JP2012074438A - Signal transmission device and inspection method of temperature compensation of light emitting device - Google Patents

Abstract

A temperature compensation inspection of a light emitting element is realized by a simple method.
In an element driving IC 12, a switching signal is input via an external terminal 52 to switch the switch, and a voltage applied to a temperature compensating unit 42 is supplied from the reference voltage generating unit 41 side. Switch to the external terminal 51 side. By applying a predetermined inspection voltage corresponding to the temperature to the temperature compensation unit 42 via the external terminal 51, the accuracy of temperature compensation of the light emitting element 11 by the temperature compensation unit 42 can be inspected by a simple method. it can.
[Selection] Figure 2

Description

  The present invention relates to a signal transmission apparatus for performing data transmission and a method for inspecting temperature compensation of a light emitting element included in the signal transmission apparatus.

  In recent years, a technique for performing data transmission between various electronic devices mounted on a vehicle such as an automobile using an optical cable is known. An electronic device connected by an optical cable includes a connector for connecting the optical cable, and this connector includes a photoelectric conversion module called FOT (Fiber Optic Transcever). This photoelectric conversion module converts between an optical signal and an electrical signal.

  A photoelectric conversion module having a transmission function is mainly composed of, for example, a light emitting element and an element driving IC. Here, the element driving IC functions as a signal transmission device that performs data transmission. By driving the light emitting element, the element driving IC responds to a data signal that is an electrical signal from an electronic device (for example, a control circuit). Output optical signal.

  Since the output power and extinction ratio of the light emitting element vary depending on the temperature, in order to keep them constant, it is necessary to control the current value of the drive current supplied to the light emitting element by the element driving IC according to the temperature. Yes (temperature compensation). For example, Patent Document 1 discloses a semiconductor light emitting module capable of accurate constant output by temperature compensation. In this semiconductor light emitting module, a control circuit that controls the output of the light emitting element varies based on a constant current supply unit that supplies a constant current to the light emitting element, a thermistor assembled on the circuit board, and a temperature detected by the thermistor. And a compensation current supply unit that supplies the compensated compensation current to the laser element. The control circuit supplies a total current of the constant current and the compensation current to the light emitting element.

  Patent Document 2 discloses a technique for suppressing fluctuations in the extinction ratio of an output optical signal of a light emitting element caused by fluctuations in ambient temperature. According to this method, a series circuit in which a temperature variation resistance element and a resistor are connected in series and a parallel circuit in which the temperature variation resistance element and a resistor are connected in parallel are connected in series. ing. A temperature sensing signal having a voltage value determined by the ambient temperature is generated at the connection between the series circuit and the parallel circuit. In addition, a current control unit is provided that outputs a current corresponding to the voltage value of the temperature sensing signal as a temperature compensation stabilization signal toward the light emission intensity control unit. The light emission intensity control unit uses the stabilization signal to generate a light emitting element drive control current for controlling the light emission intensity of the light emitting element, thereby stabilizing the extinction ratio of the light emitting element.

  Note that Patent Documents 3 and 4 also disclose a technique for compensating the temperature of a light emitting element by a thermistor, as in Patent Document 1.

JP 2006-278361 A JP 2005-268622 A JP 2005-134314 A JP-A-8-139395

  By the way, when temperature compensation is performed as in the methods disclosed in Patent Documents 1 to 4, it is necessary to inspect whether or not temperature compensation is appropriately performed, that is, its compensation characteristics. Such inspection is performed for the purpose of selecting non-defective / defective products of the IC when the formation of the IC on the wafer is completed in the manufacturing process of the element driving IC. This is performed as an electrical inspection in which a voltage is applied to the electrodes of the IC using the connected wafer probe. When the compensation characteristic is inspected, the surrounding temperature environment is generally changed, and it is inspected whether or not the temperature compensation is appropriately performed each time. As described above, since it takes a lot of time to change the temperature environment, there is a problem that the inspection time per IC increases and the price of the product increases.

  The present invention has been made in view of such circumstances, and an object thereof is to realize a temperature compensation inspection of a light emitting element by a simple method.

