JP5022377B2 - Measurement circuit and test equipment - Google Patents

Description

The present invention relates to a measurement circuit and a test apparatus. In particular, the present invention applies a DC voltage to the device under test and measures the DC current flowing through the device under test. This application is related to the following Japanese application. For designated countries where incorporation by reference of documents is permitted, the contents described in the following application are incorporated into this application by reference and made a part of this application.
1. Japanese Patent Application No. 2006-310358 Application Date November 16, 2006

  As a test item for a device under test such as a semiconductor circuit, a DC test of the device under test is known. The DC test is a test for determining pass / fail of a device under test by measuring a power supply current or a power supply voltage supplied to the device under test. For example, voltage application current measurement that measures the DC current supplied to the device under test when a predetermined DC voltage is applied to the device under test, or the device under test when a predetermined DC current is supplied to the device under test Current applied voltage measurement for measuring the supplied DC voltage is conceivable.

  When performing the DC test, it is conceivable to limit the DC current supplied to the device under test in order to prevent an overcurrent or the like from being supplied to the device under test. For example, a clamp circuit that limits the DC voltage applied to the device under test when the direct current flowing through the device under test becomes a limit value or more can be considered (see, for example, Patent Document 1).

  The direct current flowing through the device under test can be detected from, for example, a voltage drop across the resistor provided between the amplifier that supplies power supply power and the input end of the device under test. Therefore, by detecting the magnitude relationship between the first voltage with respect to the ground potential at one end of the resistor on the amplifier side and the second voltage obtained by adding a voltage corresponding to the limit value to the voltage with respect to the ground potential at the other end of the resistor, Whether or not the direct current is larger than the limit value can be detected.

  For example, the direct current is limited by inputting the first voltage divided by a predetermined voltage dividing resistor and the second voltage divided by a voltage dividing resistor having the same voltage dividing ratio to the differential amplifier. It can be detected whether or not the value is larger. By restricting the direct current according to the output of the differential amplifier, it is possible to prevent an excessive direct current from flowing through the device under test.

JP 2002-277505 A

  However, when a high voltage is applied to the device under test, the voltage applied to the voltage dividing resistor becomes a high voltage when the clamp circuit is operated based on the ground potential as described above. For this reason, when an error is generated between the voltage dividing ratio of the voltage dividing resistor corresponding to the first voltage and the voltage dividing ratio of the voltage dividing resistor corresponding to the second voltage, the CMR error becomes large and the accuracy of the clamp is increased. It may be deteriorated.

  Therefore, an object of one aspect of the present invention is to provide a measurement circuit and a test apparatus that solve the above problems. This object is achieved by a combination of features described in the independent claims. The dependent claims define further advantageous specific examples of the present invention.

  In order to solve the above problems, according to one example of the measurement circuit according to the first aspect related to the innovation included in the present specification, a DC voltage is applied to the device under test and the DC current flows through the device under test. A measurement circuit for generating a DC voltage according to an input voltage and applying the DC voltage to the device under test; an output end of the main amplification unit; and an input end of the device under test A series resistor provided in series therebetween, and a clamp circuit that limits a current value of the DC current output by the main amplifier, the clamp circuit receiving the DC voltage output by the main amplifier A first limit voltage output unit that outputs a first limit voltage having a voltage difference corresponding to the limit value of the DC current with respect to the DC voltage; a first limit voltage; and a voltage drop at both ends of the series resistor. Based on the voltage, to provide a measurement circuit having a first clamping portion which limits the DC current the main amplifier unit outputs.

  Further, according to one example of the measurement circuit according to the second aspect related to the innovation included in the present specification, a measurement circuit that applies a DC voltage to the device under test and measures a DC current flowing through the device under test is provided. A main amplifying unit that generates the DC voltage according to an input voltage and applies the DC voltage to the device under test; and is provided in series between an output terminal of the main amplifying unit and an input terminal of the device under test. A series resistor, a clamp circuit that limits a current value of the direct current output from the main amplifier, and a buffer that branches and receives the input voltage and inputs the input voltage to the clamp circuit. The DC voltage output from the main amplifying unit is received, and a first limit voltage having a voltage difference corresponding to a limit value of the DC current is output with respect to the input voltage input by the buffer. A measurement circuit having a first limit voltage output unit, the first limit voltage, and a first clamp unit that limits the DC current output from the main amplification unit based on a voltage drop across the series resistor. I will provide a.

