JPH085676A - Voltage application current measuring circuit - Google Patents

Abstract

PURPOSE:To obtain a current measuring circuit in which the DC characteristics of static current can be measured at a relatively high speed by providing a diode connected in reverse parallel with a current amplifier thereby stabilizing the voltage and current at a relatively high speed even for a load where the ratio between the stationary current and inverting operation current is high. CONSTITUTION:When a load 1 pulsates and a load current IL of several amperes flows, a discharge current IC2 flows from a bias capacitor C2. A current amplifier A3 then supplements the charging current quickly thus resetting the steady state quickly. Since noise and drift of the high current amplifier A3 have no effect on the external circuit, DC characteristics of the load 1 can be measured accurately. Since the amplifier A3 only requires a simple emitter follower, the response rate is increases by a factor of about 100, the transient time is reduced by a factor of several tens, and the measuring time of the load 1 increases by a factor of 10 or more. Consequently, economical effect is great.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures the DC characteristics of an IC (semiconductor integrated circuit) or the like, such as an LSI (large-scale integrated circuit) having a CMOS structure, in which the ratio of currents flowing at rest and during operation is large. The present invention relates to a voltage applied current measuring circuit used when performing.

[0002]

2. Description of the Related Art FIG. 4 shows, as an example, the configuration of a conventional voltage applied current measuring circuit used in a highly integrated semiconductor tester. In the figure, reference numeral 1 indicates a load whose DC characteristics are to be measured.
A bypass capacitor C2 is connected in parallel to the load 1. A DC voltage Vo is applied to the load 1 from the operational amplifier A1. The operational amplifier A1 has a structure in which the voltage Vo applied to the load 1 is fed back through the feedback circuit 3 to suppress the fluctuation of the voltage Vo applied to the load 1. This DC voltage Vo is V in the steady state when the voltage of the DC voltage source 2 is Vi.
Given by o = Vi.

A current detection circuit 4 is provided to detect the current supplied from the operational amplifier A1 to the load 1. The current detection circuit 4 includes a resistor R1 for current detection, a phase correction capacitor C1 connected in parallel with the resistor R1, and
It is composed of diodes D1 and D2 connected in antiparallel. The voltage generated in the resistor R1 for current detection is taken out by the analog subtraction circuit (differential amplifier) 5 and converted into a digital signal by the A / D converter 6, and the DC characteristic of the load 1 is measured. That is, when the voltage Vi of the DC voltage source 2 is sequentially changed, the current flowing through the load 1 can be measured for each voltage, and the DC characteristics of the load 1, for example, the power supply terminal can be measured. At this time, if there is an abnormality in the CMOS cell, the power supply current will increase or decrease from the specified value, so that it is possible to judge the device quality.

A bypass capacitor C2 is connected in parallel with the load 1. Furthermore, a phase correction capacitor C1 is connected in parallel with the resistor R1 for current detection.
Here, the reason why the bypass capacitor C2 and the phase correction capacitor C1 are present will be briefly described. Load 1 is CM
In the case of the VLSI having the OS structure, only a current of several μA (microampere) flows at rest, whereas a large current IL of about several hundred mA (milliampere) may flow in a pulse shape in the reversing operation. When the current flowing through the load 1 largely fluctuates, the bypass capacitor C2 performs an operation of compensating for the current fluctuation flowing through the load 1 during the time delay until the operational amplifier A1 detects and responds to the current fluctuation. That is, when the current flowing through the load 1 suddenly increases in a pulse shape, the discharge current is discharged from the bypass capacitor C2 to compensate the delay of the operational amplifier A1. When the current flowing through the load 1 suddenly decreases, the bypass capacitor C2 absorbs a large current that continues to flow due to the delay operation of the operational amplifier A1 as a charging current and compensates for the delay of the operational amplifier A1.

On the other hand, the phase compensating capacitor C1 is provided to prevent the operation of the operational amplifier A1 from becoming unstable due to the connection of the bypass capacitor C2. That is, the open loop gain of the operational amplifier A1 exhibits a stable attenuation characteristic of -6 dB / octave (no operation such as oscillation occurs) when it exceeds a constant frequency peculiar to the element. However, if the bypass capacitor C2 is connected,
Frequency f1 = 1 / (2πR1 · C2) determined by bypass capacitor C2 and resistor R1 for current detection
At the above frequencies, the attenuation characteristic is -12 dB / octave. If 0 dB is crossed with this attenuation characteristic, a phenomenon such as oscillation occurs and the operation becomes unstable. Therefore, it is necessary to return the attenuation characteristic to the original −6 dB / octave at a frequency before reaching 0 dB, and therefore the phase correction capacitor C1 is inserted. The frequency at that break point is f2 = 1 /
(2πR1 · C1)

According to this circuit structure, the voltage Vo applied to the load 1 can be changed by changing the voltage Vi applied from the DC voltage source 2. In the steady state, the current IL flowing through the load 1 and the current Io flowing through the resistor R1 of the current detection circuit 4 are equal, so that the voltage value Vm output from the A / D converter 6 gives Io = IL = Vm / R1. Therefore, the internal resistance RX of the load 1 is RX = V
It is possible to obtain o / Io = Vi · R1 / Vm, and it is possible to measure the change in the internal resistance RX with respect to the change in the applied voltage Vo, that is, the DC characteristic.

