JP2002098718A - Current/voltage conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current/voltage conversion circuit having a large dynamic range, and having high precision and resolution even in the case of a current changing at high speed. SOLUTION: In this circuit, operation amplifiers and I/V conversion resistances for current/voltage conversion are installed as many as the number of required ranges, and switching elements are installed in series on the I/V conversion resistances except that having the minimum range, and theses members are connected in parallel. In the circuit, when a current exceeding a set value in some range flows in the I/V conversion resistance in a smaller range by one grade than the range, the switching element is switched to the ON state, and the I/V conversion resistance in the range is allowed to become conductive, and thereby the I/V conversion resistance is changed between the ON and OFF states corresponding to the magnitude of the input current, and the voltages on both ends of each I/V conversion resistance are operated by an operation circuit, to thereby detect the current value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current / voltage conversion circuit capable of converting a current having a large dynamic range and changing at a high speed into a voltage with high accuracy, and a current generator capable of setting a current value with high resolution. is there.

[0002]

2. Description of the Related Art When measuring a magnitude of a current or a physical quantity such as an electric quantity or an electric quantity related to a current, an I / V conversion resistor is used to convert the current into a voltage. Conventionally, several types of current / voltage conversion resistors having different resistance values according to the magnitude of a target current are measured by switching with a switch, a relay, or a switching element such as a semiconductor. This is commonly referred to as range switching.

FIG. 2 shows a generally known current / voltage conversion circuit using an operational amplifier 21. Assuming that the resistance value of the I / V conversion resistor 22 is R, the output voltage V with respect to the input current I is V = −I · R. Therefore, the input current I is obtained by I = -V / R. At this time, while the operational amplifier 21 performs the linear amplification operation, the voltage e between the + and-input terminals is substantially zero.
V.

FIG. 3 shows that the current / voltage conversion circuit shown in FIG. 2 can switch the I / V conversion resistors R, 32, 33 and 34 having different values so that the range can be switched in accordance with the magnitude of the current to be measured.
1, R2, and R3 are switched by switches 35, 36, and 37, or relay contacts, or switching elements SW1, SW2, and SW3 made of semiconductor or the like.

[0007] FIG. 7 shows a current / voltage conversion circuit which can switch the range according to the magnitude of the current to be measured, similarly to FIG. 3, without using an operational amplifier.

When any one of SW1, SW2, and SW3 is turned on and the resistance value of the I / V conversion resistor at this time is R, the output voltage V with respect to the input current I becomes V = I · R. Become. Therefore, the input current I is obtained by I = V / R.

However, the range switching by the switch, the relay contact, or the switching element made of a semiconductor or the like has a relatively slow operation speed and does not open the current circuit even for a moment. In addition, it is necessary to overlap the I / V conversion resistance before the switching and the I / V conversion resistance after the switching, so that the control is complicated, and there is a problem that an error occurs in a measured value during the switching. .

For the above reasons, it is difficult to switch the range of a current whose dynamic range is large and changes at a high speed, and the measurement is performed in a range corresponding to the maximum value of the current. Therefore, the S / N ratio and the resolution when the current value is small are poor, and the measurement accuracy is lowered.

FIG. 8 shows an example of a commonly used current generator. The current setting value S1 and the voltage corresponding to the current I actually flowing to the load 61 detected by the I / V conversion resistor 32 or 33 are compared by an operational amplifier and controlled so as to match.

At this time, the settable current value is determined by the I / V conversion resistors 32 and 33 and the input resistor 64.
2 cannot be switched at high speed, so that the current value setting range cannot be widened and the resolution cannot be increased.

Further, when switching between the I / V conversion resistors 32 and 33, a period for turning on both of them is necessary in order not to open the circuit, and the feedback amount during this period does not reach a predetermined value. Unnecessary fluctuations in the output current occur due to a delay in the response of the system to the switching of the I / V conversion resistor.

[0012]

The problem to be solved is to enable high-precision and high-resolution current / voltage conversion even for a current input having a large dynamic range and changing at a high speed, such as an alternating current or a pulse current. It is assumed that.

It is another object of the present invention to provide a current generator which can set a current value with a high resolution over a wide range and does not generate unnecessary output current fluctuations due to switching of an I / V conversion resistor.