  In order to solve such a problem, the present invention provides a signal transmission device that outputs an optical signal corresponding to an electrical signal that is a data signal from an electronic device by driving a light emitting element. Here, the signal transmission device generates an element driving unit that supplies a driving current in which a modulation current corresponding to a data signal indicating light emission information of the light emitting element is superimposed on a bias current to the light emitting element, and a voltage corresponding to the temperature. The temperature of the light emitting element based on the first voltage generation unit, the second voltage generation unit that generates a predetermined voltage regardless of the temperature, and two types of voltages applied from the first and second voltage generation units By reproducing the current characteristics, a temperature compensation unit that controls the bias current and the modulation current according to the temperature, an external terminal to which an arbitrary voltage can be applied from the outside, and the first voltage generation unit to the temperature compensation unit And a switching unit capable of switching the voltage applied to the voltage applied from the external terminal side.

  The second invention provides a method for inspecting the temperature compensation of a light emitting element for inspecting a compensation characteristic of a temperature compensating unit that performs temperature compensation on a light emitting element driven by a drive current supplied from the element driving unit. . Here, the element driving unit supplies a driving current in which a modulation current corresponding to a data signal indicating light emission information of the light emitting element is superimposed on a bias current to the light emitting element, and the temperature compensation unit generates a voltage corresponding to the temperature. By reproducing the temperature-current characteristics of the light-emitting element based on the first voltage applied and the second voltage applied as a predetermined voltage regardless of the temperature, the bias current and the modulation current are changed according to the temperature. I have control. When inspecting the compensation performance by the temperature compensation unit, the voltage applied to the temperature compensation unit as the first voltage is switched to the voltage applied from the external terminal side to which an arbitrary voltage can be applied. Thus, a first step of applying a test voltage to the temperature compensation unit via an external terminal, a second step of monitoring a bias current and a modulation current output from the temperature compensation unit in accordance with the application of the test voltage, A third step of checking the compensation performance by comparing the check voltage with the monitored bias current and modulation current;

  Here, in the second invention, it is preferable that, in the first step, the first voltage applied corresponding to a predetermined temperature is applied in a simulated manner as an inspection voltage.

  In the second invention, the temperature-current characteristics of the light-emitting element can be expressed by straight lines having different slope signs on the low temperature side and the high temperature side with respect to the change point. In this case, in the first step, the temperature at each of the two points is extracted before and after the change point in the temperature-current characteristics of the light emitting element, and each of the first voltages corresponding to the extracted temperatures at the four points is determined. It is preferable to apply as an inspection voltage.

  According to the present invention, the compensation characteristic can be inspected by applying a predetermined inspection voltage corresponding to the temperature from the external terminal. For this reason, since it is not necessary to change the temperature environment, the inspection time can be short, and the manufacturing cost can be reduced, so that the price increase of the product can be suppressed.

The block diagram which shows the structure of the optical connector 1 typically Block configuration diagram schematically showing the element driving IC 12 The block diagram which shows the structure of the electric current generation part 40 typically Explanatory drawing explaining the concept of temperature compensation The block diagram which shows the structure of the addition / subtraction part 43 Explanatory drawing which shows the function of the addition / subtraction part 43 Explanatory diagram of four temperatures E1 to E4 extracted during inspection Explanatory drawing explaining the concept of temperature compensation

  FIG. 1 is a block diagram schematically showing the configuration of an optical connector 1 according to an embodiment of the present invention. The optical connector 1 according to the present embodiment is, for example, a receptacle-type female optical connector used in the optical communication field. The optical connector 1 is provided in various electronic devices such as a display and a navigation system, and is electrically connected to a printed wiring board 2 included in the electronic device. The optical connector 1 is capable of performing large-capacity optical communication between electronic devices by connecting, for example, a male optical connector to which an optical cable is attached.

  The optical connector 1 includes a photoelectric conversion module 10 called FOT (Fiber Optic Transcever). In the photoelectric conversion module 10, a plurality of lead terminals extended from a metallic lead frame are soldered onto a printed wiring board 2 included in an electronic device.

  Further, the optical connector 1 includes a sleeve 13 as an optical component interposed between the photoelectric conversion module 10 (specifically, a light emitting element 11 to be described later) and a ferrule end face (optical cable end face) in the male optical connector. I have. The sleeve 13 is composed of a light guide member formed of a transparent material having optical transparency, and a cylindrical portion provided around the light guide member.

  The photoelectric conversion module 10 is mainly composed of a light emitting element 11 and an element driving IC 12. The light emitting element 11 and the element driving IC 12 are mounted on a conductive metal lead frame in a wire-bonded state.

