Patent Description:
A distance measuring sensor that measures a distance to a subject before image capturing has been conventionally used in an imaging device or the like. The distance measuring sensor measures a distance to a subject by emitting light from a light source such as a laser diode onto a subject, and measuring a time until reflected light from the subject enters an imaging device. In a case where a distance to a moving subject is to be measured by the distance measuring sensor, it is necessary to drive the laser diode at high speed to emit light. This is for enhancing the detection accuracy of the distance. As a drive circuit that drives the laser diode at high speed, for example, a light source drive circuit that generates a predetermined current for obtaining a desired light amount of the laser diode, and first and second overshoot currents to be added to the predetermined current is used (for example, refer to Patent Document <NUM>).

In the above-described conventional technology, by flowing an overshoot current with a current value larger than the predetermined current, a light emission latency time of the laser diode is shortened and the laser diode is driven at high speed. The above-described first overshoot current is an overshoot current for charging a parasitic capacitance of the laser diode. The first overshoot current is set to a predetermined current value. Furthermore, the second overshoot current is an overshoot current having a current value adjusted in accordance with response characteristics for compensating for a variation in light emission latency time that is attributed to a variation in response characteristics of the laser diode. The first and second overshoot currents are sequentially supplied to the laser diode, and the laser diode is driven.

<CIT> is related to a high-power pulse laser diode driver. Herein, a diode array driver comprises a storage capacitor, which is charged to a desired voltage by a voltage source and a diode. Herein, the capacitor, the voltage source and die diode are considered to be a power supply. A series inductor is connected between the capacitor and a diode array. The diode array comprises a plurality of series-connected laser diodes. A switching element is connected between another end of the diode array and ground. A current monitor is connected in series with the switch. A shunt switch is connected across the diode array. When the shunt switch is closed, the diode array is effectively shorted out. The current monitor monitors the current. When the current monitor indicates that the current has reached the desired level, the shunt switch is opened. As a result, the voltage across the diode array immediately jumps up to the level required to rapidly force the current from the series inductor to the diode array. This results in a very short pulse rise time. To end the pulse, the shunt switch <NUM> is once again closed, quickly dissipating the current in the diode array in a closed loop that includes the shunt switch and the diode array. If at the same time, the grounding switch is opened, the current in the series inductor circulates through a closed loop comprising the series inductor, the shunt switch and the diode.

<CIT> is related to an optical distance measurement device. Herein, a transmitter produces a modulated current which is converted to light by an optical source. A selected optical source can be a light emitting diode LED or laser diode. Transmit modulation signal enters differential driver which produces complementary drive signals. These signals alternately drive series and shunt switches. The series switch modulates current through the optical source while the shunt transistor bypasses current around the optical source. A current limiter, controlled through signal, establishes the maximum current delivered to the optical source.

<CIT> is concerned with a pulse laser diode driver.

Herein, a circuit for a pulsed laser diode includes a first circuit path comprising one or more inductive elements and a first switch, and a second circuit path comprising a diode and a second switch. Two switches are provided to select which path the current travels during different intervals. One circuit path, i.e. a pre-charge path, can be used for precharging the inductances during one interval, and the stored energy or current in the inductances can be dumped very quickly towards the diode, using a separate circuit path, i.e. a fire path, to turn on the diode during a subsequent interval. A switch-timing controller can be provided to control the switches. The switch-timing controller can vary its control signals to the switches depending on the characteristics of the pulse to be generated.

In the above-described conventional technology, it is necessary to supply a plurality of overshoot currents to the laser diode, and the drive circuit accordingly becomes complicated, which is problematic.

The present disclosure has been devised in view of the above-described problematic point, and it is an object of the present invention to simplify the configuration of a light emission device that shortens a light emission latency time of a light emitting element such as a laser diode. This object is solved by the subject-matter of the independent claims. Further advantageous embodiments and refinements of the present invention are described in the respective subclaims. Embodiments not covered by the claimed subject-matter do not form part of the invention.

The present disclosure has been devised for solving the above-described problematic point, and the first aspect of the present disclosure is a light emission drive circuit including a light emission current wire configured to flow a light emission current for causing a light emitting element to emit light, in the light emitting element, a light emission current switch that is connected to the light emission current wire, and is configured to control the light emission current, a preliminary current wire configured to flow, in the light emission current wire, a preliminary current for exciting an inductance component of the light emission current wire before a light emission period being a period in which the light emission current flows in the light emitting element, and a preliminary current switch that is connected to the preliminary current wire, and is configured to control the preliminary current. Herein, one end of the preliminary current switch is connected to the preliminary current wire via a first resistor, and another end of the preliminary current switch is grounded. Further, one end of the light emission current switch is connected to the light emission current wire via a second resistor, and another end of the light emission current switch is grounded.

Furthermore, in the first aspect, the light emitting element may include a light emission chip that includes two electrodes arranged therein, and is configured to emit light in accordance with the light emission current flowing between the electrodes, two light emission current terminals for flowing the light emission current that are respectively arranged for the two electrodes, and a preliminary current terminal for flowing the preliminary current that is arranged on at least one of the two electrodes, the light emission current wire may be connected to the light emission current terminal, and the preliminary current wire may be connected to the preliminary current terminal.

Furthermore, in the first aspect, a bias circuit configured to supply a current substantially equal to a light emission threshold of the light emitting element, to the light emitting element as a bias current may be further included.

Furthermore, in the first aspect, the light emission current may be changed during the light emission period.

Furthermore, in the first aspect, the light emission current may be decreased during the light emission period.

Furthermore, in the first aspect, the light emitting element may include a laser diode.

Furthermore, in the first aspect, a power circuit configured to supply the light emission current may be further included.

Furthermore, in the first aspect, the power circuit may further supply the preliminary current.

Furthermore, in the first aspect, a power circuit configured to supply the preliminary current may be further included.

Furthermore, in the first aspect, a control unit configured to generate control signals of the light emission current switch and the preliminary current switch may be further included.

Furthermore, in the first aspect, the light emission current switch and the preliminary current switch may be formed by MOS transistors.

Furthermore, in the first aspect, a snubber circuit may be connected to at least one of the light emission current wire or the preliminary current wire.

Furthermore, the second of the present disclosure is a light emission device including a light emitting element, a light emission current wire configured to flow a light emission current for causing the light emitting element to emit light, in the light emitting element, a light emission current switch that is connected to the light emission current wire, and is configured to control the light emission current, a preliminary current wire configured to flow, in the light emission current wire, a preliminary current for exciting an inductance component of the light emission current wire before a light emission period being a period in which the light emission current flows in the light emitting element, and a preliminary current switch that is connected to the preliminary current wire, and is configured to control the preliminary current.

By employing the above-described aspects, an effect of flowing a preliminary current in a light emission current wire by arranging a preliminary current wire and a preliminary current switch, and exciting an inductance component of the light emission current wire is obtained. A configuration of a light emission device that shortens a latency time of light emission is expected to be simplified.

Next, modes for carrying out the present disclosure (hereinafter, referred to as embodiments) will be described with reference to the drawings. In the following drawings, the same or similar portions are assigned the same or similar reference numerals. Furthermore, embodiments will be described in the following order.