[0014]

According to the present invention, I / V conversion resistors for current / voltage conversion are provided for a required number of ranges with respect to a current input according to claim 1, and switching is performed to I / V conversion resistors other than the minimum range. In a device in which elements are provided in series and these are connected in parallel, when a current equal to or more than the set value in the range flows through an I / V conversion resistor in a range one stage smaller than the range other than the minimum range, the switching element in the range is changed to By turning it on to allow a current to flow through the I / V conversion resistor in the range, I
The current flowing through the / V conversion resistor is turned on and off, and each I / V
It is characterized in that a current value is detected by calculating a voltage between both ends of the conversion resistor by a calculation circuit.

[0015] For the current input according to claim 2, I / V conversion resistors for current / voltage conversion are provided for the required number of ranges, and switching elements are provided in parallel with the I / V conversion resistors other than the maximum range. In the case where these are connected in series, when a current equal to or more than the set value in the range flows through the I / V conversion resistor in each range other than the maximum range, the switching elements connected in parallel are turned on, and the I / V
By bypassing the current of the V conversion resistor, the current flowing through the I / V conversion resistor is increased or decreased according to the magnitude of the input current,
After detecting voltages at both ends of each I / V conversion resistor with a differential amplifier, the current value is detected by calculating with an arithmetic circuit.

Further, a current / voltage conversion circuit having a low input impedance and a wide dynamic range is obtained by combining the current / voltage conversion circuit of claim 1 and an operational amplifier.

An I / V conversion resistor, a differential amplifier, and a switching element are added to the current / voltage conversion circuit according to the third aspect, so that current / voltage conversion can be performed without using a current amplification circuit for driving a large current. Increase the current range.

A wide current value which is high in resolution and free from output current fluctuations caused by switching of the I / V conversion resistance by combining the current / voltage conversion circuit of claim 1 or 2 with an operational amplifier and a differential amplifier. A current generator characterized by having a set range is obtained.

[0019]

According to the first aspect of the present invention, a current flows from the minimum range to an I / V conversion resistor corresponding to a corresponding range according to the magnitude of the current, and an I / V corresponding to a higher range. Since no current flows through the conversion resistor, a current / voltage conversion function equivalent to range switching can be performed at high speed and automatically without switching error.

According to the present invention, according to the magnitude of the current, the current of the I / V conversion resistor in a range smaller than the corresponding range is bypassed, and the I / V conversion corresponding to a range larger than the range is bypassed.
Since a current flows through the V conversion resistor, a current / voltage conversion function equivalent to range switching can be performed at high speed and automatically without switching error.

According to a third aspect of the present invention, the current / voltage conversion circuit of the first or second aspect is combined with an operational amplifier to provide a current / voltage conversion function having a small input impedance and equivalent to range switching without switching error. Can be performed at high speed and automatically.

According to the present invention, the current flows from the minimum range to the I / V conversion resistor combined with the operational amplifier corresponding to the corresponding range according to the magnitude of the current. I / V without amplifier
Since I / V conversion is performed by the conversion resistor, a current / voltage conversion function equivalent to range switching can be performed at high speed and automatically without a switching error without using a current amplifier circuit for driving a large current.

According to a fifth aspect of the present invention, the current / voltage conversion circuit of the first aspect, the operational amplifier, and the differential amplifier are combined.
It is possible to obtain a current generator characterized by having a wide current value setting range that has high resolution and does not cause output current fluctuation due to switching of the I / V conversion resistance.

According to a sixth aspect of the present invention, the current / voltage conversion circuit of the second aspect is combined with an operational amplifier to provide a wide current value setting range with high resolution and no output current fluctuation due to switching of the I / V conversion resistance. And a current generator characterized by having the following.

[0025]

FIG. 5 is a circuit diagram showing a current / current circuit according to the first embodiment of the present invention.
5 is an embodiment of a voltage conversion circuit. Reference numerals 3, 4, and 5 denote I / V conversion resistors having resistance values of R1, R2, and R3, respectively. The magnitudes of the resistance values are R1>R2> R3, where R1 is the minimum range, R2 is the middle range, and R3 is the Corresponds to the maximum range.