  Further, according to one example of the test apparatus according to the third aspect related to the innovation included in the present specification, a test apparatus for testing a device under test, supplying a DC voltage to the device under test, A measurement circuit that measures a direct current flowing through the device under test; and a determination unit that determines pass / fail of the device under test based on the direct current measured by the measurement circuit. In response, the DC voltage is generated and applied to the device under test, a main amplifying unit, a series resistor provided in series between the output terminal of the main amplifying unit and the input terminal of the device under test, A clamp circuit that limits a current value of the DC current output by the main amplifier, and the clamp circuit receives the DC voltage output by the main amplifier, The main amplification is based on a first limit voltage output unit that outputs a first limit voltage having a voltage difference corresponding to a limit value of a direct current, the first limit voltage, and a voltage drop across the series resistor. And a first clamp unit that limits the DC current output by the unit.

  Further, according to one example of the test apparatus according to the fourth aspect related to the innovation included in the present specification, a test apparatus for testing a device under test, supplying a DC voltage to the device under test, A measurement circuit that measures a direct current flowing through the device under test; and a determination unit that determines pass / fail of the device under test based on the direct current measured by the measurement circuit. In response, the DC voltage is generated and applied to the device under test, a main amplifying unit, a series resistor provided in series between the output terminal of the main amplifying unit and the input terminal of the device under test, A clamp circuit that limits a current value of the direct current output by the main amplifier, and a buffer that branches and receives the input voltage and inputs the input voltage to the clamp circuit. A first limit voltage output that receives the DC voltage output from the main amplifier and outputs a first limit voltage having a voltage difference corresponding to a limit value of the DC current with respect to the input voltage input by the buffer. And a first clamp unit for limiting the DC current output from the main amplification unit based on a first limiting voltage and a voltage drop across the series resistor.

  The above summary of the invention does not enumerate all the necessary features of the present invention, and sub-combinations of these feature groups can also be the invention.

It is a figure which shows an example of a structure of the measurement circuit 100 which concerns on one Embodiment of this invention. 6 is a diagram illustrating another example of the configuration of the measurement circuit 100. FIG. 6 is a diagram illustrating another example of the configuration of the measurement circuit 100. FIG. It is a figure which shows an example of a structure of the test apparatus 200 which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Voltage value control part, 12 ... Resistance, 14 ... Series resistance, 16 ... Current detection part, 18 ... Current measurement part, 20 ... Main amplification part, 22 ... Differential amplifier 24... Main amplifier 26. Bypass capacitor 30... Clamp device 40... First clamp circuit 42. .. First resistor, 48, 68 ... Second resistor, 50, 70 ... Third resistor, 52, 72 ... Fourth resistor, 54 ... First comparison section, 56 ... First 1 diode, 58... First clamp section, 60... Second clamp circuit, 62... Second limit voltage output section, 74. ... Second clamp part, 80 ... Buffer, 100 ... Measurement circuit, 110 ... Determining part, 120 ... Turn input unit, 200 ... test apparatus, 300 ... device under test

  Hereinafter, the (1) aspect of the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims, and all combinations of features shown in the embodiments are described. It is not necessarily essential for the solution of the invention.

  FIG. 1 is a diagram illustrating an example of a configuration of a measurement circuit 100 according to an embodiment of the present invention. The measurement circuit 100 is a voltage application current measurement circuit that applies a predetermined DC voltage to the device under test 300 and measures a DC current flowing through the device under test 300. The measurement circuit 100 includes a voltage value control unit 10, a resistor 12, and a main amplification unit. 20, a series resistor 14, a current detection unit 16, a current measurement unit 18, a clamp device 30, and a bypass capacitor 26.

  The voltage value control unit 10 controls the voltage applied to the device under test 300. For example, the voltage value control unit 10 is a digital-analog converter, and outputs an input voltage corresponding to a given digital value.