<FIG> is a diagram illustrating a configuration example of a light emission device according to the first embodiment of the present disclosure. The drawing is a circuit diagram illustrating a configuration example of a light emission device <NUM>. The drawing is a diagram describing a principle of a light emission device of the present disclosure. The light emission device <NUM> is a light emission device used in a device that measures a distance to a subject using a time of flight (ToF) method in a camera or the like, for example. Here, the ToF method is a method of measuring a distance by emitting laser light onto a subject, and measuring a time taken for the laser light reciprocating between the device and the subject. The light emission device <NUM> in the drawing includes a light emitting element <NUM>, a preliminary current switch <NUM>, a light emission current switch <NUM>, a constant current source <NUM>, resistors <NUM> and <NUM>, capacitors <NUM> and <NUM>, wires <NUM> to <NUM> and <NUM> and <NUM>, a power line Vdd, and a grounding wire. As described later, the light emitting element <NUM> includes terminals <NUM> to <NUM>. The power line Vdd is a wire that supplies power of the light emission device <NUM>. Furthermore, among circuits in the drawing, circuits other than the light emitting element <NUM> constitute a light emission drive circuit.

The terminal <NUM> of the light emitting element <NUM> is connected to the power line Vdd via the wire <NUM>. The terminal <NUM> of the light emitting element <NUM> is connected to one end of the preliminary current switch <NUM> via the wire <NUM>. Another end of the preliminary current switch <NUM> is connected to the terminal <NUM> of the light emitting element <NUM> via the wire <NUM>. The terminal <NUM> of the light emitting element <NUM> is connected to one end of the light emission current switch <NUM> via the wire <NUM>. Another end of the light emission current switch <NUM> is grounded via the wire <NUM>, the constant current source <NUM>, and the wire <NUM>. The resistor <NUM> and the capacitor <NUM> connected in series are connected between the wire <NUM> and the grounding wire. The resistor <NUM> and the capacitor <NUM> connected in series are connected between the wire <NUM> and the grounding wire.

The light emitting element <NUM> is an element that includes a semiconductor chip and emits light by flowing a current. The light emitting element <NUM> in the drawing has a configuration in which a light emission chip <NUM> formed on the semiconductor chip is sealed in a semiconductor package. The semiconductor package includes the terminals <NUM> to <NUM>. For example, a laser diode or a light emitting diode can be applied to the light emission chip <NUM>. In the light emission device <NUM> in the drawing, the light emission chip <NUM> including a laser diode is assumed. The laser diode is a diode that emits laser light by flowing a current from an anode to a cathode. As illustrated in the drawing, an anode of the light emission chip <NUM> is connected to the terminals <NUM> and <NUM> via a wire <NUM>. Furthermore, a cathode of the light emission chip <NUM> is connected to the terminals <NUM> and <NUM> via a wire <NUM>. Note that a current for causing the light emitting element <NUM> to emit light will be referred to as a light emission current.

The preliminary current switch <NUM> and the light emission current switch <NUM> are elements reversibly transitioning to two states including a conductive state and a nonconductive state. The state transition is controlled in accordance with a control signal input to a control terminal (not illustrated). A semiconductor element such as, for example, a MOS transistor can be used as the preliminary current switch <NUM> and the light emission current switch <NUM>.

The resistor <NUM> and the capacitor <NUM> connected in series constitute a snubber circuit <NUM>, and the resistor <NUM> and the capacitor <NUM> connected in series constitute a snubber circuit <NUM>. The snubber circuits <NUM> and <NUM> are circuits for suppressing ringing of a light emission current that is generated when a switch element transitions from the conductive state to the nonconductive state, and when a switch element transitions from the nonconductive state to the conductive state. The ringing is generated by a vibrational current flowing between an inductance component of a wire or the like, and a parasitic capacitance or the like of a switch element. If a light emission current vibrates, a light amount of the light emitting element <NUM> varies, and the accuracy declines when the light emission device <NUM> is used in a distance measuring sensor or the like. By arranging the snubber circuits <NUM> and <NUM>, it is possible to suppress ringing and reduce a decline in accuracy of a distance measuring sensor or the like. The snubber circuit <NUM> is connected to a preliminary current wire, which will be described later, and the grounding wire being a low-impedance node. Furthermore, the snubber circuit <NUM> is connected between a light emission current wire and the grounding wire. Note that the configuration of the light emission device <NUM> is not limited to this example. For example, either one of the snubber circuits <NUM> and <NUM> may be arranged.

The constant current source <NUM> is a circuit that flows a constant current in the light emitting element <NUM>. By the constant current source <NUM>, a predetermined light emission current can be flowed in the light emitting element <NUM>. Specifically, the constant current source <NUM> restricts a current flowing in the light emitting element <NUM>, to a current with a predetermined value, on the basis of a source voltage supplied from the power line Vdd. A circuit formed by a bipolar transistor having a base driven to a constant voltage, for example, can be used as the constant current source <NUM>. Note that the constant current source <NUM> and the power line Vdd serve as an example of a power circuit described in the appended claims.

The driving of a light emitting element in the light emission device <NUM> can be performed in the following manner. First of all, the light emission current switch <NUM> is controlled from the outside, and the light emission current switch <NUM> is caused to transition from the nonconductive state to the conductive state. Then, a closed circuit is formed by the wires <NUM> to <NUM>, the wires <NUM> and <NUM>, and the constant current source <NUM>, and a light emission current flows from the power line Vdd to the grounding wire through the light emission chip <NUM>. As described above, the light emission current is a current having the maximum value set by the constant current source <NUM>. By setting the light emission current to a value exceeding a light emission threshold of the light emission chip <NUM>, laser light can be emitted from the light emission chip <NUM>. A period during which the light emitting element <NUM> emits light will be referred to as a light emission period. The light emission period corresponds to a period in which a light emission current flows in the light emitting element <NUM>.

However, because the wires <NUM> to <NUM> and the wires <NUM> and <NUM> have an inductance component (parasitic inductance L) as illustrated in the drawing, a rising waveform of the light emission current becomes dull. In other words, a time taken for reaching a predetermined light emission current from the transition of the light emission current switch <NUM> to the conductive state becomes longer. Thus, light emission of the light emission chip <NUM> is delayed, and the delay disturbs high-speed driving of the light emitting element <NUM>.

In view of the foregoing, in the light emission device <NUM> in the drawing, by arranging the preliminary current switch <NUM>, a preliminary current is flowed in the light emission chip <NUM>, and rising of a light emission current is made faster. Here, the preliminary current is a current preliminarily flowed in the wires <NUM> and <NUM> and the like that serve as a path for flowing a light emission current in the light emitting element <NUM>, before the light emission period. By flowing the preliminary current in the wires <NUM> to <NUM> and the wires <NUM> and <NUM> precedential to the light emission period, parasitic inductances of these wires can be excited. Specifically, before the light emission period, the light emission current switch <NUM> and the preliminary current switch <NUM> are caused to transition to the conductive state. Therefore, a preliminary current flows from the power line Vdd through a path including the wire <NUM>, the wire <NUM>, the wire <NUM>, the preliminary current switch <NUM>, the wire <NUM>, the wire <NUM>, the wire <NUM>, the light emission current switch <NUM>, the wire <NUM>, the constant current source <NUM>, the wire <NUM>, and the grounding wire.

After the wires <NUM> and <NUM> and the like are excited by the preliminary current and a value of the preliminary current reaches a value of a light emission current, the preliminary current switch <NUM> is caused to transition to the nonconductive state. A current that had been flowing by being diverted from the light emission chip <NUM> flows in the light emission chip <NUM>, and the light emission chip <NUM> emits light. Because the parasitic inductances of the wires <NUM> and <NUM> and the like are already excited, a light emission current with steep rising can be flowed in the light emission chip <NUM>.

