JP2006329892A - Light receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light receiving device that outputs a signal according to input light and can inspect an internal circuit with a simple constitution. <P>SOLUTION: The light receiving device for outputting the signal according to the input light comprises light receiving elements PDA and PDA' for converting the input light into an electrical signal, input circuits 12 and 13 for drawing current according to the electrical signal converted by the light receiving elements PDA and PDA', current mirror circuits 14 and 15 for outputting current according to the current drawn by the input circuits 12 and 13, and test circuits 111 and 112 capable of adjusting the ratio of the output current to the input current of the current mirror circuits 14 and 15 during the test. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light receiving device, and more particularly to a light receiving device that outputs a signal corresponding to input light.

  FIG. 5 is a block diagram showing an example of a conventional light receiving device.

  The conventional light receiving device 1 includes a reference voltage circuit 11, photodiodes PDA and PDA ', input circuits 12 and 13, current mirror circuits 14 and 15, a comparator 16, and resistors RA and RA'.

  The reference voltage circuit 11 is connected to the terminal T11 and generates a reference voltage Vref from the power supply voltage Vcc applied to the terminal T11. The reference voltage Vref generated by the reference voltage circuit 11 is applied to the cathodes of the photodiode PDA and the photodiode PDA ′.

  The photodiode PDA and the photodiode PDA ′ are disposed adjacent to each other. When the light receiving device 1 is mounted on a motor or the like, when light is incident on one side by the light shielding plate, the other is shielded. The amount of light incident on the photodiode PDA and the photodiode PDA ′ changes with the movement of the light shielding plate, and the amount of current flowing in the photodiode PDA and the amount of current flowing in the photodiode PDA ′ There will be a difference.

  The anode of the photodiode PDA is connected to the input circuit 12. The photodiode PDA ′ has an anode connected to the input circuit 13.

  The input circuit 12 is composed of an npn transistor QA. In the transistor QA, the anode of the photodiode PDA is connected to the base, the current mirror circuit 14 is connected to the collector, and the terminal T12 is connected to the emitter. Terminal T12 is grounded.

  The transistor QA draws current from the current mirror circuit 14 according to the amount of light incident on the photodiode PDA.

  The current mirror circuit 14 includes pnp transistors Q1 and Q2, and outputs a current corresponding to the current drawn from the transistor QA from the collector of the transistor Q2. The output current of the current mirror circuit 14 is supplied to the resistor RA. The resistor RA generates a voltage corresponding to the output current of the current mirror circuit 14 at a connection point between the collector of the transistor Q2 constituting the current mirror circuit 14 and the resistor RA. A connection point between the collector of the transistor Q2 constituting the current mirror circuit 14 and the resistor RA is connected to the inverting input terminal of the comparator 16.

  The input circuit 13 is composed of an npn transistor QA ′. The transistor QA 'has a base connected to the anode of the photodiode PDA', a collector connected to the current mirror circuit 15, and an emitter connected to a grounded terminal T12.

  The transistor QA ′ draws a current corresponding to the amount of incident light from the photodiode PDA ′ from the current mirror circuit 14.

  The current mirror circuit 15 includes pnp transistors Q4 and Q5, and outputs a current corresponding to the current drawn from the transistor QA 'from the collector of the transistor Q5. The output current of the current mirror circuit 15 is supplied to the resistor RA ′. The resistor RA ′ generates a voltage VA ′ corresponding to the output current of the current mirror circuit 15 at the connection point between the collector of the transistor Q5 constituting the current mirror circuit 15 and the resistor RA ′.

  A connection point between the collector of the transistor Q5 constituting the current mirror circuit 15 and the resistor RA 'is connected to the non-inverting input terminal of the comparator 16. The comparator 16 outputs the difference voltage between the voltage VA and the voltage VA ′ as an output voltage Vout from the terminal T13.

  FIG. 6 shows an operation explanatory diagram of a conventional example.

  In the conventional light receiving device 1, when the incident light PA to the photodiode PDA and the incident light PA ′ to the photodiode PDA ′ are the same, the voltage VA applied to the inverting input terminal of the comparator 16 and the comparator 16 Since the voltage VA 'applied to the non-inverting input terminal is substantially equal, the output voltage Vout output from the output terminal T13 is indefinite.

  If the incident light PA to the photodiode PDA is sufficiently larger than the incident light PA ′ to the photodiode PDA ′, the voltage VA of the inverting input terminal of the comparator 16 is larger than the voltage VA ′ of the non-inverting input terminal of the comparator 16. Therefore, the output of the comparator 16 is at a low level, and the output voltage Vout output from the output terminal T13 is at a low level.

