JPS6217666A - Apparatus for measuring current through voltage application - Google Patents

Abstract

PURPOSE:To contrive to increase a testing speed, by inspecting a decoupling resistor between the node of load and a smoothing capacitor and a constant voltage output terminal. CONSTITUTION:A decoupling resistor 15 is inserted between the output terminal of a constant voltage source 8 and the node of load 2 and a smoothing capacitor 9 in series and the current flowing to the load 2 from the voltage source 8 is measured by a current measuring device 4. In this case, impedance when the voltage source 8 looked the load 2 becomes high in frequency and looks constant by the impedance of the resistor 15 not dependent on frequency even if the impedance of the capacitor 9 approaches zero. Therefore, the voltage source 8 looks constant in a load condition even with respect to high frequency and the capacity of a phase compensating capacitor 13 can be set small. As a result, the time constant of the capacitor 13 is made small to make it possible to shorten a discharge time and the increase in a testing speed is attained.

Description

Detailed Description of the Invention "Industrial Application Field" This invention can be used, for example, to apply a constant voltage to an IC with a CMO3 structure, measure the current flowing at that time, and test whether the IC is normal or not. The present invention relates to a voltage applied current measuring device capable of measuring voltage applied current.

``Prior art'' Ic, such as a semiconductor memory with a CMO3 structure, basically consists of P-type FETQ and N-type FETQ, as shown in Figure 2.
ETQ□ are connected in series with each other to the DC power supply l, and the gates of these two FETQ and Q2 are commonly connected,
By giving a drive signal to this common game) G, F E
The structure is such that either T Q + or Q2 is controlled to be turned on, and at that time, the other is controlled to be turned off, and an H logic signal or a low logic signal is output to the output terminal M. One such structure is called one logic gate element or the like.

This circuit converts the on/off relationship of FETQ and Q2 from one to the other, and from the other to one stable state.
Since TQ and Q2 pass through the ON state at the same time, a short circuit current with a large current value IFF momentarily flows as shown in FIG. 3A, but in a stable state F E T Q +
Or, since either Q is always off, the drain current 19. flows in that stable state. becomes a small value ILL. Therefore, power consumption in a stationary state is reduced, and for example, in the case of a memory, there is an advantage that consumption of a hack-up battery can be reduced.

By the way, l which integrates logic gate elements with such a structure
If the off-resistance of either or both of FETQ or Ql is made to be smaller than the specified value in c2, a problem arises in that the drain N and current value ILL in a stable state become large.

For example, as shown in FIG.
When FETQI is on and FETQI is off, a current 11sx larger than the specified current value ILL flows as shown in FIG. 3B. Therefore, if a FET with such a defect is manufactured, the defective FET should be left in the OFF state and left in the running state.
If this happens, the amount of current consumption increases and the battery, etc., becomes significantly exhausted.

One possible test method for detecting such defects is a voltage applied current measurement test. This voltage applied current test is performed at the power supply terminal VD of the IC2 under test as shown in FIG.
An IT current detection resistor is connected in series between II and IT source 1, and the voltage generated across the current detection resistor 3 is input to the measuring device 4, and the current value is determined from the constant voltage measurement value. This is a test method that determines whether the current value is within a specified range and determines pass/fail.

When determining the acceptability of a CMO3 structure IC by voltage application and current measurement test, although the current to be measured is a steady 1itt with a minute current value ILL as shown in Fig. 3, F E T Q At the time of switching between + and Qt states, a short circuit current having a t current value IFF several thousand to tens of thousands of times as large as ILL flows. In other words, the ratio of the short circuit current to the current to be measured I
PF/ILL becomes a very large value. By the way, ILL”
Several liters of microamperes to several nanoamperes, IFF”
It is several hundred milliamperes to several lθ milliamperes. t
In order to reduce the voltage drop at the V2O point while oo is IFF, a smoothing capacitor 9 is required, and for this reason, the current flowing through the current detection resistor 3 is increased from the point when the short circuit current ends, resulting in a small steady current. There is an inconvenience that it takes a long time to charge the current detection resistor 3 and the smoothing capacitor 9 until it stabilizes at the value ILL. In other words, if the time it takes for the current to stabilize becomes longer, the switching period of FETQl and Q2 must be longer. As a result, the time required for testing an IC with a large number of elements increases. For example 256
x 1 IC with 1000 logic gate elements integrated
If the test is performed by switching at millisecond intervals, the time required for the test will be 256 seconds. If one IC was tested for 256 seconds, it would be impossible to test all mass-produced ICs. Therefore, higher speed is required.

