JPH05281269A - Current/voltage conversion circuit - Google Patents

Abstract

PURPOSE:To make the circuit into IC without using relays and improve the reliability through easy range setting, circuit separation and setting of limited current. CONSTITUTION:The output and reverse output from an operation amplifier OP inserted between an input terminal X and an output terminal Y are inputted an input current by current output type differential amplifiers A1 and A2 to which control input is commonly connected respectively and vias current VB is subtracted therefrom to output an output current. A control circuit C controls one operating current in the amplifiers A1 and A2 based on a setting current ISET in order to set a current range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a current-voltage conversion circuit of a direct current measuring circuit for an integrated circuit.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram of a conventional current-voltage conversion circuit.

Conventionally, a current-voltage conversion circuit generally measures a current to be measured once with a resistor and then measures the voltage. However, in order to convert the current to be measured into a voltage, it is inserted in series with the object to be measured. A circuit using an operational amplifier shown in FIG. 2 is often used in order to prevent the voltage applied to the measurement target from changing due to the voltage drop across the resistor. In FIG. 2, the operational amplifier OPA is a buffer circuit for taking out a current having a value equal to the current flowing into the input terminal X so that the voltage applied to the measurement object does not change, and the operational amplifier OPB is the operational amplifier OPA. This is a circuit for subtracting the bias voltage V _B from the output voltage.

[0004]

However, in such a conventional current-voltage conversion circuit, when the circuit shown in FIG. 2 is used, the voltage applied to the object to be measured is kept constant. However, there were the following problems. In order to take out the current to be measured, a circuit for subtracting the bias voltage as shown in FIG. 2 is necessary or an operation is required. If current limiting is performed to protect the measurement target (not in the circuit of FIG. 2), the circuit becomes more complicated. In order to change the current range, it is necessary to switch the resistance, and normally a relay or the like is used, which is inconvenient for making into an IC (integrated circuit). When performing other tests such as a high-speed digital test such as an IC tester, the resistance acts as a load, so this circuit needs to be disconnected, and a relay or the like is necessary, which is not suitable for IC implementation. The use of relays is unreliable and causes a large circuit.

The present invention solves the above problems.
An object of the present invention is to provide a highly reliable current-voltage conversion circuit which can be integrated into an IC without the need of using a relay and which can easily perform range setting, circuit disconnection and limit current setting.

[0006]

SUMMARY OF THE INVENTION The present invention is a current-voltage amplifier having an input terminal to which an input current is applied and an operational amplifier having one input connected to the input terminal and the other input connected to a bias voltage. In the conversion circuit, a voltage output terminal to which a reference resistor is connected between the common potential point and one current output is connected to the input terminal, the other current output is connected to the output terminal, and the output of the operational amplifier is connected. Two sets of current output type differential amplifiers whose control inputs are commonly connected corresponding to their current outputs, and at least one operating current of the two sets of current output type differential amplifiers is controlled based on a set current. And a control circuit for controlling the operation.

As a concrete configuration example of the present invention, in the operational amplifier, an inverting input is connected to the input terminal,
A non-inverting input is connected to the bias voltage, and the two sets of current output type differential amplifiers include a first current output type differential amplifier and a second current output type differential amplifier. The current output type differential amplifier has a first PNP transistor having an emitter connected to a positive voltage power supply, and an emitter connected to the positive voltage power supply having a base at the base and a collector of the first PNP transistor. A connected second PNP transistor, a first NPN transistor having a collector connected to the collector of the first PNP transistor and the input terminal, and a base connected to the inverting output of the operational amplifier; A second NPN transistor having a collector connected to the collector of the second PNP transistor and a base connected to the output of the operational amplifier; The second current output type differential amplifier includes a PN transistor and a third NPN transistor having a collector connected to an emitter of the second NPN transistor and an emitter connected to a negative voltage power source. A third PNP transistor having an emitter connected to a positive voltage power supply and a base connected to its own collector, and a fourth PNP transistor having an emitter connected to the positive voltage power supply and a base connected to the base of the third PNP transistor. PN
A P-type transistor and a fourth NPN whose collector is connected to the collector of the third PNP-type transistor and whose base is connected to the base of the second NPN-type transistor.
Type transistor, and a fifth NP having a collector connected to the collector and the output terminal of the fourth PNP transistor and a base connected to the inverting output of the operational amplifier.
The control circuit includes an N-type transistor, and a sixth NPN-type transistor whose collectors are connected to the emitters of the fourth NPN-type transistor and the fifth NPN-type transistor and whose emitters are connected to the negative voltage power supply, respectively. Inputs the set current to the collector, and inputs the set current to the collector, the third NPN transistor, and the sixth NP.
A seventh NPN-type transistor having a base connected to the base of the N-type transistor and an emitter connected to the negative voltage power source may be included.

