JP2005167429A - Current/voltage conversion circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a current/voltage conversion circuit having a large dynamic range and exhibiting high accuracy and resolution even for a current varying at a high rate. <P>SOLUTION: In a circuit provided with a current bypass passage by proving I/V conversion resistors for current/voltage conversion in series in the order of resistance for required number of ranges such that each I/V conversion resistor can be turned on/off by a switching element, a current is bypassed for the I/V conversion resistor passing a current lower than a range when a current exceeding a set level in that range flows through that I/V conversion resistor and the current of the I/V conversion resistor lower than that range is brought to a rated level or below. Voltage across each I/V conversion resistor is detected by means of a differential amplifier and then operated through an operating circuit thus detecting the current level. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a current / voltage conversion circuit having a large dynamic range and capable of converting a current changing at high speed into a voltage with high accuracy.

  When measuring a physical quantity such as the magnitude of current or the amount of electricity or power related to the 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 depending on the magnitude of the target current have been measured by switching with a switching element such as a switch, a relay, or a semiconductor. This is generally referred to as range switching.

FIG. 2 shows a generally known current / voltage conversion circuit using an operational amplifier 1. When the resistance value of the I / V conversion resistor 3 is R, the output voltage V is V = −I · R with respect to the input current I.
become. Therefore, the input current I is I = −V / R
Is required. At this time, the voltage e between the input terminals of + and − is substantially 0 V while the operational amplifier 1 is linearly amplifying.

  FIG. 3 shows I / V conversion resistors 3, 4, and 5 having different values R 1, R 2, and R 3, respectively, so that the current / voltage conversion circuit shown in FIG. 2 can be switched according to the magnitude of the current to be measured. Switching is performed by switches 35, 36, and 37, relay contacts, or switching elements SW1, SW2, and SW3 made of a semiconductor or the like.

  FIG. 4 shows a current / voltage conversion circuit in which range switching can be performed according to the magnitude of the current to be measured without using an operational amplifier, as in FIG.

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 is V = I · R with respect to the input current I.
become. Therefore, the input current I is I = V / R
Is required.

  However, the range switching by the above switches, etc. is relatively slow and the current circuit is not opened even for a moment. Therefore, when switching the I / V conversion resistor, the I / V conversion resistor before switching and the I after switching are switched. Since it is necessary to overlap with the / V conversion resistor, there is a drawback that the control becomes complicated and an error occurs in the measured value during that time.

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

Further, although a method for solving these drawbacks is disclosed in Patent Document 1, there is a disadvantage that the power loss of the circuit is large.
JP 2002-098718 PR Japanese Patent Application No. 2002-039917

  The problem to be solved is to enable current / voltage conversion, such as AC and pulse current, which has a large dynamic range and high-speed current input with high accuracy and resolution and low circuit power loss. To do.

  In the current / voltage conversion circuit according to claim 1, I / V conversion resistors for current / voltage conversion are provided in series in the order of the resistance value for the number of necessary ranges with respect to the current input. In a circuit in which a switching element can be turned on / off between the / V conversion resistors and a current bypass path is provided, if a current equal to or higher than the set value in the range flows through the I / V conversion resistor of the range, By bypassing the current to the I / V conversion resistor of the range, the current of the I / V conversion resistor below the range is made zero or small, and the voltage across each I / V conversion resistor is detected by the differential amplifier After that, the current value is detected by calculating with an arithmetic circuit.

  A current / voltage conversion circuit according to claim 2 is characterized in that the current / voltage conversion circuit according to claim 1 and the operational amplifier for current / voltage conversion are combined to reduce input impedance and wide dynamic range. .

  According to a third aspect of the present invention, there is provided a current / voltage conversion circuit comprising a combination of the current / voltage conversion circuit of claim 2 and an operational amplifier for current / voltage conversion. A current booster that can drive a current of the size of the range instead of bypassing the current on and off, a diode at the output, and an operational amplifier and switch circuit with a voltage follower configuration at the input, It is characterized by facilitating the on / off control of the current, reducing the leakage current at the time of turning off, reducing the error, and reducing the power loss.

