JPH0263312A - Active resistor device - Google Patents

Abstract

PURPOSE:To set a resistance with high accuracy by using both terminals of a series circuit comprising a current control element and a resistor as a resistance value output terminal. CONSTITUTION:A voltage E at a terminal 1 is fed directly to a noninverting input terminal and a voltage drop I.R0 by a current I flowing through a reference resistor 6 is applied to a multiplier 4 to an inverting input terminal. Thus, an input terminal voltage applied to the inverting input terminal of an amplifier 5 is expressed as I.R0.X, where X is a setting multiple of the multiplier 4. With the feedback quantity of the amplifier 5 selected sufficiently, since almost no current flows to a gate of a FET 3, the relation of E=I.R0.X exists in the input voltage of the amplifier 6. The relation of R=R0.X is obtained by substituting the relation of E=I.R0.X to equation I to obtain an equivalent resistance R. Thus, the equivalent resistance R varies proportional to the setting multiple X of the multiplier 4 and the resistance is set with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an active resistance device, and more particularly, to an active resistance device that can set a resistance value with high accuracy.

(Prior art) For example, when calibrating a temperature measuring device that uses a resistance temperature detector, a variable resistor whose resistance value can be set arbitrarily is connected to the resistance temperature detector connection terminal of the device instead of the resistance temperature detector. The temperature value is calibrated by connecting the variable resistor and changing the resistance value of the variable resistor in accordance with the change in the resistance value of the resistance temperature sensor.

Conventionally, the variable resistors used in such calibration work have been the Atyer resistor, which the operator sets to the desired resistance value by rotating a dial, and the variable resistor, which is used to selectively switch and connect multiple fixed resistors using a relay. A resistor device or the like configured to set a desired resistance value is used.

However, with the former device, it is difficult to automate the calibration work, and with the latter device, it is difficult to automate the calibration work, but it is difficult to obtain highly accurate low resistance values, and relays are used. There is a problem with poor responsiveness.

Therefore, it is conceivable to use an active resistance device that can set a desired resistance value using an electronic circuit, such as the one disclosed in Japanese Patent Publication No. 59-46128, for example.

FIG. 3 is a circuit diagram showing an example of an active resistance device disclosed in Japanese Patent Publication No. 59-46128. In the figure, 1.2 is the equivalent resistance terminal, and terminal 1 is F E T
3 and the non-inverting input terminal of an amplifier 5 via a multiplier 4, with terminal 2 being a common potential point. The drain of the FET 3 is connected to the common potential point via the reference resistor 6 and also to the inverting input terminal of the amplifier 5, and the gate is connected to the output terminal of the amplifier 5.

In such a configuration, if the voltage between terminals 1.2 is E and the current flowing between terminals 1.2 is I, then terminals 1.2
The equivalent resistance value R seen from the outside between
-(+), on the other hand,
Focusing on the input voltage of the amplifier 5, the output voltage E- of the multiplier 4 is applied to the non-inverting input terminal, and the voltage drop due to the current I flowing through the reference resistor 6 is added to the inverting input terminal of the multiplier 1. 4 is set as X, the output voltage E of multiplier 4 is E-=E-X (2)
become. If the resistance value of the reference resistor 6 is RO, then the voltage drop across the reference resistor 6 will be T-Ro. here,
Assuming that the feedback amount of amplifier 5 is large enough, FET3
Since almost no current flows through the gate of I4., between the input voltages of amplifier 5, I4. =E-X
...The relationship (3) holds true. These (2)
, Substituting equation (3) into equation (1) to find the equivalent resistance value R, R=R,/X...(4
)become.

That is, by configuring as shown in FIG. 3, an active resistance device in which the equivalent resistance MR changes in inverse proportion to the set magnification X of the multiplier 4 can be realized.

(Problems to be Solved by the Invention) However, according to such a conventional configuration, the equivalent resistance value R
Since changes in inverse proportion to the set multiplier X of the multiplier,
This method has the disadvantage that the resistance value to be set is subject to division, which reduces the accuracy of setting the resistance value.

The present invention has focused on such points, and its purpose is to provide an active resistance device that can set the resistance value with high accuracy.

(Means for Solving the Problems) The active resistance device of the present invention includes a current control element, a resistor connected in series with the current control element and converting the current flowing through the current control element into a voltage, and the resistor. A multiplier that multiplies the converted voltage according to a set multiplier and outputs the result, and a control signal that compares the terminal voltage of the current control element and the output voltage of the multiplier and outputs a control signal to the current control element so that these voltages are equal. The present invention is characterized in that both ends of a series circuit of the current control element and the resistor are used as resistance value output terminals.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and the same parts as in FIG. 3 are given the same reference numerals. In FIG. 1, the non-inverting input terminal of amplifier 5 includes terminal 1 and FET 3.
The source of FET 3 is directly connected to the inverting input terminal, and the connection point between the drain of FET 3 and reference resistor 6 is connected via multiplier 4 .

In such a configuration, focusing on the input voltage of the amplifier 5, the voltage E of the terminal 1 is directly applied to the non-inverting input terminal, and the voltage drop I- due to the current flowing through the reference resistor 6 is applied to the inverting input terminal. Ro is added via multiplier 4.

Therefore, if the set magnification of the multiplier 4 is X, the input voltage at the inverting input terminal of the amplifier 5 becomes I-Ro.X. Here, assuming that the feedback amount of amplifier 5 is sufficiently large, PE
Since almost no current flows through the gates of 1 and 3, between the input voltages of amplifier 5, E = I - Ro - X ・(
The relationship 5) holds true. Substituting this equation (5) into equation (1) to find the equivalent resistance FIiIR, R=R0・X...(6)
become.

That is, by configuring as shown in Fig. 1, an active resistance device in which the equivalent resistance value R changes in direct proportion to the set multiplier X of the multiplier 4 can be realized, and since division as in the conventional case is not involved, the resistance value can be set with high precision.

FIG. 2 is a diagram showing a specific example of digitally setting the set value X of the multiplier 4 in FIG. An example is shown, and (b) shows an example in which a non-multiplying type D/A converter 7 and an analog multiplier 8 are combined. According to the former configuration, the overall configuration can be simplified. On the other hand, according to the latter configuration, since the analog multiplier 8 generally has a wide band, it is possible to process voltages at higher frequencies than in the former case. By using these multiplication means, the resistance value can be set at high speed according to the digital signal, and it is suitable as a variable resistor for various automatic measurements.

Note that a buffer amplifier or an attenuator may be inserted into the current path if necessary, and the positive and negative inputs of the amplifier may be switched depending on the modified circuit configuration.

Furthermore, the current control element is not limited to F E'I', but may also be a transistor.

(Effects of the Invention) As described above, according to the present invention, an active resistance device in which the resistance value can be set with high precision can be realized, and the practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a specific example of a multiplier used in the present invention, and FIG. 3 is a circuit diagram showing an example of a conventional device.

Claims (1)

[Claims] A current control element, a resistor connected in series with the current control element and converting the current flowing through the current control element into a voltage, and the voltage converted by the resistor multiplied according to a set multiplier and output. an amplifier that compares a terminal voltage of the current control element with an output voltage of the multiplication means and outputs a control signal to the current control element so that these voltages become equal; An active resistance device characterized in that both ends of the series circuit with the resistor are resistance value output terminals.