Note that the wires <NUM> to <NUM> serve as an example of a light emission current wire described in the appended claims. The wires <NUM> and <NUM> serve as an example of a preliminary current wire described in the appended claims. The terminals <NUM> and <NUM> serve as an example of a light emission current terminal described in the appended claims. The terminals <NUM> and <NUM> serve as an example of a preliminary current terminal described in the appended claims. Note that, in the example in the drawing, in the wire <NUM> in the light emitting element <NUM>, a wire between the terminal <NUM> and an anode of the light emission chip <NUM> can be regarded as a light emission current wire, and a wire between the terminal <NUM> and the anode of the light emission chip <NUM> can be regarded as a preliminary current wire. In a similar manner, in the wire <NUM>, a wire between the terminal <NUM> and a cathode of the light emission chip <NUM> can be regarded as a light emission current wire, and a wire between the terminal <NUM> and the cathode of the light emission chip <NUM> can be regarded as a preliminary current wire.

<FIG> is a diagram illustrating an example of a driving method of the light emission device according to the first embodiment of the present disclosure. The drawing is a diagram illustrating a relationship between control signals of the preliminary current switch <NUM> and the light emission current switch <NUM>, and currents of the preliminary current switch <NUM>, the light emission current switch <NUM>, and the light emitting element <NUM>. The control signal of the preliminary current switch <NUM> and the control signal of the light emission current switch <NUM> are represented by binarizing control signals applied to gates of semiconductor elements such as MOS transistors, for example, that are to be used as the preliminary current switch <NUM> and the light emission current switch <NUM>. In the drawing, when values of the control signals of the preliminary current switch <NUM> and the light emission current switch <NUM> are "<NUM>", voltages for electrically connecting between sources and drains of the MOS transistors are applied to between gates and sources. The signal will be hereinafter referred to as an ON signal. Furthermore, in the waveform in the drawing, a dotted line indicates a line of <NUM> V or <NUM> A.

At T1, ON signals are applied to the preliminary current switch <NUM> and the light emission current switch <NUM>. Therefore, the preliminary current switch <NUM> and the light emission current switch <NUM> transition to the conductive state. A source voltage from the power line Vdd is applied to parasitic inductances of the wires <NUM> to <NUM> and the like, and a preliminary current corresponding to an excitation current of the parasitic inductances starts to flow in the wires <NUM> to <NUM> and the wires <NUM> and <NUM>. As illustrated as the current of the preliminary current switch <NUM> and the current of the light emission current switch <NUM> in the drawing, the preliminary current increases like a ramp function.

At T2, the application of the ON signal to the preliminary current switch <NUM> is stopped, and the preliminary current switch <NUM> is caused to transition to the nonconductive state. On the other hand, the light emission current switch <NUM> continues to be in the conductive state. At this time, a flow path of a current Id that had been flowing in the preliminary current switch <NUM> changes to the light emitting element <NUM>, and continues to flow via the light emission current switch <NUM>. The current Id flowing in the light emitting element <NUM> and the light emission current switch <NUM> becomes a light emission current for obtaining a desired light amount in the light emitting element <NUM>. In other words, a period from T1 to T2 corresponds to a period in which the preliminary current increases to a value equivalent to the light emission current. The current Id in the light emission current can be set to a current set by the constant current source <NUM>. When the preliminary current switch <NUM> transitions to the nonconductive state, back electromotive force is generated by parasitic inductances of the wires <NUM> and <NUM> and the like, and an overvoltage is applied to the light emission chip <NUM>. By the overvoltage, a rising time of a current flowing in the light emission chip <NUM> can be further shortened. This is because a charging time of the parasitic capacitance of the light emission chip <NUM> can be shortened.

At T3, the application of the ON signal to the light emission current switch <NUM> is stopped. Therefore, the light emission current switch <NUM> transitions to the nonconductive state, a light emission current flowing in the light emitting element <NUM> is blocked, and emission of laser light from the light emitting element <NUM> stops. A period from T2 to T3 corresponds to a light emission period.

As illustrated in the drawing, at the beginning of the light emission period, rising of a current flowing in the light emitting element <NUM> can be made steep, and a latency time until light emission of the light emitting element <NUM> can be shortened. A dashed-dotted line in the waveform of the current flowing in the light emitting element <NUM> in the drawing indicates a waveform of a current that flows in a case where the ON signal is applied to the light emission current switch <NUM> at T2 without flowing the preliminary current. Due to the influence of parasitic inductances of the wires <NUM> and <NUM> and the like, a rising time of the light emission current becomes longer, and a light emission latency time of the light emitting element <NUM> becomes longer. Furthermore, a period during which the light emission current with the value Id flows in the light emission period becomes shorter.

As described above, the light emission device <NUM> according to the first embodiment of the present disclosure excites the parasitic inductances of the wires <NUM> to <NUM> before the light emission period by flowing the preliminary current in the wires <NUM> to <NUM> in which a light emission current of the light emitting element <NUM> is to be flowed. Therefore, a rising time of the light emission current that flows in the light emitting element <NUM> in the light emission period can be shortened. The preliminary current can be flowed by connecting the preliminary current switch <NUM> and the accompanying wires <NUM> and <NUM>, and the configuration of the light emission device <NUM> can be simplified.

The light emission device <NUM> according to the above-described first embodiment uses the light emitting element <NUM> formed in a package including four terminals. In contrast to this, a light emission device <NUM> according to the second embodiment of the present disclosure differs from the above-described first embodiment in that a light emitting element including two terminals is used.

<FIG> is a diagram illustrating a configuration example of a light emission device according to the second embodiment of the present disclosure. Similarly to <FIG>, the drawing is a circuit diagram illustrating a configuration example of the light emission device <NUM>. The light emission device <NUM> in the drawing differs from the light emission device <NUM> described with reference to <FIG>, in that a light emitting element <NUM> is used in place of the light emitting element <NUM>.

The light emitting element <NUM> includes terminals <NUM> and <NUM>. Wires <NUM> and <NUM> are connected in common to the terminal <NUM>, and wires <NUM> and <NUM> are connected in common to the terminal <NUM>. Because the wire connection other than this is similar to that in <FIG>, the description will be omitted.

The light emitting element <NUM> is a light emitting element including the light emission chip <NUM>, and formed in a semiconductor package including two terminals. An anode and a cathode of the light emission chip <NUM> are respectively connected to the terminals <NUM> and <NUM>.

<FIG> is a plan view illustrating a configuration example of a light emitting element according to the second embodiment of the present disclosure. The drawing is a plan view illustrating a configuration example of the light emitting element <NUM>. The light emitting element <NUM> in the drawing includes the light emission chip <NUM>, a frame <NUM>, a diffuser panel <NUM> (not illustrated), a substrate <NUM>, bonding wires <NUM>, and a solder <NUM> (not illustrated).

The light emission chip <NUM> is a light emitting element including a plurality of vertical cavity surface emitting lasers (VCSELs) formed on a semiconductor substrate, and is a surface emitting laser element that emits laser light in a vertical direction. Circles on the surface of the light emission chip <NUM> in the drawing indicate VCSELs <NUM>. As described later, the light emission chip <NUM> includes an anode electrode <NUM> and a cathode electrode <NUM> (not illustrated) that are respectively arranged on the front surface and the rear surface of a semiconductor region <NUM> (not illustrated). The semiconductor region <NUM> can be formed by GaAs, for example. Specifically, the semiconductor region <NUM> of the light emission chip <NUM> can have a configuration in which a plurality of GaAs layers and Al(Ga)As layers having an N-type and a plurality of GaAs layer and Al(Ga)As layers having a p-type are stacked on a GaAs substrate. Therefore, p-n junction is formed, and a semiconductor multi-layer film mirror reflector is formed by the plurality of GaAs layers and Al(Ga)As layers. By flowing a forward current in the p-n junction, a carrier is injected and light emission occurs, resonance is caused by the multi-layer film mirror reflector, and laser light is emitted.

