KR20040033604A - Voltage to current converting circuit - Google Patents

Abstract

PURPOSE: A voltage current converter circuit is provided to supply a constant current without regard to the variation of an input voltage. CONSTITUTION: According to the voltage/current converter circuit, an operational amplifier(20) controls to flow a constant current according to the variation of an input voltage. A transistor(22) supplies a constant current by a current control signal of the operational amplifier. And a resistor(24) is connected between a power supply voltage and an emitter of the transistor, and determines a current according to a potential difference between the input voltage and the power supply voltage. The input voltage is supplied to a non-inversion port of the operational amplifier. And an inversion port of the operational amplifier is connected to the emitter of the transistor.

Description

Voltage Current Converter Circuits {VOLTAGE TO CURRENT CONVERTING CIRCUIT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage-current conversion circuit, and more particularly, to a voltage / current conversion circuit that always converts into a constant current regardless of a change in an input voltage.

Typically, semiconductor device manufacturers perform systematic tests to ensure that semiconductor device products meet all design parameters as part of quality assurance. Common types of tests to be performed include device parameter testing (DC testing), device logic function testing, and device timing testing (AC testing). The semiconductor device being tested is often referred to as a 'device under test' (DUT), and the test system used to perform the test described above on the DUT is often called an 'automatic test equipment (ATE)'. Is called.

The ATE must be very accurate to perform the described tests on highly sensitive DUTs such as semiconductor devices. In general, the ATE hardware is controlled by a computer that provides the correct voltage, current, timing and functional status to the DUT and executes a test program to monitor the response from the device for each test. The results of each test are then compared to preset limits and a pass / fail decision is made. The ATE hardware itself generally includes a set consisting of a power supply, an instrument, a signal generator, a pattern generator, and the like. Pin Electronics (PE) circuitry provides a space between the ATE and the DUT. More specifically, the PE circuit provides an input signal to the DUT and receives an output signal from the DUT. For example, in parameter testing, an input voltage is sent to the DUT and an output current is received from the DUT, or an input current is sent to the DUT and an output voltage is received from the DUT. Thus, a programmable current source is one of the required elements of the PE to provide the desired current to the DUT.

A current source according to the prior art used in such a PE circuit is shown in Korean Laid-Open Patent Publication No. 2001-0024938. The current source according to the prior art depends on the voltage VBE, and the voltage VBE is affected by the change due to the temperature change, which greatly affects the precision of the current source. As described above, a change of 1 ° C. also exhibits a 200% error at the minimum current setting. Moreover, current source errors according to the prior art are constant over the entire operating range, making it impossible to accurately program small values.

On the other hand, U.S. Patent No. 4,251,743 (hereinafter referred to as `` Hareyama ''), which was granted a patent to Hareyama on February 17, 1981, is configured as aging. Disclosed are current sources designed to be used in analog-to-digital (A / D) converters to compensate for temperature variations, as well as changes in the properties of elements. The current source disclosed in Hareyama also includes the concept of a current mirror.

However, the current source in Hareyama implements feedback control (i.e. closed loop control) of its output current Iout to compensate for errors. As a result, the current sources disclosed in Hareyama may not be as precise and sensitive as required due to the inherent nature of feedback control (e.g., residual error and time delay) with the need for more hardware. .

Therefore, there is a need for a precise current source circuit used in a computer controlled ATE having a good dynamic range that can eliminate or compensate for current variations caused by temperature changes.

In addition, in the conventional general method, as shown in FIG. 1, a method of converting into a current using a resistor is applied. However, it is necessary to assume that Vpin is a fixed value or that Vpin should be maintained at a constant rate according to Vpp change.

The autotest system 10 must be very accurate to perform the tests described above on a highly sensitive DUT 12 such as a semiconductor device, and provide the DUT 12 with the correct voltage, current, timing and functional status. Each computer is controlled by a computer executing a test program to monitor the response from the device for each test. The auto test system 10 includes a set consisting of a power supply, a meter, a signal generator, a pattern generator, and the like. Resistor R provides an input signal to the DUT 12 and receives an output signal from the DUT 12. Resistor R is one of the elements for which resistor R is required to provide the desired current to the DUT 12. The voltage Vpp tested from the auto test system 10 supplies current through the resistor R to the DUT 12. At this time, the current Ipp = (Vpp-Vpin) / R applied to the DUT 12 becomes.

In many cases, however, the voltage at Vpin is not constant. If the voltage of the Dut Pin changes or the characteristic does not change at a constant ratio (Linerity) according to the input current, the above conventional method cannot be applied.

In general, in the case of DC Source, most current or voltage mode can be simultaneously used, but in case of AC Source, most instruments measure voltage mode in the form of Voltage Source. There are few options for ATE.

It is therefore an object of the present invention to provide a voltage current / converter which always supplies a constant current regardless of the variation of the input voltage.

The voltage / current conversion circuit of the present invention for achieving the above object includes an operational amplifier for controlling a constant current to always flow in accordance with the change of the input voltage, a transistor for supplying a constant current by the current control signal of the operational amplifier; And a resistor connected to the emitter of the transistor to determine a current according to a potential difference between the input voltage and the power supply voltage.

1 is a configuration diagram of a current converter using a general voltage source

2 is a configuration diagram of a voltage / current conversion circuit according to an embodiment of the present invention;

3 is a simulation circuit diagram for voltage / current conversion according to an embodiment of the present invention

4 is a view illustrating an output current change characteristic according to an input power change according to an exemplary embodiment of the present invention.