  Further, if the incident light PA ′ to the photodiode PDA ′ is sufficiently larger than the incident light PA to the photodiode PDA, the voltage VA ′ of the non-inverting input terminal of the comparator 16 is larger than the voltage VA of the inverting input terminal of the comparator 16. Therefore, the output of the comparator 16 is at a high level, and the output voltage Vout output from the output terminal T13 is at a high level.

  The present applicant has investigated the above-described known technique related to the inspection of the light receiving device, but could not detect the known technique related to the inspection of the light receiving device as described above.

  However, when inspecting a conventional light receiving device, it is necessary to adjust the incident light PA to the photodiode PDA and the incident light PA ′ to the photodiode PDA ′. At this time, the pitch between the photodiode PDA and the photodiode PDA ′ is several tens μm, for example, 50 μm, so that the light incident on the photodiode PDA and the photodiode PDA ′ are incident on the photodiode PDA ′. It was very difficult to make the incident light PA ′ different. For this reason, for example, after packaging, the inspection is performed in a state similar to the actual usage state, and the wafer inspection is not performed.

  The present invention has been made in view of the above points, and an object thereof is to provide a light receiving device capable of inspecting an internal circuit with a simple configuration.

  The present invention is a light receiving device that outputs a signal corresponding to input light, and includes a light receiving element (PDA, PDA ′) that converts the input light into an electric signal and an electric signal converted by the light receiving element (PDA, PDA ′). An input circuit (12, 13) for drawing a current according to a signal, a current mirror circuit (14, 15) for outputting a current according to a current drawn by the input circuit (12, 13), and a current mirror circuit during a test And a test circuit (111, 112) that can adjust the ratio of the output current to the input current of (14, 15).

  The test circuit (111, 112) draws a current corresponding to the current drawn from the input circuit (12, 13) from the test terminal (T14, T15) and combines it with the output current of the current mirror circuit (14, 15). It is characterized by that.

  The test circuit (111, 112) has a base connected to the input circuit (12, 13), an emitter connected to the test terminal (T14, T15), and a collector connected to the output of the current mirror circuit (14, 15). It is characterized by comprising transistors (Q3, Q6).

  The test circuit (111, 112) is characterized in that the same voltage as the drive voltage (Vcc) of the current mirror circuit (14, 15) is applied to the test terminal.

  In addition, the said reference code is a reference to the last, and a claim is not limited by this.

  According to the present invention, the current corresponding to the electrical signal converted by the light receiving element that converts the input light into the electrical signal is drawn from the current mirror circuit by the input circuit, and the output current corresponding to the input current of the current mirror circuit is tested by the test circuit during the test. By adjusting the ratio, the output current can be controlled even if the input light is constant by changing the voltage of the test terminal without adjusting the input light.

〔Constitution〕
FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, the same components as those in FIG.

  In addition to the reference voltage circuit 11, the input circuits 12, 13, the current mirror circuits 14, 15, the comparator 16, the photodiode PDA, PDA ′, the resistors RA, RA ′, the light receiving device 100 of this embodiment includes a test circuit 111, 112 is provided.

  The test circuit 111 is composed of a pnp transistor Q3. The transistor Q3 has an emitter connected to the test terminal T14, a base connected to the base and collector of the transistor Q1, and a base of the transistor Q2, and a collector connected to a connection point between the collector of the transistor Q2 and the resistor RA. .

  The power supply voltage Vcc or the ground potential GND is applied to the test terminal T14 during the test, and is set to the ground potential GND during the normal operation. The transistor Q3 is turned on when the power supply voltage Vcc is applied to the terminal T14, and is turned off when the ground potential is GND.

  The transistor Q3 is turned on when the power supply voltage Vcc is applied to the test terminal T14, and operates in the same manner as the transistor Q2. As a result, the number of output transistors of the current mirror circuit 14 becomes two, and the current mirror ratio corresponding to the ratio of the output current to the input current is changed. Thereby, the voltage VA can be controlled even when the incident light of the photodiode PDA is constant.

  The test circuit 112 includes a pnp transistor Q6. The transistor Q6 has an emitter connected to the test terminal T15, a base connected to the base and collector of the transistor Q4, and the base of the transistor Q5, and a collector connected to a connection point between the collector of the transistor Q5 and the resistor RA '. Yes.