The substrate <NUM> is a substrate on which the light emission chip <NUM> is mounted. Pads <NUM> and <NUM> are arranged on the front surface of the substrate <NUM>. Electrodes of the light emission chip <NUM> are connected to the pads <NUM> and <NUM>. Furthermore, the terminals <NUM> and <NUM> are arranged on the rear surface of the substrate <NUM>. A cathode electrode (not illustrated) of the light emission chip <NUM> is connected to the pad <NUM>. On the other hand, the anode electrode <NUM> of the light emission chip <NUM> is connected to the pad <NUM> by wire bonding.

The bonding wires <NUM> connect the anode electrode <NUM> of the light emission chip <NUM> and the pad <NUM> by wire bonding. As illustrated in the drawing, by arranging the plurality of bonding wires <NUM>, interconnection resistance can be reduced.

The frame <NUM> is a casing arranged to surround the light emission chip <NUM>. The frame <NUM> seals the light emission chip <NUM> together with the diffuser panel <NUM> to be described later.

<FIG> is a cross-sectional view illustrating a configuration example of the light emitting element according to the second embodiment of the present disclosure. The drawing is a cross-sectional view illustrating a configuration example of the light emitting element <NUM>.

The diffuser panel <NUM> is arranged on the top panel of the light emitting element <NUM>, lets through laser light emitted by the light emission chip <NUM>, and converts the laser light into diffused light.

As illustrated in the drawing, the anode electrode <NUM> of the light emission chip <NUM> is connected to the pad <NUM> via the bonding wires <NUM>. The cathode electrode <NUM> arranged on the rear surface of the light emission chip <NUM> is connected to the pad <NUM> via the solder <NUM>. In other words, the cathode electrode <NUM> is soldered to the pad <NUM>. The pad <NUM> and the terminal <NUM> are connected by a plurality of via plugs <NUM> formed in the substrate <NUM>. Similarly, the pad <NUM> and the electrode <NUM> are connected by a via plug <NUM>.

In the light emitting element <NUM> in the drawing, a wiring path for reaching the cathode electrode <NUM> via the terminal <NUM>, the via plugs <NUM>, the pad <NUM>, and the solder <NUM> has a relatively-short wiring distance, and the cathode electrode <NUM> and the pad <NUM> are surface-mounted. Thus, interconnection resistance becomes small and the parasitic inductance becomes small as well. On the other hand, a wiring path for reaching the anode electrode <NUM> via the electrode <NUM>, the via plug <NUM>, the pad <NUM> and, the bonding wires <NUM> has relatively-higher interconnection resistance mainly due to the bonding wires <NUM>, and the parasitic inductance becomes large as well. For shortening a rising time of a light emission current flowing through the wiring path, it is necessary to reduce the parasitic inductance of the wiring path connected to the anode electrode <NUM>. For example, by connecting the plurality of bonding wires <NUM> in parallel, it is possible to reduce the parasitic inductance.

<FIG> is a diagram illustrating an example of mounting of the light emitting element according to the second embodiment of the present disclosure. The drawing is a diagram illustrating the layout of wires on a circuit substrate on which the light emitting element <NUM>, the light emission current switch <NUM>, and the like are mounted, and a state of mounting of the light emitting element <NUM>. Note that, in the drawing, the illustration of the snubber circuits <NUM> and <NUM> is omitted. Furthermore, the connection of the light emission current switch <NUM>, the preliminary current switch <NUM>, and the like is schematically illustrated.

As illustrated in the drawing, the wires <NUM> and <NUM> are formed on one wiring pattern, and the wires <NUM> and <NUM> are formed on another wiring pattern. The terminals <NUM> and <NUM> of the light emitting element <NUM> are mounted on these wiring patterns by soldering, for example. Therefore, the wires <NUM> and <NUM> constituting a light emission current wire, and the wires <NUM> and <NUM> constituting a preliminary current wire can be separated. As illustrated in the drawing, the parasitic inductances L exist in the wires <NUM> and <NUM>. By flowing a preliminary current in the wires <NUM> and <NUM>, these parasitic inductances can be excited. On the other hand, while parasitic inductances L' exist also in the wires <NUM> and <NUM>, the parasitic inductances L' do not affect the rising of a light emission current.

Because the wires <NUM> and <NUM> and the wires <NUM> and <NUM> are separated across the terminals <NUM> and <NUM>, it is possible to reduce a common impedance, and flow a preliminary current throughout the wires <NUM> and <NUM> on the substrate when flowing the preliminary current. In other words, a range in which a parasitic inductance affecting the rising of a light emission current is generated can be restricted to the wires inside the light emitting element <NUM>, and the influence of the parasitic inductance can be reduced.

Note that the configuration of the light emission device <NUM> is not limited to this example. For example, the frame <NUM> and the like in the light emitting element <NUM> may be omitted, and the light emission chip <NUM> can be mounted by bear chip mounting on a substrate on which the light emission current switch <NUM> and the like are mounted.

Because the configuration of the light emission device <NUM> other than this is similar to the configuration of the light emission device <NUM> that has been described in the first embodiment of the present disclosure, the description will be omitted.

As described above, the light emission device <NUM> according to the second embodiment of the present disclosure can flow a preliminary current in the wires <NUM> to <NUM> in a case where the light emitting element <NUM> having a configuration including two terminals is used, and a rising time of a light emission current flowing in the light emitting element <NUM> in the light emission period can be shortened.

The light emission device <NUM> according to the above-described second embodiment uses the light emitting element <NUM> having a configuration including two terminals. In contrast to this, a light emission device <NUM> according to the third embodiment of the present disclosure differs from the above-described second embodiment in that an element in which terminals on an anode side are separated into two is used.

<FIG> is a diagram illustrating a configuration example of a light emission device according to the third embodiment of the present disclosure. Similarly to <FIG>, the drawing is a circuit diagram illustrating a configuration example of the light emission device <NUM>. The light emission device <NUM> in the drawing differs from the light emission device <NUM> described with reference to <FIG>, in that a light emitting element <NUM> is used in place of the light emitting element <NUM>, and the preliminary current switch <NUM> is directly connected to the constant current source <NUM>.

The light emitting element <NUM> includes terminals <NUM> to <NUM>. A wire <NUM> is connected to the terminal <NUM>, and a wire <NUM> is connected to the terminal <NUM>. Furthermore, a wire <NUM> is omitted, and the preliminary current switch <NUM> is connected between the wire <NUM> and a wire <NUM>. Because the wire connection other than this is similar to that in <FIG>, the description will be omitted.

The terminals <NUM> and <NUM> of the light emitting element <NUM> are connected in common to an anode of the light emission chip <NUM>. Unlike the circuit described with reference to <FIG>, a preliminary current flows via the wire <NUM>, the terminal <NUM>, the anode of the light emission chip <NUM>, the terminal <NUM>, the preliminary current switch <NUM>, and the wire <NUM>. In other words, in the light emission current switch <NUM>, a preliminary current does not flow and only a light emission current flows. In the light emitting element <NUM> in the drawing, the terminal <NUM> serves as a preliminary current terminal.

