JP4800371B2 - Range switching circuit - Google Patents

Description

  The present invention relates to a current / voltage conversion circuit with a small measurement error due to a leakage current of a semiconductor switch and a bias current of an operational amplifier or a buffer amplifier.

  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 I / V conversion resistors having different resistance values depending on the magnitude of the target current are measured by switching with a switch, a relay, or a semiconductor switch. This is generally called range switching.

FIG. 23 shows a basic current / voltage conversion circuit in the case of two ranges as an example, and the range is switched by the semiconductor switches 23 and 25 with the I / V conversion resistors 3 and 4 in parallel.
In general, it is difficult to switch the range for currents that have a large dynamic range and change at high speed, and it is not practical when the current to be measured is small and the influence of the leakage current of the semiconductor switch causes an error. The circuit can be realized by a circuit in which countermeasures are taken in Patent Document 1, Patent Document 2, or Patent Document 3 that is the basic principle thereof.

FIG. 14 is a configuration diagram of a typical current / voltage conversion circuit disclosed in Patent Document 1 when the number of ranges is three. Ranges 1, 2, and 3 are set from the small current range, respectively. Range 1 is the minimum range.
I / V conversion resistors 3, 4, and 5 are for ranges 1, 2, and 3, respectively, and resistance values are R1, R2, and R3, which are connected in series, and current bypasses are provided to I / V conversion resistors other than range 1 Provide a circuit.
The current bypass circuit of the range 2 is switched to the terminal voltage on the I / V conversion resistor 4 side of the diode switch 6 when the drive signal of the current drive circuit 92 which is the output unit is turned off by the switch 91 in the range switching circuit 90. In some cases, the voltage is switched to the voltage output V1 side of the operational amplifier 1 as an error amplifier via the dead zone circuit 93, and the current drive circuit 92 drives the I / V conversion resistors 4 and 5 via the diode switch 6.
The same applies to range 3. Details of the operation are described in Patent Document 1.
Hereinafter, this is referred to as “resistance series current / voltage conversion circuit 1”.

FIG. 15 is a block diagram of the main current / voltage conversion circuit disclosed in Patent Document 2 when the number of ranges is three.
The I / V conversion resistors 3, 4 and 5 of each range are connected in series, and a current bypass circuit is provided for each I / V conversion resistor other than the minimum range.
The range 2 current bypass circuit converts the drive signal of the current drive circuit 104 in the range switching circuit 100 to the terminal voltage of the diode switch 6 on the I / V conversion resistor 4 side via the limit circuit 102 by the adder 103 and the dead band circuit 101. The I / V conversion resistors 4 and 5 are driven by the current drive circuit 104 via the diode switch 6 and the operation is performed for automatic range switching. It is to become.
The same applies to the current bypass circuit of range 3. Details of the operation are described in Patent Document 2.
Hereinafter, this is referred to as “resistance series current / voltage conversion circuit 2”.

  The resistor series current / voltage conversion circuit 1 and the resistor series current / voltage conversion circuit 2 are summarized as follows. When the range is off, both ends of the diode switch are set to the same potential to eliminate the leakage current, and when the range is on, the output signal of the operational amplifier is used. The current bypass circuit is driven, and FIG. 16 is a configuration diagram in which the current bypass circuit is collectively expressed when the number of ranges is two.

In addition, the current / voltage conversion circuit in Patent Document 3 directly bypasses the current to be measured at both ends of the I / V conversion resistor by a diode switch. The resistance series current / voltage conversion circuit 1 and the resistance series current / voltage conversion This is the basic principle of the circuit 2.
Hereinafter, these are collectively referred to as a “resistor series current / voltage conversion circuit”.

  Since it is disclosed in Patent Document 1, Patent Document 2, and Patent Document 3 that it can be easily expanded to 3 or more ranges by adding a range switching circuit similar to that in the case of the number of ranges 2. For the sake of clarity, in this document, the number of ranges is set to 2 or 3 except when necessary, the minimum range is set to range 1, range 2, and range 3, and the full-scale current values are set to I1FS, I2FS, and I3FS, respectively.

  In the region where the operational amplifier 1 as an error amplifier subjected to negative feedback operates linearly, when the non-inverting input terminal is connected to the ground (circuit operation reference potential) as shown in FIG. 16, the potential of the inverting input terminal is the input current I. Since the output voltage V1 is controlled so as to be always equal to the non-inverting input terminal potential regardless of the magnitude of the current input terminal voltage e, the current input terminal voltage e becomes substantially 0V. Hereinafter, in this document, e is treated as 0V for the sake of clarity.

  In FIG. 16, I / V conversion resistors 3 and 4 for converting current into voltage have resistance values R1 and R2, respectively, and their magnitudes are R1> R2, R1 corresponds to range 1, and R2 corresponds to range 2. And

The range switching circuit 80 drives a bypass circuit when the range 2 is on.
In this document, the direction of the bypass current is defined as a current discharge direction when traveling from the current drive circuit to the I / V conversion resistor, and a current suction direction when traveling from the I / V conversion resistor to the current drive circuit.