  The current / voltage conversion circuit according to claim 4 is the current / voltage conversion circuit according to claim 3, wherein the current / voltage characteristic is nonlinear between the input portion of the current booster and the output of the operational amplifier for current / voltage conversion. An element is provided to reduce the error by reducing the overshoot and undershoot of the operational amplifier for current / voltage conversion at the time of range switching.

  The current / voltage conversion circuit of the present invention does not open the current circuit, and does not require overlap control of the I / V conversion resistor. Therefore, there is an advantage that the dynamic range is large and the range can be switched at high speed. is there.

  Further, since an unnecessary I / V conversion resistor is bypassed, there is an advantage that power loss of the I / V conversion resistor or the switch circuit is small.

  We realized a large dynamic range current / voltage conversion circuit that has low power loss, low input impedance, high speed and low switching error, and can easily handle both current input and output directions.

FIG. 5 shows an embodiment of a current / voltage conversion circuit using claim 1 of the present invention.
3, 4, and 5 are I / V conversion resistors having resistance values R1, R2, and R3, respectively. The resistance values are R1>R2> R3, R1 is the minimum range, R2 is the middle range, and R3 is R3. Corresponds to the maximum range.
For the purpose of explanation, the full-scale current value of the minimum range is I1FS, the full-scale current value of the middle range is I2FS, and the full-scale current value of the maximum range is I3FS.

  Since the circuit of the present invention operates in exactly the same way with only positive and negative currents and voltages with different signs, the current and voltage values in the following description will be described as absolute values.

  6 is a switching element, which is turned on when I2 exceeds I1FS, and 7 is turned on when I exceeds I2FS. A switching element which conducts when both ends exceed a predetermined voltage. As a non-linear passive element such as a Zener diode or a varistor, or an active element that is controlled to be turned on and off from the outside, such as a transistor or FET, the on / off state may be controlled by an arithmetic circuit. FIG. 5 shows an example in which the control signals 11 and 12 output from the arithmetic circuit 2 are used for control.

  It should be noted that the current at switching on and off of the switching element is I1FS or I2FS for ease of explanation, but it may be set as required when applied to an actual system, for example, 110% of I1FS. It can be set to the value of.

  Reference numerals 8, 9, and 10 denote differential amplifiers for detecting voltages V1, V2, and V3 at both ends of each of the I / V conversion resistors 3, 4, and 5. Here, the voltage gain is 1 for easy understanding. And

  Reference numeral 2 denotes an arithmetic circuit for obtaining an input current value by calculation from the voltage values V1, V2, and V3 detected by the differential amplifiers 8, 9, and 10, and also performs on / off control of the switching elements 6 and 7.

The operation of FIG. 5 will be described below.
I is flowing in or out of the input terminal, the direction is arbitrary input current, I1 is current flowing in R1, I2 is current flowing in R2, I3 is current flowing in R3, I1X is current flowing in the switching element 6, and I2X Is a current flowing through the switching element 7.

  V1, V2, and V3 are output voltages with respect to the ground of the differential amplifiers 8, 9, and 10, respectively, and are voltages between the terminals of 3, 4, and 5, respectively.

  The switching element 6 is turned off when I is I1FS or less, turned on when I is I1FS or more, and the switching element 7 is turned off when I is I2FS or less, and turned on when I is I2FS or more.

When the above symbols are used, the current and voltage of each part have the following relationship.
I1 = V1 / R1 (1)
I2 = V2 / R2 (2)
I = V3 / R3 (3)
I = I2 + I2X (4)
I2 = I1 + I1X (5)

When I is equal to or less than I1FS, the switching elements 6 and 7 are turned off, so that I1X and I2X become 0. From (4) and (5), I = I1 (6)
From (1) and (6) I = V1 / R1 (7)
Therefore, the current value I can be obtained by the arithmetic circuit 2.

When I is greater than or equal to I1FS and less than or equal to I2FS, 6 is turned on and the current of 3 is bypassed to 0 or less than its full scale value. 7 is turned off, so I2X becomes 0. From (4), I = I2 (8)
From (2) and (8) I = V2 / R2 (9)
Therefore, the current value I can be obtained by the arithmetic circuit 2.

When I is greater than or equal to I2FS, the switching elements 6 and 7 are both turned on, so that the currents 3 and 4 are bypassed to 0 or less than each full-scale value.
Since the current I passes through 5 and is represented by (3), the current value I can be obtained by the arithmetic circuit 2.

