Light-emitting device

Abstract

To provide a light-emitting device that can reduce waveform degradation caused by capacitance of a transfer portion, compared to a case where a reference potential terminal of the transfer portion is directly connected to the reference potential without switching a connection state of the reference potential terminal.SOLUTION: A light-emitting device includes a light-emitting portion having a plurality of light-emitting elements, a transfer portion that transfers a signal to set a light-emitting element to be turned on among the plurality of light-emitting elements, and a low-pass filter that is provided between a reference potential terminal of the transfer portion and an external reference potential.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a light emitting device. [Background technology]

[0002] Patent document 1 states that "During the shift period (selection time) when the shift section 12 performs the shift operation, the control section 50 sets the control potential VC to the ground potential GND (0V), and when light is emitted, sets the control potential VC to a potential (here, floating potential (Hi-Z)) different from that during the period (selection time)." [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-140068 Summary of the Invention [Problem to be solved by the invention]

[0004] In a self-scanning light-emitting device equipped with a transfer unit, it is desirable to connect the reference potential terminal of the transfer unit to a reference potential in order to release electric charges from the transfer unit. However, in this case, it is known that the waveform of the current flowing through the light-emitting element deteriorates due to the capacitance of the transfer unit. A technology has been studied to reduce waveform deterioration by floating the reference potential terminal of the transfer unit except during transfer operation, thereby suppressing the formation of capacitance in the transfer unit (see, for example, Patent Document 1). However, in the conventional technology, in order to float the reference potential terminal, it was necessary to provide a switch mechanism on the path to switch the connection state of the reference potential terminal.

[0005] Therefore, the present disclosure aims to provide a light-emitting device that can reduce waveform degradation caused by the capacitance of the transfer section, compared to when the reference potential terminal is directly connected to the reference potential without switching the connection state of the reference potential terminal of the transfer section. [Means for solving the problem]

[0006] In order to achieve the above object, the light emitting device of the first aspect comprises a light emitting unit having a plurality of light emitting elements, a transfer unit that transfers a signal to set which of the plurality of light emitting elements is to be turned on, and a low-pass filter arranged between a reference potential terminal of the transfer unit and an external reference potential.

[0007] A light emitting device according to a second aspect is the light emitting device according to the first aspect, further comprising a transmission line provided between the reference potential terminal and the low-pass filter.

[0008] A light emitting device according to a third aspect is the light emitting device according to the second aspect, wherein the low pass filter includes a snubber circuit in which a capacitor and a resistor are connected in series.

[0009] A light emitting device according to a fourth aspect is the light emitting device according to the third aspect, wherein the low pass filter satisfies a predetermined condition for impedance matching between the low pass filter and the transmission line.

[0010] A light emitting device according to a fifth aspect is the light emitting device according to the third aspect, wherein the low pass filter further includes an inductor connected in parallel with the snubber circuit.

[0011] A light emitting device according to a sixth aspect is the light emitting device according to the first aspect, wherein the light emitting section and the transfer section are provided on a common semiconductor substrate.

[0012] A light emitting device according to a seventh aspect is the light emitting device according to the sixth aspect, wherein the transfer section includes a pn junction that is a structure equivalent to the light emitting element.

[0013] A light emitting device according to an eighth aspect is the light emitting device according to any one of the first to seventh aspects, wherein the impedance of the low pass filter is 10Ω or less in DC. [Effects of the Invention]

[0014] According to the light-emitting device of the first aspect, waveform degradation caused by the capacitance of the transfer section can be reduced compared to when the reference potential terminal of the transfer section is directly connected to the reference potential without switching the connection state of the reference potential terminal of the transfer section.

[0015] The light emitting device according to the second aspect can be similarly applied to cases where the reference potential terminal and the low-pass filter must be connected by wire bonding or the like.

[0016] According to the light emitting device of the third aspect, low frequency components can be cut by the capacitor to reduce power consumption, while the energy of high frequency components can be consumed by the resistor.

