Test apparatus and measurement apparatus for measuring an electric current consumed by a device under test

There is provided a test apparatus for testing a device under test, which includes a voltage supplying section that supplies a voltage to the device under test through a wire, a first capacitor that is arranged between the wire and a common potential in series, a current detecting section that detects a current flowing through the wire at a location closer to the device under test than the first capacitor is, an integrating section that outputs an integration value obtained by integrating a difference between the current detected by the current detecting section and a predetermined reference current, and a judging section that judges whether the device under test is a pass or a failure based on the integration value.

BACKGROUND

1. Technical Field

The present invention relates to a test apparatus and a measurement apparatus. Particularly, the present invention relates to a test apparatus and a measurement apparatus for measuring an electric current consumed by a device under test (load).

2. Related Art

A test apparatus has a function of measuring an average current to be consumed by a device under test when the device operates. The test apparatus detects a current output from a power source device that supplies a drive voltage to the device under test, and measures the average current consumed by the device under test.

Here, the power source device is slow in responding to any change in the current consumed by the load. Accordingly, the test apparatus has a bypass capacitor having relatively large capacitance, between its power source line and the ground, in order to compensate for any response delay of the current output from the power source device. With this, the test apparatus can supply a drive current to the device under test even in a case where it makes the device under test operate in such a manner as would require the current consumed by the device under test to change quickly.

Here, in a case where the test apparatus has a bypass capacitor, the current to be consumed by the device under test and the current output from the power source device do not coincide. Hence, the test apparatus cannot correctly measure the average current consumed by the device under test, by detecting the output current from the power source device.

Thus, a conceivable test apparatus to overcome this problem is such one that has, near the device under test, an AD converter which samples the drive current to be supplied to the device under test. However, since the drive current supplied to the device under test changes quickly, the test apparatus has to make the AD converter perform sampling quickly. Accordingly, the test apparatus has to be provided with a high-performance AD converter. Further, since there will be a large amount of data that should be taken in, the test apparatus has to be provided with a data memory having a large capacity.

Furthermore, in testing multiple devices under test of about several hundreds or so simultaneously, the test apparatus has to have the same number of current measuring sections as the number of devices under test. Therefore, it is preferred that the test apparatus be structured as a simple circuit in order to be able to measure the average current consumed by the device under test.

When measuring the current of the device under test, a measurement error is caused by an offset in the operating amplifier used by the measuring circuit. To solve this problem, it is necessary to adjust the offset to be equal to zero. But if a plurality of measurement channels are provided, it is necessary to adjust the offset of each channel because each operating amplifier has a different offset. To achieve this, a way to adjust the error caused by the offset automatically and with the same process is sought.

During the initial evaluation of the device under test, the value of the value of the current may be sought in addition to the test result indicating pass/fail of the current test of the device under test. Therefore, a way to easily obtain the current value is desired.

SUMMARY

Therefore, it is an object of an aspect of the innovations herein to provide a test apparatus and a measurement apparatus, which are capable of overcoming the above drawbacks accompanying the related art. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the innovations herein.

According to a first aspect related to the innovations herein, one exemplary test apparatus may include a test apparatus for testing a device under test, having: a voltage supplying section which supplies a voltage to a device under test through a wire; a first capacitor which is arranged between the wire and a common potential in series; a current detecting section which detects a current flowing through the wire at a location which is closer to the device under test than the first capacitor is; an integrating section which outputs an integration value obtained by integrating a difference between the current detected by the current detecting section and a predetermined reference current; and a judging section which judges whether the device under test is a pass or a failure based on the integration value.

According to a second aspect related to the innovations herein, one exemplary measurement apparatus may include a measurement apparatus for measuring a current flowing through a load, having: a first capacitor which is arranged between a wire for supplying a voltage to the load and a common potential in series; a current detecting section which detects a current flowing through the wire at a location closer to the load than the first capacitor is; and an integrating section which outputs an integration value obtained by integrating a difference between the current detected by the current detecting section and a predetermined reference current.

According to a third aspect related to the innovations herein, one exemplary test apparatus may include the test apparatus according to the first aspect, wherein the integrating section has: an integrating circuit which stores charges corresponding to a current indicating the difference between the current detected by the current detecting section and the reference current in a capacity element, and outputs an integration voltage that occurs across both ends of the capacity element as the integration value; and an offset correcting section that corrects an offset occurring at an input of the integrating circuit.