  The main amplifying unit 20 receives an input voltage via the resistor 12. The main amplifying unit 20 generates a DC voltage corresponding to the input voltage and applies it to the device under test 300. The main amplification unit 20 includes a differential amplification unit 22 and a main amplifier 24. The differential amplifier 22 feeds back a DC voltage at the input end of the device under test 300 and outputs a voltage corresponding to the difference between the DC voltage and the input voltage. The main amplifier 24 amplifies the voltage output from the differential amplifier 22 with a predetermined amplification factor and outputs the amplified voltage. With such a configuration, the DC voltage applied to the device under test 300 can be maintained at a predetermined voltage value corresponding to the input voltage from the voltage value control unit 10.

  The current detector 16 detects the current value of the direct current supplied from the main amplifier 20 to the device under test 300 and outputs a detection voltage corresponding to the current value. For example, the current detection unit 16 may be a resistor provided in series between the output end of the main amplification unit 20 and the input end of the device under test 300. The current measurement unit 18 measures the current value of the direct current supplied to the device under test 300 based on the detection voltage supplied from the current detection unit 16. For example, the current measuring unit 18 may be a differential amplifier that receives respective voltages at both ends of the resistor of the current detecting unit 16.

  The bypass capacitor 26 is provided between the input terminal of the device under test 300 and the ground potential. The bypass capacitor 26 compensates for a steep power supply voltage or current fluctuation at the input terminal of the device under test 300.

  The series resistor 14 is provided in series between the output terminal of the main amplifying unit 20 and the input terminal of the device under test 300. For example, the series resistor 14 may be provided in series between the output terminal of the main amplification unit 20 and the input terminal of the current detection unit 16.

  The clamp device 30 limits the current value of the direct current output from the main amplification unit 20. For example, the clamp device 30 limits the current value of the direct current within a current range that is allowed to flow through the device under test 300. As a result, it is possible to prevent an excessive current from flowing through the device under test 300 and to reduce the occurrence of problems in the device under test 300.

  In this example, the clamp device 30 includes a first clamp circuit 40 and a second clamp circuit 60. The first clamp circuit 40 defines the upper limit of the direct current flowing through the device under test 300. The second clamp circuit 60 defines the lower limit of the direct current flowing through the device under test 300.

  The first clamp circuit 40 includes a first limit voltage output unit 42, a first resistor 46, a second resistor 48, a third resistor 50, a fourth resistor 52, and a first clamp unit 58. The first limit voltage output unit 42 is, for example, a digital-analog converter, and may output a voltage corresponding to a given digital value.

  The first limit voltage output unit 42 defines an upper limit value of the direct current flowing through the device under test 300. In this example, the first limit voltage output unit 42 outputs a first limit voltage corresponding to the upper limit value of the direct current. The first limit voltage output unit 42 outputs the first limit voltage with reference to the DC voltage output from the main amplification unit 20. That is, the first limit voltage output unit 42 receives the DC voltage output from the main amplifying unit 20, and outputs a first limit voltage having a voltage difference corresponding to the upper limit value of the DC current with respect to the DC voltage. For example, when the DC voltage output from the main amplifier 20 is V1, and the voltage corresponding to the upper limit value of the DC current is Vc, the first limit voltage output from the first limit voltage output unit 42 is V1 + Vc.

  The first clamp unit 58 limits the direct current output from the main amplification unit 20 based on the first limit voltage and the voltage drop across the series resistor 14. In the present example, the first clamp unit 58 includes a first comparison unit 54 and a first diode 56.

  The first comparison unit 54 amplifies and outputs a first comparison unit difference that outputs a first comparison result voltage based on a comparison result between the drop voltage and a voltage corresponding to the first limit voltage. In this example, the first comparison unit 54 has first and second input terminals, and outputs a first comparison result voltage corresponding to a difference between voltages input to the first input terminal and the second input terminal. It is a dynamic amplifier. The voltage corresponding to the first limit voltage is a voltage obtained by dividing the voltage V2 and the first limit voltage at one end of the series resistor 14 on the device under test 300 side by the second resistor 48 and the third resistor 50. is there.