[0017] The light emitting device according to the fourth aspect can prevent the efficiency from deteriorating due to an increase in noise caused by reflection, compared to when the impedance matching condition is not satisfied.

[0018] According to the light emitting device of the fifth aspect, it is possible to more easily design the frequency characteristics of the low pass filter compared to a case where no inductor is included.

[0019] According to the light emitting device of the sixth aspect, parasitic inductance and parasitic resistance can be reduced compared to when the light emitting section and the transfer section are provided on different semiconductor substrates.

[0020] According to the light emitting device of the seventh aspect, the manufacturing process can be prevented from becoming complicated compared to when the pn junction is not a structure equivalent to that of the light emitting element.

[0021] The light emitting device according to the eighth aspect can prevent malfunctions in which light emitting elements other than the intended light emitting element emit light, compared to when the impedance of the low pass filter is greater than 10Ω in DC. [Brief explanation of the drawings]

[0022] [Figure 1]FIG. 1 is a diagram showing an example of a cross-sectional view of a conventional light emitting device 100′. [Figure 2] FIG. 1 is a diagram showing an example of an equivalent circuit of a conventional light emitting device 100′. [Figure 3] 10 is a diagram showing the results of a simulation of the difference in light-emitting pulse waveform depending on whether or not a transfer section 130 is present. FIG. [Figure 4] 3A and 3B are diagrams illustrating an example of terminal processing in the light emitting device 100 according to the present embodiment. [Figure 5] 1 is a diagram showing an example of a component arrangement for terminal processing in the light emitting device 100 according to the present embodiment. [Figure 6] 10 is a diagram illustrating an example of the filter characteristics of a low-pass filter 220. FIG. [Figure 7] FIG. 10 is a diagram showing an example of a circuit according to a first comparative example used in a first simulation. [Figure 8] FIG. 10 is a diagram showing an example of a circuit according to a comparative example 2 used in a first simulation. [Figure 9] FIG. 10 is a diagram showing an example of a circuit according to the present embodiment used in a first simulation. [Figure 10] FIG. 10 is a diagram showing the results of a first simulation. [Figure 11] FIG. 10 is a diagram showing an example of a circuit according to Comparative Example 3 used in a second simulation. [Figure 12] FIG. 10 is a diagram illustrating an example of a circuit according to Comparative Example 4 used in a second simulation. [Figure 13] FIG. 10 is a diagram showing an example of a circuit according to Comparative Example 5 used in a second simulation. [Figure 14] FIG. 10 is a diagram illustrating an example of a circuit according to the present embodiment used in a second simulation. [Figure 15] FIG. 10 is a diagram showing the results of a second simulation. DETAILED DESCRIPTION OF THE INVENTION

[0023] An example of an embodiment of the present disclosure will be described below with reference to the drawings. In each drawing, the same or equivalent components and parts are designated by the same reference numerals. Furthermore, the dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0024] Fig. 1 is a diagram showing an example of a cross-sectional view of a conventional light-emitting device 100'. This diagram corresponds to Fig. 7(a) in Patent Document 1. This diagram shows a cross-sectional view focusing on only one vertical cavity surface-emitting laser (hereinafter referred to as VCSEL: Vertical Cavity Surface Emitting Laser) when the light-emitting device 100' has multiple VCSELs as light-emitting elements.

[0025] For the sake of convenience, the active layer, tunnel junction layer, etc. are not shown in the figure. The light emitting device 100' includes a semiconductor substrate 110, a light emitting section 120, a transfer section 130, and a driver 140.

[0026] The semiconductor substrate 110 is an n-type semiconductor substrate. The semiconductor substrate 110 may be, for example, an n-type GaAs substrate. The light emitting section 120 and the transfer section 130 may be provided on a common semiconductor substrate 110. The potential on the back surface of the semiconductor substrate 110 is defined as a substrate potential VK.

