JP2010263566A - Test circuit and optical disk device - Google Patents

Abstract

In addition to inspection of characteristics of an amplifier circuit using a light receiving element, it is possible to inspect characteristics of the light receiving element.
A test circuit includes a dummy light receiving element PD_D having characteristics equivalent to those of a light receiving element PD1. The current mirror circuit 110 generates a test current in the amplifier circuit 10 for testing the characteristics of the amplifier circuit 10 by using the bipolar transistor Q2. The bipolar transistor Q1 of the current mirror circuit 110 generates a current in the dummy light receiving element PD_D for inspecting the characteristics of the dummy light receiving element PD_D when no current flows in the bipolar transistor Q1.
[Selection] Figure 2

Description

  The present invention relates to a test circuit and an optical disc apparatus for inspecting characteristics of an amplifier circuit using a light receiving element.

  As an optical disk apparatus that performs processing on an optical disk, a light receiving and amplifying apparatus that receives light reflected from the optical disk (hereinafter referred to as reflected light) and performs photoelectric conversion based on the reflected light is used. The optical disk is, for example, a disk such as a CD (Compact Disk), a DVD (Digital Versatile Disk), or a BD (Blu-ray Disk). Further, the processing performed by the optical disc device on the optical disc includes reading processing of data recorded on the optical disc and writing processing of data on the optical disc.

  2. Description of the Related Art In recent years, the scale of semiconductor integrated circuits has been increasing with the increase in integration, functionality, and speed of semiconductor integrated circuits. This complicates the inspection of functional circuits in semiconductor integrated circuits.

  In an IC (Integrated Circuit) manufacturing process, operation checks of internal circuits, elements, etc. in an IC are generally performed. For example, regarding the operation check of the photoelectric conversion element (photodiode) used in the light receiving amplification device, the operation check of the photoelectric conversion element is performed by irradiating light directly to the photoelectric conversion element. desirable. Hereinafter, the photoelectric conversion element is also referred to as a light receiving element.

  However, the size of the light receiving element is as small as several tens of μm. Therefore, there is a problem that it is very difficult to actually irradiate the light receiving element with a predetermined amount of light.

  Therefore, Patent Document 1 discloses a test circuit for solving the above-described problem and electrically inspecting characteristics of an amplifier circuit using a light receiving element with high accuracy.

  FIG. 11 is a diagram illustrating a configuration of a test circuit of an amplifier circuit that uses a light receiving element.

  Hereinafter, the test circuit disclosed in Patent Document 1 will be described with reference to FIG.

  In FIG. 11, a light receiving element PD1 is a photodiode that generates a current corresponding to the amount of light irradiated. The cathode of the light receiving element PD1 is electrically connected to the node N1. The anode of the light receiving element PD1 is connected to the ground potential.

  In the following, when the state in which the object A is electrically connected to the object B is described, it is simply described that the object A is connected to the object B.

  The amplifier circuit 10 outputs a voltage corresponding to the current generated by the light receiving element PD1 as the output voltage Vo.

  The amplifier circuit 10 includes a conversion resistor Rg_a and an amplifier 11. The conversion resistor Rg_a is a resistor having a predetermined resistance value. The amplifier 11 is an operational amplifier. A conversion resistor Rg_a is provided between the inverting input terminal of the amplifier 11 and the output terminal of the amplifier 11.

  A reference potential Vref is applied to the non-inverting input terminal of the amplifier 11 via the resistor Rref_a.

  The amplifier circuit 10 converts a current (hereinafter also referred to as a photocurrent) generated by the light applied to the light receiving element PD1 into a voltage by the conversion resistor Rg_a, and outputs the converted voltage as the output voltage Vo. The level of the output voltage Vo is determined by the resistance value of the conversion resistor Rg_a and the reference potential Vref.

  The test circuit 1000 is a circuit for inspecting the characteristics (operation) of the amplifier circuit 10.

  Test circuit 1000 includes a current mirror circuit 110, resistors R3 and R4, and a test terminal TP. Current mirror circuit 110 includes bipolar transistors Q1, Q2 and resistors R1, R2.

  Each of the bipolar transistors Q1 and Q2 is an NPN type transistor. The collector terminal of bipolar transistor Q2 is connected to node N1. The emitter terminal of bipolar transistor Q2 is connected to resistor R2. The base terminal of bipolar transistor Q2 is connected to the base terminal of bipolar transistor Q1.

  The collector terminal of bipolar transistor Q1 is connected to resistor R3. The emitter terminal of bipolar transistor Q1 is connected to resistor R1. The resistance value of the resistor R1 is the same as the resistance value of the resistor R2.

  Test terminal TP is connected to resistors R4 and R3.