<FIG> is a plan view illustrating a configuration example of a light emitting element according to the third embodiment of the present disclosure. The drawing is a plan view illustrating a configuration example of the light emitting element <NUM>. On a substrate <NUM> in the drawing, the terminal <NUM> is arranged adjacent to the terminal <NUM>, and a pad <NUM> corresponding to the terminal <NUM> is arranged adjacent to a pad <NUM>. The terminal <NUM> and the pad <NUM> are connected by a via plug (not illustrated). Similarly to the light emitting element <NUM> described with reference to <FIG>, an anode electrode <NUM> and the pad <NUM> are connected by bonding wires <NUM>. On the other hand, the anode electrode <NUM> and the pad <NUM> are connected by bonding wires <NUM>. In this manner, the anode electrode <NUM> is connected with the terminals <NUM> and <NUM> through different wiring paths.

<FIG> is a diagram illustrating an example of mounting of the light emitting element according to the third embodiment of the present disclosure. The drawing is a diagram illustrating the layout of wires and a state of mounting of the light emitting element <NUM> similarly to <FIG>.

As illustrated in the drawing, the wire <NUM> is connected to the terminal <NUM> of the light emitting element <NUM>, and the wire <NUM> is connected to the terminal <NUM>. Unlike the layout of wires in <FIG>, the wires <NUM> and <NUM> are formed on different wiring patterns in a separated manner. Therefore, paths connecting the anode electrode <NUM> of the light emission chip <NUM> and the wires <NUM> and <NUM>, which have been described with reference to <FIG>, can be separated. A range in which a parasitic inductance affecting the rising of a light emission current is generated can be restricted to the anode electrode <NUM> of the light emission chip <NUM>, and the influence of the parasitic inductance can be further reduced.

<FIG> is a diagram illustrating an example of a driving method of the light emission device according to the third embodiment of the present disclosure. Similarly to <FIG>, the drawing is a diagram illustrating a relationship between control signals of the preliminary current switch <NUM> and the light emission current switch <NUM>, and currents of the preliminary current switch <NUM>, the light emission current switch <NUM>, and the light emitting element <NUM>. The description of parts similar to those in <FIG> will be omitted.

At T1, an ON signal is applied to the preliminary current switch <NUM>. Therefore, the preliminary current switch <NUM> transitions to the conductive state, and a preliminary current starts to flow in the wire <NUM> from the wire <NUM> through an anode of the light emission chip <NUM>. Similarly to <FIG>, a preliminary current increasing like a ramp function flows.

At T2, the application of the ON signal to the preliminary current switch <NUM> is stopped and the preliminary current switch <NUM> is caused to transition to the nonconductive state, and an ON signal is applied to the light emission current switch <NUM> and the light emission current switch <NUM> is caused to transition to the conductive state. A flow path of a current Id that had been flowing in the preliminary current switch <NUM> changes to the light emitting element <NUM> and the light emission current switch <NUM>, and the current Id flows through the changed flow path. Because the parasitic inductance of a wiring path for reaching the anode of the light emission chip <NUM> from the wire <NUM> and the terminal <NUM> of the light emitting element <NUM> is excited by the preliminary current, a rising time of a current flowing in the light emission current switch <NUM> and the light emitting element <NUM> can be shortened.

At T3, the application of the ON signal to the light emission current switch <NUM> is stopped. Therefore, the light emission current switch <NUM> transitions to the nonconductive state, a light emission current flowing in the light emitting element <NUM> is blocked, and emission of laser light from the light emitting element <NUM> is stopped.

As described with reference to <FIG>, as compared with a wire on the cathode side of the light emission chip <NUM>, a wire on the anode side has a relatively-large parasitic inductance due to the influence of bonding wires. In view of the foregoing, as illustrated in <FIG>, by separating wires on the anode side into bonding wires <NUM> and <NUM>, and flowing a preliminary current in both of the bonding wires <NUM> and <NUM>, the parasitic inductance of a path for reaching the anode electrode <NUM> from the terminal <NUM> of the light emitting element <NUM> can be further excited. Therefore, a rising time of a light emission current can be shortened. For example, in a case where a light emission current is set to <NUM> A, a rising time of the light emission current of the light emitting element <NUM> can be set to about <NUM> ps. Even in a case where a light emission period is short, the light emission device <NUM> according to the present disclosure can be applied. For example, the light emission device <NUM> according to the present disclosure can be applied to pulse driving that repeats a light emission period of <NUM> ns, and the like.

<FIG> is a plan view illustrating another configuration example of a light emitting element according to the third embodiment of the present disclosure. The drawing is a plan view illustrating another configuration example of the light emitting element <NUM>. In the light emitting element <NUM> in the drawing, pads <NUM> and <NUM> are respectively arranged adjacent to two facing sides of a rectangular light emission chip <NUM>. From the anode electrode <NUM>, the bonding wires <NUM> are connected to the pad <NUM> and the bonding wires <NUM> are connected to the pad <NUM>. Because the bonding wires <NUM> and <NUM> can be arranged on different sides of the light emission chip <NUM>, relatively-larger numbers of bonding wires <NUM> and <NUM> can be arranged. Connection resistance can be further reduced.

Because the configuration of the light emission device <NUM> other than this is similar to the configuration of the light emission device <NUM> that has been described in the third embodiment of the present disclosure, the description will be omitted.

As described above, the light emission device <NUM> according to the third embodiment of the present disclosure includes the light emitting element <NUM> in which the pad <NUM> and the bonding wires <NUM>, and the pad <NUM> and the bonding wires <NUM> are arranged as wires on the anode side of the light emission chip <NUM>. These two wires are respectively connected to the terminal <NUM> serving as a light emission current terminal, and the terminal <NUM> serving as a preliminary current terminal. Therefore, the influence of parasitic inductances of wires on the anode side of the light emission chip <NUM> can be reduced. On the other hand, by performing solder mounting, parasitic inductances of wires on the cathode side of the light emission chip <NUM> can be reduced, and an easier mounting (connection) method can be applied.

The light emission device <NUM> according to the above-described third embodiment uses the light emitting element <NUM> having a configuration including three terminals, and performs driving by flowing a preliminary current and a light emission current. In contrast to this, a light emission device <NUM> according to the fourth embodiment of the present disclosure differs from the above-described third embodiment in that a bias current is further supplied to a light emitting element.

<FIG> is a diagram illustrating a configuration example of a light emission device according to the fourth embodiment of the present disclosure. Similarly to <FIG>, the drawing is a circuit diagram illustrating a configuration example of the light emission device <NUM>. The light emission device <NUM> in the drawing differs from the light emission device <NUM> described with reference to <FIG>, in that a switch <NUM> and a constant current source <NUM> are further included.

One end of the switch <NUM> is connected to the wire <NUM>, and another end of the switch <NUM> is grounded via the constant current source <NUM>. Because the wire connection of the circuits other than this is similar to that in the light emission device <NUM> illustrated in <FIG>, the description will be omitted.

The switch <NUM> is an element reversibly transitioning to two states including a conductive state and a nonconductive state, and a MOS transistor can be used similarly to the preliminary current switch <NUM> and the light emission current switch <NUM>. The switch <NUM> is a switch that controls a bias current to be flowed in the light emitting element <NUM>. Here, the bias current is a current flowed in the light emitting element <NUM> before a light emission period, and is a current smaller than a light emission current. As described with reference to <FIG>, by flowing a forward current in the light emission chip <NUM>, a carrier is injected and laser light is emitted. However, for emitting laser light, it is necessary to inject a carrier with predetermined concentration, and a time lag is generated between a supply start of the forward current and the emission of laser light. In view of the foregoing, by flowing the bias current in the light emitting element <NUM> before the light emission period, a time lag until the emission of laser light can be shortened. A current close to a light emission threshold, which is a threshold current for generating light emission in the light emitting element <NUM>, for example, can be applied as the bias current. For example, a current with <NUM> mA can be adopted as the bias current.