[0027] The light emitting section 120 has a plurality of light emitting elements. The light emitting section 120 includes a first semiconductor layer 121, a second semiconductor layer 122, and a light emission control thyristor 123.

[0028] The first semiconductor layer 121 is an n-type semiconductor layer formed on the semiconductor substrate 110. The first semiconductor layer 121 may be, for example, a distributed Bragg reflector (DBR) in which AlGaAs layers with different Al compositions are alternately stacked. The second semiconductor layer 122 is a p-type semiconductor layer formed on the first semiconductor layer 121. The second semiconductor layer 122 may be a DBR, similar to the first semiconductor layer 122. In this way, the light emitting unit 120 may have a resonator structure in which the first semiconductor layer 121 functioning as an n-type lower reflecting mirror and the second semiconductor layer 122 functioning as a p-type upper reflecting mirror are stacked in this order on an n-type semiconductor substrate. This forms a VCSEL as a light emitting element.

[0029] The light-emission control thyristor 123 is a thyristor formed on the second semiconductor layer 122. The light-emission control thyristor 123 may have an anode connected to a light-emission potential terminal 124 to which a light-emission potential VLD is supplied, and a cathode connected to the anode of the VCSEL. In other words, the light-emission control thyristor 123 may be connected in series with the VCSEL.

[0030] The transfer unit 130 transfers a signal that sets which of the plurality of light-emitting elements to turn on. The transfer unit 130 corresponds to the "shift unit 12" in Patent Document 1. The transfer unit 130 includes a third semiconductor layer 131, a fourth semiconductor layer 132, and an SLED circuit 133.

[0031] The third semiconductor layer 131, like the first semiconductor layer 121, is an n-type semiconductor layer formed on the semiconductor substrate 110. The fourth semiconductor layer 132, like the second semiconductor layer 122, is a p-type semiconductor layer formed on the third semiconductor layer 131. In this way, the transfer section 130 may include a pn junction, which is a structure equivalent to a light-emitting element.

[0032] The SLED circuit is a self-scanning light-emitting element array that realizes self-scanning of light-emitting elements. SLED is an abbreviation for Self-scanning Light Emitting Device. The SLED circuit may include a shift thyristor and a coupling transistor.

[0033] The structures of the light emitting section 120 and the transfer section 130 may be similar to those in Patent Document 1, and therefore further detailed description will be omitted. The description in Patent Document 1 may be incorporated herein by reference.

[0034] Here, a capacitance section is formed between the p-type fourth semiconductor layer 132 and the n-type semiconductor substrate 110. More specifically, the fourth semiconductor layer 132 needs to be connected to a reference potential (e.g., GND) to release the charge from the SLED circuit 133, but when the VCSEL emits light, the substrate potential VK becomes approximately 1 V, so a reverse bias is applied to the pn junction of the transfer section 130. As a result, the pn junction acts as a capacitance section. In this case, the transfer section 130 occupies approximately half the area of ​​the chip, so a significant capacitance is formed.

[0035] A terminal 134 that controls the potential of the capacitance section to a control potential VC is connected to the fourth semiconductor layer 132. Note that the terminal 134 may be connected to an external reference potential, and therefore will hereafter be referred to as a reference potential terminal 134.

[0036] 2 is a diagram showing an example of an equivalent circuit of a conventional light emitting device 100'. This diagram corresponds to FIG. 7(b) in Patent Document 1. The light emitting section 120 is represented by a series connection of a light emission control thyristor 123, a VCSEL (composed of a first semiconductor layer 121 and a second semiconductor layer 122), and an internal resistance Rv, and a parallel connection of the series connection with a capacitance C1.

[0037] The light-emitting unit 120 is configured by connecting a plurality of series-connected VCSELs and light-emission control thyristors 123 in parallel. Therefore, the series-connected VCSELs and light-emission control thyristors 123 other than the series connection including the VCSEL to be emitted act as capacitance C1 connected in parallel to the series connection including the VCSEL to be emitted.