  The second resistor 48 connects one end of the series resistor 14 on the device under test 300 side and the second input terminal of the first comparator 54. The third resistor 50 connects the output terminal of the first limit voltage output unit 42 and the connection point of the second resistor 48 and the second input terminal. The resistance value of the third resistor 50 is preferably sufficiently larger than the resistance value of the second resistor 48. For example, the resistance value of the second resistor 48 may be about 5 kΩ, and the resistance value of the third resistor 50 may be about 200 kΩ. In this case, assuming that the voltage drop across the series resistor 14 is Vf, the voltage applied to the second input terminal of the first comparator 54 is (200 kΩ × (V1−Vf) +5 kΩ × (V1 + Vc)) / (200 kΩ + 5 kΩ) = V1 + (5 kΩ × Vc−200 kΩ × Vf) / 205 kΩ.

  The first resistor 46 connects one end of the series resistor 14 on the main amplification unit 20 side and the first input terminal of the first comparison unit 54. The fourth resistor 52 is provided between one end of the first resistor 46 on the first comparison unit 54 side and one end of the series resistor 14 on the main amplification unit 20 side. Here, the resistance value of the first resistor 46 is preferably equal to the resistance value of the second resistor 48, and the resistance value of the fourth resistor 52 is preferably substantially equal to the resistance value of the third resistor 50. That is, the voltage applied to the first input terminal of the first comparison unit 54 is the voltage V1 at one end of the series resistor 14 on the main amplification unit 20 side. For this reason, the first comparison unit 54 calculates the difference (5 kΩ × Vc) between the voltage V1 applied to the first input terminal and the voltage V1 + (5 kΩ × Vc−200 kΩ × Vf) / 205 kΩ input to the second input terminal. −200 kΩ × Vf) / 205 kΩ is amplified and output. That is, the first comparison unit 54 outputs a voltage corresponding to the magnitude relationship between Vc and Vf weighted by the resistance values of the second resistor 48 and the third resistor 50.

  The first diode 56 limits the direct current output from the main amplifying unit 20 by limiting the input voltage input to the main amplifying unit 20 based on the first comparison result voltage. In this example, the first diode 56 has a cathode connected to the output terminal of the first comparison unit 54 and an anode connected to the input terminal of the main amplification unit 20. Further, the first comparison unit 54 turns the first diode 56 on when (5 kΩ × Vc−200 kΩ × Vf) is negative, that is, when the direct current flowing through the device under test 300 is larger than the upper limit value. 1 Outputs the comparison result voltage. As a result, the voltage drop across the resistor 12 increases, and the input voltage to the main amplifier 20 is limited. For this reason, the direct current flowing through the device under test 300 is limited to be smaller than the upper limit value. Further, the first comparison unit 54 sets the first diode 56 in the OFF state when (5 kΩ × Vc−200 kΩ × Vf) is positive, that is, when the direct current flowing through the device under test 300 is smaller than the upper limit value. The comparison result voltage is output. With such a configuration, the direct current flowing through the device under test 300 can be set to a predetermined upper limit value or less.

  Further, as described above, the second clamp circuit 60 controls the input voltage of the main amplifying unit 20 so that the direct current flowing through the device under test 300 is equal to or higher than a predetermined lower limit value. The second clamp circuit 60 includes a second limit voltage output unit 62, a first resistor 66, a second resistor 68, a third resistor 70, a fourth resistor 72, and a second clamp unit 78. The second limit voltage output unit 62 is, for example, a digital / analog converter, and may output a voltage corresponding to a given digital value.

  The second limit voltage output unit 62 defines a lower limit value of the direct current flowing through the device under test 300. In this example, the second limit voltage output unit 62 outputs a second limit voltage corresponding to the lower limit value of the direct current. The second limit voltage output unit 62 outputs the second limit voltage with reference to the DC voltage output from the main amplification unit 20. That is, the second limit voltage output unit 62 receives the DC voltage output from the main amplification unit 20, and outputs a second limit voltage having a voltage difference corresponding to the lower limit value of the DC current with respect to the DC voltage. For example, when the DC voltage output from the main amplifier 20 is V1, and the voltage corresponding to the upper limit value of the DC current is Vc, the second limit voltage output from the second limit voltage output unit 62 is V1-Vc.

  The second clamp unit 78 limits the direct current output from the main amplification unit 20 based on the second limit voltage and the voltage drop across the series resistor 14. In this example, the second clamp part 78 includes a second comparison part 74 and a second diode 76.