The constant current source <NUM> is a circuit that flows the bias current in the light emitting element <NUM>. The constant current source <NUM> is a circuit that restricts a current flowing in the light emitting element <NUM>, to a predetermined bias current on the basis of a source voltage supplied from the power line Vdd, similarly to the constant current source <NUM>.

Note that a circuit including the switch <NUM> and the constant current source <NUM> serves as an example of a bias circuit described in the appended claims.

<FIG> is a diagram illustrating an example of a driving method of the light emission device according to the fourth embodiment of the present disclosure. The drawing is a diagram illustrating a relationship between control signals of the preliminary current switch <NUM>, the light emission current switch <NUM>, and the switch <NUM>, and currents of the preliminary current switch <NUM>, the light emission current switch <NUM>, the switch <NUM>, and the light emitting element <NUM>. The description of parts similar to those in <FIG> will be omitted.

At T1, ON signals are applied to the preliminary current switch <NUM> and the switch <NUM>. Therefore, the preliminary current switch <NUM> and the switch <NUM> transition to the conductive state, a preliminary current flows and a bias current Ib flows in the light emitting element <NUM>. Because the bias current Ib being a current close to the light emission threshold flows in the light emitting element <NUM>, a carrier is injected to p-n junction of the light emission chip <NUM> incorporated inside the light emitting element <NUM>.

At T2, the application of the ON signal to the preliminary current switch <NUM> is stopped, and the ON signal is applied to the light emission current switch <NUM>. In addition to the bias current Ib, the current Id flows in the light emitting element <NUM>. Because a carrier is injected to the light emission chip <NUM> in the period from T1 to T2, the light emitting element <NUM> starts to emit laser light immediately after the inflow of the current Id.

At T3, the application of the ON signals to the switch <NUM> and the light emission current switch <NUM> is stopped. Therefore, emission of laser light from the light emitting element <NUM> is stopped.

In this manner, by flowing the bias current in the light emitting element <NUM> before the light emission period, a latency time of emission of laser light from the light emitting element <NUM> can be shortened. It is possible to reduce an error generated when the light emission device <NUM> is used in a distance measuring sensor or the like.

As described above, the light emission device <NUM> according to the fourth embodiment of the present disclosure can further shorten a time from the supply of a light emission current to the emission of laser light in the light emitting element <NUM>, by flowing the bias current in the light emitting element <NUM>.

The light emission device <NUM> according to the above-described third embodiment restricts a current flowing in the light emitting element <NUM>, using the constant current source <NUM>. In contrast to this, a light emission device <NUM> according to the fifth embodiment of the present disclosure differs from the above-described third embodiment in that a current flowing in the light emitting element <NUM> is restricted using a resistor.

<FIG> is a diagram illustrating a configuration example of a light emission device according to the fifth embodiment of the present disclosure. Similarly to <FIG>, the drawing is a circuit diagram illustrating a configuration example of the light emission device <NUM>. The light emission device <NUM> in the drawing differs from the light emission device <NUM> described with reference to <FIG>, in that resistors <NUM> and <NUM> are included in place of the constant current source <NUM>.

One end of the preliminary current switch <NUM> is connected to the wire <NUM> via the resistor <NUM>, and another end of the preliminary current switch <NUM> is grounded. One end of the light emission current switch <NUM> is connected to the wire <NUM> via the resistor <NUM>, and another end of the light emission current switch <NUM> is grounded. The snubber circuit <NUM> is connected between the wire <NUM> and the grounding wire, and the snubber circuit <NUM> is connected between the wire <NUM> and the grounding wire. Because the wire connection of the circuits other than this is similar to that in the light emission device <NUM> illustrated in <FIG>, the description will be omitted.

Note that a wire <NUM> between the preliminary current switch <NUM> and the resistor <NUM>, and a wire <NUM> between the preliminary current switch <NUM> and the grounding wire constitute a preliminary current wire together with the wire <NUM>. A wire <NUM> between the light emission current switch <NUM> and the resistor <NUM>, and the wire <NUM> between the light emission current switch <NUM> and the grounding wire constitute a light emission current wire together with the wires <NUM> and <NUM>.

The resistor <NUM> is a resistor that restricts a preliminary current to a predetermined value. A preliminary current that flows when the preliminary current switch <NUM> transitions to the conductive state is restricted to a value obtained by dividing a source voltage supplied from the power line Vdd, using the resistor <NUM>, if ON resistance of the preliminary current switch <NUM> in the conductive state and the like are ignored.

The resistor <NUM> is a resistor that restricts a light emission current flowing in the light emitting element <NUM>, to a predetermined value. A light emission current that flows when the light emission current switch <NUM> transitions to the conductive state is restricted to a value obtained by dividing a source voltage supplied from the power line Vdd, using the resistor <NUM>, if ON resistance of the light emission current switch <NUM> in the conductive state, a forward voltage of the light emitting element <NUM>, and the like are ignored.

By changing values of the resistors <NUM> and <NUM>, a preliminary current and a light emission current can be individually set. For example, the resistors <NUM> and <NUM> having values that set the preliminary current and the light emission current to substantially equal currents can be adopted. Note that a circuit including the resistor <NUM> and the power line Vdd serves as an example of a power circuit described in the appended claims. A circuit including the resistor <NUM> and the power line Vdd serves as an example of a power circuit described in the appended claims.

On the other hand, the resistors <NUM> and <NUM> having values that set the preliminary current and the light emission current to currents with different values can also be adopted. In a case where the preliminary current and the light emission current are set to currents with different values, a light emission current that flows when a period is shifted from a period for flowing a preliminary current, to the light emission period can be changed. An example of a case where the preliminary current and the light emission current are set to currents with different values will be described next.

<FIG> is a diagram illustrating an example of a driving method of the light emission device according to the fifth embodiment of the present disclosure. The drawing is a diagram illustrating a relationship between control signals of the preliminary current switch <NUM> and the light emission current switch <NUM>, and currents of the preliminary current switch <NUM>, the light emission current switch <NUM>, and the light emitting element <NUM>. The description of parts similar to those in <FIG> will be omitted.

In the example in the drawing, a current set by the resistor <NUM> is denoted by Idl, and a current set by the resistor <NUM> is denoted by Id2. Furthermore, the current Id1 is a current larger than the current Id2.

At T1, an ON signal is applied to the preliminary current switch <NUM>. Therefore, the preliminary current switch <NUM> transitions to the conductive state, and the current Id1 flows.

At T2, the application of the ON signal to the preliminary current switch <NUM> is stopped, and the ON signal is applied to the light emission current switch <NUM>. As described above, because the current Id1 is larger than the current Id2, due to the influence of the parasitic inductance of the wire <NUM> and the like, the current Id1 flows as a light emission current in the light emitting element <NUM> immediately after the shift to T2. The current changes from Id1 to Id2 like a ramp function. In this manner, at the beginning of the light emission period, a light emission current larger than the current Id2 set by the resistor <NUM> flows.

At T3, the application of the ON signal to the light emission current switch <NUM> is stopped. Therefore, the current Id2 that had been flowing in the light emitting element <NUM> is blocked.