The range controller 81 generates a voltage output V21 like the graph of I-V21 shown in FIG. 16 from the output voltage V1 of the operational amplifier 1 and the lower end voltage V2 of R2.
The buffer amplifier 10 buffers the lower end voltage V2 of R2, and is provided as necessary.

The outline of the circuit operation of FIG. 16 is as follows.
The arithmetic circuit 2 performs A / D conversion of voltage signals, current calculation, range on / off control signal control, etc., and functions by combining hardware such as an operational amplifier, a differential amplifier, a comparator, and an A / D converter. There are many different implementation methods using known techniques such as realization of functions or a combination of these and a microcomputer system to realize functions by hardware and software. However, in the present invention, if necessary functions can be obtained, Since the method does not matter, it is indicated by an arithmetic circuit as a generic name. For the differential amplifier and hardware differential amplifier, the data after A / D conversion may be subtracted by software to obtain the difference.

  When the input current I is less than I1FS, the arithmetic circuit 2 turns off the range 2 on / off control signal, and the range control unit 81 sets the output voltage V21 of the current drive circuit 82 to the same value as the voltage V2 at the lower end of R2, so that the diode The potential difference between both ends of the switch 6 is 0V, and the diode switch is turned off and no current flows, so the current I21 becomes 0A.

Accordingly, the input current I flows through R1 and R2, and I = I1, and the arithmetic circuit 2 measures the voltage V1 at the lower end of R1,
I = V1 / (R1 + R2) (1)
The value of the input current I is obtained by the following calculation.

When the input current I exceeds I1FS, the arithmetic circuit 2 turns on the range 2 on / off control signal, and the operational amplifier 1
I = I1 + I21 (2)
The output voltage V1 is increased or decreased so that the output voltage of the current drive circuit 82 increases or decreases accordingly, the diode switch 6 is turned on, and the bypass current I21 is driven.
The arithmetic circuit 2 measures the voltage V2 at the lower end of R2 at that time,
I = V2 / R2 (3)
The value of the input current I is obtained by the following calculation.

  As described above, the diode switch 6 functions as a current on / off switch between the current drive circuit 82 and the lower end of R2. Here, the current drive circuit 82 is not a simple on / off switch operation, but has a major feature in that it operates as an amplifier having a broken input / output relationship. The analog switch cannot be turned on / off relatively. This is particularly advantageous when measuring a large current by switching the range.

However, in FIG. 16, when the number of ranges increases, if there is no buffer amplifier or buffer amplifier corresponding to the buffer amplifier 10, the connection point between the input current path and the arithmetic circuit 2 increases, and these bias currents are added to the input current to be measured. Therefore, when measuring a minute current, there are a drawback that it becomes a measurement error factor and a disadvantage that the circuit scale becomes large.
Japanese Patent Application No. 2003-400908 Japanese Patent Application No. 2006-147509 Japanese Patent Application 2000-268065

  The problem to be solved is to obtain a current / voltage conversion circuit with a small measurement error due to a leakage current of a semiconductor switch and a bias current of an operational amplifier or a buffer amplifier.

  A current / voltage conversion circuit according to claim 1 is provided with an operational amplifier for error amplification and an operational amplifier for I / V conversion using an I / V conversion resistor as a negative feedback resistor, and one of the current on / off semiconductor switches. Connect the terminal to the inverting input terminal of the operational amplifier for error amplification, connect the other terminal to the inverting input terminal of the operational amplifier for I / V conversion, and connect the non-inverting input terminal of the operational amplifier for I / V conversion. The output of the operational amplifier for error amplification or the ground can be selected by the semiconductor switch for range on / off, and the semiconductor switch for current on / off and / or the semiconductor switch for range on / off are turned on / off. By doing so, it is possible to control on / off of the current flowing through the I / V conversion resistor with less leakage current of the semiconductor switch, and the output voltage of the operational amplifier for I / V conversion and its non-inverting input Potential child voltage is characterized in that comprising a voltage proportional to the current flowing through the I / V conversion resistor.

  A current / voltage conversion circuit called a multiplexed current / voltage conversion circuit according to claim 2 is provided in parallel with the required number of ranges of circuits related to I / V conversion for each range of the current / voltage conversion circuit according to claim 1. By combining this with an operational amplifier for error amplification, it is possible to control on / off of any range with less leakage current of the semiconductor switch.

  The multiplexed current / voltage conversion circuit according to claim 3 is the multiplexed current / voltage conversion circuit according to claim 2, wherein the current on / off semiconductor switch and the inverting input terminal of the operational amplifier for I / V conversion are connected. If a greater effect is required by inserting a resistor, a dead band circuit is provided between the semiconductor switch for range on / off and the output terminal of the error amplification operational amplifier to widen the output voltage range of the error amplification operational amplifier. It is a feature.

(Erasure)

  The range switching circuit of the present invention reduces the measurement error caused by the leakage current of the semiconductor switch and the bias current of the buffer amplifier, etc., even for minute currents such as the nanoampere level and picoampere level, which have been difficult in the past. An effect that a voltage conversion circuit can be realized can be obtained.