6, 7 have a predetermined voltage VA at both ends.
There is a switching element that conducts when the voltage becomes equal to or higher than VB. The switching element can be realized by a diode, a non-linear element such as a Zener diode or a varistor, or a required number connected in series or in parallel. Or a transistor or FET
The on-off may be controlled by an arithmetic circuit.
FIG. 5 shows a case where a diode is used as an example. It is assumed that the absolute value of VB is set to be larger than the absolute value of VA.

Reference numeral 2 denotes an arithmetic circuit for calculating an input current value from the voltage values V1, V2, and V3 obtained by current / voltage conversion by the respective I / V conversion resistors.

The operation of FIG. 5 will be described below. I is an input current, I1 is a current flowing in R1, I2 is a current flowing in R2, and I3 is a current flowing in R3. V1 is a terminal voltage of R1 with respect to the ground. V2 is a terminal voltage of R2 with respect to the ground, and V3 is a terminal voltage of R3 with respect to the ground.

Using the above symbols, the current and voltage of each part have the following relationship. I1 = V1 / R1 (1)

At this time, if the absolute value of V1 is smaller than the absolute values of VA and VB, 6 and 7 are turned off, so that I2 = I3 = 0 (2)

The absolute value of V1 is larger than the absolute value of VA,
When VB is smaller than the absolute value of VB, 6 turns on and 7 turns off, so I2 = V2 / R2 (3) I3 = 0 (4)

When the absolute value of V1 is larger than the absolute values of VA and VB, 6 and 7 are turned on, so that I2 = V2 / R2 (5) I3 = V3 / R3 (6)

From the current path, I is I = I1 + I2 + I3 (7)

When I is obtained from the equations (1) to (7), it is expressed as follows: I = V1 / R1 + V2 / R2 + V3 / R3 (8)

According to the equation (8), the input current value I
Terminal voltages V1, V2, V3 of the conversion resistor with respect to the ground
Is divided by each resistance value, and then added, it can be found that it is obtained.

Therefore, the magnitude of the current I can be obtained by performing the operation of the equation (8) in the operation circuit 2. The arithmetic circuit can be easily formed by a generally known inverting and adding circuit using an operational amplifier.

Alternatively, an A / D converter is provided in the arithmetic circuit,
Alternatively, the current I can be obtained by incorporating a voltage / frequency converter and a counter, converting the voltage output of each I / V conversion resistor into a digital value, and then calculating the equation (8) by software.

Further, the magnitudes of V1 and V2, that is, I1 and I
The above operation in which the respective currents I2 and I3 flowing through R2 and R3 according to the magnitude of R2 are turned on and off corresponds to the input current I
This is equivalent to automatically switching the range in accordance with.

Since the present method does not require a complicated control circuit for range switching, high-speed operation is possible, and an error associated with range switching is small. As a result, current / voltage conversion can be performed with high accuracy and resolution even with a current input having a large dynamic range and changing at a high speed, such as an alternating current or a pulse current.

In the embodiment of FIG. 5, there are three ranges. However, if the number of I / V conversion resistors and switching elements is increased, a current / voltage conversion circuit having more stages can be constructed.

FIG. 9 shows an embodiment of a current / voltage conversion circuit according to claim 2 of the present invention. Reference numerals 3, 4, and 5 denote I / V conversion resistors having resistance values of R1, R2, and R3, respectively. The magnitudes of the resistance values are R1>R2> R3, where R1 is the minimum range, R2 is the middle range, and R3 is the Corresponds to the maximum range.

6 and 7 each have a predetermined voltage VA at both ends.
There is a switching element that conducts when the voltage becomes equal to or higher than VB. The switching element can be realized by a diode, a non-linear element such as a Zener diode or a varistor, or a required number connected in series or in parallel. Or a transistor or FET
The on-off may be controlled by an arithmetic circuit.
FIG. 9 shows a case where a diode is used as an example.

Note that the absolute values of VA and VB are voltage values that do not turn on while a current corresponding to the range to be measured flows in R1 and R2.

Reference numerals 42, 43, and 44 denote differential amplifiers for obtaining voltages across the I / V conversion resistors. Here, the gain is set to 1 for easy understanding of the description.