  From the above, it can be seen that the magnitude of the current I can be obtained by the circuit of FIG. The arithmetic circuit 2 can be easily made using a generally known inverting adder circuit or comparator using an operational amplifier.

  Alternatively, an A / D converter or a voltage / frequency converter and a counter are incorporated in the arithmetic circuit, and the voltage output for each I / V conversion resistor is converted to a digital value, then (7), (9 ) And (3) can be calculated by software to determine the current I.

  In addition, the above-described operation in which the currents I1 and I2 flowing in 3 and 4 according to the magnitudes of V1 and V2, that is, the magnitudes of I1 and I2, are turned on and off automatically according to the input current I. This is equivalent to switching.

  Since this method does not require complicated control such as overlap control of I / V conversion resistors for range switching, high-speed operation is possible and there are few errors associated with range switching. As a result, current / voltage conversion can be performed with high accuracy and resolution even with current inputs that have a large dynamic range and change at high speed, such as alternating current and pulse current.

  In the embodiment shown in 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 configured.

  When active elements such as transistors 7 and FETs are used for 6 and 7, the magnitude relationship between I and I1FS and I2FS for controlling the arithmetic circuit 2 via the control signals 11 and 12 is determined by V2 and V3. This can be easily done by means such as comparing the voltage level and the reference voltage with a comparator.

  FIG. 6 shows an embodiment of a current / voltage conversion circuit using claim 1 relating to claim 2 of the present invention, wherein 1 is an operational amplifier for current / voltage conversion. The other circuit numbers are the same as those in the first embodiment, and the operations are also the same.

  e is a voltage between the negative input terminal and the positive input terminal of the operational amplifier 1 and is approximately 0 V in a region where the operational amplifier operates linearly. In the circuit of FIG. 6, the positive input terminal of the operational amplifier is connected to the ground. Therefore, in the linear operation region, the − input terminal is also 0V and e becomes 0V.

  Accordingly, in the circuit of FIG. 6, the negative input terminal of the operational amplifier 1 is always controlled to be 0. When the current value I is equal to or less than I1FS as in the operation of FIG. 5, the switching elements 6 and 7 are turned off. I is obtained in (7). When I is greater than or equal to I1FS and less than or equal to I2FS, 6 is turned on, and I is obtained in (9). When I is greater than or equal to I2FS, both switching elements 6 and 7 are turned on. , I is obtained in (3), so that the current value I can be obtained by the arithmetic circuit 2 as a whole.

  The feature of FIG. 6 is that, in addition to the automatic range switching function of the first embodiment, the input impedance becomes almost zero.

  Although there are three ranges in the embodiment of FIG. 6, if the number of I / V conversion resistors and switching elements is increased, a current / voltage conversion circuit having a multistage range can be configured.

FIG. 7 shows an embodiment of a current / voltage conversion circuit to which claim 2 relating to claim 3 of the present invention is applied. Reference numerals 13 and 14 denote current boosters having a sufficiently high input impedance. Is assumed to be 1, and the current can sufficiently drive the full-scale current of each range.
Reference numerals 15 and 16 represent operational amplifiers that are voltage follower circuits having a voltage gain of 1 and a high input impedance.

19 and 20 are for carrying the output voltage difference when the outputs of 15 and 16 are connected to the output of the operational amplifier 1 when 6 and 7 are turned on.
23 and 24 are elements having a non-linear voltage-current characteristic in which current is difficult to flow with high impedance when the voltage at both ends thereof is below a certain value, and current is easily flowed with low impedance when exceeding a certain voltage. Although a diode is shown in FIG. 7, other Zener diodes, varistors, or the like may be used as long as they have equivalent characteristics.
The other circuit numbers are the same as those in the second embodiment, and the operation is also the same.

The operation of FIG. 7 will be described below.
The switching element 6 is turned off when I is I1FS or less, turned on when I is I1FS or more, and the switching element 7 is turned off when I is I2FS or less, and turned on when I is I2FS or more.

  When I is equal to or less than I1FS, 15 is a voltage gain 1, so the output voltage is also V4 with respect to the input voltage V4. However, the switching element 6 is off and the input impedance of 13 is sufficiently high. V4. Here, since the voltage gain of 13 is 1, its output voltage V6 is also equal to V4.