According to a fourth aspect related to the innovations herein, one exemplary test apparatus may include the test apparatus according to the first aspect, further including an AD converting section that measures the integration value, wherein the AD converting section has: a recording section that records digital values obtained by measuring the integration value for each measurement cycle; and a processing section that scales the digital values obtained respectively for each measurement cycle recorded on the recording medium with measured values obtained when only the reference current is input before or after a series of measurements.

The above summary of the invention is not intended to list all necessary features of the present invention, but sub-combinations of these features can also provide an invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

One aspect of the present invention will be described below through an embodiment of the invention, but the embodiment below is not intended to limit the invention set forth in the claims, or all the combinations explained in the embodiment are not necessarily essential to the means of solving provided by the invention.

FIG. 1shows the configuration of a test apparatus10according to the present embodiment, together with a device under test (DUT)200. The test apparatus10comprises a signal generating section17, a voltage supplying section18, a measurement apparatus20, a reference voltage generating section21, a signal acquiring section22, and a system control device23, and tests the DUT200.

The DUT200is tested by the test apparatus10, for example, while it is loaded on a performance board or the like. The signal generating section17supplies a test signal corresponding to a test pattern to the DUT200.

The voltage supplying section18supplies a voltage to the DUT200through a wire12. The voltage supplying section18may, for example, supply a voltage for driving the DUT200, to a power source terminal of the DUT200. The voltage supplying section18may, for example, detect a voltage (drive voltage Vdd) at a point (a detection end14) on the wire12that is near the DUT200and control its output voltage such that the detected drive voltage Vdd becomes a predetermined value.

The measurement apparatus20measures an average consumption current of the DUT200(for example, an average consumption current when the DUT200is in operation). Then, the measurement apparatus20judges whether the average consumption current of the DUT200is larger or not (or smaller or not) than a predetermined reference current IREF. Note that the measurement apparatus20may, for example, be located at a device interface section such as a socket or the like, into which the performance board and the DUT200are inserted.

The reference voltage generating section21generates a reference voltage VREFfor generating the reference current IREF, and supplies it to the measurement apparatus20. The reference voltage generating section21supplies the reference voltage VREFto the measurement apparatus20, for example, prior to a test, in accordance with the control of the system control device23.

The signal acquiring section22judges whether an output signal to be output from the DUT200in response to a test signal is a pass or a failure. In addition, the signal acquiring section22judges whether the DUT200is a pass or a failure based on a result of judgment by the measurement apparatus20.

The system control device23includes a memory which stores a program therein, a CPU which executes the program, etc. The system control device23exchanges data with the signal generating section17, the voltage supplying section18, the reference voltage generating section21, and the signal acquiring section22to control the testing operation of the test apparatus10.

FIG. 2shows the configuration of the measurement apparatus20according to the present embodiment, together with the voltage supplying section18and the DUT200. The measurement apparatus20comprises a first capacitor24, a second capacitor26, a current detecting section28, an integrating section30, a judging section32, a setting section34, and a control section36.

The first capacitor24is arranged between the wire12and a common potential in series. For example, the first capacitor24may be connected to the wire12at a location closer to the voltage supplying section18than the detection end14is. The common potential may, for example, be a ground potential, or any other reference potential. When the current to be consumed by the DUT200changes quickly and an output current IPfrom the voltage supplying section18lags behind in responding to that change, the first capacitor24can supply the DUT200with a current to be consumed that amounts to this change.

The second capacitor26is arranged between the wire12and the common potential in series at a location closer to the DUT200than the first capacitor24is. The second capacitor26may, for example, be connected to the wire12at a location farther from the DUT200than the detection end14is.

Further, the second capacitor26has smaller capacitance than the first capacitor24. The capacitance of the second capacitor26may be, for example, about 1/10 to 1/1000 of the capacitance of the first capacitor24. When a high-frequency noise such as a ripple or the like gets superimposed on the wire12, the second capacitor26can drop the noise to the common potential (for example, the ground potential). Accordingly, it is preferred that the second capacitor26be connected to the wire12at a location as close to the DUT200as possible.

The current detecting section28detects a current IRMflowing through the wire12, at a location that is closer to the DUT200than the first capacitor24is and farther from the DUT200than the second capacitor26is. That is, the current detecting section28detects the current IRMflowing through the wire12at a location between the first capacitor24and the second capacitor26.