[0008]

Operation: One current output is connected to the input terminal, the other current output is connected to the output terminal, and the control input is commonly connected to the output of the operational amplifier corresponding to the current output. The dynamic amplifier receives the input current, subtracts the bias voltage of the operational amplifier, limits the current, and outputs an output current equal to the input current. Further, the control circuit controls the operating current of at least one of the two sets of current output type differential amplifiers based on the set current to set the current range.

Due to the above, it is not necessary to use a relay.
C can be achieved, and range setting, circuit disconnection and limiting current setting can be easily performed, and reliability can be improved.

[0010]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a current-voltage conversion circuit according to an embodiment of the present invention.

In FIG. 1, the current-voltage conversion circuit includes an input terminal X to which an input current I _IN is applied, and an operational amplifier OP having one input connected to the input terminal X and the other input connected to a bias voltage V _B. With.

A feature of the present invention is that the operational amplifier OP includes an inverting output for inverting and outputting an output voltage, and a voltage output terminal Y having a reference resistance R ₀ connected to a common potential point. And one current output is connected to the input terminal X and the other current output is connected to the output terminal Y, and the operational amplifier OP
A pair of current output type differential amplifiers whose control inputs are commonly connected to the output and the inverted output corresponding to the current output,
And a control circuit C for controlling an operating current of at least one of the two sets of current output type differential amplifiers based on the set current.

According to the present invention, in the operational amplifier OP, the inverting input is connected to the input terminal X and the non-inverting input is connected to the bias voltage V _B. The current output type differential amplifier A1 includes a current output type differential amplifier A1 and the second current output type differential amplifier A2 includes a current output type differential amplifier A2.
Transistor Q ₃ as a first PNP type transistor whose emitter is connected to positive voltage power supply V _CC and positive voltage power supply V
A transistor Q ₄ to the base and its own collector of emitter connected transistors Q ₃ as a second PNP transistor whose base is connected to the _CC, the transistor Q ₃
First NP whose collector is connected to the input terminal X and the base is connected to the inverting output of the operational amplifier OP
As an N-type transistor, the collector of the transistor Q ₁ and the collector of the transistor Q ₄ are connected to each other, and the operational amplifier O
As a second NPN transistor whose base is connected to the output of P, a transistor Q ₂ and a third NPN whose collector is connected to the emitters of the transistors Q ₁ and Q _{2 and} whose emitter is connected to the negative voltage power supply V _EE and a transistor Q ₅ as type transistor, the current output type differential amplifier A2 includes a transistor Q ₈ as a third PNP type transistor having a base to the own collector emitter connected to a positive voltage source V _CC is connected, the positive Voltage power supply V _CC
The transistors Q ₉ as a fourth PNP transistor to the base of emitter connected transistors Q ₈ base connected, the base to the base of the transistor Q ₂ collector connected to the collector of the transistor Q ₈ is connected As a fourth NPN type transistor, a transistor Q ₆ and a collector and output terminal Y of the transistor Q ₉
Fifth transistors Q ₇ as NPN-type transistor, a collector connected to the emitter of the transistor Q ₆ and the transistor Q ₇ emitter to the negative voltage source V _EE base to the inverted output of the collector is connected an operational amplifier OP is connected to the There includes a transistor Q ₁₀ as a sixth NPN-type transistor connected, the control circuit C, the self-collector type a set current collector and the transistor Q ₅
And a transistor Q ₁₁ as a seventh NPN transistor whose base is connected to the base of the transistor Q _{10 and} whose emitter is connected to the negative voltage power supply V _EE .

The operation of the current-voltage conversion circuit having such a configuration will be described.