  As a result, the voltage at both ends of 23 becomes V4, and the voltage V22 between both terminals of 23 becomes 0. Therefore, the current I1X has almost no leakage current affecting the accuracy, and becomes almost completely 0. The circuit is in an ideal off state.

  7 is also turned off, so that I2X is also set to 0 in the same manner as I1X, and the bypass circuit is also in an ideal off state.

  Therefore, since I passes through all 3, I can be obtained by the arithmetic circuit 2 using equation (7).

When I is greater than or equal to I1FS and less than or equal to I2FS, 6 is turned on, the input voltage V5 and the output voltage V6 of 13 are equal to the output voltage V0 of 1, and the voltage V22 between both terminals is V22 = V4−V0. (10)
Therefore, when this exceeds the voltage at which 23 is turned on, 23 is turned on, 13 drives the current I1X, and the current of 3 is bypassed to 0 or less than its full scale value.

7 is off, and I2X is an ideal 0 as in the case where I is equal to or less than I1FS.
At this time, since I passes through all 4, I can be obtained by the arithmetic circuit 2 using equation (9).

  When I is equal to or greater than I2FS, both switching elements 6 and 7 are turned on. Therefore, when I is equal to or greater than I1FS and equal to or less than I2FS, I1X and I2X flow in the same mechanism as when I1X flows as a bypass current. The currents 3 and 4 are bypassed to 0 or less than each full scale value.

  Since the current I passes through 5 and is obtained in (3), the current value I can be obtained by the arithmetic circuit 2.

From the above, it can be seen that the magnitude of the current I can be obtained by the circuit of FIG.
In addition, the above-described operation in which the currents I1 and I2 flowing in 3 and 4 according to the magnitudes of V1 and V2, that is, the magnitudes of I1 and I2, are turned on and off automatically according to the input current I. This is equivalent to switching.

  In the embodiment of FIG. 7, 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 configured.

  Since this method does not require complicated control such as overlap control of I / V conversion resistors for range switching, high-speed operation is possible and there are few errors associated with range switching. As a result, current / voltage conversion can be performed with high accuracy and resolution even with current inputs that have a large dynamic range and change at high speed, such as alternating current and pulse current.

  5 and 6, when the current to be bypassed is increased, an element having a large current capacity of 6 and 7 is required. However, the leakage current at the off time that causes measurement error must be small. Actually, it is often difficult to obtain such an element, but in the circuit of this embodiment, the switching elements 6 and 7 are for turning on and off the voltage, and it is not necessary to pass a current, and other elements are included. The main feature is that a circuit with a large current drive and a small leakage current can be easily configured with only elements that are generally easily available.

  Further, according to the circuit of FIG. 7, the power supplies of the current boosters 13 and 14 can be made independent of the other circuits. For example, the output of 14 is the minimum necessary to cover the voltage drop inside the current booster V3 and V32. It is also an advantage that the power loss can be reduced by using a limited voltage as a power source for the current booster.

  In the small current range, the circuit shown in FIG. 6 and FIG. 7 can be used in which the bypass circuit is turned on and off with a direct switching element as shown in FIG. 6 and the current booster as shown in FIG. 7 is used in the large current range. is there.

  Further, in order to achieve the target operation, for example, the positions of 6 and 19 and 7 and 20 are exchanged, and these are not necessarily the positions shown in FIG. 7, and various variations are conceivable.

FIG. 1 shows an embodiment of a current / voltage conversion circuit to which claim 3 relating to claim 4 of the present invention is applied.
In the circuit examples of FIGS. 6 and 7, overshoot or undershoot occurs in the output of the operational amplifier 1 when the switches 6 and 7 are turned on and off depending on the magnitude of the target current value, causing an error factor. However, the circuit example of FIG. 1 prevents this.

  In FIG. 1, 6 and 7 are switches for short-circuiting both ends of 19 and 20, respectively, and are ON / OFF controlled by the arithmetic circuit 2. 6 and 7 both turn on and off the voltage, and almost no current needs to flow, so a general analog switch for a small current is sufficient.

  19 and 20 are resistors having impedances sufficiently higher than the total impedance of 17 and 21, 18 and 22 so that the input voltages V5 and V8 of 13 and 14 are not affected when 6 and 7 are off.