[0038] The transfer unit 130 is represented by a parallel connection of a pn junction (indicated by a diode symbol in this figure) formed by the third semiconductor layer 131 and the fourth semiconductor layer 132, a capacitance C2 formed by the pn junction, and a series connection of the SLED circuit 133. For simplification, only a shift thyristor is shown for the SLED circuit 133. Here, the capacitance C2 formed in the transfer unit 130 deteriorates the light emission pulse waveform.

[0039] 3 is a diagram showing the results of a simulation of the difference in light emission pulse waveform depending on whether or not the transfer unit 130 is present. Waveform w1 shows the light emission pulse waveform when the transfer unit 130 is not provided. Waveform w2 shows the light emission pulse waveform when the transfer unit 130 is provided and the reference potential terminal 134 is directly connected to the reference potential.

[0040] As shown in this figure, the addition of capacitance C2 due to the pn junction not only causes the rise and fall of the pulse waveform to become dull, but also causes waveform degradation such as shoulders due to resonance including parasitic inductance of the implementation.

[0041] Here, the capacitance formed between the p-type fourth semiconductor layer 132 and the n-type semiconductor substrate 110 does not affect the waveform if the fourth semiconductor layer 132 is separated from the reference potential. Therefore, by floating the fourth semiconductor layer 132 except during transfer operations, it is possible to suppress the formation of capacitance in the transfer unit 130. The conventional technology shown in Patent Document 1 reduces waveform degradation caused by the capacitance formed in the transfer unit 130 in this way.

[0042] However, the reference potential terminal 134 connected to the fourth semiconductor layer 132 is formed as a pad on the surface layer of the VCSEL element, and is connected by wire bonding from the pad to an external reference potential such as a package or mounting board. Therefore, the connection from the reference potential terminal 134 to the reference potential is made outside the VCSEL element.

[0043] To float the fourth semiconductor layer 132, a switch mechanism must be provided on the connection path to turn off the connection to the reference potential. Therefore, such a switch mechanism must be provided in the device that controls the VCSEL, in the VCSEL driver, or separately on the mounting board. Furthermore, if a separate switch mechanism is provided, a signal for switching must be supplied to the switch mechanism.

[0044] Therefore, in the present disclosure, by devising terminal processing, waveform degradation caused by the capacitance of the transfer section 130 is reduced compared to when the reference potential terminal 134 is directly connected to the reference potential without switching the connection state of the reference potential terminal 134.

[0045] 4 is a diagram showing an example of terminal processing in the light emitting device 100 according to this embodiment. In this figure, the same or equivalent components and parts as those in FIG. 1 are denoted by the same reference numerals, and explanations thereof will be omitted hereinafter except for differences.

[0046] In this embodiment, the light emitting device 100 includes a low-pass filter 220 provided between the reference potential terminal 134 of the transfer section 130 and an external reference potential.

[0047] In this embodiment, the light emitting device 100 may further include a transmission line 210 provided between the reference potential terminal 134 and the low-pass filter 220. As described above, the transmission line 210 may be a bonding wire that is wire-bonded from a pad formed on the surface of the VCSEL element to a reference potential outside the VCSEL element. The length of the transmission line 210 may be, for example, 10 mm or more.

[0048] Here, low-pass filter 220 may include a snubber circuit in which capacitor 221 and resistor 222 are connected in series. A snubber circuit is generally a protection circuit provided to prevent malfunctions caused by a sudden voltage rise that occurs when a switch in an electronic circuit is opened or closed.

[0049] In this case, the low-pass filter 220 may satisfy a predetermined condition for impedance matching with the transmission line 210. Here, assuming that the bonding wire is 3 cm and the impedance of the transmission line 210 is approximately 45 Ω, the resistance value of the resistor 222 is set to approximately 46 Ω (47 Ω when a standard number for the nominal resistance value displayed in three digits is used), which is equivalent to the impedance of the transmission line 210.