5A is a waveform diagram of an input AC voltage of a simulation result according to an exemplary embodiment of the present invention.

5B is a waveform diagram of an output AC current of simulation results according to an embodiment of the present invention.

6 is a circuit diagram of a voltage / current conversion circuit implemented using a QUAD OP amplifier of AD8554 manufactured by Analog Devices Inc. and a PNP transistor of KEC Co., Ltd.

7 is a simulation result diagram illustrating a change state of a current when an output voltage of the voltage / current conversion circuit diagram of FIG. 6 is changed.

Explanation of symbols on the main parts of the drawings

10: Auto Test System 12: DUT

20: operational amplifier 22: transistor

24: resistance

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, if it is determined that a specific description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

2 is a configuration diagram of a voltage / current conversion circuit according to an embodiment of the present invention;

The operational amplifier 20 controls the constant current to always flow in accordance with the variation of the input voltage, the transistor 22 supplying the constant current by the current control signal of the operational amplifier 20, and the emitter of the transistor. And a resistor 24 connected to determine a current according to a potential difference between the input voltage and the power supply voltage.

Referring to Figure 2 described above will be described in detail the operation of the preferred embodiment of the present invention.

An input terminal 18 for inputting a voltage, a non-inverting terminal (+) connected to the input terminal 18, an operational amplifier 20 having an output terminal connected to the base of the transistor 22, and the transistor ( The inverting terminal (-) of the operational amplifier 20 is connected to the emitter of 22, the resistor 24 is connected to the power supply Vcc, and is connected to the emitter of the transistor 22, and the transistor 22 The collector of is connected to the output terminal 26.

When the base potential is determined to operate in the active region of the transistor 22 of the present invention, the amount of the collector-emitter current Ice is determined by the hfe of the transistor 22, and the voltage between the collector and the emitter within the range. Regardless of Vce, a constant current can flow through the output terminal 26. Where Vce> 1.0V.

Therefore, the amount of current already determined in the emitter of the transistor 22 can be used as a constant current regardless of the voltage of the DUT 12.

First, operational amplifier 20 determines the base potential to operate in the active region of transistor 22. Even if the input voltage of the transistor 22 changes, it must be in the active region. At this time, the base voltage Vb of the transistor 22 is fed back by changing the potential of the collector voltage Vc of the transistor 22 according to the voltage V input to the non-inverting terminal (+) of the operational amplifier 20. Controlled. At this time, the transistor 22 maintains the active state of the active region.

The current between the emitter and the collector of the transistor 22 is determined by the potential difference between the power supply voltage Vcc and the voltage V input to the input terminal 18 by the pull-up resistor 24. In this case, the transistor 22 may maintain the current Ice between the collector and the collector constantly regardless of the potential change between the collector and the emitter in the active region. That is, the voltage difference between the voltage of the node 28 (input voltage V) and the power supply voltage Vcc is determined by the resistor 24 so that a constant current always flows through the collector of the transistor 22.

3 is a simulation circuit diagram for the voltage / current conversion according to an embodiment of the present invention,

4 is a view illustrating a characteristic change of output current according to an input power change according to an exemplary embodiment of the present invention.

5A is a waveform diagram of an input AC voltage of a simulation result according to an embodiment of the present disclosure;

5B is a waveform of output AC current of a simulation result according to an exemplary embodiment of the present invention.

15V, the second power source V2, and -15V, the third power source V3, are respectively supplied to the power supply terminal of the operational amplifier 40, and the first power source (+) is supplied to the non-inverting terminal (+) of the operational amplifier 40. 3V which is V1) was supplied, and 5V which is 4th power source V4 was supplied as the power supply voltage Vcc. Simulation result using FIG. 3 As shown in FIG. 4, the current change characteristic has linearity according to the power change of the input voltage.

When the input AC voltage of FIG. 5A is applied, the output AC current is shown in FIG. 5B.

Fig. 6 is a circuit diagram of a voltage / current conversion circuit implemented using an AD8554's QUAD OP amplifier manufactured by Analog Devices Inc. and a PNP transistor manufactured by KEC Corporation.

Simulation results using FIG. 6 showed linear characteristics as shown in FIG. 7, and it was confirmed that the characteristics appeared within 1 μΑ. As a result of the experiment confirming the change in current when the output voltage is converted in FIG. 7, the output voltage was varied from 0.7V to 1.06V for both the case of the input voltage of 3.6V and 2.2V, but also within 1 μA. It can be seen that it showed satisfactory characteristics with error degree.

As described above, the present invention has the advantage that the current supplied to the DUT is always controlled even when the input voltage supplied from the auto test system is changed so that a desired current can be supplied regardless of the variation of the input voltage.

Although the present invention has been described in detail only with respect to specific embodiments, it is apparent to those skilled in the art that modifications or changes can be made within the scope of the technical idea of the present invention, and such modifications or changes belong to the claims of the present invention. something to do.

Claims (4)

In the voltage / current conversion circuit, An operational amplifier that controls a constant current to flow at all times according to the variation of the input voltage, A transistor for supplying a constant current by the current control signal of the operational amplifier; And a resistor connected between a power supply voltage and an emitter of the transistor and configured to determine a current according to a potential difference between the input voltage and the power supply voltage. The method of claim 1, The input voltage is supplied to a non-inverting terminal of the operational amplifier. The method of claim 2, The inverting terminal of the operational amplifier is connected to the emitter of the transistor. The method of claim 3, wherein And the operational amplifier controls the base potential of the transistor to operate the transistor in an active region.