During an initial period To in the light emission period, a current larger than the current Id2 flows in the light emitting element <NUM>. By the current flowing during the period To, an excessive current larger than a steady light emission current (Id2) in the light emission period flows in the light emission chip <NUM> of the light emitting element <NUM>. Therefore, charging of the parasitic capacitance of the light emission chip <NUM> such as, for example, capacitance components between the anode electrode <NUM> and the cathode electrode <NUM> that have been described with reference to <FIG> can be performed at high speed, and the application of a voltage to the semiconductor region <NUM> can be performed at high speed. Furthermore, injection of the carrier to the light emission chip <NUM> can also be performed at high speed.

In this manner, by flowing a light emission current with a high value in the light emitting element <NUM> at the beginning of the light emission period, it becomes possible to execute so-called overdrive, and shorten a light emission latency time.

<FIG> is a diagram illustrating another configuration example of a light emission device according to the fifth embodiment of the present disclosure. A light emission device <NUM> in the drawing is different from the light emission device <NUM> described with reference to <FIG>, in that a resistor <NUM> and a switch <NUM> are further included. Note that, in the drawing, the illustration of reference numerals of the wire <NUM> and the like is omitted.

One end of the switch <NUM> is connected to the terminal <NUM> of the light emitting element <NUM> via the resistor <NUM>, and another end of the switch <NUM> is grounded. Because the wire connection of the circuits other than this is similar to that in the light emission device <NUM> illustrated in <FIG>, the description will be omitted.

The switch <NUM> transitions to the conductive state in the light emission period, and controls a light emission current with a value different from the light emission current switch <NUM>.

The resistor <NUM> is a resistor that restricts a light emission current flowing in the light emitting element <NUM>, to a predetermined value. By individually flowing a light emission current via the resistor <NUM> using the switch <NUM>, a light emission current with a different value can be flowed in the light emitting element <NUM>. In other words, a light emission current flowing in the light emitting element <NUM> during the light emission period can be changed. Specifically, the resistor <NUM> can be set to a resistance value varying in accordance with the current Id1 described with reference to <FIG>, and during the period To, the switch <NUM> can be caused to transition to the conductive state in place of the light emission current switch <NUM>. Therefore, the current Id1 having a rectangular waveform can be supplied to the light emitting element <NUM>.

Note that the configuration of the light emission device <NUM> is not limited to this example. For example, a light emission current can be changed by causing the switch <NUM> to transition to the conductive state during a period other than the initial period of the light emission period.

Note that, in the fifth embodiment of the present disclosure, a preliminary current and a light emission current are restricted using the resistors <NUM> and <NUM>, but the constant current source <NUM> and the like can be applied similarly to the other embodiments. Furthermore, in the above-described first to fourth embodiments, a circuit that uses the resistors <NUM> and <NUM> in place of the constant current source <NUM> can be employed.

As described above, the light emission device <NUM> according to the fifth embodiment of the present disclosure can further shorten a light emission latency time by flowing a light emission current with a different value in the light emitting element <NUM>.

In the light emission device <NUM> according to the above-described third embodiment, wires on the anode side of the light emission chip <NUM> are branched into the two terminals <NUM> and <NUM> of the light emitting element <NUM>. In contrast to this, a light emission device <NUM> according to the sixth embodiment of the present disclosure differs from the above-described third embodiment in that wires on the cathode side of the light emission chip <NUM> are branched into two terminals of a light emitting element.

<FIG> is a diagram illustrating a configuration example of a light emission device according to the sixth embodiment of the present disclosure. Similarly to <FIG>, the drawing is a circuit diagram illustrating a configuration example of the light emission device <NUM>. The light emission device <NUM> in the drawing differs from the light emission device <NUM> described with reference to <FIG>, in that a light emitting element <NUM> is included in place of the light emitting element <NUM>.

The light emitting element <NUM> includes terminals <NUM>, <NUM>, and <NUM>. One end of the constant current source <NUM> is connected to the power line Vdd, and another end is connected to one end of the preliminary current switch <NUM> and one end of the light emission current switch <NUM>. Another end of the preliminary current switch <NUM> is connected to the terminal <NUM> of the light emitting element <NUM> via the wire <NUM>, and another end of the light emission current switch <NUM> is connected to the terminal <NUM> of the light emitting element <NUM> via the wire <NUM>. The terminal <NUM> of the light emitting element <NUM> is grounded. The snubber circuit <NUM> is connected between the power line Vdd and the wire <NUM>, and the snubber circuit <NUM> is connected between the power line Vdd and the wire <NUM>. Furthermore, the snubber circuits <NUM> and <NUM> are connected to the power line Vdd being a low-impedance node.

The light emitting element <NUM> is different from the light emitting element <NUM> in that the anode of the light emission chip <NUM> is connected to the shared terminal <NUM>, and the cathode is connected to the two terminals <NUM> and <NUM> in a separated manner.

As described above, the light emission device <NUM> according to the sixth embodiment of the present disclosure can make the rising of a light emission current faster in the light emitting element <NUM> in which wires to the cathode of the light emission chip <NUM> are connected to two terminals in a separated manner.

The light emission device <NUM> according to the above-described second embodiment has a configuration in which the light emitting element <NUM> including the light emission chip <NUM> is mounted on a circuit substrate. In contrast to this, a light emission device <NUM> according to the seventh embodiment of the present disclosure differs from the above-described third embodiment in that semiconductor elements such as the light emission chip <NUM>, the preliminary current switch <NUM>, and the light emission current switch <NUM> are sealed in one package.

<FIG> is a diagram illustrating a configuration example of a light emission device according to the seventh embodiment of the present disclosure. Similarly to <FIG>, the drawing is a circuit diagram illustrating a configuration example of the light emission device <NUM>. The light emission device <NUM> in the drawing differs from the light emission device <NUM> described with reference to <FIG>, in that the constant current source <NUM> is omitted, and the light emission chip <NUM> is mounted in place of the light emitting element <NUM>. Furthermore, in the light emission device <NUM> in the drawing, MOS transistors <NUM> and <NUM> are arranged as examples of the preliminary current switch <NUM> and the light emission current switch <NUM>. As the MOS transistors <NUM> and <NUM>, n-channel MOS transistors can be used.

The light emission device <NUM> in the drawing has a configuration in which the light emission chip <NUM>, the MOS transistors <NUM> and <NUM>, and the snubber circuits <NUM> and <NUM> are sealed in one package. In other words, the light emission device <NUM> in the drawing has a modular configuration including the light emission chip <NUM>, MOS transistors, and the like, as an example.

The light emission device <NUM> in the drawing includes terminals <NUM> to <NUM>. The terminal <NUM> is connected to an anode of the light emission chip <NUM> via the wire <NUM>. A drain of the MOS transistor <NUM> is connected to the anode of the light emission chip <NUM> via the wire <NUM>. A source of the MOS transistor <NUM> is connected to a cathode of the light emission chip <NUM> via the wire <NUM>. A drain of the MOS transistor <NUM> is connected to the cathode of the light emission chip <NUM> via the wire <NUM>. A cathode of the MOS transistor <NUM> is connected to the terminal <NUM> via the wire <NUM>. A gate of the MOS transistor <NUM> is connected to the terminal <NUM>, and a gate of the MOS transistor <NUM> is connected to the terminal <NUM>. The snubber circuit <NUM> is connected between the wire <NUM> and the terminal <NUM>. The snubber circuit <NUM> is connected between the wire <NUM> and the terminal <NUM>.