[0050] The capacitance of capacitor 221 may be set based on the cutoff frequency determined by the time constant with respect to the resistance value of resistor 222. Here, the capacitance of capacitor 221 is set to 0.1 μF.

[0051] The low-pass filter 220 may further include an inductor 223 connected in parallel with the snubber circuit. The inductance of the inductor 223 may be set based on the cutoff frequency. Here, the inductance of the inductor 223 is set to 1 μH.

[0052] In this way, the low-pass filter 220 may be configured by a parallel circuit of the inductor 223 and a snubber circuit in which the capacitor 221 and the resistor 222 are connected in series.

[0053] 5 is a diagram showing an example of component arrangement for terminal processing in the light emitting device 100 according to this embodiment. This diagram shows the component arrangement when the reference potential terminal 134 of the VCSEL element mounted on the mounting substrate is connected to an external reference potential (GND of the mounting substrate in this diagram) via a transmission line 210 and a low-pass filter 220, as viewed from above.

[0054] To connect the reference potential terminal 134 to an external reference potential, the transmission line 210, the capacitor 221, the resistor 222, and the inductor 223 may be arranged, for example, as shown in this figure.

[0055] 6 is a diagram showing an example of the filter characteristics of low-pass filter 220. In this diagram, the horizontal axis represents frequency in units of Hz. In this diagram, the left vertical axis represents impedance in units of Ω. In this diagram, the right vertical axis represents phase difference in units of degrees.

[0056] In this figure, waveform w3 shows the impedance characteristics of low-pass filter 220. Therefore, the values ​​on the left vertical axis are applied to waveform w3. Furthermore, waveform w4 shows the phase characteristics of low-pass filter 220. Therefore, the values ​​on the right vertical axis are applied to waveform w4.

[0057] As shown by waveform w3, the low-pass filter 220 has impedance characteristics that are lower in the low-frequency range than in the high-frequency range, and higher in the high-frequency range than in the low-frequency range.

[0058] More specifically, the impedance of low-pass filter 220 may be 10 Ω or less at DC. This is because it has been confirmed that a DC impedance greater than 10 Ω causes malfunctions in which light-emitting elements other than the intended light-emitting element emit light. To reliably prevent malfunctions, the impedance of low-pass filter 220 may preferably be 0.01 Ω or less at DC.

[0059] The impedance of low-pass filter 220 may be 20 Ω or more in the range of 3 MHz to 1 GHz. Here, the impedance of transmission line 210 is assumed to be approximately 45 Ω, so the impedance of low-pass filter 220 may be ⅓ to 3 times the impedance of transmission line 210 in the range of 3 MHz to 1 GHz.

[0060] Furthermore, looking at waveform w3, it can be seen that the impedance converges to just under 50 Ω (approximately 46 Ω) from 10 MHz to 1 GHz. In this way, low-pass filter 220 may satisfy the condition for impedance matching with transmission line 210 connecting reference potential terminal 134 and low-pass filter 220 in the high-frequency range.

[0061] Below, we will explain the operation and effect of this embodiment by showing the results of two simulations. The first simulation is a simulation assuming a single-junction VCSEL driven by CW (Continuous Wave) for iToF (Indirect Time of Flight). The second simulation is a simulation assuming a triple-junction VCSEL driven by pulse for dToF (Direct Time of Flight).

[0062] 7 is a diagram showing an example of a circuit according to Comparative Example 1 used in the first simulation. In this figure, the same or equivalent components and parts as those in FIG. 2 are denoted by the same reference numerals, and explanations thereof will be omitted hereinafter except for differences. Comparative Example 1 assumes a case in which the transfer unit 130 is not provided. Therefore, in Comparative Example 1, the capacitance C2 due to the pn junction of the transfer unit 130 is not formed.

[0063] L1 and L2 are parasitic inductances. More specifically, L1 corresponds to the parasitic inductance in the path from the power supply that supplies the light-emitting potential VLD to the anode side of the VCSEL (more specifically, the anode of the light-emission control thyristor 123). L2 corresponds to the parasitic inductance in the path from the cathode side of the VCSEL to the driver 140. In the simulation, the inductances of L1 and L2 were both set to 0.35 nH.