  The light emitting element 11 outputs an optical signal to the optical cable side via the sleeve 13. For example, a semiconductor laser can be used as the light emitting element 11. That is, the optical connector 1 according to the present embodiment is configured as a transmission connector for transmitting an optical signal via an optical cable.

  In addition to the light emitting element 11 and the element driving IC 12, the photoelectric conversion module 10 includes a light receiving element and an element driving IC that amplifies an electric signal from the light receiving element and outputs the amplified signal as a data signal to a control circuit of the electronic device. Furthermore, by providing, you may comprise so that an optical signal can be transmitted / received.

  FIG. 2 is a block diagram schematically showing the element driving IC 12. The element driving IC 12 performs data transmission between the control circuit (printed wiring board 2) of the electronic device and the optical cable by driving the light emitting element 11. That is, the element driving IC 12 drives the light emitting element 11 according to the data signals VINP and VINN which are electric signals from the control circuit of the electronic device, and thereby the light corresponding to the data signals VINP and VINN from the light emitting element 11. Output a signal. The element driving IC 12 includes a power management unit 20 and a main control unit 30 when this is functionally grasped.

  Here, the power management unit 20 and the main control unit 30 are not only functionally separated but also the power systems are independent of each other. Specifically, a switch 15 is provided in a power supply line that supplies operating power from the power supply unit 50 to the main control unit 30. By switching the on / off state of the switch 15, the power source of the main control unit 30 can be turned on or off. If the switch 15 is on, the main control unit 30 is turned on. If the switch 15 is off, the main control unit 30 is turned off. On the other hand, the power supply line that supplies the operating power from the power supply unit 50 to the power management unit 20 is always set to ON. That is, the power management unit 20 is different from the main control unit 30 in that the power management unit 20 is constantly set in an operating state.

  The power management unit 20 manages the power on / off of the main control unit 30 based on the data signals VINP and VINN. Specifically, when the power management unit 20 determines the input of the data signals VINP and VINN, it controls the switch 15 to be turned on. If the power management unit 20 determines that the data signals VINP and VINN are not input for a predetermined period after the switch 15 is turned on, the power management unit 20 controls the switch 15 from on to off.

  The main control unit 30 is a unit that mainly performs data transmission, and specifically outputs an optical signal from the light emitting element 11 based on the data signals VINP and VINN. The main control unit 30 is mainly composed of a receiving unit 31, a buffer unit 32, an element driving unit 33, and a current generating unit 40.

  The receiving unit 31 receives data signals VINP and VINN output from the control circuit (printed wiring board 2) of the electronic device. As a specification of data transmission between the receiving unit 31 and the control circuit of the electronic device, a low voltage differential signal suitable for transmission of a high-speed digital signal called LVDS (Low Voltage Differential Signaling) can be used. The LVDS performs signal transmission using a voltage difference between transmission lines by applying different voltages to a pair of transmission lines. That is, the receiving unit 31 receives the data signals VINP and VINN via the pair of transmission lines. The data signals VINP and VINN received by the receiving unit 31 are output to the element driving unit 33 through the buffer unit 32.

  The element drive unit 33 outputs an optical signal corresponding to the data signals VINP and VINN by driving the light emitting element 11. Specifically, the element driving unit 33 supplies the light emitting element 11 with a driving current obtained by superimposing the light emission information of the light emitting element 11, that is, the modulation current Imod corresponding to the data signals VINP and VINN on the bias current Ibias. The bias current Ibias and the modulation current Imod are supplied from the current generator 40.

  FIG. 3 is a block diagram schematically showing the configuration of the current generator 40. The current generator 40 has a temperature compensation function of the light emitting element 11 and controls the bias current Ibias and the modulation current Imod according to the temperature. The current generation unit 40 includes a reference voltage generation unit 41 and a temperature compensation unit 42.

  The reference voltage generation unit 41 generates two types of voltages A and B necessary for current control accompanying temperature compensation (first and second voltage generation units). One voltage A generated by the reference voltage generator 41 tends to be a constant value regardless of the temperature. On the other hand, the other voltage B generated by the reference voltage generator 41 has a tendency that the value changes according to the temperature (ambient ambient temperature). The proportional relationship is such that the value becomes smaller. Here, FIG. 4 is an explanatory diagram for explaining the concept of temperature compensation, and (a) shows the relationship between the voltages A and B by the reference voltage generator 41 and the temperature.