  When a test voltage is applied to the test terminal TP, the test voltage is converted into a current Ia determined by the base-emitter voltage (Vbe) of the bipolar transistor Q1 and the resistor R3. That is, in this case, the current Ia flows through the collector terminal of the bipolar transistor Q1.

  In this case, the current mirror circuit 110 having the resistors R1 and R2 having the same resistance value causes the current Ib having the same current value as the current Ia to flow through the collector terminal of the bipolar transistor Q2. That is, the current Ib flows from the inverting input terminal of the amplifier 11 to the collector terminal of the bipolar transistor Q2. That is, the current Ib is drawn from the inverting input terminal of the amplifier 11. In this case, the amplifier circuit 10 outputs a voltage corresponding to the current Ib as the output voltage Vo.

  However, in the test circuit described in Patent Document 1, when there is a defect (for example, disconnection) in the wiring connecting the light receiving element and the amplifier circuit, the defect cannot be detected.

  For this reason, Patent Document 2 discloses a test circuit that can detect disconnection of a wiring connecting a light receiving element and an amplifier circuit.

  FIG. 12 is a diagram illustrating a configuration of a test circuit disclosed in Patent Document 2. In FIG.

  Hereinafter, the test circuit will be described with reference to FIG.

  Since amplifier circuit 10 shown in FIG. 12 has the same configuration and function as amplifier circuit 10 of FIG. 11, detailed description will not be repeated.

  In FIG. 12, the light receiving element PD2 is a photodiode that generates a current corresponding to the amount of light irradiated. The light receiving element PD2 has terminals T1 and T2 on the cathode. The terminal T1 is connected to the non-inverting input terminal of the amplifier 11. The terminal T2 is connected to the test circuit 1100.

  The test circuit 1100 is a test circuit capable of detecting a defect in the wiring connecting the light receiving element PD2 and the amplifier circuit 10.

  The test circuit 1100 includes a test terminal TP, a switch circuit 1110, a constant current circuit 1120, and an ON / OFF circuit 1130.

  The state of the switch circuit 1110 is set to either an on state or an off state by external control. When the switch circuit 1110 is turned on, the terminal T2 and the constant current circuit 1120 are electrically connected. When the switch circuit 1110 is turned off, the terminal T2 and the constant current circuit 1120 are electrically disconnected.

  The ON / OFF circuit 1130 sets the state of the switch circuit 1110 to either an on state or an off state.

  In the circuit shown in FIG. 12, the current flowing between the amplifier 11 and the test circuit 1100 always passes through the wiring connecting the light receiving element PD2 and the amplifier 11 and the terminal T2 of the light receiving element PD2.

  Therefore, when a defect such as a disconnection occurs in the wiring connecting the light receiving element PD2 and the amplifier 11, the test circuit 1100 cannot supply a current to the non-inverting input terminal of the amplifier 11. Therefore, since the output voltage Vo of the amplifier circuit 10 does not change, it can be detected that there is a defect (for example, disconnection) in the wiring connecting the light receiving element PD2 and the amplifier 11.

  If the techniques disclosed in Patent Documents 1 and 2 are used, a direct current voltage is applied to the test terminal TP provided on the semiconductor substrate without actually irradiating the light receiving element (photodiode) on the semiconductor substrate. Just by applying, it becomes possible to inspect (test) the characteristics of the amplifier circuit in the same manner as when DC light is irradiated, and the test can be completed easily in a short time. Therefore, the economic effect is great, and an inexpensive IC or semiconductor integrated circuit can be supplied.

JP-A-8-129046 Japanese Patent Laid-Open No. 10-284707

  However, the test circuits disclosed in Patent Documents 1 and 2 can inspect (test) the characteristics of the amplifier circuit using the light receiving element, but cannot inspect the characteristics of the light receiving element.

  The present invention has been made in order to solve the above-described problems, and its purpose is to inspect the characteristics of the light receiving element in addition to the characteristics of the amplifier circuit using the light receiving element. It is to provide a test circuit and the like.

  In order to solve the above-described problem, a test circuit according to an aspect of the present invention outputs a voltage corresponding to a photocurrent generated by a light receiving element that generates a photocurrent that is a current corresponding to the amount of light irradiated. This is a circuit for inspecting the characteristics of the amplifier circuit. The test circuit includes a current mirror circuit configured using a first bipolar transistor and a second bipolar transistor electrically connected to the light receiving element, the same element as the light receiving element, and the characteristics of the light receiving element. A dummy light receiving element having equivalent characteristics, and a test terminal electrically connected to the first bipolar transistor and the dummy light receiving element are provided. The current mirror circuit uses the second bipolar transistor to generate a test current for testing the characteristics of the amplifier circuit in the amplifier circuit. The first bipolar transistor of the current mirror circuit generates a current in the dummy light receiving element for inspecting the characteristics of the dummy light receiving element by being in a state where no current flows in the first bipolar transistor.