A power circuit that supplies a preliminary current and a light emission current can be connected to the terminals <NUM> and <NUM> of the light emission device <NUM> in the drawing. Specifically, the terminal <NUM> can be connected to the power line Vdd, and the terminal <NUM> can be connected to the constant current source <NUM> described with reference to <FIG>. Furthermore, the drawing illustrates a control unit <NUM> that generates a control signal for controlling the light emission device <NUM>. The control unit <NUM> can generate ON signals of the MOS transistors <NUM> and <NUM>, and supply the ON signals as control signals. The terminals <NUM> and <NUM> are connected to the control unit <NUM>, and control signals corresponding to the MOS transistors <NUM> and <NUM> are respectively supplied. Furthermore, the terminal <NUM> can be connected to a low-impedance node. Specifically, the terminal <NUM> can be grounded.

In this manner, by mounting the light emission chip <NUM> and semiconductor elements on one package, the light emission device <NUM> can be downsized.

Note that the configuration of the light emission device <NUM> is not limited to this example. For example, a configuration in which the control unit <NUM> is mounted on one package together with the light emission chip <NUM> can also be employed.

Note that, in the above-described first to sixth embodiments, a configuration in which the light emission device <NUM> includes the control unit <NUM> can also be employed.

Because the configuration of the light emission device <NUM> other than this is similar to the configuration of the light emission device <NUM> that has been described in the second embodiment of the present disclosure, the description will be omitted.

As described above, the light emission device <NUM> according to the seventh embodiment of the present disclosure can downsize the light emission device <NUM> by mounting the light emission chip <NUM> and the semiconductor elements on one package.

The technology according to the present disclosure (present technology) can be applied to various products. For example, the present technology may be implemented as a light emission device mounted on an imaging device such as a camera.

<FIG> is a block diagram illustrating a schematic configuration example of a camera serving as an example of an imaging device to which the present technology can be applied. A camera <NUM> in the drawing includes a lens <NUM>, an image sensor <NUM>, an imaging control unit <NUM>, a lens drive unit <NUM>, an image processing unit <NUM>, an operation input unit <NUM>, a frame memory <NUM>, a display unit <NUM>, a recording unit <NUM>, and a light emission device <NUM>.

The lens <NUM> is an image capturing lens of the camera <NUM>. The lens <NUM> condenses light from a subject to enter the image sensor <NUM>, which will be described below, and forms an image of the subject.

The image sensor <NUM> is a semiconductor element that captures an image on the basis of light from the subject condensed by the lens <NUM>. The image sensor <NUM> generates an analog image signal corresponding to emitted light, converts the analog image signal into a digital image signal, and outputs the digital image signal.

The imaging control unit <NUM> controls image capturing in the image sensor <NUM>. The imaging control unit <NUM> controls the image sensor <NUM> by generating a control signal and outputting the control signal to the image sensor <NUM>. Furthermore, the imaging control unit <NUM> can perform autofocusing in the camera <NUM> on the basis of an image signal output from the image sensor <NUM>. Here, the autofocusing is a system for detecting a focal position of the lens <NUM>, and automatically adjusting the focal position. As the autofocusing, a method of detecting a focal position by detecting an image plane phase difference on the basis of phase difference pixels arranged in the image sensor <NUM> (image plane phase difference autofocusing) can be used. Furthermore, a method of detecting a position at which image contrast becomes the highest, as a focal position (contrast autofocusing) can also be applied. The imaging control unit <NUM> performs autofocusing by adjusting the position of the lens <NUM> via the lens drive unit <NUM> on the basis of the detected focal position. Note that the imaging control unit <NUM> can be formed by, for example, a digital signal processor (DSP) provided with firmware.

The lens drive unit <NUM> drives the lens <NUM> on the basis of the control of the imaging control unit <NUM>. The lens drive unit <NUM> can drive the lens <NUM> by changing the position of the lens <NUM> using a built-in motor.

The image processing unit <NUM> processes an image signal generated by the image sensor <NUM>. Examples of the processing include demosaic for generating an image signal of a deficient color among image signals corresponding to red, green, and blue for each pixel, noise reduction for removing noise of an image signal, encoding of an image signal, and the like. The image processing unit <NUM> can be formed by, for example, a microcomputer provided with firmware.

The operation input unit <NUM> receives an operation input from a user of the camera <NUM>. For example, a press button or a touch panel can be used as the operation input unit <NUM>. An operation input received by the operation input unit <NUM> is transmitted to the imaging control unit <NUM> and the image processing unit <NUM>. Thereafter, processing corresponding to the operation input such as, for example, image capturing processing of a subject is activated.

The frame memory <NUM> is a memory that stores a frame being an image signal corresponding to one screen. The frame memory <NUM> is controlled by the image processing unit <NUM>, and holds a frame in the process of image processing.

The display unit <NUM> displays an image processed by the image processing unit <NUM>. For example, a liquid crystal panel can be used as the display unit <NUM>.

The recording unit <NUM> records an image processed by the image processing unit <NUM>. For example, a memory card or a hard disc can be used as the recording unit <NUM>.

The light emission device <NUM> emits laser light for measuring a distance to a subject. Furthermore, the above-described imaging control unit <NUM> further performs control of the light emission device <NUM> and measurement of a distance to a subject. The measurement of a distance to a subject in the camera <NUM> can be performed in the following manner. First of all, the imaging control unit <NUM> controls the light emission device <NUM> to emit laser light. Next, laser light reflected by a subject is detected by the image sensor <NUM>. Next, the imaging control unit <NUM> measures a time from when laser light is emitted from the light emission device <NUM>, to when laser light is detected by the image sensor <NUM>, and calculates a distance to the subject.

Heretofore, a camera to which the present invention can be applied has been described. Among the configurations described above, the present technology can be applied to the light emission device <NUM>. Specifically, the light emission device <NUM> described with reference to <FIG> can be applied to the light emission device <NUM>. If the light emission device <NUM> is applied to the light emission device <NUM>, high-speed emission of laser light can be performed.

Note that, here, a camera has been described as an example, but the present technology may be applied to other devices such as a mobile terminal or an unmanned carrier, for example.

Lastly, the above description of each embodiment is an example of the present disclosure, and the present disclosure is not limited to the above-described embodiments. Thus, it should be appreciated that various changes can be made in accordance with the design and the like without departing from the technical idea according to the present disclosure, aside from the above-described embodiments.

Claim 1:
A light emission drive circuit comprising:
a light emission current wire (<NUM>) configured to flow a light emission current for causing a light emitting element (<NUM>) to emit light, in the light emitting element (<NUM>);
a light emission current switch (<NUM>) that is connected to the light emission current wire (<NUM>), and is configured to control the light emission current;
a preliminary current wire (<NUM>) configured to flow, in the light emission current wire (<NUM>), a preliminary current for exciting an inductance component (<NUM>) of the light emission current wire (<NUM>) before a light emission period being a period in which the light emission current flows in the light emitting element (<NUM>); and
a preliminary current switch (<NUM>) that is connected to the preliminary current wire (<NUM>), and is configured to control the preliminary current,
wherein one end of the preliminary current switch (<NUM>) is connected to the preliminary current wire (<NUM>) via a first resistor (<NUM>), and another end of the preliminary current switch (<NUM>) is grounded, and wherein one end of the light emission current switch (<NUM>) is connected to the light emission current wire (<NUM>) via a second resistor (<NUM>), and another end of the light emission current switch (<NUM>) is grounded.