Reference numeral 2 denotes an arithmetic circuit for calculating an input current value from voltage values V1, V2, and V3 obtained by current / voltage conversion by an I / V conversion resistor and a differential amplifier, respectively.

The operation of FIG. 9 will be described below. I is an input current, I1 is a current flowing through R1, and I2 is a current flowing through R2. V1, V2, and V3 are R1, R
2, the voltage between both terminals of R3 is detected by each differential amplifier. Using the above symbols, the current and voltage of each part are as follows.

When the input current I is within the range covered by R1, since 6 is set to be off, I = I1 (11). V1 is expressed as follows: V1 = I1 × R1 (12) From (11) and (12), the input current I is obtained by I = V1 / R1 (13).

When the input current I exceeds the size of the range covered by R1, 6 turns on, and a part of the input current I becomes R1.
Therefore, the input current I cannot be obtained in the equation (13) because the input current I is bypassed at 6 without passing through.

Here, when the input current I is within the range covered by R2, since 7 is set to be off, I = I2 (14). V2 is V2 = I2 × R2 (15). From (14) and (15), the input current I is obtained by I = V2 / R2 (16).

When the input current I exceeds the size of the range covered by R2, 7 is turned on and a part of the input current I becomes R2.
Therefore, the input current I cannot be obtained in the equation (16) because the signal is bypassed at 7 without passing through.

At this time, V3 is as follows: V3 = I × R3 (17) Therefore, from (17), the input current I is obtained by the following equation: I = V3 / R3 (18)

From the above, the input current value I is (13) (1
6) The magnitude of the input current I can be obtained by selecting the minimum range value among the current values obtained by the equation (18) within the range of the current value covered by each range. That is, this is performed by the two arithmetic circuits. The operation circuit can be easily formed by a generally known comparator, signal selection circuit, or the like.

As another method, an A / D converter is provided in the arithmetic circuit,
Alternatively, the current I can be obtained by incorporating a voltage / frequency converter and a counter, converting the voltage output of each I / V conversion resistor into a digital value, and then calculating and selecting the value by software.

The magnitudes of V1 and V2, that is, I1 and I2
The above operation of bypassing the current at 6 and 7 according to the magnitude of 2 corresponds to automatically performing range switching according to the input current I.

Since the present method does not require a complicated control circuit for range switching, high-speed operation is possible, and the error accompanying range switching is small. As a result, current / voltage conversion can be performed with high accuracy and resolution even with a current input having a large dynamic range and changing at a high speed, such as an alternating current or a pulse current.

In the embodiment of FIG. 9, there are three ranges. However, if the number of I / V conversion resistors and switching elements is increased, a current / voltage conversion circuit having more ranges can be constructed.

FIG. 1 shows an embodiment of a current / voltage conversion circuit according to claim 1 of the present invention, wherein 1 is an operational amplifier.

3, 4, and 5 have resistance values of R1 and R, respectively.
2, the R / V conversion resistance of R3, and the magnitude of the resistance value is R
1>R2> R3, where R1 corresponds to the minimum range, R2 corresponds to the middle range, and R3 corresponds to the maximum range.

Reference numerals 6 and 7 denote switching elements which are turned on when the voltage at both ends exceeds a predetermined voltage VZ. In general, a non-linear element such as a diode, a Zener diode, or a varistor can be realized as a single unit or a required number connected in series or in parallel. Alternatively, transistors and FETs or the like may be used and the on / off of the switching elements 6 and 7 may be controlled by an arithmetic circuit.

Reference numeral 2 denotes an arithmetic circuit for calculating a voltage value obtained by current / voltage conversion by each I / V conversion resistor to obtain an input current value. Control lines 6 and 7 as needed with control lines 8 and 9

The operation of FIG. 1 will be described below. I is an input current, I1 is a current flowing in R1, I2 is a current flowing in R2, and I3 is a current flowing in R3. V1 is the output voltage of the operational amplifier 1 and the terminal voltage of the lower side of R1 with respect to the ground. V2 is a terminal voltage with respect to the ground below R2, and V3 is a terminal voltage with respect to the ground below R3.

E is the voltage between the-input terminal and the + input terminal of the operational amplifier 1, which is almost 0 V in a region where the operational amplifier operates linearly. In the circuit of FIG. 1, the + input terminal of the operational amplifier is connected to the ground. Therefore, in the linear operation region, the-input terminal is also at 0V, and e is at 0V.