  That is, the test circuit provides a dummy light receiving element having characteristics equivalent to those of the light receiving element. The current mirror circuit uses the second bipolar transistor to generate an inspection current for inspecting the characteristics of the amplifier circuit in the amplifier circuit that outputs a voltage corresponding to the photocurrent generated by the light receiving element. The first bipolar transistor of the current mirror circuit generates a current in the dummy light receiving element for inspecting the characteristics of the dummy light receiving element by being in a state where no current flows in the first bipolar transistor. The dummy light receiving element has characteristics equivalent to those of the light receiving element.

  Therefore, in addition to the inspection of the characteristics of the amplifier circuit using the light receiving element, the characteristics of the light receiving element can be inspected.

  The first bipolar transistor is an NPN type transistor, the NPN type transistor is formed on a P type substrate, and the dummy light receiving element is formed by an N type diffusion region as a collector region in the NPN type transistor and a P type substrate. May be.

  That is, the first bipolar transistor and the dummy light receiving element are integrally formed. Therefore, the test circuit can be downsized.

  Further, the area of the first light receiving region that is a region for receiving light in the dummy light receiving element may be larger than the area of the second light receiving region that is a region for receiving light in the light receiving element.

  Further, the first light receiving region of the dummy light receiving element may be covered with a light shielding film so that the first light receiving region is not irradiated with light.

  Thereby, even if light is irradiated toward the dummy light receiving element, the dummy light receiving element is not irradiated with light. Therefore, it is possible to increase the accuracy of the inspection of the characteristics of the light receiving element.

  According to the present invention, in addition to the inspection of the characteristics of the amplifier circuit using the light receiving element, the characteristics of the light receiving element can be inspected.

It is a figure which shows the structure of the light reception amplifier circuit in 1st Embodiment. It is a figure for demonstrating operation | movement of the light reception amplification circuit when the operation mode of a light reception amplification circuit is a 1st test mode. It is a figure which shows the characteristic line which shows the relationship between an output voltage and a test current. It is a figure for demonstrating operation | movement of the light reception amplification circuit when the operation mode of a light reception amplification circuit is a 2nd test mode. It is a figure for demonstrating the characteristic of a dummy light receiving element. It is sectional drawing of the said board | substrate in case the circuit structure of the light reception amplifier circuit is formed in the board | substrate using the prior art. It is sectional drawing of the bipolar transistor and dummy light receiving element in 1st Embodiment. It is sectional drawing of the bipolar transistor and dummy light receiving element in the modification of 1st Embodiment. It is a top view of the bipolar transistor and the dummy light receiving element in the modified example of the first embodiment. It is a figure which shows an example of a structure of an optical disk device. It is a figure which shows the structure of the test circuit of the amplifier circuit which uses a light receiving element. It is a figure which shows the structure of the test circuit shown by patent document 2. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

<First Embodiment>
FIG. 1 is a diagram showing a configuration of a light receiving amplifier circuit 101 in the first embodiment.

  Referring to FIG. 1, light receiving amplification circuit 101 includes an amplification circuit 10, a resistor Rref_a, a light receiving element PD <b> 1, and a test circuit 100.

  Since amplifier circuit 10 in FIG. 1 has the same configuration and function as amplifier circuit 10 in FIG. 11, detailed description thereof will not be repeated. Hereinafter, the amplifier circuit 10 will be briefly described. A conversion resistor Rg_a is provided between the inverting input terminal of the amplifier 11 included in the amplifier circuit 10 and the output terminal of the amplifier 11. A resistor Rref_a is connected to the non-inverting input terminal of the amplifier 11. The resistor Rref_a is an impedance matching resistor. A reference potential Vref is applied to the non-inverting input terminal of the amplifier 11 via the resistor Rref_a.

  Since light receiving element PD1 in FIG. 1 is the same element as light receiving element PD1 in FIG. 11, detailed description will not be repeated. Hereinafter, the light receiving element PD1 will be briefly described. The light receiving element PD1 is a photodiode that generates a current corresponding to the amount of light irradiated. The cathode of the light receiving element PD1 is connected to the inverting input terminal of the amplifier 11. The anode of the light receiving element PD1 is connected to the ground potential.

  The test circuit 100 is different from the test circuit 1000 of FIG. 11 in that the resistors R3 and R4 are not included and the dummy light receiving element PD_D is further included. Other than that, it is the same as test circuit 1000, so detailed description will not be repeated.

