Electronic devices]
FIG. 10 is a diagram showing an example of a system configuration of an electronic device 800 which is an application example of the embodiment of the present technology.

The electronic device 800 is a mobile terminal equipped with the semiconductor laser driving device 10 according to the above-described embodiment. The electronic device 800 includes an imaging unit 810, a semiconductor laser driving device 820, a shutter button 830, a power button 840, a control unit 850, a memory unit 860, a wireless communication unit 870, a display unit 880, and a battery 890.

The imaging unit 810 is an image sensor that captures an image of a subject. The semiconductor laser driving device 820 is the semiconductor laser driving device 10 according to the embodiment described above.

The shutter button 830 is a button for instructing the timing of imaging in the imaging unit 810 from outside the electronic device 800. The power button 840 is a button for instructing the power of the electronic device 800 to be turned on and off from outside the electronic device 800.

The control unit 850 is a processing unit responsible for the overall control of the electronic device 800. The storage unit 860 is a memory that stores data and programs necessary for the operation of the electronic device 800. The wireless communication unit 870 performs wireless communication with the outside of the electronic device 800. The display unit 880 is a display that displays images, etc. The battery 890 is a power supply source that supplies power to each part of the electronic device 800.

Taking a specific phase (e.g., rising timing) of the light emission control signal that controls the imaging unit 810 and semiconductor laser driving device 820 as 0 degrees, the amount of light received from 0 degrees to 180 degrees is detected as Q1, and the amount of light received from 180 degrees to 360 degrees is detected as Q2. The imaging unit 810 also detects the amount of light received from 90 degrees to 270 degrees as Q3, and the amount of light received from 270 degrees to 90 degrees as Q4. The control unit 850 calculates the distance d from the object from these amounts of light received Q1 to Q4 using the following formula, and displays it on the display unit 880.

d=(c/4πf)×arctan {(Q3-Q4)/(Q1-Q2)}

In the above formula, the unit of distance d is, for example, meters (m). c is the speed of light, and its unit is, for example, meters per second (m/s). arctan is the inverse function of the tangent function. The value of "(Q3-Q4)/(Q1-Q2)" indicates the phase difference between the incident light and the reflected light. π indicates the ratio of the circumference of a circle to its diameter. Furthermore, f is the frequency of the incident light, and its unit is, for example, megahertz (MHz).

Figure 11 is a diagram showing an example of the external configuration of an electronic device 800 which is an application example of an embodiment of the present technology.

This electronic device 800 is housed in a housing 801, has a power button 840 on the side, and has a display unit 880 and a shutter button 830 on the front. In addition, an imaging unit 810 and an optical area for a semiconductor laser driving device 820 are provided on the back.

As a result, the display unit 880 can not only display a normal captured image 881, but also a depth image 882 corresponding to the distance measurement results using ToF.

In this application example, a mobile terminal such as a smartphone is used as an example of the electronic device 800, but the electronic device 800 is not limited to this and may be, for example, a digital camera, a game console, or a wearable device.

Note that the above-described embodiment shows an example for realizing the present technology, and there is a corresponding relationship between the matters in the embodiment and the matters specifying the invention in the claims. Similarly, there is a corresponding relationship between the matters specifying the invention in the claims and the matters in the embodiment of the present technology having the same name. However, the present technology is not limited to the embodiment, and can be realized by making various modifications to the embodiment without departing from the gist of the technology.

Note that the effects described in this specification are merely examples and are not limiting, and other effects may also exist.

The present technology can also be configured as follows.
(1) a semiconductor laser;
a laser driver disposed so as to overlap at least a portion of the semiconductor laser;
A semiconductor laser driving device in which a heat generating portion of the laser driver and the semiconductor laser are arranged so as not to overlap each other.
(2) The semiconductor laser driving device according to (1), wherein the distance between the heat generating portion of the laser driver and the semiconductor laser is 1 mm or less.
(3) The semiconductor laser driving device according to (1) or (2), wherein the laser driver is built into a substrate on which the semiconductor laser is mounted.
(4) The semiconductor laser driving device according to any one of (1) to (3), wherein the heat generating portion is a circuit that drives the semiconductor laser.
(5) The semiconductor laser includes a plurality of laser diodes;
The semiconductor laser driving device according to any one of (1) to (4), wherein the heat generating portion is a plurality of transistors for driving corresponding ones of the plurality of laser diodes.
(6) The semiconductor laser driving device according to any one of (1) to (5), wherein the heat generating portion is disposed at one predetermined location of the laser driver.
(7) The semiconductor laser driving device according to any one of (1) to (5), wherein the heat generating portion is disposed in a plurality of predetermined locations of the laser driver.
(8) The semiconductor laser driving device according to any one of (1) to (7), wherein the heat generating portion is arranged in a predetermined shape around the semiconductor laser.

10 Semiconductor laser driving device 100 Substrate 101 Connection via 102 Thermal via 200 Laser driver 201 to 206 Heat generating portion 210 Driving portion 211 Transistor (nMOS transistor)
220 Pulse data receiving unit 230 Operation mode register 240 Temperature sensor 250 Abnormality detection unit 260 Switch 270 AD converter 280 Power supply control unit 290 Constant current generating circuit 300 Semiconductor laser 301 Laser diode 400 Photodiode 500 Passive component 600 Side wall 700 Diffusion plate 800 Electronic device 801 Housing 810 Imaging unit 820 Semiconductor laser driving device 830 Shutter button 840 Power button 850 Control unit 860 Storage unit 870 Wireless communication unit 880 Display unit 881 Captured image 882 Depth image 890 Battery

Claims (7)

A semiconductor laser;
a laser driver disposed so as to overlap at least a portion of the semiconductor laser;
A semiconductor laser driving device, wherein the distance between a specific heat generating portion in the laser driver and the semiconductor laser is within a range of 0 to 1 mm . 2. The semiconductor laser driving device according to claim 1, wherein the laser driver is built in a substrate on which the semiconductor laser is mounted. 2. The semiconductor laser driving device according to claim 1, wherein the heat generating portion is a circuit for driving the semiconductor laser. the semiconductor laser comprises a plurality of laser diodes;
2. The semiconductor laser driving device according to claim 1, wherein the heat generating portions are a plurality of transistors for driving corresponding ones of the plurality of laser diodes. 2. The semiconductor laser driving device according to claim 1, wherein the heat generating portion is disposed at one predetermined location on the laser driver. 2. The semiconductor laser driving device according to claim 1, wherein the heat generating portion is disposed at a plurality of predetermined locations of the laser driver. 2. The semiconductor laser driving device according to claim 1, wherein the heat generating portion is arranged in a predetermined shape around the semiconductor laser.

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