  The power supply voltage Vcc or the ground potential GND is applied to the test terminal T15 during the test, and is always set to the ground potential GND during the normal operation. The transistor Q5 is turned on when the power supply voltage Vcc is applied to the test terminal T15, and turned off when the voltage at the test terminal T15 is set to the ground potential GND. When the transistor Q6 is turned on, it operates in the same manner as the transistor Q5. As a result, the output transistor of the current mirror circuit 15 is composed of two transistors, Q5 and Q6, so that the current mirror ratio corresponding to the ratio of the output current to the input current is changed. Thus, the voltage VA ′ can be controlled even when the incident light to the photodiode PDA ′ is constant.

[Operation]
FIG. 2 is a diagram for explaining the operation of an embodiment of the present invention.

  The operation of the light receiving device 100 of this embodiment will be described.

First, the incident light PA to the photodiode PDA and the incident light PA ′ to the photodiode PDA ′ are made uniform, and the voltages at the test terminals T14 and T15 are both set to the ground potential GND. At this time, the output current ratio of the current mirror circuits 14 and 15 is
(Iq2 / Iq1) = (Iq5 / Iq4) (1)
It can be expressed as Iq1 is a current flowing through the transistor Q1, Iq2 is a current flowing through the transistor Q2, Iq4 is a current flowing through the transistor Q4, Iq5 is a current flowing through the transistor Q5, and the transistors Q1, Q2, Q4, and Q5 are usually
Iq1 = Iq4, Iq2 = Iq5
Is set to Therefore, the voltage VA applied to the inverting input terminal of the comparator 16 and the voltage VA ′ applied to the non-inverting input terminal of the comparator 16 become substantially equal, and the output of the comparator 16 becomes indefinite. Therefore, the output voltage Vout at the output terminal T13 is indefinite.

  Next, the power supply voltage Vcc is applied to the test terminal T14, and the test terminal T15 is set to the ground potential GND. When the power supply voltage Vcc is applied to the test terminal T14, the transistor Q3 is turned on, and a current Iq3 flows through the transistor Q3.

When the current Iq3 flows through the transistor Q3, the left side of the equation (1) becomes {(Iq2 + Iq3) / Iq1} (2)
It is represented by At this time, the transistors Q1, Q2, Q4, and Q5 are normally Iq1 = Iq4, Iq2 = Iq5
Is set to
{(Iq2 + Iq3) / Iq1}> (Iq5 / Iq4)
It becomes.

  Therefore, since the voltage VA applied to the inverting input terminal of the comparator 16 is sufficiently larger than the voltage VA ′ applied to the non-inverting input terminal of the comparator 16, the output of the comparator 16 is at a low level. Therefore, the output voltage Vout at the output terminal T13 is at a low level.

  Further, the test terminal T14 is set to the ground potential GND, and the power supply voltage Vcc is applied to the test terminal T15. When the power supply voltage Vcc is applied to the test terminal T15, the transistor Q6 is turned on and a current Iq6 flows through the transistor Q6.

When the current Iq6 flows through the transistor Q6, the right side of the equation (1) becomes {(Iq5 + Iq6) / Iq4} (2)
It is represented by At this time, the transistors Q1, Q2, Q4, and Q5 are normally Iq1 = Iq4, Iq2 = Iq5
Is set to
(Iq2 / Iq1) <{(Iq5 + Iq6) / Iq4}
It becomes.

  Therefore, since the voltage VA ′ applied to the non-inverting input terminal of the comparator 16 is sufficiently larger than the voltage VA applied to the inverting input terminal of the comparator 16, the output of the comparator 16 becomes high level. Therefore, the output voltage Vout at the output terminal T13 is at a high level.

〔Inspection method〕
Next, an inspection method for the light receiving device 100 will be described.

  FIG. 3 shows a block diagram of the inspection system.

  The inspection system 200 includes an inspection device 211, a drive circuit 212, probes 213-1 to 213-5, and an illumination device 214, and inspects the light receiving device 100 while being mounted on the wafer 300. A large number of light receiving devices 100 are mounted on the wafer 300.

  The inspection device 211 controls the drive circuit 212 and the illumination device 214 according to a preset program and inspects the light receiving device 100. The drive circuit 212 applies a voltage to the probes 213-1, 213-2, 213-4, and 213-5 according to a control signal from the inspection device 211, detects the voltage of the probe 213-3, Supply. The probe 213-1 contacts the terminal T11 of the light receiving device 100. The probe 213-2 contacts the terminal T12 of the light receiving device 100. The probe 213-3 contacts the terminal T13 of the light receiving device 100. The probe 213-4 contacts the terminal T14 of the light receiving device 100. The probe 213-5 contacts the terminal T15 of the light receiving device 100.

  Next, the operation at the time of inspection will be described.

  FIG. 4 shows a flowchart when the inspection apparatus 211 is inspected.