  The temperature compensation unit 42 performs current control corresponding to the temperature by reproducing the temperature-current characteristics of the light-emitting element 11 based on the two types of voltages A and B applied from the reference voltage generation unit 41 (current of the current compensation). Temperature compensation). In the present embodiment, the temperature-current characteristic of the light-emitting element 11 is expressed by a straight line having a negative slope on the low temperature side and a positive slope on the high temperature side with the change point as a boundary. The temperature compensation unit 42 includes an addition / subtraction unit 43 and an output unit 44 when this is functionally grasped.

  FIG. 5 is a block diagram showing a configuration of the addition / subtraction unit 43. The addition / subtraction unit 43 includes an amplification circuit 45 that performs an amplification process on the voltage B, an amplification circuit 46 that performs an amplification process on the voltage A or an inverted output by comparison with the voltage B, and voltages A and B from the amplification circuits 45 and 46. Is composed of a synthesizing circuit 47 for synthesizing (adding and subtracting). That is, the adder / subtractor 43 performs each of amplification processing, inversion processing, and synthesis processing for each of the two types of voltages A and B generated by the reference voltage generation unit 41. Through each of these processes, the temperature voltage specification of the light-emitting element 11 expressed by a straight line having a positive slope on the low temperature side and a negative slope on the high temperature side at the change point C is reproduced (FIG. 4B). reference). Thereby, the addition / subtraction unit 43 outputs a predetermined voltage corresponding to the temperature (voltage reflecting the temperature-voltage characteristics).

  Here, as shown in FIG. 6A, by setting the gain of the amplifier circuit 45 to which the voltage B is input, the slope of the straight line on the high temperature side, that is, the high temperature side from the change point C, is set. Can do. Further, as shown in FIG. 6B, by setting the gain of the amplifier circuit 46 to which the voltage A is input, the position of the conversion point C in the vertical direction (voltage magnitude direction position) and the change point C are lower. The slope of the straight line on the side can be set. As will be described later, the gains of the amplifier circuits 45 and 46 are optimum values through experiments and simulations from the viewpoint of obtaining temperature-current characteristics (FIG. 4C) in consideration of temperature compensation of the light emitting element 11. Is preset.

  Referring to FIG. 3 again, the output unit 44 derives the temperature-current characteristic from the temperature-voltage characteristic by converting the voltage and the current, and thereby the bias current Ibias and the modulation in consideration of the temperature compensation of the light-emitting element 11. A current Imod is generated. By the conversion of the output unit 44, the temperature-current characteristics of the light-emitting element 11 expressed by the straight line having a negative slope on the low temperature side and a positive slope on the high temperature side from the above-described temperature-voltage characteristics (FIG. 4). (C)) is reproduced.

  Referring to FIG. 2 again, as one of the features of this embodiment, the element driving IC 12 includes external terminals 51 and 52 to which a predetermined signal (voltage) can be input from the outside. The function of the external terminals 51 and 52 will be described later.

  As shown in FIG. 3, a switch 53 is provided in a path through which the voltage B is applied from the reference voltage generation unit 41 to the temperature compensation unit 42 (addition / subtraction unit 43). The switch 53 can switch the voltage applied to the adder / subtractor 43 between a voltage B from the reference voltage generator 41 and an arbitrary voltage (hereinafter referred to as “test voltage”) C from the external terminal 51. . The switch 53 can be switched through a switching signal D inputted via the external terminal 52.

  In the element driving IC 12 having such a configuration, the compensation characteristic of the temperature compensation unit 42 that performs temperature compensation on the light emitting element 11 can be inspected. This inspection is executed as an electrical inspection in which a voltage is applied to the electrodes of the IC using a wafer probe connected to a tester when the formation of the IC on the wafer is completed in the manufacturing process of the element driving IC. Specifically, the inspection of the compensation performance by the temperature compensation unit 42 is performed by the following process.

  First, the switch 53 is switched by inputting the switching signal D through the external terminal 52. That is, the voltage applied to the temperature compensation unit 42 is switched from the reference voltage generation unit 41 side (voltage B according to temperature) to the external terminal 51 side (inspection voltage C). Thus, the inspection voltage C is applied to the temperature compensation unit 42 via the external terminal 51 (first process).

  Next, the bias current Ibias and the modulation current Imod output from the temperature compensation unit 42 with the application of the inspection voltage C are monitored (second step).