First, definitions of terms used in this document are shown.
In this document, the unit of voltage is [V], the unit of current is [A], and the unit of resistance is [Ω]. For the sake of clarity, the description is omitted when the unit is clear in context. There is.
In addition, since the voltage and current of each part of the circuit differ only in the sign depending on the direction of the input current I and operate on the circuit in the same way as the positive and negative, the voltage and current values in the following description are positive or The absolute value will be used for explanation.

  In addition, there are cases where the symbol and the resistance value Rn are written side by side in the explanatory diagram regarding the resistance. In order to make it easy to understand, there is a case where the resistance is specified by the resistance value Rn instead of the sign when specifying the resistance within a range not causing misunderstanding.

  A circuit combining the I / V conversion operational amplifier using the I / V conversion resistor as a negative feedback resistor, a range on / off semiconductor switch, and a current on / off semiconductor switch according to claim 2 as the required number of ranges. A current / voltage conversion circuit that is provided in parallel and is combined with an operational amplifier to enable range switching is referred to as a “multiplexed current / voltage conversion circuit”.

FIG. 20 shows the input / output relationship of the dead zone circuit, and FIGS. 21 and 22 show examples of known dead zone circuits.
For the following explanation, the dead zone circuit when the absolute value of the dead zone set voltage is the same value is defined by the following equation.
Vout = db (Vin, Edb) (4)
Where Vin is the input voltage, Edb is the dead band setting voltage, Vout is the dead band output voltage,
When Vin <-Edb Vout = Vin + Edb
When −Edb ≦ Vin <+ Edb, Vout = 0
When + Edb ≦ Vin, Vout = Vin−Edb
And

  As is clear from the above description, since the dead zone circuit is turned on / off at the magnitude of its input voltage, an external on / off control signal is unnecessary, and the dead zone circuit is not included in the switch circuit in each drawing of this document. When applied, there is no on / off control signal.

FIG. 24 shows an example of voltage-current characteristics of a general diode. When the forward voltage VF is several hundred mV or less, the current is almost 0 A, and when the forward voltage VF is more than that, the current increases rapidly. The diode is turned on.
FIG. 25 shows an example of voltage-current characteristics of a diode switch connected in both directions in parallel. The switch characteristics shown in FIG.

In the present invention, the current switch characteristic of the diode is used.
There are diode-connected transistors, diode-connected FETs, varistors, Zener diodes, etc. as elements having such a voltage-current characteristic equivalent to diodes. It is indicated by “switch” and is indicated by a diode symbol in the drawing.

  As is clear from the above description, since the “diode switch” is turned on / off at the magnitude of the voltage at both terminals, an on / off control signal from the outside is not necessary, and the switch in each drawing of this document When a “diode switch” is applied to the circuit, there is no on / off control signal.

In this document, field effect transistors (hereinafter referred to as FETs) and photo MOS relays can be used as switching elements in addition to these diode switches, and these are collectively referred to as “FET switches”.
In addition, there is a general analog switch as an on / off switch for an analog circuit, and it can be used as a switch in the present invention in many cases.
Accordingly, it is sufficient that the circuit has only a switching function. When any of a diode switch, FET switch, and general analog switch can be used, it is generically called “semiconductor switch”.

Also, in this document, when parts and circuit blocks are the same in the drawings, they are indicated by the same reference numerals or the same reference numerals with suffixes such as A, B, etc. The description will not be repeated.
Further, the embodiments described below are merely “examples”, and various variations derived from combinations, applications, derivations, and analogies can be easily considered as methods for realizing equivalent functions. They are all within the scope of the present invention as long as they are based on the principle.
Based on the above, the best mode for carrying out the invention will be described below as an example.

FIG. 2 is an example of a basic circuit with a range number of 1 for a multiplexed current / voltage conversion circuit according to claim 1 of the present invention, and the range is called a range 1.
The current on / off semiconductor switch 23 is on / off controlled by a range on / off control signal that is an output of the arithmetic circuit 2, and is input to an analog switch, a photo mos relay, an FET, a transistor, a diode switch, a mechanical relay, or the like. A general switching element may be used as long as the current can be turned on / off.

The resistor 14 and the switch 15 are for preventing the output from being saturated when the negative feedback loop of the operational amplifier 1 is opened when the range 1 is off. When the range 1 is off, the switch 15 is turned on to resist the input current I. 14, the operational amplifier 1 is normally negatively fed back, and if any other range is added and any range is always turned on, the resistor 14 and the switch 15 may be omitted. When the number of ranges is 1, the switch 15 is turned off when the range 1 is on.
As a result, the output voltage V0 of the operational amplifier 1 is controlled so that its inverting input terminal is always 0V regardless of the magnitude of the input current I. This is assumed in the following explanation.
Since the operation of the resistor 14 and the switch 15 is not directly related to the original current / voltage conversion function, it is omitted in the description here.