  Hereinafter, the test circuit 100 will be briefly described. Each of bipolar transistors Q1 and Q2 included in current mirror circuit 110 in test circuit 100 is an NPN type transistor. The collector terminal of bipolar transistor Q2 is connected to the cathode of light receiving element PD1. The collector terminal of the bipolar transistor Q2 is also an output terminal of the current mirror circuit 110.

  The collector terminal of bipolar transistor Q1 is connected to test terminal TP. The collector terminal of the bipolar transistor Q1 is also an input terminal of the current mirror circuit 110.

  A resistor R1 is provided between the emitter terminal of the bipolar transistor Q1 and the ground potential. A resistor R2 is provided between the emitter terminal of the bipolar transistor Q2 and the ground potential.

  The dummy light receiving element PD_D is a photodiode. The electrical characteristics of the dummy light receiving element PD_D are the same as the electrical characteristics of the light receiving element PD1. The dummy light receiving element PD_D and the light receiving element PD1 are formed in the same process in the manufacturing process.

  The collector terminal of the bipolar transistor Q1 is connected to the cathode of the dummy light receiving element PD_D. The anode of the dummy light receiving element PD_D is connected to the ground potential.

  Note that the current mirror circuit 110 is not limited to an NPN transistor, and may be configured using two PNP transistors.

  Next, the operation of the light receiving amplification circuit 101 will be described. The light receiving amplification circuit 101 has a normal operation mode, a first test mode, and a second test mode as operation modes. The first test mode is a mode for inspecting (testing) the characteristics (operation) of the amplifier circuit 10. The second test mode is a mode for inspecting (testing) the characteristics of the light receiving element PD1.

  When the operation mode of the light receiving amplification circuit 101 is the normal operation mode, the light receiving element PD1 emits light according to the amount of light irradiated (hereinafter referred to as a photocurrent) by irradiating the light receiving element PD1 with light. appear. Here, the photocurrent generated by the light receiving element PD1 is defined as Iin. In this case, a photocurrent Iin flows from the inverting input terminal of the amplifier 11 toward the light receiving element PD1.

  In this case, the output voltage Vo of the amplifier circuit 10 is expressed by the following formula 1.

Vo = Rg_a × Iin (Formula 1)

  Note that when the operation mode of the light receiving amplification circuit 101 is the normal operation mode, no voltage is applied to the test terminal TP. Therefore, no current flows through the collector terminal of bipolar transistor Q1.

  Next, the operation of the light receiving amplification circuit 101 when the operation mode of the light receiving amplification circuit 101 is the first test mode will be described.

  FIG. 2 is a diagram for explaining the operation of the light receiving amplification circuit 101 when the operation mode of the light receiving amplification circuit 101 is the first test mode.

  In this case, in order to test (test) the characteristics (operation) of the amplifier circuit 10, a test current (hereinafter also referred to as test current) I1 flows toward the collector terminal of the bipolar transistor Q1 via the test terminal TP. Thus, a test voltage is applied to the test terminal TP from the outside. Here, as an example, it is assumed that the resistance value of the resistor R1 is the same as the resistance value of the resistor R2.

  In this case, the current mirror circuit 110 causes a current I1a having the same current value as the test current I1 to flow through the collector terminal of the bipolar transistor Q2. That is, the current mirror circuit 110 uses the bipolar transistor Q2 to check the characteristics of the amplifier circuit 10 with a current equivalent to the value of the current flowing between the test terminal TP and the bipolar transistor Q1. Are generated in the amplifier circuit 10.

  In this case, the output voltage Vo of the amplifier circuit 10 is a voltage represented by the following Expression 2.

Vo = Rg_a × I1a (Formula 2)

  In this case, the relationship between the output voltage Vo and the test current I1 is indicated by the following characteristic line L1.

  FIG. 3 is a diagram showing a characteristic line L1 indicating the relationship between the output voltage Vo and the test current I1.

  In the region R1, the output voltage Vo increases in proportion to the test current I1a. In the region R1, the slope of the characteristic line L1 is Rg_a. In the region R2, since the amplifier 11 operates in the saturation region, the value of the output voltage Vo is constant.

  Therefore, when the amplifier 11 is operated in the saturation region, it is possible to inspect (test) whether the gain Rg_a of the amplifier 11 is a predetermined value by changing (sweeping) the test current I1. . Further, it can be inspected whether or not the potential of the output voltage Vo in the region R2 becomes low and a large signal amplitude cannot be obtained. That is, the characteristic (operation) of the amplifier circuit 10 (amplifier 11) can be inspected.

  Next, the operation of the light receiving amplifier circuit 101 when the operation mode of the light receiving amplifier circuit 101 is the second test mode will be described.