Here, we will discuss the fifth configuration for speeding up that can be considered in the conventional technology.
As shown in the figure. In the circuit shown in FIG. 5, the output terminal of the operational amplifier 5 is connected to the inverting input terminal of the operational amplifier 5 via the current detection resistor 3, thereby forming a negative feedback loop, and the non-inverting input terminal of the operational amplifier 5. A voltage source 7 is connected to constitute a constant voltage source 8. The voltage of this constant voltage source 8 is supplied to the load 2.

With this structure, the operational amplifier 5 performs a feedback operation so that the voltage at the inverting input terminal becomes equal to the voltage of the voltage source 7, and provides a constant voltage Vs equal to the voltage of the voltage source 7 to the load 2. load 2
Assume that the circuit has a circuit structure in which only a small current flows during a steady state, but large pulse-like currents flow at a period proportional to the operating speed, like the previously described CMOS IC.

A smoothing capacitor 9 is connected near the load 2.

This smoothing capacitor 9 is provided to compensate for a drop in the voltage Vs caused by a delay in the response of the constant voltage source 8 when a large pulsed current flows through the load 2. In other words, the 6th
When a pulsed current flows through the load 2 as shown in Figure A, the voltage Vs at the current supply point S to the load 2 is as shown in Figure 6B.
Changes as shown in . In the figure, the curve formula shows the voltage fluctuation characteristics when the smoothing capacitor 9 is not connected, and the curve B shows the voltage fluctuation characteristics when the smoothing capacitor 9 is connected.The voltage fluctuation value when the smoothing capacitor 9 is connected.
, is Vr+blLt-t/CL (ItL is the current value at steady state, and t is the pulse width of the pulsed current).

On the other hand, the current detection resistor 3 is connected in parallel with a switch element 11 and a pair of diodes 12A connected in antiparallel.

Connect 12B in parallel. The switch element 11 and the diodes 12A and 1211 are provided to prevent a large voltage drop from occurring across the resistor 3 when a pulsed current flows through the load 8. Therefore, the switch element 11 is the sixth
As shown in Figure C, it is controlled to be on during a period M that includes a period during which a pulsed current flows.

Is the switch element 11 capable of high-speed response and on/off control? (2) FETs are generally used because signals do not leak into the circuit and it is preferable to have a small leakage current.

The current detection resistor 3 further includes a phase compensation capacitor 13.
are connected in parallel. By connecting this phase compensation capacitor 13, the amount of phase rotation of the operational amplifier 5 is compensated for, thereby preventing unstable operation and improving the S/N ratio.

"Problems to be Solved by the Invention" By the way, according to the above-mentioned circuit structure, the constant voltage source 8 is equipped with a feedback loop (i.e., operates in an i-return operation), so the output impedance is low, and the smoothing capacitor 9 Since it has a structure that prevents a drop in the voltage applied to the load 2, it is possible to supply a pulsed current with a considerably high frequency.

However, as the repetition frequency of the pulsed current is increased, a problem arises in that the time from the end of the pulsed current until the current returns to a steady state must be shortened. In other words, since the purpose here is to measure the current value ILL in a steady state, the steady state current is measured by the measuring device 4 from the time when the pulsed current ends to the time when the state where the steady current flows returns. Must. Therefore, the upper limit frequency at which the pulsed current can flow is determined by the time from the end of the pulsed current until the current returns to the steady state.

The circuit shown in FIG. 5 has the disadvantage that it takes a relatively long time from the point at which the pulsed current ends until the current stabilizes. The reason for this will be explained below.

FIG. 7 shows voltage and current waveforms at various parts of the circuit shown in FIG. 5. 7A shows the load current flowing through the load 2, and FIG. 7B shows the charging and discharging current of the smoothing capacitor 9. That is, in this example, -ICL is the discharging current and +lCL is the charging current.

When a pulsed current begins to flow through the load 2, the smoothing capacitor 9 discharges a discharge current -ICL and operates to prevent the voltage Vs (FIG. 7D) supplied to the load 2 from decreasing. The switch element 11 is turned on before the pulsed current starts flowing.

When the pulsed current is cut off, t't (ir Q 'tM
I t immediately returns to the steady state current ILL.