The range ON / OFF switch circuit 120 is ON / OFF controlled by a range ON / OFF control signal that is an output of the arithmetic circuit 2, and is an analog signal such as an analog switch, a photo mos relay, an FET, a transistor, a diode switch, or a mechanical relay. As long as it can be turned on / off, a general switching element may be used.
The resistor 33 pulls down the non-inverting input terminal of the operational amplifier 12 to the ground when the switch circuit 120 is off.

FIG. 17 shows another circuit example of the switch circuit 120, in which 121 is a known dead band circuit and 122 is an inverting amplifier.
In this example, the resistance values of the resistors in the circuit of FIG. 17 are all equal, and accordingly, the gains of all the inverting amplifiers are −1.
When the on / off control signal connected to Vcont is set to 0V, the input Vin is output to Vout as it is.
When the on / off control signal is set to a voltage Vdis that is larger than the maximum value expected of Vin and is input to Vcont, it acts as a deadband setting voltage of the deadband circuit 121 and Vout becomes 0V.
From the above, it can be seen that FIG. 17 performs a switch operation that is on / off controlled by the voltage of Vcont. According to this switch, the switch operation becomes gentle, and there is an effect that the spike noise of each operational amplifier output due to the fact that the response of the negative feedback circuit cannot follow is reduced.
Note that Vdis may be a constant value (fixed value), and it is an advantage that compatibility with a comparator, an inverter, or the like is good.

An I / V conversion resistor 3 in FIG. 2 is an I / V conversion resistor having a resistance value R1, and constitutes an I / V conversion circuit together with the operational amplifier 12.
The buffer amplifier 10 is for buffering the non-inverting input terminal voltage of the operational amplifier 12 for I / V conversion and passing it to the arithmetic circuit 2, and is provided as necessary in view of the input impedance of the connection destination, not essential. Just do it.

The circuit operation of FIG. 2 will be described below.
The operational amplifier 12 for I / V conversion controls the output voltage V11 so that the potential of the inverting input terminal becomes equal to the non-inverting input terminal potential V12 by the negative feedback operation.
Accordingly, when the range on / off switch circuit 120 and the current on / off semiconductor switch 23 are turned off, V12 is pulled down to the ground by the resistor 33 and becomes 0V, and the inverting input terminal potential is also 0V. Here, since the potential of the inverting input terminal of the operational amplifier 1 is controlled to be always 0V, as a result, the voltage between both terminals of the current on / off semiconductor switch 23 is 0V and the leakage current is extremely small. The current flowing through the I / V conversion resistor 3 is 0 A, that is, the range 1 is turned off.

When the range on / off switch circuit 120 and the current on / off semiconductor switch 23 are turned on, V12 becomes a voltage V12 obtained by subtracting the voltage drop of the switch circuit 120 from V0, and the inversion of the operational amplifier 12 for I / V conversion. The potential at the input terminal is also the same potential.
As a result, the potential difference between both ends of the current on / off semiconductor switch 23 becomes V12, and the input current I is driven via the I / V conversion resistor 3 by the operational amplifier 12 for I / V conversion. become.

At this time, the current value I flowing through the I / V conversion resistor 3 can be obtained by dividing the potential difference between both ends by R1, but the inverting input terminal potential and the non-inverting input terminal potential V12 of the operational amplifier 12 for I / V conversion are Therefore, the current value I is obtained by calculating the potential difference V1 by the arithmetic circuit 2 using the output V11 and the non-inverting input terminal potential V12 and dividing by the R1. That is,
I = (V11−V12) / R1
= V1 / R1 (5)
become.

The feature of this circuit is that current ON / OFF control is possible, and the potential difference V1 between the output voltage of the operational amplifier 12 for I / V conversion and the non-inverting input terminal voltage is the current value flowing through the I / V conversion resistor 3. Since there is no need to connect a circuit element requiring a bias current, such as a buffer amplifier or an arithmetic circuit, in addition to the current on / off semiconductor switch 23 to the path of the input current I, the measurement error caused by them is reduced. It does not occur.
In other words, this current / voltage conversion circuit is effective not only for range switching for a large current but also for a relatively small current.

FIG. 3 shows another basic circuit example of the number of ranges 1 of the multiplexed current / voltage conversion circuit according to claim 1 of the present invention.
This is obtained by replacing the current on / off semiconductor switch 23 of FIG. 2 with the diode switch 6 and the range switching operation is the same as that of the first embodiment, and therefore the description thereof is omitted.
When the range on / off switch circuit 120 is turned off, V12 becomes 0 V, the potential across the diode switch also becomes 0 V, and there is an advantage that the leakage current is reduced and the on / off control becomes unnecessary.

FIG. 4 shows still another basic circuit example of the number of ranges 1 for the multiplexed current / voltage conversion circuit according to claim 1 of the present invention.
The difference from the output of the operational amplifier 12 for current / voltage conversion is taken with the output of the error amplifier 1 as a reference.
Since the range switching operation is the same as that of the first embodiment, description thereof is omitted.