Using the above symbols, the current and voltage of each part have the following relationship. However, it is assumed that it is an ideal state where the offset current and the bias current of the operational amplifier can be ignored. I1 = (e−V1) / R1 = −V1 / R1 (31)

When the absolute value of V1 is smaller than the absolute value of VZ, 6 is turned off. I2 = 0 (32) When the absolute value of V1 is larger than the absolute value of VZ, 6 is turned on. I2 = (e−V2) / R2 = −V2 / R2 (33)

When the absolute value of V2 is smaller than the absolute value of VZ, 7 is turned off. I3 = 0 (34) When the absolute value of V2 is larger than the absolute value of VZ, 7 is turned on. I3 = (e−V3) / R3 = −V3 / R3 (35)

From the current path, I is I = I1 + I2 + I3 (36)

When I is obtained from the equations (31) to (36), it is expressed as follows: I = -V1 / R1-V2 / R2-V3 / R3 (37)

According to the equation (37), the input current value I is
Terminal voltage V1 with respect to the ground at the lower end of the / V conversion resistor,
It can be seen that it can be obtained by dividing V2 and V3 by each resistance value and then adding them.

Therefore, the magnitude of the current I can be obtained by performing the operation of the expression (37) by the operation circuit 2. The arithmetic circuit can be easily formed by a generally known inverting and adding circuit using an operational amplifier.

Further, an A / D converter or a voltage / frequency converter and a counter are incorporated in the arithmetic circuit, and each I / V
The current I can also be obtained by converting the voltage output of each conversion resistor into a digital value and then calculating the equation (37) by software.

The magnitudes of V1 and V2, that is, I1 and I2
The above operation of turning on and off the currents I2 and I3 flowing through R2 and R3 in accordance with the magnitude of 2 corresponds to automatically performing range switching according to the input current I.

Since the present method does not require complicated control for switching the range, high-speed operation is possible, and the error associated with switching the range is small. As a result, current / voltage conversion can be performed with high accuracy and resolution even with a current input having a large dynamic range and changing at a high speed, such as an alternating current or a pulse current. Furthermore, the method has a very low input impedance as in FIG.

Although the embodiment of FIG. 1 has three ranges, if the number of I / V conversion resistors and switching elements is increased, a current / voltage conversion circuit having more stages can be constructed.

As in the embodiment of FIG. 1, even when the operational amplifier and the circuit of FIG. 9 are combined, a current / voltage conversion circuit having a low input impedance and capable of automatic range switching can be constructed similarly to FIG.

By the way, in the current / voltage conversion circuit shown in FIG. 1, the operational amplifier 1 must be able to drive the current I. Therefore, when the current value increases, it becomes necessary to combine a current amplification circuit or a power amplifier.

FIG. 4 relates to claim 4, and FIG.
4 between the input common line of the current / voltage conversion circuit
This is an embodiment of a current / voltage conversion circuit in which the I / V conversion resistor R4 and the switching element 45 are added and the inputtable current range is widened without using a large output current amplifier circuit.

Reference numerals 42, 43, and 44 denote differential amplifiers for obtaining voltages between terminals of the I / V conversion resistors 3, 4, and 5, respectively. Here, the gain is set to 1 for easy understanding of the description.

The switching element 45 is turned off when the both ends are equal to or lower than the fixed voltage VX, similarly to 6 and 7, and has an equivalently high impedance. A non-linear element such as a diode, a Zener diode, or a varistor can be used because it becomes an impedance. Alternatively, a transistor, a FET, or the like may be used, and its on-off may be controlled by an arithmetic circuit.

When the resistance value of the I / V conversion resistor R4 is high enough not to affect the normal operation of the operational amplifier 1, the switching element 45 may not be provided.

As described above, since the operational amplifier 1 operates linearly in a range where the input current I can be driven, e becomes 0, and R4 is set regardless of the presence or absence of the switching element 45.
1 does not flow, so that the same operation as in FIG. 1 is performed.

At this time, I4 = 0 (41) V4 = 0 (42)

The input current I is equal to the input current I of the operational amplifier 1.
Is beyond the range in which the operational amplifier 1 can be driven, the operational amplifier 1 is out of the linear operation region, and thus e is not 0.

