JPH0438303Y2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to a voltage applied current measuring device that can be used, for example, in an IC test device for testing semiconductor integrated circuit elements.

"Background of the Invention" Methods for testing semiconductor integrated circuit elements (hereinafter referred to as ICs) include functional testing, which operates the IC to determine whether it performs a specified function, and DC testing, which tests whether the DC characteristics of each terminal of the IC are normal.

The DC test includes a voltage application current measurement test that checks whether a specified current flows when a specified voltage is applied to a terminal, and a voltage application current measurement test that checks whether a specified current flows when a specified voltage is applied to a terminal.When a specified current is applied to a terminal, a specified voltage is generated at that terminal. There is a current applied voltage measurement test to see whether or not.

The voltage applied current measuring device is provided with a voltage supply source that applies a desired voltage to a terminal of a subject, and a current measuring means that is supplied from this voltage supply source to the subject.

On the other hand, in functional tests, a DC power supply that can change the voltage is connected to the current terminal of the test object, and the functional test is performed while varying the power supply voltage applied to the test object from this DC power supply.

For this reason, conventionally, the voltage supply source used for the voltage applied current measurement test and the DC power supply that supplies the power supply voltage to the test object during the functional test are shared.

"Prior Art" Figure 4 shows a conventional DC power supply device. 10 in the diagram
0 indicates a voltage supply source that applies a desired voltage to each terminal of the test object 100 such as an IC. A current measuring means 300 is connected in series to the output side of the voltage supply source 200.
and a voltage VO to the test object 100 through the gable 400.
is applied.

Cable 400 has voltage detection line 402 in addition to voltage supply line 401 . This voltage detection line 402 is connected to a terminal of the subject 100 on the subject 100 side, and feeds back the voltage of this terminal to the voltage supply source 200. Reference numeral 500 indicates a voltage feedback circuit that feeds back the detected voltage of the voltage detection line 402 to the voltage supply source. This voltage feedback circuit 500 is constituted by an amplifier with high input impedance, and this high input impedance amplifier extracts the voltage without passing current through the voltage detection line 402, thereby eliminating voltage measurement errors due to the direct current resistance of the wire. I'm trying to prevent it from happening.

The output voltage of the voltage feedback circuit 500 is connected to the resistor 501.
is fed back to the voltage supply source 200 through. The voltage supply source 200 includes an operational amplifier 201 and a voltage setting device 2.
02 and a resistor 203. A non-inverting input terminal of the operational amplifier 201 is connected to a common potential point 600, and the voltage of the voltage setter 202 is supplied to the inverting input terminal of the operational amplifier 201 through a resistor 203. Also, the voltage feedback circuit 500
The feedback voltage is fed back to the inverting input terminal of operational amplifier 201.

The voltage setting device 202 is actually a DA converter, and the DA converter is configured to receive a digital signal from a controller so that the output voltage of the voltage supply source 202 can be changed at high speed.

The output terminal of the operational amplifier 201 is the current measuring means 3.
Connected to 00. The current measuring means 300 includes a current detection resistor 301 and this current detection resistor 30.
A subtraction circuit 30 that detects the voltage generated across 1
2, and an AD converter 303 that converts the output voltage of this subtraction circuit 302 into a digital signal as necessary.
and a range switching means 304 connected in parallel to the current detection resistor 301.

The range switching means 304 is composed of a plurality of series circuits consisting of a switch and a resistor, and when the switch is turned on, the current detection resistor 301 is switched on.
Connect another resistor in parallel to the current detection resistor 3.
The current measurement range is switched by changing the resistance value of 01.

On the other hand, the amplifier constituting the voltage feedback circuit 500 connects its output terminal to the inverting input terminal and operates as an amplifier with a gain of 1 by applying full feedback, so that the potential of the shield 403 is equal to the voltage of the voltage supply line 401 and the voltage detection line 402. In-phase drive is performed to maintain this state. By this in-phase drive, the voltage supply line 401 and the voltage detection line 402 and the shield 403 are held at the same potential.
By removing the influence of leakage resistance Ra and capacitance Ca between the voltage detection line 402 and the voltage detection line 402,
1 and voltage detection line 402 from external noise,
In particular, the influence of leakage current is removed when measuring minute currents. The operation of applying the potential of the signal line to the shield in this manner is called common-mode guard drive. Therefore, the wiring 700 connecting the output side of the amplifier constituting the feedback circuit 500 and the shield 403 will be referred to as guard voltage applying means.