When the range ON / OFF switch circuit 120 is ON, if the ON resistance value is sufficiently smaller than the resistance value R2 of the resistor 33 and can be ignored, V0≈V12. Therefore, in this circuit, the current value can be obtained by the equation (5). Can do.
This has the advantage that the number of circuits can be reduced because only one buffer amplifier 10 is required even if the number of ranges increases.

FIG. 5 shows still another embodiment of the range number 1 of the basic circuit of the multiplexed current / voltage conversion circuit according to claim 1 of the present invention.
The difference between the output V11 of the operational amplifier 12 for current / voltage conversion and the non-inverting input terminal potential V12 in FIG. 2 is stopped, and the current value I is directly calculated by V11.
Since the range switching operation is the same as that of the first embodiment, description thereof is omitted.

When the on / off semiconductor switch 23 has a sufficiently small on-resistance like the FET switch and the voltage drop due to the input current I becomes almost 0V, the inverting input terminal potential V12 of the operational amplifier 12 for current / voltage conversion is 0V. Can be considered
I = (V11−V12) / R1
≒ V11 / R1 (6)
Thus, the current value I can be directly calculated from the output voltage V11.
This has the advantage of reducing the circuit.

FIG. 6 is a circuit example of a current / voltage conversion circuit according to claim 1 of the present invention.
The circuit is the same as that shown in FIG. 3, but current / voltage conversion circuits are provided for discharging current and for sucking current, respectively.
Since the range switching operation is the same as that of the first embodiment, description thereof is omitted.
The input current value I is the same as in Example 1. I = V1P / R1 + V1N / R1 (7)
Is required.
Normally, since either one of the diode switches 6 and 6A is turned off, at least one of V1P and V1N in the equation (7) becomes 0V.

The switch circuit 130 for range ON / OFF enables reverse bias voltage application to the diode switches 6 and 6A when OFF, and is ON / OFF controlled by a range ON / OFF control signal that is an output of the arithmetic circuit 2. As long as analog signals such as analog switches, photo moss relays, FETs, transistors, mechanical relays can be turned on / off, general switch elements may be used, and a constant voltage source for setting a reverse bias voltage may be used.
As a reference example, another circuit example of the switch circuit 130 is shown in FIG.

  When it is desired to apply a reverse bias voltage to prevent leakage current due to an offset voltage in the peripheral circuits of the diode switches 6 and 6A, the reverse bias voltages −E1 and + E2 that can cancel the maximum offset voltage that is expected are set in the switch circuit 130. When the switch circuit 130 is off, the reverse bias voltage is applied to the non-inverting input terminals of the I / V conversion operational amplifiers 12 and 12A, and the inverting input terminals are also controlled to have the same potential. As a result, the diode switch 6 , 6A will be reverse biased to the required voltage.

It is not necessary to connect a circuit element that requires a bias current to the signal current path, and the reverse bias voltage can be applied with a simple circuit to prevent leakage current due to the offset voltage of the diode switch peripheral circuit. It is an advantage.
The above circuit can also be applied to a resistance series current / voltage conversion circuit, and FIG. 1 shows an example thereof.

FIG. 7 is a circuit example of a multiplexed current / voltage conversion circuit according to claim 2 of the present invention.
This circuit is an extension of the circuit of FIG. Similarly, it can be expanded to any number of ranges.
The range switching operation is the same as in FIG.
The input current I is obtained by the sum of the current values of each range. In this example, I = V1 / R1 + V2 / R2 (8)
It is.
When only one of the ranges is turned on, the range to be turned off among V1 and V2 in equation (8) is 0V.

The resistor 14 and the switch 15 are for preventing the output of the negative feedback loop of the operational amplifier 1 from being opened and saturating the output when both the range 1 and the range 2 are turned off.
The input protection circuit 16 is a protection circuit for bypassing an excessive input or a current input when the entire range is off, and is not essential because it does not relate to the measurement function.

Each range can be arbitrarily turned on / off by the arithmetic circuit 2 using the range on / off control signal. Therefore, the current is automatically calculated using the current values obtained from the V / V or V1, V2 I / V conversion signals. You can change the range.
As an example, the flowchart of FIG. 30 and FIG. 31 shows the procedure of range switching when shifting to the upper range at 110% FS (full scale) when the input current increases and shifting to the lower range at 9% FS when the input current decreases.
FIG. 30 shows a case in which an overlap time for turning on both ranges at the time of range switching is provided. FIG. 31 shows a case in which the overlap time is not required.

  The feature of this circuit is that it is easy to extend the number of ranges and easily turn on / off any range, and it is not necessary to connect a circuit element that requires a bias current to the path of the input current. .

FIG. 8 is another circuit example of the multiplexed current / voltage conversion circuit according to claim 2 of the present invention, in which an I / V conversion resistor 17 having a resistance value R0 is added to the current / voltage conversion circuit of FIG. .
One range can be easily added by directly connecting the I / V conversion resistor 17 to the operational amplifier 1, and the current value of the range can be obtained by V0 / R0.
The range switching operation is the same as in FIG.