By the way, when a pulsed current flows, this pulsed current flows through a parallel circuit consisting of the current detection resistor 3, the diode 12A, the switch element 11, and the phase compensation resistor 13. Diode 12A and switch element 1
1 has on-resistance. In other words, it is not possible to completely short-circuit both ends of the current detection resistor 3, so the phase compensation capacitor 13 has a diode 12A.
And the voltage generated in the on-resistance of the switch element 11 is charged. Since this charging current is given from the operational amplifier 5 with low output impedance, its charging time constant is extremely small and the voltage generated across the capacitor 13 is ζ. reaches the predetermined voltage MCI in a short time as shown in FIG.

On the other hand, when the pulsed current is cut off, the voltage applied to the phase compensation capacitor 13 becomes the voltage generated by the steady current flowing through the current detection resistor 3. This voltage has a very small value compared to the voltage VCI charged in the capacitor 13. As a result, the 'Qt load charged in the capacitor 13 is discharged through a parallel circuit consisting of the switch element 11, the diode 12A, and the resistor 3. When the charging voltage VCI of the capacitor 13 has a voltage value sufficient to make the diode 12A conductive, it is discharged through the diode 12A, but as the voltage decreases, the on-resistance of the diode 12A gradually increases and it turns off. Diode 1 after all
After 2A is turned off, discharge occurs through the switch element 11 and the resistor 3. Assuming that the on-resistance value of the switch element 11 is R02 and the resistance value of the resistor 3 is RH, and the magnitude relationship is R1, N<R14, from the time when the pulsed current falls until the switch element 11 turns off. The discharge time constant during the period Tt becomes a value C1IxRH determined by the capacitance value CH of the capacitor 13 and the on-resistance value R0 of the switch element 11. If the on-resistance of the switch element 11 is, for example, about 100 Ω, this time constant has a value larger than the rise time constant during charging.

Furthermore, when the switch element ti is turned off after a period Tt, the only discharge path of the capacitor 13 is the resistor 3.

If the resistance value R of the resistor 2ii3 is selected to be too KΩ, its time constant will be 1000 times the time constant when the switch element 11 is in the on state. Therefore, the voltage of the capacitor 13 decreases at a very slow rate as shown in period Ts in FIG. 7E.

If the voltage generated across the resistor 3 is measured in the measuring circuit 4 while the discharge current of the capacitor 13 is flowing through the resistor 3, and the value of the current flowing through the resistor 3 is measured, the current flowing through the negative ri 12 It cannot be said that the steady current was accurately measured.

Therefore, it is required to shorten the discharge time of the capacitor 13. In order to shorten the discharging time of the capacitor 13, one or both of the following can be done: reduce the capacitance N value C of the capacitor 13, or select a smaller resistance value R1 of the current accumulating grinder 3. This can be realized by reducing the on-resistance value ROM of the switching element 11 to a sufficiently small value.

However, the resistance value r1. of the current detection resistor 3. The value of cannot be made small in order to satisfy the conditions for extracting a minute current as a voltage.

In addition, as long as the on-resistance value ROM of the switch element 11 is used as a switch element 11 with a small leakage current and an FET that prevents on-off control signals from leaking into the circuit, the lower limit of the on-resistance is about several ohms to several tens of ohms. However, it is impossible to find a switch element with a smaller on-resistance than this.

For these reasons, the only way to ultimately reduce the discharge time constant of the capacitor 13 is to select a small capacitance value for the capacitor 13. However, if the capacitance value C8 of the capacitor 13 is selected to be small, the stability of the closed loop that constitutes the constant voltage source 8 will deteriorate, and if the repetition frequency of the pulsed current flowing through the load 2 is increased, the constant voltage source 8 may oscillate or become unstable. It becomes a state.

If the load 2 is specified in advance to operate under certain conditions, the capacitance of the capacitor 13, the capacity of the smoothing capacitor 9, the frequency characteristics of the operational amplifier, etc. should be appropriately set so that it operates stably under those conditions. I can. However, in order to operate as a general-purpose tester, it must be designed to operate stably over as wide a range as possible, especially against changes in the load drive frequency, assuming that the load conditions will change.

In other words, as explained earlier, a pulsed current flows through the load 2, so in order to keep the drop in supply voltage as low as 1rli when a pulsed current flows, the smoothing capacitor 9 with a relatively large capacitance value is required. It is absolutely necessary.