Here, since the current detecting section28detects the current flowing through the wire12at the location closer to the DUT200than the first capacitor24is, it can detect a current, which is the sum of the current supplied from the voltage supplying section18to the DUT200and the current supplied from the first capacitor24to the DUT200. That is, the current detecting section28can detect a current that coincides with a drive current IDDto be supplied to the DUT200. Accordingly, even in a case where the output voltage IPfrom the voltage supplying section18gets behind in responding to any change in the current to be consumed by the DUT200and hence the current to be consumed by the DUT200and the output current IPfrom the voltage supplying section18lose coincidence, the current detecting section28can correctly detect the drive current IDDto be supplied to the DUT200.

Note that the second capacitor26likewise supplies a current to the DUT200when the current to be consumed by the DUT200changes quickly. However, since the capacitance of the first capacitor24is larger than that of the second capacitor26, the current to be supplied from the first capacitor24to the DUT200is larger than the current to be supplied from the second capacitor26to the DUT200(for example, about 10 times to 1000 times larger). Accordingly, the current IRMflowing through the wire12between the first capacitor24and the second capacitor26can be said to be approximately the same as the drive current IDDto be supplied to the DUT200. Thus, the current detecting section28can correctly detect the drive current IDDto be supplied to the DUT200.

The current detecting section28may include, for example, a detection resistor42and a potential difference detecting section44. The detection resistor42is arranged so as to intervene in the wire12at a location between the first capacitor24and the second capacitor26in series. The detection resistor42may be, for example, a minute resistor of about several milliohms. The potential difference detecting section44outputs a detection voltage VXwhich is proportional to the potential difference between both the ends of the detection resistor42. Such a current detecting section28can output the detection voltage VXwhich is proportional to the current IRMflowing through the wire12between the first capacitor24and the second capacitor26.

Instead of the above, the current detecting section28may include a coil arranged intervening in the wire12at a location between the first capacitor24and the second capacitor26in series, and a detecting section which detects the current flowing through that coil. Such a current detecting section28can also detect the current IRMflowing through the wire12between the first capacitor24and the second capacitor26.

The integrating section30outputs an integration value obtained by integrating the difference between the current IRMdetected by the current detecting section28and the predetermined reference current IREF. For example, the integrating section30may store the charges that correspond to the current indicating the difference between the current IRMdetected by the current detecting section28and the predetermined reference current IREF, in any capacity element. Then, for example, the integrating section30may output an integration voltage that occurs across both the ends of the capacity element in which the charges are stored, as the integration value. An example of a detailed configuration of the integrating section30will be explained with reference toFIG. 3.

Since this integrating section30integrates the difference between the current IRMdetected by the current detecting section28and the reference current IREF, it will output an integration value (integration voltage) which is larger than 0 in a case where the average current of the current IRMis equal to or smaller than the reference current IREF, and which is equal to or smaller than 0 in a case where the average current of the current IRMis larger than the reference current IREF. Here, the current IRMdetected by the current detecting section28coincides with the drive current Idd to be supplied to the DUT200. That is, the average current of the current IRMcoincides with the average consumption current of the DUT200. As known from this, the integrating section30can output an integration value (integration voltage) which is larger than 0 when the average consumption current of the DUT200is equal to or smaller than the reference current IREFand which is equal to or smaller than 0 when the average consumption current of the DUT200is larger than the reference current IREF.

The judging section32judges whether the DUT200is a pass or a failure based on the integration value output from the integrating section30. The judging section32may judge whether the average consumption current of the DUT200is larger or not (or smaller or not) than the predetermined reference current IREF, by, for example, comparing whether the integration value output from the integrating section30is larger or not (or smaller or not) than a predetermined threshold (for example, 0). The judging section32may, for example, output a judgment which indicates a pass (the average consumption current is equal to or smaller than the predetermined reference current IREF) in a case where the integration value is positive, and which indicates a failure (the average consumption current is larger than the predetermined reference current IREF) in a case where the integration value is negative.

The setting section34sets the integrating section30to be at the reference current IREF, prior to a test. The setting section34may, for example, set the reference current IREFaccording to the type, grade, or the like of the DUT200, or the content of the test on the DUT200or the like. This allows the measurement apparatus20to judge, for example, whether the average consumption current of the DUT200exceeds an upper limit (or falls below a lower limit) designated as the specifications of the DUT200.