FIG. 9 is still another circuit example of the multiplexed current / voltage conversion circuit according to claim 2 of the present invention, and the multiplexed current / voltage conversion circuit in the case where a difference is obtained for each range based on the output of the error amplifier 1. This is an example.
Since the range switching operation is the same as that of the sixth embodiment, the description of the operation is omitted.
When the ON resistance value of the range ON / OFF switch circuit 120 is sufficiently smaller than the resistance value R3 of the resistor 33 and can be ignored, V0≈V12, and the ON resistance value of the range ON / OFF switch circuit 120A is the resistance value R4 of the resistor 34. If it is much smaller and can be ignored, V0≈V22, so the current value can also be obtained from this equation using equation (8).

FIG. 10 shows still another circuit example of the multiplexed current / voltage conversion circuit according to claim 2 of the present invention, which is an embodiment of the multiplexed current / voltage conversion circuit in which the difference calculation is unnecessary.
When the current on / off semiconductor switch 23 has a sufficiently small on-resistance like the FET switch and the voltage drop due to the current I1 becomes almost 0V, the inverting input terminal potential of the operational amplifier 12 for current / voltage conversion is V12≈0V. When the current on / off semiconductor switch 25 has a sufficiently small on-resistance like the FET switch and the voltage drop due to the current I2 becomes almost 0 V, the potential of the inverting input terminal of the operational amplifier 13 for current / voltage conversion Can be regarded as V22≈0V, so that the output voltage of the operational amplifier 12 is V11 and the output voltage of the operational amplifier 13 is V21. I = (V11−V12) / R1 + (V21−V22) / R2
= V11 / R1 + V21 / R2 (9)
Can directly calculate the current value I, which has the advantage of reducing the number of circuits.
When only one of the ranges is turned on, the range to be turned off among V11 and V21 in equation (9) is 0V.

FIG. 11 is a circuit example of a multiplexed current / voltage conversion circuit according to claim 3 of the present invention. In the circuit of FIG. 7, diode switches 6 and 7 are used as current on / off switches, and resistance values R11 and R21 are set. In this case, resistors 18 and 19 are inserted, and no dead zone circuit is provided between the operational amplifier 1 and the switch circuits 120 and 120A.
The relationship between the input current I and the output voltage V0 of the operational amplifier 1 in the case of sequentially turning on only one range without R11 and R21 is as shown in FIG. 26, and the maximum value of V0. Is almost the same as the voltage across the diode switches 6 and 7 and is non-linear and highly temperature-dependent, with a maximum variation of typically ± 0.8 to 1.2 V, and the output voltage V0 of the operational amplifier 1 is switched over. It is difficult to set the calculation condition as follows.
However, FIG. 26 shows a case where the number of ranges is expanded to n.

On the other hand, when resistors R11 and R21 are inserted as shown in FIG. 11 and a dead zone circuit is not provided between the operational amplifier 1 and the switch circuits 120 and 120A, only one of the ranges is turned on in order from the minimum range. In this case, the relationship between the input current I and the output voltage V0 of the operational amplifier 1 is as shown in FIG. However, FIG. 27 shows a case where the number of ranges is expanded to n.
When only range 1 is on, the inverting input terminal potential V12 of the I / V conversion operational amplifier 12 is equal to the non-inverting input terminal potential and thus becomes V0. Therefore, when the voltage between both terminals of the diode switch is VF1,
V0 = V12
= VF1 + R11 · I (10)
If R11 is set appropriately and VF1 is made relatively small with respect to R11 · I, the relationship between V0 and input current I becomes a stable proportional relationship, and the same applies to other ranges, so V0 is calculated. It is a feature and an advantage that it can be used for the calculation conditions of the circuit 2.
The above operation is exactly the same even if the positions of the diode switches 6 and R11 or the diode switches 7 and R21 are exchanged.

FIG. 12 shows another circuit example of the multiplexed current / voltage conversion circuit according to claim 3 of the present invention. The operational amplifier 1 and the non-inverting input terminals of the I / V conversion operational amplifiers 12 and 13 in the circuit of FIG. it is provided with a switch circuit 140,140A having an insensitive zone between. FIG. 19 shows an example of switch circuits 140 and 140A.
In FIG. 19, 141 is a known dead band circuit, 143 and 144 are constant voltage sources for the dead band setting voltage, and 142 is an inverting amplifier.

The dead band setting voltages + Edb, -Edb of the dead band circuit 141 are set by the constant voltage sources 143, 144.
In this example, the resistance values of the resistors in the circuit are all equal, and accordingly, the gains of all the inverting amplifiers are -1.

The inverting amplifier 142 inverts the range on / off disable control input Vcont.
As a result, the range on / off disable control input Vcont is added to the dead band setting voltage of the dead band circuit 141, and the set voltage can be changed by Vcont.
Here, when Vcont is set to 0 V, the dead zone circuit 141 is not affected, and the switch circuit is enabled.