By the way, in the MOS type LSI, as shown in FIG. 5A, the ratio of the current Io flowing at rest to the IL flowing at reversal operation is large. As described above, for example, only Io of about several μA flows at rest, while current flows in proportion to the number of elements performing the reversal operation at the time of reversal operation, and reaches IL of several hundred mA when the current is large. The current ratio is often 1000 times or more. This high current IL
Flows through the diode D1 or D2 connected in parallel with the resistor R1 for current detection, and the charging / discharging current can be supplied from the operational amplifier A1 to the bypass capacitor C2 without being affected by the time constant of the resistor R1 and the capacitor C1. There is. From the above description, the current I flowing at rest
When o is a small value, the resistance value of the current detection resistor R1 is large, and the phase correction capacitor C1 must be connected in parallel with the current detection resistor R1.
It can be understood that the bypass capacitor C2 is necessary and the diodes D1 and D2 are provided.

Here, the discharge and charge of the bypass capacitor C2 and the states of Vo and Io will be described with reference to FIG. Figure 5
When a pulsed current IL 1 flows through the load 1 as shown by A, the bypass capacitor C2 discharges the current Ic2 (FIG. 5B) into the load 1 to compensate for the delay of the operational amplifier A1. Therefore, the voltage Vo of the bypass capacitor C2 decreases (FIG. 5C). The decrease in the voltage of the bypass capacitor C2 is fed back to the operational amplifier A1 by the feedback circuit 3, and the charging current I is supplied from the operational amplifier A1 side to the bypass capacitor C2.
o (FIG. 5D) begins to flow. This charging current Io is initially a resistor R1 for current detection and a capacitor C1 for phase compensation.
Flowing through.

Due to this increase in current, the voltage V1 generated in the resistor R1 rises, either one of the diodes D1 or D2 (D1 in this example) is turned on, and most of the charging current Io flows through the diode D1. Therefore, Io becomes maximum with a slight delay, and then τ = R1 · C1
Decreases and reaches a steady state after a delay time Td. The delay time Td becomes a value larger than τ.

[0010]

As described above, the CMO
In the case of an S-structured LSI, the load current at rest and at reversing operation becomes 1000 times or more, so the delay time Td to reach the steady state becomes long, and in the precision measurement, the measurement is started after that, so the measurement time This is an obstacle to testing a large number of ICs. Moreover, in recent years,
The integration degree of the LSI is improved, the load current is required to be several amperes (A) or more at the time of the reversing operation, and the current ratio thereof may be tens of thousands times or more. Therefore, the capacity of the bypass capacitor is as large as 10 μF (microfarad), and it becomes an obstacle to speeding up the measurement. In addition, in devices with complicated logic circuits such as gate arrays and microcontrollers, there are many combinations for testing, and there is a great demand for measuring quiescent current at high speed.

For high-speed measurement, the noise of the operational amplifier has become a problem, and it is required that the operational amplifier has low noise, high-speed operation and large current. The diode is required to have low leakage and large current. For example, assuming that the noise voltage Von of 10 μV at 100 kHz is superimposed on the voltage Vo, the capacity of the bypass capacitor is 10
As μF, the noise current Ion flowing in the current Io is I
on = Von / Zc2 = 10 × 10−6 × 2π × 105
A large noise current Ion of × 10 × 10−6 = 62.8 μA flows through the current detection resistor. Moreover, when a large current operation is performed by the operational amplifier, temperature drift due to heat generation occurs, which is also a cause of erroneous measurement.

An object of the present invention is to stabilize the voltage / current at a relatively high speed even if the load has a large current ratio between the quiescent current and the inverting operation, and the DC characteristics of the quiescent current at a relatively high speed. The present invention intends to provide a voltage applied current measuring circuit capable of measuring

[0013]

In order to achieve the above object, the present invention connects a current amplifier and a diode connected in series and antiparallel to the current amplifier between an output terminal of an operational amplifier and a load. The configuration is The current amplifier may be one that emits or absorbs a large current with a slight voltage current, so an emitter follower that supplies and absorbs a large current may be used. Therefore, when the diode is turned on, a large amount of current can be quickly supplied to the load. Therefore, the operational amplifier does not need a large current supply capability. And since the diode is off when measuring the quiescent current,
Even if there is noise in the current amplifier, the noise current does not flow in the current supply line. Further, even if drift or the like occurs in the current amplifier, the voltage fluctuation is not transmitted to the load side. However, the current amplifier only needs to operate at high speed and have a large current supply capability.