The control section36controls the integration period of the integrating section30. For example, the control section36controls the integrating section30to start integrating at a test start timing and controls the integrating section30to terminate integrating at a test end timing.

Further, in a case where the integrating section30stores the charges corresponding to the current indicating the difference between the current IRMdetected by the current detecting section28and the reference current IREFin the capacity element, the control section36may, prior to a test, discharge the charges stored in the current detecting section28in its capacity element to zero the charges from the capacity element. By doing so, the control section36can make a correct integration voltage be output from the integrating section30.

Since the measurement apparatus20as described above stores the integration value, it has only one sampling value that should be retained and does not therefore have to have a data memory or the like. Further, this measurement apparatus20can correctly compare the average consumption current of the DUT200and the reference current IREFeven when the current to be consumed by the DUT200fluctuates quickly. Furthermore, since the measurement apparatus20can be a simply-structured circuit to be able to measure the average consumption current of the DUT200, a small apparatus scale will suffice even in a case where, for example, several-hundred DUTs200are to be tested at a time.

FIG. 3shows one example of the configuration of the integrating section30and the judging section32according to the present embodiment. For example, the integrating section30may include an integrating circuit50, a reference current source52, a current letting-flow section54, and a discharging section56. Further, the judging section32may include a comparator58, for example.

The integrating circuit50stores the charges corresponding to the current indicating the difference between the current IRMdetected by the current detecting section28and the reference current IREFin the capacity element, and outputs an integration voltage VMthat occurs across both the ends of the capacity element as an integration value. For example, the integrating circuit50may include an operating amplifier60and an integrating capacitor62. The operating amplifier60has its non-inverting input terminal connected to the common potential. The integrating capacitor62is connected between the output terminal and inverting input terminal of the operating amplifier60.

The integrating circuit50having this configuration stores charges corresponding to an input current input to the inverting input terminal of the operating amplifier60in the integrating capacitor62. Then, the integrating circuit50can output the integration voltage VMthat occurs across both the ends of the integrating capacitor62in which the charges are stored. Note that the integrating circuit50outputs the integration voltage VM, which has been inverted in positive/negative characteristic from the result of integrating the input current.

The reference current source52gets the reference current IREFto flow out from the inverting input terminal of the operating amplifier60. The current letting-flow section54makes the current IRMdetected by the current detecting section28flow into the inverting input terminal of the operating amplifier60. Accordingly, the reference current source52and the current letting-flow section54can supply the current indicating the difference obtained by subtracting the reference current IREFfrom the current IRMdetected by the current detecting section28to the inverting input terminal of the operating amplifier60as an input current thereto.

The reference current source52may, for example, include a first voltage follower circuit64and a first reference resistor66. The first voltage follower circuit64has its input terminal supplied with a reference voltage −VREFfrom the setting section34and outputs a voltage equal to the reference voltage −VREFfrom its output terminal. The first reference resistor66is connected between the output terminal of the first voltage follower circuit64and the inverting input terminal of the operating amplifier60, and has a predetermined resistance value RREF1. The reference current source52having this configuration can make the reference current IREF(=VREF/RREF1), which is obtained by dividing the reference voltage VREFby the resistance value RREF1, flow out from the inverting input terminal of the operating amplifier60.

The current letting-flow section54may, for example, include a second voltage follower circuit68and a second reference resistor70. The second voltage follower circuit68has its input terminal supplied with the detection voltage VXfrom the current detecting section28and outputs a voltage equal to the detection voltage VXfrom its output terminal. The second reference resistor70is connected between the output terminal of the second voltage follower circuit68and the inverting input terminal of the operating amplifier60, and has a predetermined resistance value RREF2. The current letting-flow section54having this configuration can make the current IRM(=VX/RREF2), which is obtained by dividing the detection voltage VXby the resistance value RREF2, flow into the inverting input terminal of the operating amplifier60. The resistance value RREF2may, for example, be determined beforehand based on the relationship between the detection voltage VXfrom the current detecting section28and the current IRMflowing through the wire12.

The discharging section56discharges the charges stored in the integrating capacitor62of the integrating circuit50prior to a test. For example, the discharging section56may include a discharging switch72, a first switch74, and a second switch76. The discharging switch72causes a short circuit across both the ends of the integrating capacitor62in discharging the integrating capacitor62. Further, the discharging switch72opens both the ends of the integrating capacitor62during a test.