When the voltage Vdis is set to a voltage Vdis larger than expected (Vin−Edb), the output of the dead band circuit 141 becomes 0V, and the switch circuit is disabled.
140 circuit function Vout = db (Vin, Edb, Vcont) (11)
It shall be indicated by
However, when Vcont = 0V, use the equation (4). Vout = db (Vin, Edb) (12)
When Vcont ≧ Vdis,
Vout = 0V (13)
And

  Here, the dead band setting voltage Edb1 of the minimum range 1 of FIG. 12 is set to 0V, and the dead band setting voltage of the range 2 is Edb2 in which the input current when the range 1 is on is equal to the value of V0 when the full scale value I1FS is increased. The dead band setting voltage is set to be equal to V0 when the input current when the range is turned on, which is one range smaller, becomes a full scale value.

In this case, if there is no R11, R21, the dead band setting voltage Edb2 of range 2 may be set to the maximum value VF1 of the potential difference between both ends of the diode switch 6.
Similarly, after range 3, Edb3 = Edb2 + VF2 (14)
:
The relationship between the input current I and the output voltage V0 of the operational amplifier 1 when sequentially turning on from the minimum range assuming that only one of the ranges is turned on under the conditions is as shown in FIG. The change width is almost the voltage across the diode switch, is nonlinear and has high temperature dependence, and usually has a large variation of ± 0.8 to 1.2 V at the maximum, making it difficult to make V0 a calculation condition such as range switching. It is.
However, FIG. 28 shows a case where the number of ranges is expanded to n.

On the other hand, when resistors R11 and R21 are inserted as shown in FIG. 12 and a dead zone circuit is provided in the switch circuits 140 and 140A, the dead zone set voltage is set according to the above principle.
Edb1 = 0V (15)
Edb2 = Edb1 + R11 · I1FS + VF1 (16)
Edb3 = Edb2 + R21 · I2FS + VF2 (17)
:
It becomes. At this time, when only one of the ranges is turned on, the relationship between the input current I and the output voltage V0 of the operational amplifier 1 when sequentially turning on from the minimum range is a polygonal monotonically increasing relationship as shown in FIG. .
However, FIG. 29 shows a case where the number of ranges is expanded to n.

When only range 1 is on, the inverting input terminal potential of the operational amplifier 12 for I / V conversion is equal to the non-inverting input terminal potential V12, so that the potential difference across the diode switch 6 is VF1.
V0 = V12 + Edb1
= VF1 + R11 · I + Edb1 (18)
If R11 is set appropriately and VF1 is made relatively small relative to R11 · I, the relationship between V0 and input current I becomes a stable proportional relationship with Edb1 as an offset, and the same applies to other ranges. Therefore, V0 can be used as a calculation condition of the calculation circuit 2 and is advantageous.

FIG. 13 is a circuit example of another current / voltage conversion circuit according to the present invention, which is a combination of a multiplexed current / voltage conversion circuit and a resistor series current / voltage conversion circuit.
The resistor 3 is an I / V conversion resistor for a range 1 having a resistance value R1, the resistor 153 is an I / V conversion resistor for a range 2 having a resistance value R2, and the resistor 154 is an I / V conversion resistor for a range 3 having a resistance value R3. / V conversion resistor, range 1 is a multiplexed current / voltage conversion circuit according to claim 2, and range 2 and range 3 are configured by a known resistance series current / voltage conversion circuit 150.

When the potential difference of the I / V conversion resistance of the resistance series current / voltage conversion circuit 150 is obtained, the comparison reference potential is normally the potential of the inverting input terminal of the operational amplifier 152, but in this circuit example, it is the same potential. By inputting to the arithmetic circuit 2 from the non-inverting input terminal via the buffer amplifier 151, the measurement accuracy deterioration due to the bias current of the buffer amplifier 151 is eliminated.
On / off control of each range is performed by controlling the range 1 on / off control signal, the range 2, 3 on / off control signal, and the range 3 on / off control signal by the arithmetic circuit 2.
The diode switches 6 and 7 may be FET switches.

The operations of the multiplexed current / voltage conversion circuit and the resistor series current / voltage conversion circuit are as described above. The outline of the circuit operation when combining them will be described below.
When using this circuit, it is assumed that both the switch circuits 120 and 120A are controlled so that there is no period during which the negative feedback loop of the operational amplifier 1 is not opened.

The output of the operational amplifier 152 is controlled so that the potential of the inverting input terminal becomes equal to the non-inverting input terminal to which the output voltage of the switch circuit 120A is applied.
Therefore, when the range 2, 3 on / off control signal is off, the potential of the non-inverting input terminal of the operational amplifier 152 is 0V, the inverting input terminal is also 0V, and the voltage between both terminals of the diode switch 7 is also 0V. The series current / voltage conversion circuit 150 is turned off.