  Then, the compensation performance is inspected by comparing the inspection voltage C with the monitored bias current Ibias and modulation current Imod (third step).

  In such an inspection method, in the first step, the voltage B applied from the reference voltage generator 41 corresponding to a predetermined temperature is applied in a simulated manner as the inspection voltage C. In this case, as shown in FIG. 7, two temperatures are extracted before and after the change point in the temperature-current characteristics of the light emitting element 11, and the reference voltage generator 41 corresponds to the total four temperatures E1 to E4. Each of the voltages B applied from 1 is applied as an inspection voltage C.

  As described above, the temperature-current characteristic of the light-emitting element 11 is expressed by a straight line having a negative slope on the low temperature side and a positive slope on the high temperature side with the change point as a boundary. Therefore, by extracting the two temperatures E1 and E2 before the change point (lower temperature side than the change point) and applying each of the voltages B corresponding to the temperatures E1 and E2 as the inspection voltage C, the change point is obtained. A straight line on the low temperature side (temperature-current characteristic) can be simulated. Thereby, it is possible to inspect whether or not the temperature-current characteristics on the low temperature side are appropriately reflected as temperature compensation.

  On the other hand, by extracting two temperatures E3 and E4 after the change point (higher temperature than the change point) and applying each of the voltages B corresponding to the temperatures E3 and E4 as the inspection voltage C, the change point is obtained. A straight line on the high temperature side (temperature-current characteristics) can be simulated. Thereby, it is possible to inspect whether or not the temperature-current characteristics on the high temperature side are appropriately realized as temperature compensation.

  As described above, in the present embodiment, the element driving IC 20 includes the reference voltage generator 41 that generates the predetermined voltage A and the voltage B corresponding to the temperature, and the temperature that controls the bias current Ibias and the modulation current Imod according to the temperature. And a compensation unit 42. The temperature compensation unit 42 performs current control according to the temperature by reproducing the temperature-current characteristics of the light emitting element 11 based on the voltages A and B applied from the reference voltage generation unit 41.

  Since the output power and extinction ratio of the light emitting element 11 vary depending on the temperature, it is necessary to control the current value according to the temperature in order to keep them constant (temperature compensation). For example, the temperature-current characteristic of the light emitting element 11 is expressed by a straight line whose slope changes from negative to positive at the change point. Such a temperature-current characteristic is based on these two kinds of voltages A and B by having a reference voltage generation unit 41 that generates a voltage A that is a constant voltage and a voltage B that changes according to the temperature. The above-described temperature-current characteristics can be reproduced. Thereby, the temperature compensation of the light emitting element 11 can be realized with a simple and small configuration.

  Further, in the present embodiment, the element driving IC 12 supplies an external terminal 51 to which an arbitrary inspection voltage C can be applied from the outside, and a voltage applied from the reference voltage generating unit 41 to the temperature compensating unit 42 as The switch 53 (switching part) which can be switched to the voltage applied from the 51 side is provided.

  According to such a configuration, the accuracy of temperature compensation of the light emitting element 11 by the temperature compensation unit 42 can be inspected. That is, if the inspection voltage C cannot be applied via the external terminal 51, the temperature compensation accuracy must be inspected by changing the temperature environment of the element driving IC 12. In this case, as described above, it is necessary to change the temperature environment corresponding to the four temperatures, and the inspection method becomes complicated and the working time increases. In this respect, according to the present embodiment, it is sufficient to apply the predetermined inspection voltage C corresponding to the temperature from the external terminal 51, so that the temperature compensation unit 42 can be inspected by a simple method.

  In the above-described embodiment, only one temperature compensation unit 42 is provided, but a plurality of temperature compensation units 42 may be provided. In this case, each temperature compensation unit 42 is set in advance so that each process of the amplification process, the inversion process, and the synthesis process is set in accordance with various light emitting elements 11 that may be mounted. It is possible to prepare a temperature compensation unit 42 that can handle various light emitting elements 11. In the case of such a configuration, it is preferable that selection of the individual temperature compensation units 42 is realized from the outside in accordance with selection of the PAD wiring. Thereby, it is not necessary to redesign the element driving IC 12 according to the light emitting element 11, and an apparatus having excellent versatility can be provided.

  Further, according to the above-described embodiment, the temperature-current characteristics of the light-emitting element are expressed by a straight line having a negative slope (temperature slope) on the low temperature side and a positive slope (temperature slope) on the high temperature side with respect to the change point. The form which illustrated was illustrated. However, the temperature-current characteristics of the light-emitting element are various depending on the characteristics of the element, and the present invention is not limited to this.