  FIG. 4 is a diagram for explaining the operation of the light receiving amplification circuit 101 when the operation mode of the light receiving amplification circuit 101 is the second test mode.

  In this case, in order to inspect (test) the characteristics (operation) of the light receiving element PD1, the test light (hereinafter also referred to as inspection current) I2 flows from the dummy light receiving element PD_D toward the test terminal TP. Therefore, a test voltage (for example, a negative voltage) is applied to the test terminal TP. Hereinafter, the test voltage applied to the test terminal TP is also referred to as a test terminal voltage.

  In this case, the state of the bipolar transistor Q1 is an off state in which no current flows from the collector to the emitter. Therefore, the test current I2 flows from the cathode of the dummy light receiving element PD_D toward the emitter. That is, the test current I2 flows in the dummy light receiving element PD_D. The dummy light receiving element PD_D is a photodiode. Therefore, the test current I2 flows in the forward direction with respect to the dummy light receiving element PD_D. Therefore, the characteristics of the dummy light receiving element PD_D can be inspected.

  That is, the bipolar transistor Q1 of the current mirror circuit 110 is in a state in which no current flows through the bipolar transistor Q1, thereby generating a current in the dummy light receiving element PD_D for inspecting the characteristics of the dummy light receiving element PD_D.

  FIG. 5 is a diagram for explaining the characteristics of the dummy light receiving element PD_D.

  FIG. 5 shows characteristic lines L2 and L2A indicating the relationship between the test terminal voltage and the test current I2. Each of the characteristic lines L2 and L2A is a characteristic line indicating the forward characteristic of the dummy light receiving element PD_D.

  The characteristic line L2 is a characteristic line when the value of the series resistance component that exists equivalently with respect to the dummy light receiving element PD_D is normal. That is, the characteristic line L2 is a characteristic line when the characteristics of the dummy light receiving element PD_D are normal. In the following, the value of the series resistance component that exists equivalent to the dummy light receiving element PD_D is referred to as a series resistance component value.

  In this case, for example, the series resistance component value can be calculated by calculating the slope of the characteristic line L2 at the point A when the test terminal voltage is VTP.

  The characteristic line L2 is a characteristic line when the value of the series resistance component value is larger than the normal value. Also in this case, the series resistance component value can be calculated by calculating the slope of the characteristic line L2A at the point B when the test terminal voltage is VTP.

  When the operation mode of the light receiving amplification circuit 101 is the second test mode, the characteristics of the dummy light receiving element PD_D are inspected. As described above, the electrical characteristics of the dummy light receiving element PD_D are the same as the electrical characteristics of the light receiving element PD1. Therefore, the characteristics of the light receiving element PD1 can be inspected by inspecting the characteristics of the dummy light receiving element PD_D as an alternative to the light receiving element PD1.

  Further, a surge protection diode is generally provided between the test terminal TP and the ground terminal so that the test circuit is not destroyed by a surge voltage at the time of inspection. However, the dummy light receiving element PD_D in the light receiving amplification circuit 101 in this embodiment also serves as a surge protection diode. Therefore, in this embodiment, a surge protection diode is not required, and the chip size of the light receiving amplification circuit 101 can be prevented from being excessively increased by the surge protection diode.

  As will be described in detail later, the upper portion of the dummy light receiving element PD_D is covered with a light shielding film so that the dummy light receiving element PD_D is not irradiated with light. The light shielding film is, for example, a metal film used as a wiring. Thereby, even if stray light is irradiated toward the dummy light receiving element PD_D at the time of inspection, an inspection error due to a current generated by the stray light (hereinafter referred to as stray light current) does not occur. Therefore, it is possible to increase the accuracy of the inspection of the characteristics of the dummy light receiving element PD_D (light receiving element PD1).

  Next, the downsizing of the circuit which is the point of the present invention will be described.

  FIG. 6 is a cross-sectional view of the substrate when the circuit configuration of the light receiving amplification circuit 101 is formed on the substrate using the conventional technique.

  In FIG. 6, the bipolar transistor Q1 and the dummy light receiving element PD_D are formed in a P-type substrate 50.

  The bipolar transistor Q1 includes an emitter terminal E1, a base terminal B1, a collector terminal C1, an emitter region 51, a base region 52, and a collector region 53. The emitter region 51, the base region 52, and the collector region 53 are an N + type diffusion region, a P type diffusion region, and an N type diffusion region, respectively.

  In order to lower the collector resistance of bipolar transistor Q1, an N + type diffusion region (hereinafter also referred to as N + buried layer) 54 is generally formed between collector region 53 and P type substrate 50.