When no switching element is provided, e is 0
When the switching element is provided when
When the absolute value of V exceeds VX, a current flows through the resistor R4.
That is, the input current I flows through R1, R2, R3, and R4.

Using the respective symbols in FIG. 4, the following relational expressions hold. I1 = (e−V1) / R1 (43) I2 = (e−V2) / R2 (44) I3 = (e−V3) / R3 (45) I4 = V4 / R4 ... (46)

From the equations (41) to (46), I becomes I = (e−V1) / R1 + (e−V2) / R2 + (e−V3) / R3 + V4 / R4 (47) Therefore, the current value I can be obtained by calculating the equation (47) in the arithmetic circuit 2.

It is to be noted that the reference numerals 41 and 45 can also function as protection circuits for the operational amplifier and its peripheral elements against excessive input current.

In addition to the combination of the circuit of FIG. 9 and the operational amplifier, an I / V conversion resistor R4 and a switching element are added between the input common line of the current / voltage conversion circuit and the ground as shown in FIG. Similar to the circuit of FIG. 4, it is possible to obtain a current / voltage conversion circuit in which the inputtable current range is widened without using a large output current amplifier circuit.

FIG. 6 shows an embodiment of the current generator according to claim 5, which is a combination of the operational amplifier 1 and the current / voltage conversion circuit of FIG.

However, two I / V conversion resistors, 3 and 4, are shown. That is, 3 and 4 are I / V conversion resistors having resistance values of R1 and R2, respectively, and the magnitude of the resistance value is R1> R2.

Reference numeral 61 denotes a load to which a current is supplied. Reference numeral 6 denotes a switching element that conducts when both ends become equal to or higher than a predetermined voltage VZ. The switching element 6 can be realized by a diode, a non-linear element such as a Zener diode or a varistor, or a required number connected in series or in parallel. Alternatively, a transistor, a FET, or the like may be used, and an arithmetic circuit may be separately provided to control on / off thereof.

Reference numerals 42 and 43 denote I / V conversion resistors 3,
4 is a differential amplifier for obtaining voltages V1 and V2 between terminals. Here, the gain is set to 1 for easy understanding of the description.

Reference numerals 62 and 63 denote negative feedback resistors having resistance values K.R1 and K.R2 which are K times R1 and R2, respectively, where K is a constant value.

Reference numerals 64 and 65 denote input resistances of set voltages S1 and S2 obtained by converting a current set value for the operational amplifier 1 into a voltage. Various methods are known for S1 and S2, such as a D / A converter or a constant voltage source output which is divided by a variable resistor.

As can be seen from FIG. 6, here, the operational amplifier 1 and the negative feedback resistors 62 and 63 also have a function of an arithmetic circuit for obtaining the current I.

The operation of FIG. 6 will be described below.
The current I flowing to the load is expressed as follows: I = V1 / R1 + V2 / R2 (51)

As is well known as the operation of the inverting amplifier, S1 / R11 + S2 / R12 = -V1 / (KR1) -V2 / (KR2) =-(1 / K) (V1 / R1 + V2 / R2) (52)

From (51) and (52), S1 / R11 + S2 / R12 = − (1 / K) · I (53)

When I is obtained from (53), I = −K · (S1 / R11 + S2 / R12) = − (K / R11) · S1- (K / R12) · S2 (54)

From (54), it is understood that the current I can be set over a wide range with high resolution by the current set values S1 and S2 if the respective resistance values are appropriately set. That is, (K / R1
If 1) or (K / R12) is reduced, the current setting resolution by S1 and S2 is increased.

In the example of FIG. 6, the I / V conversion resistance is R
The current range can be made wider by increasing the number to R3, R4,...

Similarly, in the example of FIG.
However, if the number of input resistors is increased and the set value input is increased to S3, S4,..., The set range can be further widened.

If an element that slowly switches on and off such as a diode is used as the sixth switching element, a current generator that does not generate output current fluctuations due to switching of the I / V conversion resistance is obtained. be able to.