  The second comparison unit 74 may be a differential circuit having substantially the same characteristics as the first comparison unit 54. The first input terminal of the second comparison unit 74 is connected to the connection point of the first resistor 66 and the fourth resistor 72. The second input terminal of the second comparison unit 74 is connected to the connection point of the second resistor 68 and the third resistor 70. The second diode 76 has an anode connected to the output terminal of the second comparison unit 74 and a cathode connected to the input terminal of the main amplification unit 20. The second diode 76 limits the lower limit of the direct current flowing through the device under test 300 by limiting the lower limit of the input voltage to the main amplification unit 20 based on the second comparison result voltage output from the second comparison unit 74. Restrict.

  The first resistor 66, the second resistor 68, the third resistor 70, and the fourth resistor 72 are the same as the first resistor 46, the second resistor 48, the third resistor 50, and the fourth resistor 52 in the first clamp circuit 40. A similar connection may be made.

  With such a configuration, the second comparison unit 74 outputs the second comparison result voltage that turns on the second diode 76 when the drop voltage in the series resistor 14 is smaller than the second limit voltage, and the drop When the voltage is higher than the second limit voltage, a second comparison result voltage that turns off the second diode 76 is output. With such a configuration, the direct current flowing through the device under test 300 can be set to a predetermined lower limit value or more.

  Further, the clamping device 30 in this example operates based on the DC voltage V1 output from the main amplifying unit 20. Therefore, the voltage applied to the first resistor (46, 66), the second resistor (48, 68), the third resistor (50, 70), and the fourth resistor (52, 72) can be reduced. Therefore, it is possible to reduce CMR errors caused by variations in resistance values of these resistors. In particular, when the DC voltage V1 output from the main amplifier 20 is a high voltage, the effect becomes more remarkable.

  When the clamp device 30 operates with reference to the ground potential, it is necessary to supply the clamp device 30 with a high-voltage power supply voltage corresponding to the DC voltage output from the main amplification unit 20. However, since the clamping device 30 in this example operates based on the DC voltage output from the main amplifying unit 20, it is not necessary to supply a high-voltage power supply voltage. For example, a power supply voltage that can operate in a range of + Vc to −Vc may be supplied.

  FIG. 2 is a diagram illustrating another example of the configuration of the measurement circuit 100. The measurement circuit 100 in this example is different from the configuration of the measurement circuit 100 described in FIG. 1 in that the fourth resistance (52, 72) is not included. Further, the third resistor 50 in this example is provided between the connection point of the first resistor 46 and the first comparison unit 54 and the output terminal of the first limit voltage output unit 42. Similarly, the third resistor 70 is provided between the connection point of the first resistor 66 and the second comparison unit 74 and the output terminal of the second limit voltage output unit 62. The other configurations are the same as the components given the same reference numerals in FIG.

  In FIG. 1, the DC voltage V1 output from the main amplifier 20 is applied to both ends of the first resistor (46, 66) and the fourth resistor (52, 72) connected in series. Therefore, as shown in FIG. 2, even if the fourth resistor (52, 72) is omitted in the measurement circuit 100, the operation is the same as that of the measurement circuit 100 described in FIG. In this example, since the connection destination of the third resistors 50 and 70 is changed, the polarities of the output voltages of the first limit voltage output unit 42 and the second limit voltage output unit 62 are also changed. For example, the output voltage of the first limit voltage output unit 42 may be V1-Vc, and the output voltage of the second limit voltage output unit 62 may be V1 + Vc.

  FIG. 3 is a diagram illustrating another example of the configuration of the measurement circuit 100. The measurement circuit 100 in this example further includes a buffer 80 with respect to the configuration of the measurement circuit 100 described in FIG. Other components may have the same functions and configurations as the components denoted by the same reference numerals in FIG.

  The buffer 80 branches and receives the input voltage input to the main amplification unit 20 and inputs it to the clamp device 30. In this example, the buffer 80 branches and receives the input voltage from the connection point between the resistor 12 and the input terminal of the main amplifier 20.