The first switch74connects the input terminal of the first voltage follower circuit64to the common potential in the discharging operation. The first switch74connects the input terminal of the first voltage follower circuit64to the reference voltage −VREFduring a test. The second switch76connects the input terminal of the second voltage follower circuit68to the common potential in the discharging operation. The second switch76connects the input terminal of the second voltage follower circuit68to the detection voltage VXduring a test.

The discharging section56having this configuration can discharge the charges stored in the integrating circuit50in the discharging operation. Also, the discharging section56can store the charges corresponding to the current indicating the difference between the current IRMdetected by the current detecting section28and the reference current IREFin the integrating circuit50during a test.

The comparator58compares the integration voltage VMoutput from the integrating circuit50with the common potential (for example, the ground potential), and outputs a judgment corresponding to the result of comparison. That is, the comparator58can detect whether the integration voltage VMoutput from the integrating circuit50is positive or negative, and output a judgment corresponding to whether it is positive or negative.

For example, in a case where the integration voltage VMis positive (for example, equal to or larger than 0), the comparator58may judge that the average consumption current of the DUT200is equal to or smaller than the predetermined reference current IREFand hence output a pass judgment. Further, for example, in a case where the integration voltage VMis negative (for example, smaller than 0), the comparator58may judge that the average consumption current of the DUT200is larger than the predetermined reference current IREFand output a failure judgment. As such, since the comparator58needs only to detect the positive or negative characteristic of the integration voltage VMoutput from the integrating circuit50, judging whether a pass or a failure is available with a simple configuration.

FIG. 4shows one example of the drive current Idd to be supplied to the DUT200during a test (which is equal to the current to be consumed by the DUT200). For example, the test apparatus10may control the DUT200to operate during a test such that a drive current Idd as shown inFIG. 4flows through the DUT200.

That is, the test apparatus10may control the DUT200to operate during a test such that the drive current Idd switches between 0.50 A and 1.00 A within a 4 μs period (with a duty ratio of 50%) as shown inFIG. 4. As a result, the average consumption current of the DUT200after the time (0 μs) is 0.75 A. In the example ofFIG. 4, prior to the time (0 μs), the test apparatus10controls the DUT200to operate such that the average consumption current is 0.50 A.

FIG. 5shows a result of simulating the output current IPoutput from the voltage supplying section18in a case where the DUT200is controlled to operate as shown inFIG. 4.FIG. 5shows a simulation result under a regulated condition that the first capacitor24is 330 μF, the second capacitor26is 1 μF, a wire resistance from the voltage supplying section18to the detection end14is 5 mΩ, a wire resistance from the detection end14to the DUT200is 5 mΩ, and the voltage value of the detection end14is 1.20V.FIG. 6toFIG. 9show simulation results obtained under the same condition.

As shown inFIG. 5, the voltage supplying section18outputs an output current IPwhich does not timely respond to the average consumption current of the DUT200. Specifically, the voltage supplying section18outputs an output current IPwhich will reach the average consumption current (0.75 A) of the DUT200at a time 200 μs.

FIG. 6shows a result of simulating the drive voltage Vdd in a case where the DUT200is controlled to operate as shown inFIG. 4. The voltage supplying section18reduces its output voltage during a period in which it increases its output current IP. Then, the voltage supplying section18returns the output voltage to its original after the output voltage IPgets stabilized. Accordingly, the drive voltage Vdd gradually decreases until before the output current IPbecomes stabilized (time 0 μs to time 200 μs) and gradually increases after the output current IPbecomes stabilized (after time 200 μs), as shown inFIG. 6.

FIG. 7shows a result of simulating a current ICL1which flows through the first capacitor24in a case where the DUT200is controlled to operate as shown inFIG. 4. The current ICL1which flows through the first capacitor24changes its amplitude in synchronization with the fluctuations of the drive current Idd.

In a case where the output current IPlags behind in responding to a change in the average consumption current of the DUT200, the first capacitor24supplies a current to fill the shortage, which is the difference obtained by subtracting the output current IPfrom the average consumption current, to the DUT200. Accordingly, during the period in which the voltage supplying section18increases the output current IP(before time 200 μs), the average value of the current ICL1takes a negative value. After the time at which the output current IPbecomes stabilized (after time 200 μs), the average value of the current ICL1increases from a negative value toward 0.