According to the above configuration, the voltage set in the voltage setting device 202 is output from the operational amplifier 201 and supplied to one terminal of the subject 100. The voltage at this terminal is passed through the voltage detection line 402 to the voltage feedback circuit 50.
0 and fed back to the voltage supply source 200.

The operational amplifier 201 operates so that this feedback voltage and the voltage given from the voltage setter 202 become equal. Therefore, the voltage drop in the current measuring means 300 and the voltage supply line 401 is corrected, and the voltage set in the voltage setting device 202 is accurately applied to the terminal of the subject 100.

The current measuring means 300 is applied with the voltage set by the voltage setting device 202 being applied to the terminal of the subject 100.
sets the current IL flowing into the test object 100, compares whether or not this IL is a specified value, and determines whether or not the DC characteristics of this terminal are normal.

"Problem that the invention attempts to solve" In the circuit shown in FIG. 4, the voltage feedback circuit 50
0 and the guard voltage applying means 700 can be rewritten into an equivalent circuit as shown in FIG. In the equivalent circuit shown in FIG. 5, Ca indicates the capacitance between the shield 403 of the cable 400 and the voltage detection line 402, and Ra indicates the leakage resistance of the cable 400, the printed board, etc.

By providing the guard voltage applying means 700, the capacitance Ca and the insulation resistance Ra are equivalently connected between the inverting input terminal and the non-inverting input terminal of the amplifier constituting the voltage feedback circuit 500. . This connection structure constitutes a positive feedback circuit, which poses a problem in operational stability. For this reason, conventionally, as shown in FIG. 6, a time constant circuit 502 for preventing oscillation is connected to the input side of the amplifier constituting the voltage feedback circuit 500, or as shown in FIG. 7, a guard voltage supply means 700 is connected. A structure is adopted in which the circuit is composed of an amplifier 701 and a time constant circuit 702 is connected to the input side of the amplifier 701.

By adopting the circuit structure shown in FIGS. 6 and 7, the stability of the system is improved, but the time constant circuit 502 or 702 slows down the response of the feedback circuit 500, which slows down the response speed of the system. There are drawbacks. In other words, in order to shorten the test time,
When the voltage applied to the terminal 0 is changed stepwise at high speed and the value of the current IL at each voltage value is sequentially measured, the time constant circuit 50 provided in the feedback circuit 500 or the card voltage applying means 700
2 or 702, the voltage applied to the terminal of the test object 100 does not faithfully follow the change in the set voltage of the voltage setting device 202, resulting in a disadvantage that the test takes a long time.

The reason why the response speed of the system is slow will be explained in more detail. In the case of the circuit structure shown in FIG. 6, the voltage taken out through the voltage detection line 402 is
2, its rise is delayed and input to the feedback circuit 500. Therefore, as shown in FIG. 8A, the set voltage V _M of the voltage setter 202 is set to V _M1 at the time _TO.
When changing from V _M2 to V M2, the voltage supply means 200
Because the feedback voltage fed back to the test object 100 is delayed,
As shown in FIG. 8B, the voltage VO applied to the voltage exceeds the target value and overshoots, and then stabilizes at the set voltage V _M2 of the voltage setter 202. Along with this, the current I _L flowing into the subject 100 changes as shown in FIG.
This must be continued until VO and current I _L stabilize. In other words, the current must be measured after waiting a period of time π from the time T _O when the voltage VO applied to the subject 100 is changed until the current I _L stabilizes.

On the other hand, as shown in FIG.
In the case of a structure in which 00 is configured by an amplifier 701 and a time constant circuit 702 is connected to the input side of the amplifier 701, the feedback voltage fed back to the voltage supply source 200 is fed back without delay, and the feedback voltage is fed back to the test object 100. A voltage that accurately follows the voltage change of the voltage setting device 202 is applied.

However, the guard voltage applied to the shield 403 of the cable 400 changes with a delay due to the time constant circuit 702. Therefore, a potential difference occurs between the voltage detection line 402 and the shield 403, and this potential difference causes a charging current (or discharging current) to be generated in the capacitance Ca.
flows. This charging current flows through a loop that passes through the voltage detection line 402, the voltage supply line 401, and the current measurement means 200, the amplifier 201 constituting the voltage supply source 200, the power supply, and returns from the power supply to the amplifier 701.

The time during which this charging current flows is determined by the time constant circuit 702.
The time is determined by the time constant of . Therefore, in this case as well, the current must be measured at a timing delayed by the time π determined by the time constant of the time constant circuit 702 from the point in time when the voltage applied to the subject 100 is changed.