  The dummy light receiving element PD_D formed using the conventional technique includes an anode terminal A1, a cathode terminal K1, an anode region 55, a P well 56, a cathode region 57, a P + type diffusion region 58, and a P well 59. Consists of The anode region 55 and the cathode region 57 are a P + type diffusion region and an N type diffusion region, respectively.

  As shown in FIG. 6, generally, when the test circuit 100 of FIG. 1 of the present invention is formed in the light receiving amplifier circuit using the conventional technique, the bipolar transistor Q1 and the dummy light receiving element PD_D are adjacent to each other. Further, the bipolar transistor Q1 and the dummy light receiving element PD_D are formed on the P-type substrate 50. In this case, there arises a problem that the chip size of the light receiving amplifier circuit becomes large.

  Therefore, the inventor of the present invention pays attention to the layer structure of the bipolar transistor Q1 as an NPN transistor, and a parasitic diode formed between the collector region 53 of the bipolar transistor Q1 and the P-type substrate 50 is used as a dummy light receiving element. I found out to use it.

  FIG. 7 is a cross-sectional view of the bipolar transistor Q1 and the dummy light receiving element PD_D in the first embodiment.

  7, since the same reference numerals as those in FIG. 6 are attached, the detailed description will not be repeated.

  In FIG. 7, the impurity concentration in collector region 53 of bipolar transistor Q1 is made the same as the impurity concentration in cathode region 57 of dummy light receiving element PD_D shown in FIG.

  Thus, the structure of the collector region 53 in the parasitic diode D1 formed between the collector region 53 of the bipolar transistor Q1 and the P-type substrate 50 is equivalent to the structure of the cathode region 57 in the dummy light receiving element PD_D shown in FIG. It can be.

  Therefore, the parasitic diode D1 can be used as the dummy light receiving element PD_D. In this case, the parasitic diode D1 as the dummy light receiving element PD_D is formed by the N type diffusion region as the collector region 53 of the bipolar transistor Q1 and the P type substrate 50. In this case, the collector region 53 of the bipolar transistor Q1 is also used as the cathode region of the parasitic diode D1 (dummy light receiving element PD_D). That is, in the present embodiment, the bipolar transistor Q1 and the dummy light receiving element PD_D can be integrally formed.

  In this case, the collector terminal C1 is also used as the cathode terminal of the dummy light receiving element PD_D.

  In the parasitic diode D1 as the dummy light receiving element PD_D, a region for receiving light (hereinafter referred to as a light receiving region) is formed with a light shielding film 61 above the light receiving region so that the light receiving region is not irradiated with light. . That is, the light receiving region is covered with the light shielding film 61. The light shielding film 61 is, for example, a metal film used as a wiring.

  Thereby, even if stray light is irradiated toward the dummy light receiving element PD_D at the time of inspection, an inspection error due to a current generated by the stray light (hereinafter referred to as stray light current) does not occur. Therefore, it is possible to increase the accuracy of the inspection of the characteristics of the dummy light receiving element PD_D (light receiving element PD1).

  As described above, the test circuit 100 according to the present embodiment has the characteristics (series resistance component value) of the light receiving element PD1 (dummy light receiving element PD_D) in addition to the inspection of the characteristics of the amplifier circuit 10 using the light receiving element PD1. Inspection can be performed.

  When this series resistance component value is large, there is a large resistance between the amplifier 11 and the light receiving element PD1, so that the high frequency characteristics of the amplifier 11 are deteriorated. In recent years, as typified by BD (Blu-ray Disk), high-speed optical disc recording / reproduction has been demanded, and accordingly, high-frequency characteristics of a light receiving and amplifying device have been demanded. By testing the characteristics of the element PD_D), it is possible to easily detect the amplifier 11 (IC) whose high-frequency characteristics do not satisfy (deteriorate) the predetermined value.

  Further, since the bipolar transistor Q1 and the dummy light receiving element PD_D can be integrally formed, the chip area of the test circuit 100 including the bipolar transistor Q1 and the dummy light receiving element PD_D can be reduced. Therefore, the photoreceiver / amplifier circuit 101 including the test circuit 100 can be reduced in size. As a result, the cost of the photoreceiver / amplifier circuit 101 can be reduced.

(Modification of the first embodiment)
In the modification of the present embodiment, a structure for further downsizing the test circuit 100 as compared with the first embodiment is shown. Further, by setting the size of the dummy light receiving element PD_D to be equal to or larger than the size of the light receiving element PD1, the characteristic difference between the dummy light receiving element PD_D and the light receiving element PD1 is reduced.

  As described above, in FIG. 7, in order to lower the collector resistance of the bipolar transistor Q1, an N + type diffusion region (hereinafter also referred to as an N + buried layer) is generally provided between the collector region 53 and the P type substrate 50. ) 54 is formed.