FIG. 8shows a result of simulating a current ICL2which flows through the second capacitor26in a case where the DUT200is controlled to operate as shown inFIG. 4. The current ICL2which flows through the first capacitor24changes its amplitude in synchronization with the fluctuations of the drive current Idd. However, since the second capacitor26has much smaller capacitance than that of the first capacitor24, it cannot supply a current enough to fill the shortage, which is the difference obtained by subtracting the output current IPfrom the average consumption current, to the DUT200. Hence, the average value of the current ICL2takes 0 even when any change occurs in the average consumption current of the DUT200.

FIG. 9shows a result of simulating the current IRMwhich flows through the wire12between the first capacitor24and the second capacitor26in a case where the DUT200is controlled to operate as shown inFIG. 4. As shown inFIG. 9, the average value of the current IRMis 0.75 A all the time. That is, even during the period in which the voltage supplying section18increases the output current IP(before time 200 μs), the average value of the current IRMcoincides with the average consumption current of the DUT200.

The test apparatus10judges whether the average consumption current of the DUT200is larger than the predetermined reference current IREFor not, based on the integration value obtained by integrating the difference between the current IRMflowing through the wire12between the first capacitor24and the second capacitor26and the reference current IREF. Accordingly, the test apparatus10can accurately judge whether the average consumption current of the DUT200is larger than the reference current IREFor not at all the times.

FIG. 10shows the configuration of the test apparatus10according to a first modification of the present embodiment, together with the DUT200.FIG. 11shows one example of a reference current IREFwhich is set by a search section82of the test apparatus10according to the first modification. The test apparatus10according to the present modification has generally the same functions and configuration as those of the test apparatus10shown inFIG. 1, so those members that have generally the same configuration and function as those of the members shown inFIG. 1will be denoted by the same reference numerals in the drawing and explanation for such members will be omitted but for any differences.

The test apparatus10according to the present modification may further comprise a search section82. In the present modification, the CPU in the system control device23executes a measuring program for measuring the current value of a current flowing through a wire, and hence makes the system control device23function as the search section82. The search section82varies the reference current IREFfrom test to test based on the judgment produced in the previous test by using a binary search method, and determines the current value (absolute value) of the current IRMflowing through the wire12.

To be more specific, the search section82first sets the reference current IREF, which takes the center value of a measurement range, which is a range of current values to be measured. Then, the search section82makes the test apparatus10perform the test. That is, the search section82makes the test apparatus10judge whether the average consumption current of the DUT200is larger than the reference current IREFor not.

Subsequently, the search section82determines to which of the upper and lower ranges within the measurement range that are divided at the level of the reference current IREFthe current IRMflowing through the wire12belongs. Then, the search section82sets the range determined to include the current IRMas a new measurement range, and sets a new reference current IREF, which takes the center value of the new measurement range. Then, the search section82repeats the above process plural times and narrows down the range to which the current IRMflowing through the wire12belongs to determine the current value (absolute value) of the current IRMflowing through the wire12.

As shown inFIG. 11for example, the search section82, for example, first sets the center of a first measurement range (for example, 0 A to 1 A) to be the reference current IREF(for example, 0.5 A). Then, the search section82makes the test apparatus10perform a first test. The search section82determines to which of a lower range (0 A to 0.5 A) and an upper range (0.5 A to 1 A), which are obtained by dividing the measurement range to upper and lower parts at the reference current IREF, the current IRMflowing through the wire12belongs, based on the judgment (a pass or a failure) obtained from the first test. In the present example, the first test turns out a failure judgment and hence the search section82determines that the current IRMbelongs to the upper range (0.5 A to 1 A).

Then, the search section82sets the determined range (0.5 A to 1 A) as a new measurement range, and sets a new reference current IREF(for example, 0.75 A), which takes the center value of the new measurement range. Then, the search section82makes the test apparatus10perform a second test and repeats the same process as that in the first test.

The search section82do the same things for the third test and thereafter. Then, the search section82narrows down the range to which the current IRMbelongs, and ultimately determines the current value of the current IRM. As obvious from the above, the test apparatus10according to the present modification can measure the absolute value of the average consumption current of the DUT200.