Time constants R ₁ and C ₁ of time constant circuits 502 and 702
In order to prevent system oscillation, the capacitance Ca between the shield 403 and the voltage supply line 402 and the time constant Ra・Ca of the insulation resistance Ra must be selected so that the relationship R ₁・Ca > Ra・Ca is satisfied. No. As a result, the timing of current measurement must be delayed by a relatively large amount, which has the drawback of increasing the time required for measurement.

``Means for solving problems'' This idea takes time to measure the current when using a structure that applies a guard voltage to the cable shield, and the guard voltage is only effective when measuring minute currents. When measuring a relatively large current, the cable shield is separated from the voltage feedback system, and a switching means is provided to apply a common potential to the shield.

According to the configuration of this invention, when necessary, that is, when measuring a relatively large current, the switching means is switched to disconnect the cable shield from the voltage feedback circuit, thereby constructing the transfer feedback circuit. The capacitance and insulation resistance between the cable shield and the voltage detection line no longer constitute a positive feedback loop for the amplifier.

As a result, when the switching means is switched, there is no need to connect the time constant circuit for preventing oscillation, so the time constant circuit can also be disconnected from the circuit. Therefore, the response speed of the voltage feedback circuit becomes faster, and a rapidly changing voltage can be applied to the current terminal of the test object, especially in a functional test in which the circuit is operated by flowing a steady current. Therefore, the time required for functional testing can be shortened.

``Example'' Figure 1 shows an example of this invention. In FIG. 1, parts corresponding to those in FIG. 4 are designated by the same reference numerals.

In this example, a time constant circuit 502 is provided on the input side of an operational amplifier 501, and a gate application means 700 is configured by wiring.

In this invention, a switching means is provided which separates the gate application means 700 from the voltage feedback circuit 500 and connects the shield 403 of the cable 400 to the common potential point 600.

In this example, the common connection point between the output terminal and the inverting input terminal of the operational amplifier constituting the voltage feedback circuit 500 is connected to one fixed contact 801 of the switching means 800, and the other fixed contact 802 of the switching means 800 is connected to the common potential. Connect to point 600. The movable contact of the switching means 800 is connected to the shield 403 of the cable 400 through the wiring constituting the guard applying means 700.

With this configuration, by converting the switching means 800 to the fixed setting 802 as necessary, the shield 403 of the cable 400 can be switched to the voltage feedback circuit 50.
0 and at the same time connect the cable's 400 shield 403 to a common potential point 600.

Along with this, another switching means 900 is provided which operates in conjunction with the switching of the switching means 800, and this switching means 900 performs the operation of disconnecting the time constant circuit 502 from the circuit.

Switching means 800 and 900 are current switching means 304
When the range switching exceeds a certain range, the switching operation is automatically performed in conjunction with this.

That is, in the range for measuring the DC characteristics of the terminal of the test object 100, the switching means 800 is brought into contact with the contact 801, and at this time, the switching means 900 is turned on and the time constant circuit 502 is connected to the circuit.
When performing a functional test on the subject 100, the switching means 800 is brought into contact with the contact point 802, and the switching means 900
can be linked to turn off and disconnect the time constant circuit 502 from the circuit.

With this configuration, when performing a DC test on the terminal of the test object 100, the current measuring means 300
Since the range switching means 304 is switched to the micro current measurement range, a guard voltage can be applied to the shield 403. Therefore, in a state where a minute current is to be measured, leakage current is prevented from flowing through the leak resistance Ra, and the minute current can be measured with high accuracy.

On the other hand, when performing a functional test of the test object 100, a relatively large current is passed, so there is a leak resistance between the shield 403 of the cable 400 and the voltage detection line 402.
Even if some leakage current flows through Ra, it does not cause a large error, so the switching means 800 may be connected to the contact 802 and the shield 403 of the switching cable 400 may be connected to the common potential point 600.

When the shield 400 is connected to the common potential point 600, the leak resistance Ra and capacitance Ca between the shield 400 and the voltage detection line 402 do not constitute a positive feedback loop for the operational amplifier that constitutes the voltage feedback circuit 500.

As a result, the time point counting circuit 502 can also be disconnected by turning off the switching means 900. Time constant circuit 50
Voltage feedback circuit 5 can be disconnected from 2.
The response speed of the voltage setting device 202 becomes faster, and even if the voltage applied to the terminal of the test object 100 is changed at high speed, the voltage can be changed accurately by faithfully following the change in the set voltage of the voltage setting device 202 without causing an overshoot. I can do it.

Therefore, the functional test can be executed at high speed, and the time required for the test can be shortened.