  Therefore, in the first embodiment, the structure of the parasitic diode D1 as the dummy light receiving element PD_D shown in FIG. 7 is different from the structure of the dummy light receiving element PD_D in FIG. For this reason, the portion with the N + type diffusion region 54 cannot be used as a dummy light receiving element.

  However, an object of the present invention is to inspect the characteristics (series resistance component value) of the light receiving element PD1 (dummy light receiving element PD_D). Therefore, even if the collector resistance of the bipolar transistor Q1 is high, there is no problem as a test circuit. Therefore, in the modification of the present embodiment, the N + type diffusion region 54 is not formed.

  FIG. 8 is a cross-sectional view of the bipolar transistor Q1 and the dummy light receiving element PD_D in the modification of the first embodiment.

  In FIG. 8, the same reference numerals as those in FIG. 7 are given, and the detailed description will not be repeated.

  In FIG. 8, the N + type diffusion region 54 is not formed between the collector region 53 and the P type substrate 50. Thereby, the parasitic capacitance between the anode and the cathode in the dummy light receiving element PD_D can be reduced.

  In the parasitic diode D1 as the dummy light receiving element PD_D, a region for receiving light (hereinafter referred to as a light receiving region) is formed with a light shielding film 61 above the light receiving region so that the light receiving region is not irradiated with light. . That is, the light receiving region is covered with the light shielding film 61.

  Further, by configuring the bipolar transistor Q1 and the dummy light receiving element PD_D as shown in FIG. 8, the common area of the bipolar transistor Q1 and the dummy light receiving element PD_D can be increased. Therefore, in the modification of the first embodiment, the chip area of the test circuit 100 can be further reduced as compared with the first embodiment.

  As a result, even if the size of the dummy light receiving element PD_D (the area of the first light receiving region described later) is equal to or larger than the size of the light receiving element PD1 (the area of the second light receiving region described later), the first embodiment The photoreceiver / amplifier circuit 101 including the test circuit 100 in the modified example can be downsized, and a highly accurate inspection can be performed.

  FIG. 9 is a top view of the bipolar transistor Q1 and the dummy light receiving element PD_D in the modification of the first embodiment.

  9, since the same reference numerals as those in FIG. 8 are the same as those in FIG. 8, detailed description thereof will not be repeated.

  As shown in FIG. 9, in the modification of the first embodiment, the area of the dummy light receiving element PD_D for receiving light (hereinafter referred to as the first light receiving area) receives light at the light receiving element PD1. The area of the collector region 53 is increased so that the area is equal to or larger than the area of the region for the purpose (hereinafter referred to as the second light receiving region).

  In FIG. 9, the “PD_D-dedicated portion” is a portion where only the dummy light receiving element PD_D is formed. In the collector region 53, the above-described light shielding film 61 is formed on the portion corresponding to the “PD_D dedicated portion”.

  The “shared portion of Q1 and PD_D” is a portion formed by sharing the bipolar transistor Q1 and a part of the dummy light receiving element PD_D.

  Therefore, the chip area of the test circuit 100 can be reduced by the area of “the shared portion of Q1 and PD_D”.

  Note that the process of making the impurity concentration in the collector region 53 of the bipolar transistor Q1 the same as the impurity concentration in the cathode region 57 of the dummy light receiving element PD_D in FIG. This is done by forming PD_D.

  The present invention is not limited to the above structure, and a structure in which the dummy light receiving element PD_D (parasitic diode D1) is disposed adjacent to the light receiving element PD1 may be employed. Further, the size of the dummy light receiving element PD_D (parasitic diode D1) may be equal to the size of the light receiving element PD1. Thus, it goes without saying that the performance difference between the dummy light receiving element PD_D (parasitic diode D1) and the light receiving element PD1 can be reduced.

  In the modification of the first embodiment, a region for receiving light in the collector region 53 of the bipolar transistor Q1 (hereinafter referred to as a light receiving region) is a light receiving region so that the light receiving region is not irradiated with light. A light-shielding film 61 is formed on the upper part. That is, the light receiving region is covered with the light shielding film 61. The light shielding film 61 is, for example, a metal film used as a wiring.

  Thereby, even if stray light is irradiated toward the dummy light receiving element PD_D at the time of inspection, an inspection error due to a current generated by the stray light (hereinafter referred to as stray light current) does not occur. Therefore, the inspection accuracy of the characteristics of the dummy light receiving element PD_D (light receiving element PD1) can be increased.

<Second Embodiment>
Next, an optical disc apparatus 500 that uses the light receiving amplification circuit 101 of the first embodiment or a modification of the first embodiment will be described.