FIG. 12shows the configuration of the measurement apparatus20according to a second modification of the present embodiment, together with the DUT200. The measurement apparatus20according to the present modification has generally the same functions and configuration as those of the measurement apparatus20shown inFIG. 2, and thus those members that have generally the same configuration and function as those of the members shown inFIG. 2will be denoted by the same reference numerals in the drawing and explanation for such members will be omitted but for any differences.

The measurement apparatus20according to the present modification comprises a first integrating section30-1, a second integrating section integrating section, a first judging section32-1, a second judging section32-2, and a selecting outputter84instead of the integrating section30and the judging section32. Each of the first integrating section30-1and the second integrating section integrating section stores charges corresponding to a current indicating the difference between the current IRMdetected by the current detecting section28and the predetermined reference current IREFin a capacity element, and outputs the integration voltage that occurs across both the ends of the capacity element. Each of the first integrating section30-1and the second integrating section integrating section may, for example, have the configuration shown inFIG. 3.

The first judging section32-1judges whether the DUT200is a pass or a failure based on the integration voltage output from the first integrating section30. The second judging section32-2judges whether the DUT200is a pass or a failure based on the integration voltage output from the second integrating section30. Each of the first judging section32-1and the second judging section32-2may, for example, have the same configuration and function as those of the judging section32. The selecting outputter84selects and outputs the judgment output from a designated one of the first judging section32-1and the second judging section32-2.

The control section36controls the integration period and discharge period of the first integrating section30-1and second integrating section integrating section. Further, the control section36notifies the selecting outputter84of a designated one of the first judging section32-1and the second judging section32-2from which the judgment should be output.

Here, the control section36selects the first integrating section30-1and the second integrating section integrating section alternately from test to test, such that the selected one stores charges and outputs an integration value. Then, the control section36controls the second integrating section integrating section to discharge the stored charges while the first integrating section30-1is storing charges. Further, the control section36controls the first integrating section30-1to discharge the stored charges while the second integrating section integrating section is storing charges.

The measurement apparatus20according to this modification can eliminate time in which no test can be performed for the purposes of discharging. Hence, the test apparatus10having this measurement apparatus20can shorten the time taken for tests.

FIG. 13shows a configuration of a test apparatus300according to a third modification of the present invention, along with the DUT200. The test apparatus300according to the present modification has generally the same functions and configuration as those of the test apparatus10shown inFIGS. 1 to 3, so those members that have generally the same configuration and function as those of the members shown inFIGS. 1 to 3will be denoted by the same reference numerals in the drawing and explanation for such members will be omitted but for any differences.

The test apparatus300tests the DUT200and is provided with the signal generating section17, the voltage supplying section18, a measurement apparatus310, the reference voltage generating section21, the signal acquiring section22, the system control device23, and an AD converting section320. The measurement apparatus310has the same function and configuration as the measurement apparatus20. The measurement apparatus310is provided with the first capacitor24, the second capacitor26, a current detecting section330, an integrating section340, a judging section350, and a control section360. The control section360may have the same function as the setting section34and the control section36.

FIG. 14shows a configuration of the current detecting section330according to the present modification, along with the voltage supplying section18and the DUT200. The current detecting section330may include the detection resistor42, the potential difference detecting section44, and an input switching section332. The detection resistor42can be used in place of the coil. The input switching section332selects one of (i) a detection input for detecting the current IRMflowing through the wire12and (ii) a correction input that is equivalent to an input causing the current flowing through the wire12to be zero. The input causing the current flowing through the wire12to be zero may be exemplified by an input causing a short between the inputs of the potential difference detecting section44.

When the input switching section332selects the correction input, the output Vx of the potential difference detecting section44outputs the offset error. For example, when the offset of the potential difference detecting section44is 100 μV and the gain is 100, the offset error voltage is (offset)×(gain+1)=10.1 mV. If Idd is 2 A and the detection resistor42is 5 mΩ, the gain is 100, and therefore the signal output voltage is 1V. In this case, the measurement of 2 A includes an offset error voltage of approximately 1%, which is not a small error.

FIG. 15shows an exemplary configuration of the integrating section340according to the present modification. The integrating section340includes the integrating circuit50, the discharging section56, a reference current source342, a reference switching section344, and an offset correcting section346. The integrating circuit50includes the operating amplifier60and the integrating capacitor62. The integrating circuit50stores, in the integrating capacitor62, a charge corresponding to the difference in current between the reference current IREFand the current IRMdetected by the current detecting section330. This integrating capacitor62is an example of a capacity element. The integrating circuit50outputs the integration voltage VMgenerated at both ends of the capacity element as the integration value. The discharging section56includes the discharging switch72. Before beginning the test, the discharging section56discharges the charge stored in the integrating circuit50.