Smoothing capacitor 1 with a large capacitance value for load 2
3 are connected in parallel, when load 2 is viewed from constant voltage tA8, it appears as a capacitive load. Therefore, the impedance of the load tends to gradually decrease as the frequency of the current flowing in a pulsed manner increases. When the frequency exceeds this result, the impedance of the load approaches zero, and the operation of the constant voltage source 8 becomes unstable.

"Means for Solving the Problems" In the present invention, a decoupling resistor is inserted in series between the output terminal of a constant voltage source and a load including a smoothing capacitor.

By inserting the decoupling resistor in series between the constant voltage source and the load in this manner, when the load is viewed from the constant current source 8, the decoupling resistor appears to be connected in series with the load. As a result, even if the impedance of the smoothing capacitor is reduced by changing the repetition frequency of the pulsed current, the impedance on the load side will never approach zero because of the presence of the impedance of the decoupling resistor.

Therefore, even if the repetition frequency of the pulsed current flowing through the load becomes higher than the conventional upper limit value, there is no risk that the operation of the constant voltage source 8 will become unstable. In other words, the effect of a decrease in the impedance of the smoothing capacitor is reduced. Therefore, the capacitance value of the phase compensation capacitor can be set small.

Since the capacitance value of the phase compensation capacitor can be made small, the charge stored in the phase compensation capacitor can be discharged within a relatively short time after the pulsed current falls. As a result, the time from the fall of the pulsed current to the measurement of the steady current can be shortened, so the repetition frequency of the pulsed current can be set high, thereby enabling high-speed testing.

"Example" Fig. 1 shows an embodiment of the voltage applied current measuring device according to the present invention. In Fig. 1, parts corresponding to Fig. 5 are denoted by the same reference numerals, and explanations of the overlapping parts are omitted. But,
This invention is characterized by a structure in which a decoupling resistor 15 is connected in series between the constant voltage source 8 and the connection point between the load 2 and the smoothing capacitor 9.

The decoupling resistor "a15" is about 10 ohms when the capacitance value of the smoothing capacitor 9 is about 091 microfarads.

"Operations and Effects of the Invention" By providing the decoupling resistor 15 in this way, even if the repetition frequency of the pulsed current is variously changed, the constant voltage #8 can be maintained.
The amount of change in impedance when looking at the load 2 side becomes smaller. In particular, when the repetition frequency of the pulsed current is set to a high frequency, the impedance of the smoothing capacitor 9 approaches zero, but the impedance of the decoupling resistor 15 remains constant regardless of changes in frequency. voltage aa
The load impedance seen from can be seen as constant.

Therefore, the load condition of the constant voltage source 8 appears constant even at high frequencies, and as a result, the capacitance value of the phase compensation capacitor 13 can be selected to be small. 13 and the current detection resistor 3 can have a small time constant. Therefore, the time from the fall of the pulsed current until the charge in the phase compensation capacitor 13 is discharged can be shortened, and high-speed testing can be performed.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram for explaining one embodiment of the present invention,
Figure 2 is a connection diagram to explain an example of the object under test that performs a voltage applied current measurement test, Figure 3 is a waveform diagram showing the current waveform flowing through the object under test, and Figure 4 is the same as explained in Figure 2. A connection diagram explaining the configuration for measuring the current flowing through the object under test,
5rjJ is a connection diagram for explaining the conventional voltage application current measurement 'jt\f, and FIGS. 6 and 7 are waveform diagrams for explaining the operation of FIG. 5. 2: Load, 3: Current detection resistor, 4: Current measuring device, 5
: Operational amplifier, 7: Voltage source, 8: Constant voltage source, 9: Smoothing capacitor, 11: Swiss element, 12A, 12B
: Diode, 15: Decoupling resistor. Patent Applicant: Takeda Riken Kogyo Co., Ltd. Representative: Kusano, Vehicle Engineer 1, 2, 6, MJ, 5

Claims (1)

[Claims] (1) A: A constant voltage source equipped with a feedback circuit to provide a constant voltage to a load that periodically consumes a large value of load current; B: Measure the current flowing from this constant voltage source to the load. C. a phase adjustment capacitor connected in parallel to the current detection resistor to prevent the constant voltage source from becoming unstable due to the load current flowing through the constant voltage source; D. A smoothing capacitor connected in parallel to the above load to stabilize the voltage applied to the load against fluctuations in load current, and E. To short-circuit both ends of the above current output resistor during periods when a large load current flows. A voltage applied current measuring device comprising: a switching element; and F, a decoupling resistor inserted in series between the output terminal of the constant voltage source and the connection point of the load and smoothing capacitor.