"Modified Embodiment" FIG. 2 shows a modified embodiment of this invention. In this example, an amplifier 70 is used as the guard voltage applying means 700.
The case where 1 is used is shown. In this example, amplifier 701
A switching means 80 is connected between the output terminal of the shield 403 and the shield 403.
Set 0.

By switching the switching means 800 to the contact 802, the shield 403 of the cable 400 is connected to the common potential point 600. Leave the connection between the input terminals.

By switching the switching means 800 to the contact 802, the leak resistance Ra and capacitance Ca can be changed to the amplifier 70.
1 and is indirectly disconnected from the feedback circuit 500. As a result, even if the output voltage of the amplifier 701 is delayed by the time constant of the time constant circuit 702 with respect to a change in the voltage of the voltage detection line 401, the operation of flowing charging current into the capacitor Ca is not performed.

Therefore, even if the voltage of the voltage detection line 401 changes at a high speed, a normal feedback voltage can be provided to the voltage supply source 200. Therefore, the voltage supply means 20
Even if the voltage applied to the test object 100 at 0 is changed at high speed, the feedback voltage will also change following the change in voltage, so overshoot will occur in the voltage applied to the test object 100 from the voltage supply means 200. The voltage of the voltage setter 202 is also stabilized without the need to do so.

FIG. 3 shows still another embodiment of this invention. This example shows a case where switching means 800 is provided between amplifier 701 forming guard voltage applying means 700 and operational amplifier forming feedback circuit 500.

In other words, a structure is shown in which the switching means 800 is provided on the input side of the amplifier 701, and the shield 403 remains connected to the input side of the amplifier 701.

By switching the switching means 800 to the contact 802, the input terminal of the amplifier 701 is connected to the time constant circuit 70.
2 to the common potential point 600, and can apply the potential of the common potential point 600 to the shield 403 of the cable 400.

In this case as well, when the switching means 800 is switched to the contact 802, the leak resistance Ra and capacitance Ca between the time constant circuit 702, the shield 403, and the voltage detection line 402 are disconnected from the voltage feedback circuit 500. As a result, the response speed of the voltage feedback circuit 500 becomes faster, and by accurately applying a rapidly changing voltage to the test object 100, a functional test can be performed in a shortened time.

“Effects of the device” As explained above, according to this device, subject 1
When measuring a minute current, such as when measuring the DC characteristics of the terminal 00, the shield 403 of the cable 400
A guard voltage is applied to the cable 400, and this guard voltage removes the adverse effects of current measurement due to the leakage resistance Ra and capacitance Ca of the cable 400, making it possible to accurately measure minute currents.

Furthermore, when performing a test in which a relatively large current is passed through the power supply terminal of the test object 100, such as a functional test of the test object, the guard voltage application circuit is cut off, thereby increasing the response speed of the voltage feedback circuit. Therefore, the response of the voltage applied to the terminal of the subject 100 can be made faster.

In other words, when a voltage that changes stepwise is applied to the terminal, the overshoot that occurs at each step converges in a short time, so the current measurement at each voltage can be measured without a large delay from the point at which the voltage changes. Therefore, functional tests can be performed at high speed.

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing one embodiment of this invention, Figs. 2 and 3 are connection diagrams for explaining other embodiments of this invention, and Fig. 4 shows a conventional voltage applied current measuring device. 5 is a connection diagram showing an equivalent circuit of the voltage feedback circuit in a conventional device. FIGS. 6 and 7 are connection diagrams for explaining the connection structure of a conventional guard voltage applying means. Figure, 8th
The figure is a waveform diagram for explaining the operation of a conventional voltage applied current measuring device. 100...Test, 200...Voltage supply source, 3
00... Current measuring means, 304... Range switching means, 400... Cable, 401... Voltage supply source, 402... Voltage detection line, 403... Shield, Ra... Leak resistance, Ca... Capacitance , 50
0... Voltage feedback circuit, 600... Common potential point, 7
00...Guard voltage application means, 800...Switching means.

Claims (1)

[Scope of Claim for Utility Model Registration] A. A voltage supply source that applies voltage to the terminals of the test object via a voltage supply line; B. The terminal voltage of the test object is extracted through a voltage detection line and returned to the voltage supply source; A voltage feedback circuit for maintaining the terminal voltage of the test object at a desired voltage; C. A current measuring means for measuring the current flowing through the test object through the voltage supply line; D. A current measuring means provided in the current measuring means and measuring a current value. E a guard voltage applying means that applies the same voltage as the voltage applied to the voltage supply line to a shield that protects the voltage supply line and the voltage detection line; and a switching means for applying a voltage at a common potential point to the guard voltage applying means in conjunction with switching to the guard voltage applying means.