  In addition, the first limit voltage output unit 42 and the second limit voltage output unit 62 in FIG. 1 operate based on the DC voltage output from the main amplification unit 20, but the first limit voltage output unit 42 and the second limit voltage output unit 42 in this example are the same. The 2 limit voltage output unit 62 operates based on the input voltage output from the buffer 80.

  Moreover, although the DC voltage output from the main amplifier 20 is applied to one end of the fourth resistor (52, 72) in FIG. 1, the one end of the fourth resistor (52, 72) in this example is applied to the one end of the fourth resistor (52, 72). The input voltage output from the buffer 80 is applied.

  When the amplification factor in the main amplifying unit 20 is, for example, 1 time, the same effect as that of the measurement circuit 100 described in FIG. However, the amplification factor in the main amplification unit 20 is not limited to 1 time.

  FIG. 4 is a diagram showing an example of the configuration of the test apparatus 200 according to one embodiment of the present invention. The test apparatus 200 is an apparatus for testing a device under test 300 such as a semiconductor circuit, and includes a measurement circuit 100, a pattern input unit 120, and a determination unit 110.

  The measurement circuit 100 is the same circuit as the measurement circuit 100 described with reference to FIGS. That is, the measurement circuit 100 supplies power to the device under test 300 and measures the voltage application current of the device under test 300.

  The determination unit 110 determines pass / fail of the device under test 300 based on the measurement result in the measurement circuit 100. For example, the determination unit 110 may determine pass / fail of the device under test 300 based on whether or not the current value of the direct current measured by the current measurement unit 18 described in FIG. 1 is within a predetermined range.

  When performing a direct current test when the device under test 300 is stationary, the measurement circuit 100 may perform measurement in a state where the pattern input unit 120 does not input a test pattern. When performing a DC test during operation of the device under test 300, the measurement circuit 100 may perform measurement in a state where the pattern input unit 120 is inputting a test pattern.

  The pattern input unit 120 may input, for example, a test pattern that sequentially changes the state of a predetermined logic circuit included in the device under test 300 to the device under test 300. In this case, it is possible to detect whether or not the logic circuit is normal. The pattern input unit 120 may input a test pattern for sequentially operating a plurality of logic circuits included in the device under test 300 to the device under test. In this case, a defective portion in the device under test 300 can be specified.

  As mentioned above, although the aspect (1) of this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

Claims (9)