  First, the inspection apparatus 211 drives the illumination apparatus 214 in step S <b> 1-1 to uniformly irradiate the entire wafer 300 with light.

  The inspection device 211 applies the power supply voltage Vcc to the terminal T11 in step S1-2, grounds the terminal T12, applies the power supply voltage Vcc to the test terminal T14 in step S1-3, and grounds the test terminal T15. As a result, the voltage VA at the inverting input terminal of the comparator 16 can be made sufficiently larger than the voltage VA ′ at the non-inverting input terminal of the comparator 16. Therefore, when the light receiving device 100 is in a normal state, the output of the comparator 16 is at a low level, and the output voltage Vout at the output terminal T13 is at a low level.

  The inspection device 211 monitors the output voltage Vout of the output terminal T13 in step S1-4, and if the output voltage Vout of the output terminal T13 is low in step S1-5, next, the test terminal in step S1-6. The power supply voltage Vcc is applied to T15, and the test terminal T14 is grounded. As a result, the voltage VA ′ at the non-inverting input terminal of the comparator 16 can be made sufficiently larger than the voltage VA at the inverting input terminal of the comparator 16. Therefore, if the light receiving device 100 is in a normal state, the output of the comparator 16 is at a high level, and the output voltage Vout at the output terminal T13 is at a high level.

  The inspection device 211 monitors the output voltage Vout of the output terminal T13 in step S1-7, and if the output voltage Vout of the output terminal T13 is high in step S1-8, the light receiving device 100 is normal in step S1-9. It is determined that the state is correct, and the process is terminated. If the inspection device 211 determines in step S1-5 that the output voltage Vout of the output terminal T13 is high level or in step S1-8, the output voltage Vout of the output terminal T13 is low level, the light receiving device 100 It is determined that there is an error, and error notification is performed in step S1-10.

  After the inspection, the light receiving device 100 determined to be normal by the inspection device 211 is cut from the wafer 300 and mounted on the lead frame. After being mounted on the lead frame, the terminals T11 to T15 are wired to the leads by wire bonding or the like. At this time, the test terminals T14 and T15 are wired to leads that are at the ground level. As a result, at the time of product, the test terminals T14 and T15 are set to the ground level, the transistors Q3 and Q6 are always turned off, and the test circuits 111 and 112 are deactivated.

〔effect〕
According to the present embodiment, the voltage applied to the test terminals T14 and T15 is switched between the power supply voltage Vcc and the ground potential GND in a state in which the photodiodes PDA and PDA ′ are irradiated with uniform light, and output from the output terminal T13. By detecting the output voltage Vout, the internal circuit of the light receiving device 100 can be inspected. Therefore, it is not necessary to control the amount of light and the inspection can be performed easily. Further, according to the present embodiment, wafer inspection can be easily realized.

[Others]
In this embodiment, the light receiving device 100 on which two photodiodes PDA and PDA ′ are mounted has been described as an example, but the same applies to a light receiving device on which one or more photodiodes are mounted. Needless to say, the internal circuit can be inspected. In this embodiment, the photodiode is described as an example of the light receiving element. However, the light receiving element is not limited to the photodiode, and the same inspection can be performed on other light receiving elements such as a phototransistor. it can.

It is a block block diagram of one Example of this invention. It is operation | movement explanatory drawing of one Example of this invention. It is a block block diagram of an inspection system. It is a flowchart at the time of the test | inspection of the inspection apparatus 211. FIG. It is a block block diagram of an example of the past. It is operation | movement explanatory drawing of an example of the past.

Explanation of symbols

100 Photodetector PDA, PDA 'Photodiode 11 Reference voltage circuit, 12, 13 Input circuit, 14, 15 Current mirror circuit 16 Comparator RA, RA' Resistors T14, T15 Test terminals

Claims (4)

A light receiving device that outputs a signal according to input light,
A light receiving element for converting the input light into an electrical signal;
An input circuit for drawing a current according to the electrical signal converted by the light receiving element;
A current mirror circuit that outputs a current according to the current drawn by the input circuit;
And a test circuit capable of adjusting a ratio of an output current to an input current of the current mirror circuit during a test. The test circuit adjusts the ratio of the output current to the input current of the current mirror circuit by drawing a current corresponding to the current drawn into the input circuit from the test terminal and combining it with the output current of the current mirror circuit. The light receiving device according to claim 1. 3. The test circuit according to claim 2, comprising a transistor having a base connected to the input circuit, an emitter connected to the test terminal, and a collector connected to the output of the current mirror circuit. Light receiving device. 4. The light receiving device according to claim 1, wherein the test circuit is applied with the same voltage as the drive voltage of the current mirror circuit to the test terminal. 5.

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