The reference current source342outputs the reference current IREFfrom the input of the integrating circuit50. The reference current source342includes the first voltage follower circuit64and the first reference resistor66. The second reference resistor70has the same function as the first current letting-flow section54. The reference switching section344selects whether the reference input of the reference current source342connects to the reference voltage VREFor to the ground voltage.

The offset correcting section346corrects the offset occurring at the input of the integrating circuit50. The offset correcting section346includes the correction capacitor402that stores the offset error voltage output by the current detecting section330, when the input switching section332selects the correction input and the reference switching section344selects the ground voltage, i.e. during correction. When the input switching section332selects the detection input and the reference switching section344selects the reference voltage, i.e. during measurement, the offset correcting section346outputs a voltage equal to −1 times the offset error voltage stored in the correction capacitor402. The switch404is a short during correction and is open during measurement.

As shown inFIG. 15, the offset error voltage stored in the correction capacitor402is input to the positive input of the operating amplifier400and the output is fed back to the negative input of the operating amplifier400, so that the output V1of the operating amplifier400is equal to the stored offset error voltage. On the other hand, the output V1is connected to the feedback portion of the first voltage follower circuit64via the resistance406, and therefore, if the resistance406and the resistance408have equal resistance values, the value equal to −1 times the output V1is superimposed on the output V2of the first voltage follower circuit64. This generates a reference current component that cancels out the current caused by the offset error voltage, thereby decreasing the effect of the offset error voltage.

FIG. 16shows an exemplary configuration of the judging section350according to the present modification. The judging section350includes an offset holding section352that holds the offset occurring at the output of the integrating circuit50, when the input switching section332selects the correction input and the reference switching section344selects the ground voltage, i.e. during correction. The offset holding section352includes an offset capacitor452and a switch454. The offset occurring at the output of the integrating circuit50is stored in the offset capacitor452. The switch454is a short during correction and is open during measurement.

When the input switching section332selects the detection input and the reference switching section344selects the reference voltage, i.e. during measurement, the judging section350judges whether the DUT200is defective based on the offset voltage held by the offset capacitor452of the offset holding section352. This enables correcting of the offset occurring upstream from the comparator58, so that the current can be accurately measured.

A low-voltage amplifying section354may be provided that amplifies the integration value and supplies the amplified integration value to the judging section350. Since the offset correction sets the integration value to a sufficiently low level, amplifying the integration value using the low-voltage amplifying section354has significant meaning.

The AD converting section320measures the integration value. The AD converting section320can record the digital values obtained by measuring the integration value for each measurement cycle in a recording section, measure the values obtained when only the reference current is input before or after a series of measurements, and scale the digital values of each measurement cycle recorded on the recording medium with the measured values. The recording section and the processing section that performs the scaling process may be provided to the system control device23. The AD converting section320enables the current value to be scaled by measuring the reference current only once before or after the series of measurements. This scaling is used to obtain the current value of the digital values measured in each measurement cycle.

FIG. 17shows an exemplary operation of the test apparatus300according to the third embodiment. Here, XSTSP represents the control signal of the switch404, XIN represents the control signal of the input switching section332, and XREF represents the control signal of the reference switching section344. Current measurement is performed while all of these control signals are logic L, i.e. during the period t(n). In the current measurement, the difference between the current Idd flowing through the DUT200and the reference current, shown by the dotted lines inFIG. 17, is detected as the output VM(V4) of the integrating circuit50. The defectiveness judgment is based on whether the output VM(V4) is positive or negative. Furthermore, ta represents the period over which the output VM(V4) is held, and the integration value, which is the output from the AD converting section320, is acquired during this period. The acquired integration value is scaled with the integration value of only the reference current measured during the period t(ref).

One aspect of the present invention has been explained above using an embodiment, but the technical scope of the present invention is not limited to the scope described in the above embodiment. Various modifications or alterations can be made upon the above-described embodiment. It is obvious from the claims that any embodiment upon which such modifications or alterations are made can also be included in the technical scope of the present invention.