A measurement circuit that applies a DC voltage to a device under test and measures a DC current flowing through the device under test,
A main amplifying unit that generates the DC voltage according to an input voltage and applies the generated DC voltage to the device under test;
A series resistor provided in series between the output terminal of the main amplifier and the input terminal of the device under test;
A clamp circuit that limits a current value of the direct current output by the main amplification unit,
The clamp circuit is
A first limit voltage output unit that receives the DC voltage output by the main amplification unit and outputs a first limit voltage having a voltage difference corresponding to a limit value of the DC current with respect to the DC voltage;
A measurement circuit comprising: a first clamp unit configured to limit the DC current output from the main amplification unit based on the first limit voltage and a voltage drop across the series resistor. The first clamp part is
A first comparison unit that outputs a first comparison result voltage based on a comparison result between the drop voltage and a voltage according to the first limit voltage;
The measurement circuit according to claim 1, further comprising: a first diode that limits the DC current by limiting the input voltage based on the first comparison result voltage. The first limit voltage output unit outputs the first limit voltage according to the upper limit value of the direct current,
The first diode has a cathode connected to an output terminal of the first comparison unit, an anode connected to an input terminal of the main amplification unit,
The first comparison unit outputs the first comparison result voltage for turning on the first diode when the drop voltage is larger than a voltage corresponding to the first limit voltage, and the drop voltage is The measurement circuit according to claim 2, wherein the first comparison result voltage for turning off the first diode is output when the voltage is smaller than a voltage corresponding to the first limit voltage. The first comparison unit includes first and second input terminals, and outputs a first comparison result voltage according to a difference between voltages input to the first input terminal and the second input terminal. Dynamic circuit,
The first clamp part is
A first resistor that connects one end of the series resistor on the main amplification unit side and the first input terminal of the first comparison unit;
A second resistor that connects one end of the series resistor on the device under test side and the second input terminal of the first comparator, and has a resistance value substantially equal to the first resistor;
The output terminal of the first limit voltage output unit is connected to a connection point between the second resistor and the second input terminal, and further includes a third resistor having a resistance value larger than that of the second resistor. The described measurement circuit.   The first clamp unit is provided between one end of the first resistor on the first comparison unit side and one end of the series resistor on the main amplification unit side, and has a resistance value substantially equal to the third resistor. The measurement circuit according to claim 4, further comprising a fourth resistor. A second limit voltage output unit that receives the DC voltage output by the main amplification unit and outputs a second limit voltage having a voltage difference corresponding to a lower limit value of the DC current with respect to the DC voltage;
A second clamping unit for limiting a lower limit of the direct current output from the main amplification unit based on the second limiting voltage and a voltage drop across the series resistor;
The second clamp part is
A second comparison unit that outputs a second comparison result voltage based on a comparison result between the drop voltage and a voltage corresponding to the second limit voltage;
The anode is connected to the output terminal of the second comparison unit, the cathode is connected to the input terminal of the main amplification unit, and the DC voltage is limited by limiting the lower limit of the input voltage based on the second comparison result voltage. A second diode that limits the lower limit of the current,
The second comparison unit outputs the second comparison result voltage that turns on the second diode when the drop voltage is smaller than a voltage corresponding to the second limit voltage, and the drop voltage is 5. The measurement circuit according to claim 4, wherein the second comparison result voltage for turning off the second diode is output when the voltage is higher than a voltage corresponding to the second limit voltage. 6. A measurement circuit that applies a DC voltage to a device under test and measures a DC current flowing through the device under test,
A main amplifying unit that generates the DC voltage according to an input voltage and applies the generated DC voltage to the device under test;
A series resistor provided in series between the output terminal of the main amplifier and the input terminal of the device under test;
A clamp circuit that limits a current value of the direct current output by the main amplification unit;
A buffer that branches and receives the input voltage and inputs the input voltage to the clamp circuit;
The clamp circuit is
A first limit voltage output that receives the DC voltage output from the main amplifier and outputs a first limit voltage having a voltage difference corresponding to a limit value of the DC current with respect to the input voltage input by the buffer. And
A measurement circuit comprising: a first clamp unit configured to limit the DC current output from the main amplification unit based on the first limit voltage and a voltage drop across the series resistor. A test apparatus for testing a device under test,
A measurement circuit for supplying a direct current voltage to the device under test and measuring a direct current flowing through the device under test;
A determination unit for determining pass / fail of the device under test based on the direct current measured by the measurement circuit;
The measurement circuit includes:
A main amplifying unit that generates the DC voltage according to an input voltage and applies the generated DC voltage to the device under test;
A series resistor provided in series between the output terminal of the main amplifier and the input terminal of the device under test;
A clamp circuit that limits a current value of the direct current output by the main amplification unit, and
The clamp circuit is
A first limit voltage output unit that receives the DC voltage output by the main amplification unit and outputs a first limit voltage having a voltage difference corresponding to a limit value of the DC current with respect to the DC voltage;
A test apparatus comprising: a first clamp unit that limits the DC current output from the main amplification unit based on the first limit voltage and a voltage drop across the series resistor. A test apparatus for testing a device under test,
A measurement circuit for supplying a direct current voltage to the device under test and measuring a direct current flowing through the device under test;
A determination unit for determining pass / fail of the device under test based on the direct current measured by the measurement circuit;
The measurement circuit includes:
A main amplifying unit that generates the DC voltage according to an input voltage and applies the generated DC voltage to the device under test;
A series resistor provided in series between the output terminal of the main amplifier and the input terminal of the device under test;
A clamp circuit that limits a current value of the direct current output by the main amplification unit;
A buffer that branches and receives the input voltage and inputs the input voltage to the clamp circuit;
The clamp circuit is
A first limit voltage output that receives the DC voltage output from the main amplifier and outputs a first limit voltage having a voltage difference corresponding to a limit value of the DC current with respect to the input voltage input by the buffer. And
A test apparatus comprising: a first clamp unit that limits the DC current output from the main amplification unit based on the first limit voltage and a voltage drop across the series resistor.

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