[0064] R1 is a parasitic resistor. In the simulation, the resistance value of R1 was set to 0.3 Ω. The capacitance of C1 was estimated to be 35 pF based on the drive current loop inductance of 700 pF (estimated value at the time of design) and the resonance period (~1 ns).

[0065] FIG. 8 is a diagram showing an example of a circuit according to Comparative Example 2 used in the first simulation. In this figure, the same or equivalent components and parts as those in FIG. 7 are denoted by the same reference numerals, and explanations thereof will be omitted hereinafter except for differences. Comparative Example 2 assumes a case in which a transfer unit 130 is provided and the reference potential terminal 134 is connected to the reference potential without passing through the low-pass filter 220. Therefore, in Comparative Example 2, a capacitance C2 is formed by the pn junction of the transfer unit 130. In the simulation, the capacitance of C2 was set to 200 pF.

[0066] 9 is a diagram showing an example of a circuit according to this embodiment used in the first simulation. In this figure, the same or equivalent components and parts as those in FIG. 8 are denoted by the same reference numerals, and descriptions thereof will be omitted hereinafter except for differences. This embodiment assumes that a transfer unit 130 is provided and that the reference potential terminal 134 is connected to the reference potential via a low-pass filter 220. Therefore, in this embodiment, the low-pass filter 220 is formed between the transmission line 210 and the reference potential by a parallel circuit of a snubber circuit in which a capacitor 221 and a resistor 222 are connected in series, and an inductor 223.

[0067] Figure 10 shows the results of the first simulation. In this figure, the horizontal axis represents time in units of [s]. In this figure, the left vertical axis represents voltage in units of [V]. In this figure, the right vertical axis represents current in units of [A].

[0068] In this figure, the solid line indicates the VCSEL current waveform according to this embodiment, the dotted line indicates the VCSEL current waveform according to Comparative Example 1, and the dashed line indicates the VCSEL current waveform according to Comparative Example 2. Therefore, the values ​​on the right side of the vertical axis apply to the solid, dotted, and dashed lines. In this figure, the dashed-dotted line indicates the cathode voltage waveform according to this embodiment. Therefore, the values ​​on the left side of the vertical axis apply to the dashed-dotted line.

[0069] In this figure, comparing the solid line and the dashed line, the solid line shows a waveform closer to the dotted line than the dashed line. This indicates that by passing the signal through the low-pass filter 220, a waveform closer to that obtained when the transfer unit 130 is not provided is obtained compared to when the signal is not passed through the low-pass filter 220. In other words, the light-emitting device 100 according to this embodiment can reduce waveform degradation caused by the capacitance of the transfer unit 130 compared to when the reference potential terminal 134 of the transfer unit 130 is directly connected to the reference potential without switching the connection state of the reference potential terminal 134.

[0070] 11 is a diagram showing an example of a circuit according to Comparative Example 3 used in the second simulation. In this figure, the same or equivalent components and parts as those in FIG. 7 are denoted by the same reference numerals, and explanations will be omitted hereinafter except for the differences. In Comparative Example 3, the VCSEL is changed from a single junction to a triple junction, as compared to Comparative Example 1.

[0071] 12 is a diagram showing an example of a circuit according to Comparative Example 4 used in the second simulation. In this figure, the same reference numerals are used for components and parts that are the same as or equivalent to those in FIG. 11, and descriptions thereof will be omitted hereinafter except for differences. Comparative Example 4 assumes a case where a transfer unit 130 is provided and the reference potential terminal 134 is connected to the reference potential via a buffer.

[0072] In this diagram, Rb represents the internal resistance of the buffer, and Cb represents the output capacitance of the buffer. In other words, the buffer is represented by Rb and Cb. In the simulation, the resistance value of Rb was set to 5 Ω, and the capacitance of Cb was set to 15 pF.