[0014]

FIG. 1 shows an embodiment of the present invention. Parts corresponding to those in FIG. 4 are designated by the same reference numerals. Although generally similar to the conventional circuit of FIG. 4, in addition to the conventional circuit, operational amplifier A1
The current amplifier A3 is connected to the output terminal of
Output current is supplied or absorbed to the load 1 side through a pair of diodes D3 and D4 reversely connected in parallel. This is because a large current is quickly supplied or absorbed to the load 1 side. Therefore, the conventional pair of diodes D1 and D2
Becomes unnecessary. A large amount of current is supplied by the current amplifier A3 and the diodes D3 and D4.

The operation of the circuit is almost the same as that of the conventional circuit (FIG. 4), but since a large current is rapidly supplied or absorbed, the transient state time of the entire circuit becomes very short, and the steady state is quickly achieved. Converge to. Moreover, the operational amplifier A1 may be a normal operational amplifier, and it is not necessary to supply a large current, so that the problem of noise and the problem of drift are solved.

The current amplifier A3 is required to supply a large amount of current, but the emitter follower shown in FIG. 3 is sufficient for its configuration and can be solved by a simple circuit. Since a large current is required to be supplied, drift and noise occur in the current amplifier A3. However, when a large current is supplied all at once and the entire circuit instantly approaches a steady state, both the diodes D3 and D4 are cut off. Therefore, the influence does not appear on the current supply line, and does not affect the supply current Io or the load current IL.

FIG. 2 shows a waveform diagram of the voltage and current of the circuit of FIG. When the load 1 inverts, a load current IL of several amps flows as shown in FIG. 2A. The current required for this initially discharges the current Ic2 from the bypass capacitor C2 (FIG. 2B). As a result, the power supply voltage Vo of the load 1 decreases (FIG. 2C), the voltage Vo is fed back to the operational amplifier A1, and the current Io from the operational amplifier A1 starts to increase (FIG. 2).
D). Therefore, the voltage drop across the current detection resistor R1
Io becomes large, the diode D3 becomes conductive, and the large current I1 suddenly flows from the current amplifier A3 to the load 1 side to quickly supplement the current shortage (FIG. 2E).

Therefore, the bypass capacitor C2 is immediately charged (FIG. 2B), the load voltage Vo is restored, and the voltage Vo is fed back to the operational amplifier A1 to reduce its output current Io (FIG. 2D) for current detection. When the voltage drop of the resistor R1 becomes small, the diode D3 is cut off and the supply of the large current I1 is stopped (FIG. 2E). After that, the overall state returns to the steady state. By adding the current amplifier A3, the transient time to return to the steady state becomes one of several places of the conventional circuit, and the response speed becomes nearly 100 times faster.
Therefore, the measurement speed becomes very high.

[0019]

As described in detail above, the present invention provides
When the load 1 performs a pulse-shaped inverting operation and a load current IL of several amperes flows, a discharge current Ic2 flows from the bypass capacitor C2, whereas the charge current is quickly replenished with a large current from the current amplifier A3. Then, quickly return to the steady state. Moreover, the influence of noise and drift of the large current amplifier A3 does not appear outside, and the DC characteristics of the load 1 can be measured accurately at high speed. Moreover, the current amplifier A3
Is a simple emitter follower, and the response speed is 1
It is nearly 00 times faster, the transition time is several tenths,
The load 1 measurement time is 10 times faster. Therefore, the present invention is very useful and has not only a technical effect but also an economic effect. .

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the embodiment of FIG.

FIG. 3 is a configuration diagram of an example of a current amplifier A3.

FIG. 4 is a configuration diagram of a conventional voltage applied current measuring circuit.

5 is a waveform diagram for explaining the operation of the circuit of FIG.

[Explanation of symbols]

 1 load 2 DC voltage source 3 feedback circuit 4 current detection circuit 5 analog subtractor 6 A / D converter A1 operational amplifier A3 current amplifier D1, D2 diode D3, D4 diode R1 current detection resistor C1 phase compensation capacitor C2 bypass Capacitor

Claims (1)

[Claims] 1. A DC voltage source (2) for applying a predetermined DC voltage to a load (1) whose current-voltage characteristic is to be measured through an operational amplifier (A1), and a bypass capacitor connected in parallel to the load (1). (C2), a feedback circuit (3) for feeding back the voltage applied to the load (1) to the operational amplifier (A1), and between the output terminal of the operational amplifier (A1) and the load (1). Resistor for current detection (R1) connected to detect current and resistor for current detection (R1)
Voltage composed of a current detection circuit (4) consisting of a capacitor (C1) for phase correction connected in parallel to the above, and an analog subtraction circuit (5) for extracting the voltage generated in the current detection circuit (4). In the applied current measuring circuit, between the output terminal of the operational amplifier (A1) and the load, a current amplifier (A3) and a diode pair (connected in series and antiparallel to the current amplifier (A3) are connected. D
3, D4), and a voltage applied current measuring circuit.