  For example, as shown in FIG. 8, by setting the gain of the amplifier circuit 45 to which the voltage B is input and the gain of the amplifier circuit 46 to which the voltage A is input, a negative value is obtained on the low temperature side with respect to the change point C. It is possible to reproduce the temperature voltage specification of the light emitting element expressed by the slope and a straight line having a positive slope on the high temperature side ((b) in the figure). This makes it possible to reproduce the temperature-current characteristics of the light-emitting element expressed by a straight line having a positive slope on the low temperature side and a negative slope on the high temperature side as shown in FIG. It becomes.

  Further, the present invention is not limited to the above-described embodiment, and various light-emitting elements that are reproduced by setting the gain of the amplifier circuit 45 to which the voltage B is input and the gain of the amplifier circuit 46 to which the voltage A is input, respectively. The temperature compensation can be performed based on the temperature-current characteristics.

DESCRIPTION OF SYMBOLS 1 Optical connector 2 Printed wiring board 10 Photoelectric conversion module 11 Light emitting element 12 Element drive IC
DESCRIPTION OF SYMBOLS 13 Sleeve 15 Switch 20 Power management unit 30 Main control unit 31 Reception part 32 Buffer part 33 Element drive part 40 Current generation part 41 Reference voltage generation part 42 Temperature compensation part 43 Addition / subtraction part 44 Output part 45 Amplification circuit 46 Amplification circuit 47 Synthesis circuit 50 Power supply 51 External terminal (for inspection voltage C)
51 External terminal (for switching signal D)
53 switch

Claims (4)

In a signal transmission device that outputs an optical signal corresponding to an electrical signal that is a data signal from an electronic device by driving a light emitting element,
An element driving unit that supplies a driving current in which a modulation current corresponding to the data signal indicating light emission information of the light emitting element is superimposed on a bias current to the light emitting element;
A first voltage generator for generating a voltage according to temperature;
A second voltage generator that generates a predetermined voltage regardless of temperature;
Temperature compensation for controlling the bias current and the modulation current according to temperature by reproducing the temperature-current characteristics of the light-emitting element based on two kinds of voltages applied from the first and second voltage generators And
An external terminal to which an arbitrary voltage can be applied from the outside;
A signal transmission device comprising: a switching unit capable of switching a voltage applied from the first voltage generation unit to the temperature compensation unit to a voltage applied from the external terminal side. In the method for inspecting the temperature compensation of the light emitting element for inspecting the compensation characteristic of the temperature compensating unit that performs temperature compensation on the light emitting element driven by the drive current supplied from the element driving unit,
The element driver is
Supplying a driving current in which a modulation current corresponding to a data signal indicating light emission information of the light emitting element is superimposed on a bias current to the light emitting element;
The temperature compensation unit is
The bias current is reproduced by reproducing the temperature-current characteristics of the light-emitting element based on a first voltage applied as a voltage corresponding to temperature and a second voltage applied as a predetermined voltage regardless of the temperature. And controlling the modulation current according to temperature,
When inspecting the compensation performance by the temperature compensation unit,
By switching the voltage applied to the temperature compensation unit as the first voltage to the voltage applied from the external terminal side to which an arbitrary voltage can be applied, the temperature compensation unit is connected via the external terminal. A first step of applying an inspection voltage to
A second step of monitoring the bias current and the modulation current output from the temperature compensation unit upon application of the inspection voltage;
A method for inspecting temperature compensation of a light emitting device, comprising: a third step of inspecting compensation performance by comparing the inspection voltage with the monitored bias current and modulation current.   3. The temperature compensation of a light emitting element according to claim 2, wherein in the first step, the first voltage applied corresponding to a predetermined temperature is applied in a simulated manner as the inspection voltage. Inspection method. The temperature-current characteristics of the light-emitting element can be expressed by straight lines having different signs of inclination on the low temperature side and the high temperature side with respect to the change point,
In the first step, the temperature at each of the two points is extracted before and after the change point in the temperature-current characteristics of the light-emitting element, and each of the first voltages corresponding to the extracted four temperatures is obtained. The inspection method for temperature compensation of a light emitting element according to claim 2, wherein the inspection voltage is applied as the inspection voltage.

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