[0073] 13 is a diagram showing an example of a circuit according to Comparative Example 5 used in the second simulation. In this figure, the same or equivalent components and parts as those in FIG. 12 are denoted by the same reference numerals, and explanations thereof will be omitted hereinafter except for differences. Comparative Example 5 assumes that the reference potential terminal 134 is terminated with high impedance.

[0074] In this figure, Rh represents the termination resistor. In the simulation, the resistance value of Rh was set to 1 MΩ.

[0075] 14 is a diagram showing an example of a circuit according to this embodiment used in the second simulation. In this figure, the same or equivalent components and parts as those in FIG. 9 are denoted by the same reference numerals, and explanations will be omitted hereinafter except for differences. In the second simulation, the VCSEL is changed from a single junction to a triple junction, as compared to the first simulation.

[0076] 15 is a diagram showing the results of the second simulation. In this diagram, the horizontal axis represents time in units of [s], and the vertical axis represents current in units of [A].

[0077] In this figure, the solid line indicates the VCSEL current waveform according to this embodiment, the dotted line indicates the VCSEL current waveform according to Comparative Example 3, the dashed line indicates the VCSEL current waveform according to Comparative Example 4, and the dashed line indicates the VCSEL current waveform according to Comparative Example 5.

[0078] In this figure, comparing the solid line, dashed line, and dashed-dotted line, the solid line shows the waveform closest to the dotted line. This shows that, compared to connecting the reference potential terminal 134 to the reference potential via a buffer or terminating it with high impedance, connecting it to the reference potential via the low-pass filter 220 results in a waveform closer to that obtained when the transfer unit 130 is not provided.

[0079] More specifically, the dashed line indicates that in Comparative Example 4, coupled oscillation with the Enh current loop causes the signal to fall faster than when the transfer unit 130 is not provided, but the response including the Enh terminal wiring appears significantly later. Furthermore, the dashed-dotted line indicates that the slowing of the fall is actually worsened in Comparative Example 5. In contrast, the solid line indicates that the present embodiment achieves fall characteristics that are substantially the same as when the transfer unit 130 is not provided.

[0080] As described above, in this embodiment, it can be said that the reference potential terminal 134 can be stabilized at the reference potential except during light emission pulse driving due to the capacitance between the reference potential terminal 134 and the cathode and the low-pass characteristics of the low-pass filter 220. Therefore, according to this embodiment, a stable transfer operation is possible.

[0081] Furthermore, since the low-pass filter 220 has high impedance during light emission pulse driving, the voltage at the reference potential terminal 134 follows the change in the cathode voltage, and is therefore hardly affected by the capacitance between the reference potential terminal 134 and the cathode.

[0082] In this case, by snubber terminating the high frequency components via an appropriate transmission line 210, resonance due to voltage changes at the reference potential terminal 134 during light emission pulse driving can be prevented, and the voltage changes can be approximately matched and terminated to the reference potential.

[0083] As described above, according to this embodiment, it is possible to drastically reduce waveform degradation caused by the capacitance between the reference potential terminal 134 and the cathode, which is a problem when adding the transfer unit 130. In this case, according to this embodiment, it is not necessary to switch between a GND connection state during transfer operation and an open state during light-emitting operation, which makes it possible to simplify the circuit and its control. Therefore, according to the light-emitting device 100 of this embodiment, it is possible to reduce waveform degradation caused by the capacitance of the transfer unit 130 without switching the connection state of the reference potential terminal 134 of the transfer unit 130, compared to when the reference potential terminal 134 is directly connected to the reference potential.

[0084] Furthermore, the present disclosure is not limited to the above, and it goes without saying that various modifications can be made without departing from the spirit of the present disclosure.