In the example of FIG. 6, 42 and 43 are described as differential amplifiers. However, the position of the load 61 is on the output terminal side of the operational amplifier 1 and one of the I / V conversion resistors 3 and 4 is provided. If the terminal is located at a position to be connected to the ground, 42, 43
May not be required.

FIG. 10 shows an embodiment of the current generator according to claim 6, which is a combination of the operational amplifier 1 and the current / voltage conversion circuit of FIG.

However, two I / V conversion resistors, 3 and 4, are shown. That is, 3 and 4 are I / V conversion resistors having resistance values of R1 and R2, respectively, and the magnitude of the resistance value is R1> R2.

Reference numeral 61 denotes a load to which the current I is supplied. Reference numeral 6 denotes a switching element which conducts when both ends become equal to or higher than a predetermined voltage VZ. Although the switching element 6 is described here as a diode, a non-linear element such as a Zener diode or a varistor alone or a required number connected in series or parallel may be used. realizable. Alternatively, a transistor, a FET, or the like may be used, and an arithmetic circuit may be separately provided to control on / off thereof.

Reference numerals 42 and 43 denote I / V conversion resistors 3,
4 is a differential amplifier for obtaining voltages V1 and V2 between terminals. Here, the gain is set to 1 for easy understanding of the description. Here, when the current flowing through the I / V conversion resistor 3 exceeds the maximum current value I1MAX in that range, the output voltage of the differential amplifier 42 is set to be saturated at VZ1. For that purpose, if necessary, the differential amplifier 42
It is only necessary to add a limiter circuit.

Reference numerals 101 and 102 denote resistance values RF1 and RF1, respectively.
RF2 is a negative feedback resistor. Reference numerals 64 and 65 denote input resistances of set voltages S1 and S2 obtained by converting a current set value for the operational amplifier 1 into a voltage, respectively. Various methods are known for S1 and S2, such as a D / A converter or a constant voltage source output which is divided by a variable resistor.

As can be seen from FIG. 10, the operational amplifier 1 and the negative feedback resistors 101 and 102 also have a function of an arithmetic circuit for obtaining the current I.

The operation of FIG. 10 will be described below. When the current I is equal to or less than I1MAX, the switching element 6 is off, and V1 is represented by V1 = R1 · I (61). When the current I exceeds I1MAX, the switching element 6 is turned on, and V1 becomes V1 = VZ1 (62).

V2 is as follows: V2 = R2 · I (63)

As is well known as the operation of the inverting amplifier, the following holds: S1 / R11 + S2 / R12 = -V1 / RF1-V2 / RF2 (64)

When the current I is equal to or less than I1MAX (61),
When I is obtained by substituting (63) into (64), I =-(S1 / R11 + S2 / R12) / (R1 / RF1 + R2 / RF2) (65)

When the current I exceeds I1MAX, (6
2) When (63) is substituted into (64) to obtain I, I =-(S1 / R11 + S2 / R12 + VZ1 / RF1) / (R2 / RF2) (66)

From (65) and (66), it can be seen that the current I can be set over a wide range with high resolution by using the current set values S1 and S2 if the respective resistance values are appropriately set.

In the example of FIG. 10, the I / V conversion resistance is R
The current range can be made wider by increasing the number to R3, R4,...

In the example of FIG. 10, the setting input is S1, S
However, if the number of input resistors is increased and the set value input is increased to S3, S4,..., The set range can be further widened. Note that the number of I / V conversion resistors and the number of set value inputs need not be the same.

If a switching element such as a diode, which slowly switches on and off, such as a diode, is used as the switching element 6, a current generator that does not generate output current fluctuations due to switching of the I / V conversion resistor can be obtained. Can be.

[0119]

As described above, according to the first or second aspect of the present invention, the accuracy and resolution are high even with a current input having a large dynamic range and changing at a high speed, such as an alternating current or a pulse current. A current / voltage conversion circuit can be obtained.

According to the third aspect of the present invention, it is possible to obtain a current / voltage conversion circuit having low input impedance, high speed, high resolution, and high dynamic range.

Further, according to the fourth aspect of the present invention, the accuracy can be improved even with a current input having a large dynamic range and changing at a high speed, such as an alternating current or a pulse current, without using a current amplifier circuit for driving a large current. And high resolution, current /
A voltage conversion circuit can be obtained.