  As in the second embodiment, e is the voltage between the negative input terminal and the positive input terminal of the operational amplifier 1 for current / voltage conversion, and is approximately 0 V in the region where the operational amplifier operates linearly. In the circuit of FIG. Since the + input terminal of 1 is connected to the ground, the output voltage V 0 of 1 is controlled so that the − input terminal is always 0 V in one linear operation region.

  21 and 22 are resistors for avoiding the direct connection between the output terminals 15 and 16 and the output terminal 1 through the low impedance states 17 and 18 when the switches 6 and 7 are turned on. In the following description, the resistance values R5 and R7 are assumed to be 0 for ease of understanding.

Reference numerals 17 and 18 are used to provide an output voltage V0 of 1 and input voltages V5 and V8 of 13 and 14 and potential differences V21 and V31 when the bypass circuit is in an ON state. In the following, it is an element having a non-linear current-voltage characteristic in which no current flows at high impedance, current flows at a low impedance above V21 and V31, and the voltage is constant at V21 and V31. In the figure, a zener diode is shown, but other nonlinear elements may be used as long as they have similar characteristics.
The other circuit numbers are the same as those in the third embodiment, and the operation is also the same.

The operation of FIG. 1 will be described below.
The switch 6 is turned on when I is I1FS or less, turned off when I is I1FS or more, and the switch 7 is turned on when I is I2FS or less, and is turned off when I is I2FS or more.

  When I is equal to or less than I1FS, I1X and I2X become 0 by the same circuit operation as in the third embodiment, and both bypass circuits are in an ideal off state. I can be obtained by the arithmetic circuit 2 using.

If I is greater than or equal to I1FS and less than or equal to I2FS, 6 is off and 7 is on. Since the change in I before and after 6 turns from on to off is minute and the difference can be ignored, the values of V2 and V3 are considered to be unchanged. When the output voltage of 1 when V is ON is V0 and the output voltage when OFF is V0X, V0 = V1 + V2 + V3 (11)
V0X = V21 + V22 + V2 + V3 (12)
become. When subtracting both sides of (11) and (12) and rearranging, V0X−V0 = V21 + V22−V1 (13)
become. The same applies when 6 is turned on from off.

Therefore, (13) indicates the magnitude of the change in the output voltage of the operational amplifier 1 when the switch 6 changes on and off. Where V21 is V21 = V1-V22
= R1 · I1FS-V22 (14)
If this is set, the output change of 1 becomes 0 and no overshoot or undershoot occurs in the current I, so that it is possible to eliminate the cause of error caused by these.

When I is equal to or greater than I2FS, both 6 and 7 are turned off. Since the change in I before and after 7 turns from on to off is minute and the difference can be ignored, the value of V3 is considered to be unchanged. When 6 is off and 7 is on, the output voltage of 1 is V0, and the output voltage when off is V0X. V0 = V21 + V22 + V2 + V3 (15)
V0X = V31 + V32 + V3 (16)
become. When subtracting both sides of (15) and (16) and rearranging, V0X−V0 = V31 + V32−V21−V22−V2 (17)
become. The same applies when 7 is turned on from off.

Therefore, (17) indicates the magnitude of the change in the output voltage of the operational amplifier 1 when the switch 7 changes on and off when the switch 6 is on. Here, V31 is V31 = V21 + V22 + V2-V32
= V21 + V22 + R2 / I2FS-V32 (18)
If this is set, the output change of 1 becomes 0, and no overshoot or undershoot occurs in the current I. Therefore, it is possible to prevent an error factor due to these.

  That is, according to the circuit of FIG. 1, it is possible to obtain a current / voltage conversion circuit that has a low input impedance and has few error factors due to current overshoot and undershoot at the time of range switching, and can perform automatic range switching at high speed.

  In order to achieve the desired operation, the switches 6 and 7 do not necessarily have to be in the positions shown in FIG. 1, such as being arranged in series between 21 and 17, 22 and 18, respectively. Can be considered.