[0085] The following additional notes are provided regarding the above-described embodiments. (((1))) a light emitting section having a plurality of light emitting elements; a transfer unit that transfers a signal that sets a light emitting element to be turned on among the plurality of light emitting elements; a low-pass filter provided between a reference potential terminal of the transfer unit and an external reference potential; A light emitting device comprising:

[0086] (((2))) a transmission line provided between the reference potential terminal and the low-pass filter; The light emitting device according to (((1))).

[0087] (((3))) the low-pass filter includes a snubber circuit in which a capacitor and a resistor are connected in series; The light-emitting device according to (((2))).

[0088] (((4))) the low-pass filter satisfies a predetermined condition of impedance matching with the transmission line; The light-emitting device according to (((3))).

[0089] (((5))) the low-pass filter further includes an inductor connected in parallel with the snubber circuit. The light-emitting device according to (((3))) or (((4))).

[0090] (((6))) the light emitting unit and the transfer unit are provided on a common semiconductor substrate; A light emitting device according to any one of (((1))) to (((5))).

[0091] (((7))) The transfer section includes a pn junction, which is a structure equivalent to the light emitting element. The light-emitting device according to (((6))).

[0092] (((8))) The impedance of the low-pass filter is 10 Ω or less at DC. A light emitting device according to any one of (((1))) to (((7))).

[0093] According to (((1))), it is possible to reduce waveform degradation caused by the capacitance of the transfer section compared to when the reference potential terminal of the transfer section is directly connected to the reference potential without switching the connection state of the reference potential terminal of the transfer section.

[0094] According to (((2))), it can be similarly applied to the case where the reference potential terminal and the low-pass filter must be connected by wire bonding or the like.

[0095] According to (((3))), low frequency components can be cut by a capacitor to reduce power consumption, while the energy of high frequency components can be consumed by a resistor.

[0096] According to (((4))), it is possible to suppress the increase in noise due to reflection and the deterioration of efficiency, compared to when the impedance matching condition is not satisfied.

[0097] According to (((5))), it is possible to easily design the frequency characteristics of the low-pass filter compared to when no inductor is included.

[0098] According to (((6))), parasitic inductance and parasitic resistance can be suppressed compared to when the light emitting section and the transfer section are provided on different semiconductor substrates.

[0099] According to (((7))), the manufacturing process can be prevented from becoming complicated compared to when the pn junction is not a structure equivalent to the light emitting element.

[0100] According to (((8))), it is possible to suppress malfunctions in which light emitting elements other than the intended light emitting element emit light, compared to when the impedance of the low pass filter is greater than 10Ω in DC. [Explanation of symbols]

[0101] 100 Light-emitting device 110 Semiconductor substrate 120 Light-emitting part 121 First semiconductor layer 122 Second semiconductor layer 123 Light-emitting control thyristor 130 Transfer Unit 131 Third semiconductor layer 132 Fourth semiconductor layer 133 SLED circuit 134 Reference potential terminal 140 Driver 210 Transmission Line 220 Low-pass filter 221 Capacitor 222 Resistance 223 Inductor

Claims

1. a light emitting section having a plurality of light emitting elements; a transfer unit that transfers a signal that sets a light emitting element to be turned on among the plurality of light emitting elements; a low-pass filter provided between a reference potential terminal of the transfer unit and an external reference potential; A light emitting device comprising:

2. a transmission line provided between the reference potential terminal and the low-pass filter; The light emitting device according to claim 1 .

3. the low-pass filter includes a snubber circuit in which a capacitor and a resistor are connected in series; The light emitting device according to claim 2 .

4. the low-pass filter satisfies a predetermined condition of impedance matching with the transmission line; The light emitting device according to claim 3 .

5. the low-pass filter further includes an inductor connected in parallel with the snubber circuit. The light emitting device according to claim 3 .

6. the light emitting unit and the transfer unit are provided on a common semiconductor substrate; The light emitting device according to claim 1 .

7. the transfer portion includes a pn junction that is a structure equivalent to the light emitting element; The light emitting device according to claim 6 .

8. The impedance of the low-pass filter is 10 Ω or less in DC. The light emitting device according to claim 1 .

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