According to a fifth or sixth aspect of the present invention, there is provided a current generator having a high resolution and a wide current value setting range which does not cause output current fluctuation due to switching of an I / V conversion resistor. Obtainable.

[Brief description of the drawings]

FIG. 1 is an embodiment of a current / voltage conversion circuit using an operational amplifier.

FIG. 2 is a generally known current / voltage conversion circuit using an operational amplifier.

FIG. 3 is a generally known current / voltage conversion circuit with a range switching function using an operational amplifier.

FIG. 4 is an embodiment of a current / voltage conversion circuit in which an input current range is expanded by adding an I / V conversion resistor, a differential amplifier, and a switching element to the current / voltage conversion circuit of FIG. 1;

FIG. 5 is an embodiment of a current / voltage conversion circuit.

FIG. 6 is a current generator embodiment.

FIG. 7 is an example of a generally known current / voltage conversion circuit with a range switching function.

FIG. 8 is a circuit example of a generally known current generator.

FIG. 9 is an embodiment of a current / voltage conversion circuit.

FIG. 10 is a current generator embodiment.

[Description of Signs] 1, 21, 31 Operational amplifier 3, 4, 5, 22, 32, 33, 34, 41 I / V conversion resistor 6, 7, 45 Switching element 8, 9 Switching element control signal 2 Operation circuit 35 , 36, 37 Switch 42, 43, 44 Differential amplifier 61 Load 62, 63, 101, 102 Negative feedback resistance 64, 65 Operational amplifier input resistance

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H03F 1/34 G01R 15/08 A F-term (Reference) 2G025 BA08 2G035 AA01 AB01 AC01 AC02 AC15 AD04 AD08 AD10 AD20 AD45 AD47 AD54 AD65 5H410 BB05 CC02 DD02 EA12 EB37 FF05 GG03 JJ03 5J090 AA01 AA47 CA32 CA65 CA71 DN02 FA11 FA17 FA18 HA02 HA09 HA19 HA25 HA38 HA39 KA02 KA17 KA27 KA34 KA35 MA13 MN01 TA01

Claims (6)

[Claims] An I / V conversion resistor for current / voltage conversion is provided for a required number of ranges, a switching element is provided in series to an I / V conversion resistor other than the minimum range, and these are connected in parallel. I of the range one step smaller than the range
When a current equal to or more than the set value in the range flows through the / V conversion resistor, the switching element in the range is turned on,
By allowing the current to flow through the I / V conversion resistors in the range, the current flowing through the I / V conversion resistors is turned on / off according to the magnitude of the input current, and the voltage across both ends of each I / V conversion resistor is set. A current / voltage conversion circuit, wherein a current value is detected by calculating a current value in a calculation circuit. 2. I / V conversion resistors for current / voltage conversion are provided for a required number of ranges, switching elements are provided in parallel with I / V conversion resistors other than the maximum range, and these are connected in series. When a current equal to or greater than the set value in the range flows through the I / V conversion resistor in each range, the switching elements connected in parallel are turned on, and the current of the I / V conversion resistor in the range is bypassed, thereby reducing the input current. After the current flowing through the I / V conversion resistor is increased or decreased according to the magnitude, and the voltage at both ends of each I / V conversion resistor is detected by the differential amplifier,
A current / voltage conversion circuit, wherein a current value is detected by performing a calculation in a calculation circuit. 3. A current / voltage conversion circuit comprising a combination of the current / voltage conversion circuit according to claim 1 and an operational amplifier, wherein the current / voltage conversion circuit has a small input impedance and a wide dynamic range. 4. The dynamic range is extended by adding an I / V conversion resistor, a differential amplifier, and a switching element to the current / voltage conversion circuit of claim 3 without using a current amplification circuit for driving a large current. A current / voltage conversion circuit characterized by the above-mentioned. 5. A combination of a current / voltage conversion circuit, an operational amplifier, and a differential amplifier according to claim 1, which has high resolution and
A current generator having a wide current value setting range in which output current variation does not occur due to / V conversion resistance switching. 6. A wide current value setting range in which the current / voltage conversion circuit of claim 2 and an operational amplifier are combined to provide a high resolution and no output current fluctuation due to switching of the I / V conversion resistance. Characterized current generator.