  FIG. 8 shows an application example of the current / voltage conversion circuit of FIG. 7 to a current generator. 81 is an operational amplifier for feedback control, 82 is a control circuit for setting the magnitude of the output current and ON / OFF control of the switches 6 and 7, 83 is an input resistance to the -input terminal of 81, and 84 is a feedback resistance 85, 86 and 87 are switches for selecting which of the I / V conversion signals V1, V2 and V3 to use as feedback signals, and 88 is a control signal for selecting 85, 86 and 87 output from 82. 90 is a load.

  The other items are the same as in FIG. Here, for ease of explanation, the resistance values RS and RF of 83 and 84 are set to the same value.

  In FIG. 8, according to the magnitude of the current IL to be supplied to 90, when 85, 86 and 87 are turned on and the I / V conversion signal voltage VF of any optimum range is fed back to 84, the output at 82 is 81. It is generally well known that the output of 81 is controlled so that the set values VS and VF to be set have the same value with opposite polarities. That is, FIG. 8 shows that the present invention can be easily applied as a feedback signal detector in a feedback circuit.

In the same way
It can be easily applied to the negative feedback circuit described in detail. That is, the current / voltage conversion circuit of the present invention can be applied as a negative feedback signal detector of a large dynamic range current generator.

  A current / voltage conversion circuit with high accuracy and resolution and low power loss can be obtained even with current inputs that have a large dynamic range and change at high speed, such as alternating current and pulse current. It can be easily applied to the control field.

This is a current / voltage conversion circuit using an operational amplifier and a current booster. (Example 4) This is a generally known current / voltage conversion circuit using an operational amplifier. This is a generally known current / voltage conversion circuit with a range switching function using an operational amplifier. This is an example of a generally known current / voltage conversion circuit with a range switching function. This is a basic circuit of a current / voltage conversion circuit with a range switching function. (Example 1) It is a basic circuit of a current / voltage conversion circuit with a range switching function using an operational amplifier. (Example 2) It is a circuit example of a current / voltage conversion circuit with a range switching function using an operational amplifier and a current booster. Example 3 It is a circuit example of a current generator using a current / voltage conversion circuit with a range switching function. (Example 5)

Explanation of symbols

2 Arithmetic circuit
1, 15, 16, 81 Operational amplifiers 8, 9, 10 Differential amplifiers 13, 14 Current boosters 3, 4, 5 I / V conversion resistors 19, 20, 21, 22 Resistors 23, 24 Diodes 6, 7, 17, 18, 85, 86, 87 Switching element 11, 12, 88 Switching element control signal 35, 36, 37 Switch 82 Control circuit 83 Operational amplifier input resistance 84 Negative feedback resistance 90 Load

Claims (4)

  I / V conversion resistors for current / voltage conversion are provided in series in the order of the resistance value for the required number of ranges, and each I / V conversion resistor can be turned on and off with a switching element. In a circuit having a path, when a current equal to or greater than the set value in the range flows through the I / V conversion resistor of the range, the switching element of the bypass path of the range is turned on, and the I / V conversion resistance of the range or less is turned on. The current is reduced to 0 or smaller, the voltage across the I / V conversion resistors is detected with a differential amplifier, and then the current value is detected by calculating with an arithmetic circuit, resulting in a large dynamic range and high speed. A current / voltage conversion circuit characterized in that even a changing current can be accurately converted into a voltage.   The current / voltage conversion circuit according to claim 1 and an operational amplifier for current / voltage conversion are combined. The current has a large dynamic range, can be converted into a voltage with high accuracy, and has a small input impedance. / Voltage conversion circuit.   3. A current / voltage conversion circuit comprising a combination of the current / voltage conversion circuit of claim 2 and an operational amplifier for current / voltage conversion, wherein the switching element is turned on / off between the I / V conversion resistor and the I / V conversion resistor. Instead of bypassing the circuit, a bypass circuit is configured with a current booster that can drive a current in the range, a diode at the output, and an operational amplifier and switch with a voltage follower at the input. A current / voltage conversion circuit which can be easily turned on and off even by bypass, and has a small error by reducing a leakage current at the time of off.   4. The current / voltage conversion circuit according to claim 3, wherein an element having a non-linear current / voltage characteristic is provided between an input part of an operational amplifier for current / voltage conversion and a current booster, for current / voltage conversion at the time of range switching. A current / voltage conversion circuit characterized in that the overshoot and undershoot of the output of the operational amplifier are reduced to thereby reduce errors.

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