In FIG. 1, transistors Q ₅ , Q ₁₀ ,
Q ₁₁ is a current mirror for externally setting the operating current of the current output type differential amplifiers A1 and A2 by the setting current I _SET . The output of the current output type differential amplifier A2 is taken out to the outside as a current output, but it is sufficient to simply connect the reference resistor R ₀ to convert it into a voltage. The operational amplifier OP and the current output type differential amplifier A1 operate as a normal buffer. That is, the voltage of the input terminal X becomes the bias voltage V _B. If the input bias current of the operational amplifier OP is negligible, the input current I _IN is entirely supplied from the transistor Q ₁ or the transistor Q ₃ . If the input current I _IN is zero, the collector currents of the transistors Q ₁ and Q ₃ have opposite directions and have the same absolute value. That is, the transistor Q ₁ ,
The collector currents of Q ₂ are almost equal, and the transistors Q ₁ ,
The base potentials of Q ₂ are almost equal. When the input current I _IN flows in, the base voltage is controlled by the operational amplifier OP so that the difference in collector current between the transistor Q ₁ and the transistor Q ₃ becomes equal to the input current I _IN . At this time, I _IN = I ₁ tanh (−ΔV / 2VT) where VT = kT / q, q: elementary charge, k: Boltzmann constant, T: absolute temperature.

Since the same base voltage difference ΔV is given to the bases of the transistors Q ₆ and Q ₇ , the output current I _{OUT of the} current output type differential amplifier A2 is also I _OUT = I ₂ tanh (-ΔV / 2VT). From these equations, I _OUT = I _IN × I ₂ / I ₁ is obtained.

As is clear from the above equation, if I ₁ = I ₂ , then I _OUT = I _IN , and an output current I _OUT equal to the input current I _IN is obtained. At this time, the output current I _OUT can be arbitrarily set by the bias voltage V _B to the measurement target, but the output current I _OUT is the bias voltage V _B.
Therefore, no circuit and operation for subtracting the bias voltage V _B is required. The output current I _OUT is ±
Being limited to I ₁ , it essentially comprises current limiting means.

Although FIG. 1 shows the configuration of I ₁ = I ₂ , the current I ₂ may be fixed and used. At this time, a current normalized by the current I ₂ is obtained at the output, and the full scale is determined by the current I ₁ . That is, the range can be easily set from the outside without using a switch or the like. Further, if I ₁ = 0, no current flows in the input terminal X and therefore does not affect other measurements. Only a small collector capacitance is added as a load, and the influence on a high-speed digital test is extremely small.

When the h _FE (current amplification factor) of the transistor changes depending on the current, an error occurs, so a circuit for canceling the base current may be added. If a Wilson current mirror is used for the current mirror, the current matching will be better. Although a known differential amplifier can be used as the operational amplifier, in the application to the digital LSI tester, the number of elements can be reduced by using the first stage of the comparator. The operational amplifier may be a simple one, and may be a buffer that performs level shift in some cases (the current output type operational amplifier A1 sufficiently fulfills the role of the operational amplifier).

[0020]

The present invention has an excellent effect that it is possible to form an IC without the use of a relay, and it is easy to set the range, disconnect the circuit and set the limiting current and improve the reliability. When used in a digital LSI tester for DC test of IC circuits, there is a great advantage in miniaturization.

[Brief description of drawings]

FIG. 1 is a block diagram of a current-voltage conversion circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional current-voltage conversion circuit.

[Explanation of symbols]

 A1, A2 current output type differential amplifier C control circuit I_IN Input current I₁, I₂ Current I_OUTOutput current I_SET Set current OP, OPA, OPB Operational amplifier Q₁~ Q₁₁ Transistor R Resistance R₀ Reference resistance V_B Bias voltage V_CC Positive voltage power supply V_EE Negative voltage power supply X input terminal  Y, Z output terminal

Claims (1)

[Claims] 1. A current-voltage conversion circuit comprising an input terminal to which an input current is applied and an operational amplifier having one input connected to the input terminal and the other input connected to a bias voltage, and a common potential point A voltage output terminal to which a reference resistor is connected, and one current output connected to the input terminal, the other current output connected to the output terminal, and the control input corresponding to the output of the operational amplifier. And commonly connected two sets of current output type differential amplifiers, and a control circuit for controlling an operating current of at least one of the two sets of current output type differential amplifiers based on a set current. Current-voltage conversion circuit characterized by.