  FIG. 10 is a diagram showing an example of the configuration of the optical disc apparatus 500. As shown in FIG. Note that FIG. 10 also shows an optical disc DC10 that is not included in the optical disc apparatus 500 for the sake of explanation. The optical disk DC10 is a disk such as a CD (Compact Disk), a DVD (Digital Versatile Disk), or a BD (Blu-ray Disk).

  Referring to FIG. 10, optical disc apparatus 500 includes a laser diode 510, an optical unit 520, a light receiving amplification circuit 101, and an optical disc controller 530.

  The laser diode 510 includes a diffraction grating 521, a beam splitter 522, a collimator lens 523, a rising mirror 524, an objective lens 525, and a detection lens 526.

  The beam emitted from the laser diode 510 is separated into three beams by the diffraction grating 521. The separated three beams are irradiated onto the rising mirror 524 via the beam splitter 522 and the collimator lens 523.

  The rising mirror 524 reflects the three irradiated beams to irradiate the three beams toward the objective lens 525. The objective lens 525 collects the three irradiated beams and irradiates the optical disc DC10 with the three collected beams.

  The three beams irradiated on the optical disc DC10 are reflected by the optical disc DC10. The three beams reflected by the optical disc DC10 are applied to the beam splitter 522 via the objective lens 525, the rising mirror 524, and the collimator lens 523.

  The beam splitter 522 reflects the three irradiated beams to irradiate the detection lens 526 with the three beams. The detection lens 526 irradiates the light receiving unit (not shown) of the light receiving amplification circuit 101 with the three irradiated beams. The light receiving unit of the light receiving amplification circuit 101 is, for example, the light receiving element PD1.

  The optical signal contained in the irradiated beam is photoelectrically converted by the light receiving amplification circuit 101. By the photoelectric conversion, the optical signal is converted into an electric signal. Then, the photoreceiver / amplifier circuit 101 transmits an electrical signal to the optical disk controller 530.

  The optical disk controller 530 includes an RF signal processing circuit 531. The RF signal processing circuit 531 performs processing for adjusting the waveform, signal processing, and the like on the electrical signal received from the light receiving amplification circuit 101.

  As described above, the optical disc apparatus 500 using the light receiving and amplifying circuit 101 of the present invention can realize high-speed data access (recording / reproduction) with respect to the optical disc DC10. Further, as described above, the light receiving amplification circuit 101 can be downsized. Therefore, the optical disc apparatus 500 using the light receiving and amplifying circuit 101 can be downsized. Therefore, not only can the degree of freedom be ensured in the optical design of the optical disc apparatus 500, but the reliability of the entire optical disc apparatus 500 can be improved.

  Further, the miniaturized optical disc apparatus 500 can be mounted on a slim type optical drive used in a mobile personal computer or the like.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention is useful as a test circuit for an amplifier circuit using a light receiving element. The present invention is useful when high-speed data access is required for an optical disc.

PD1 Light receiving element PD_D Dummy light receiving element Q1, Q2 Bipolar transistor TP Test terminal 10 Amplifier circuit 11 Amplifier 100 Test circuit 101 Light receiving amplifier circuit 110 Current mirror circuit 500 Optical disk device

Claims (5)

A test circuit for inspecting the characteristics of an amplifier circuit that outputs a voltage corresponding to the photocurrent generated by a light receiving element that generates a photocurrent that is a current corresponding to the amount of light applied,
The test circuit includes:
A current mirror circuit configured using a first bipolar transistor and a second bipolar transistor electrically connected to the light receiving element;
A dummy light-receiving element that is the same element as the light-receiving element and has characteristics equivalent to the characteristics of the light-receiving element;
A test terminal electrically connected to the first bipolar transistor and the dummy light receiving element;
The current mirror circuit uses the second bipolar transistor to generate a test current in the amplifier circuit for testing the characteristics of the amplifier circuit,
The first bipolar transistor of the current mirror circuit generates a current in the dummy light-receiving element for inspecting the characteristics of the dummy light-receiving element when no current flows through the first bipolar transistor. ,
Test circuit. The first bipolar transistor is an NPN transistor,
The NPN transistor is formed on a P-type substrate,
The dummy light receiving element is formed by an N type diffusion region as a collector region in the NPN type transistor and the P type substrate.
The test circuit according to claim 1. The area of the first light receiving region that is a region for receiving light in the dummy light receiving element is an area that is equal to or larger than the area of the second light receiving region that is a region for receiving light in the light receiving element.
The test circuit according to claim 1 or 2. The first light receiving region of the dummy light receiving element is covered with a light shielding film so that the first light receiving region is not irradiated with light;
The test circuit according to claim 1. A light receiving amplification circuit including the test circuit according to claim 1,
Optical disk device.

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