When the range 2, 3 on / off control signal is turned on, the right terminal potential of the diode switch 7 becomes a value obtained by subtracting the voltage between both terminals of the switch 120A from V0, and the resistance series current / voltage conversion circuit 150 is turned on. If the range 3 on / off control signal is off, range 2 is valid, and if it is on, range 3 is valid.
Either one of range 1 and range 2 or range 3 may be turned on or both, and current value I is I = V1 / R1 + V2 / (R2 + R3) when range 3 is off (19)
When range 3 is on, I = V1 / R1 + V3 / R3 (20)
It can be obtained by the operation of

In this circuit, when the range 2, 3 on / off control signal is turned off, the resistance series current / voltage conversion circuit 150 is turned off and disconnected from the range 1 by the diode switch 7, so that the buffer amplifier on the resistance series current / voltage conversion circuit 150 side. In addition, there is an advantage that an error factor caused by a bias current of an element used in the arithmetic circuit 2 does not easily affect the range 1 side which is a small current range.
Note that the number of ranges can be arbitrarily increased with the same configuration as in this circuit example.

  As described above, the small current range in which the influence on the measured value of the bias current of the buffer amplifier or the arithmetic circuit cannot be ignored is constituted by the multiplexed current / voltage conversion circuit according to claim 2 or 3, and the other ranges are not. By configuring with a known resistor series current / voltage conversion circuit, current / voltage that can be controlled on / off in any range with a relatively small number of ranges and high accuracy with little influence from leakage current and bias current of the elements used. Obtaining a conversion circuit is a feature and advantage of this circuit example.

  According to the multiplexed current / voltage conversion circuit of the present invention, it is possible to obtain a current / voltage conversion circuit with a small measurement error due to a leakage current of a semiconductor switch and a bias current of an operational amplifier or a buffer amplifier.

It is an Example of a resistance series current / voltage conversion circuit which has a current drive circuit with a reverse bias. 2 is a basic circuit example of a multiplexed current / voltage conversion circuit according to the present invention. 1 is a basic circuit of a multiplexed current / voltage conversion circuit using a diode switch of the present invention. This is a basic circuit of a multiplexed current / voltage conversion circuit in the case where the difference from the output of the operational amplifier for current / voltage conversion is taken with reference to the output of the error amplifier. This is a basic circuit of a multiplexed current / voltage conversion circuit when the output of the operational amplifier for current / voltage conversion is directly used as a current detection signal. It is an example of a basic circuit of a multiplexed current / voltage conversion circuit capable of applying a reverse bias voltage to the diode switch of the present invention. 2 is an example of a multiplexed current / voltage conversion circuit of the present invention. It is an example of a multiplexed current / voltage conversion circuit in which an I / V conversion resistor R0 is connected to the operational amplifier for error amplification of the present invention. It is an example of a multiplexed current / voltage conversion circuit when a difference is taken for each range with reference to the output of the error amplifier of the present invention. It is an example of a multiplexed current / voltage conversion circuit that does not require differential calculation according to the present invention. It is an example of a multiplexed current / voltage conversion circuit in which a resistor is connected to the diode switch of the present invention. It is an example of the multiplexed current / voltage conversion circuit using the series resistance of the diode switch of this invention, and a dead zone circuit. It is an example of the current / voltage conversion circuit which combined the multiplexed current / voltage conversion circuit of this invention, and the resistance series current / voltage conversion circuit. It is a block diagram of the resistance series current / voltage conversion circuit 1 using the disclosed switch. It is a block diagram of the resistance series current / voltage conversion circuit 2 using the disclosed dead zone circuit and limit circuit. It is the block diagram which expressed collectively the resistance series current / voltage conversion circuit 1 and resistance series current / voltage conversion circuit 2 which were already disclosed. It is an example of a circuit of the switch part of a range switching circuit. It is an example of a reverse bias application circuit. It is an example of a switch circuit. It is an input-output characteristic figure of a dead zone circuit. It is an example of a dead zone circuit by a Zener diode. It is an example of a known dead zone circuit. This is a known range / switchable current / voltage conversion circuit. It is the schematic of the voltage-current characteristic of a general diode. It is an example of the voltage-current characteristic of the diode switch connected bidirectionally in parallel. It is an input current-operation amplifier output voltage relationship diagram at the time of ON control for only one range of a multiplexed current / voltage conversion circuit using a range switching circuit without resistance and dead band. It is an input current-operation amplifier output voltage relationship diagram at the time of ON control for only one range of a multiplexed current / voltage conversion circuit using a range switching circuit with resistance and no dead zone. It is an input current-operation amplifier output voltage relationship diagram at the time of ON control for only one range of a multiplexed current / voltage conversion circuit using a range switching circuit with no resistance and a dead zone. It is an input current-operation amplifier output voltage relationship diagram at the time of ON control for only one range of a multiplexed current / voltage conversion circuit using a range switching circuit with a resistance and dead band. It is a flowchart of the example of a range switching control procedure in consideration of the range on delay time. It is a flowchart of the example of a range switch control procedure which does not consider range on delay time.

1, 12, 12A, 13 operational amplifier 2 arithmetic circuit 3, 3A, 4, 5, 17, 153, 154 I / V conversion resistor 6, 6A, 7 Diode switch 8, 9, 10, 10A, 11, 151, 152 Buffer amplifier 14, 18, 19, 33, 33A, 34 Resistor 15, 91, 91A Switch 16 Input protection circuit 20, 20A, 21, 22 Differential amplifier 23, 24, 25, 26 Semiconductor switch 27, 28 Inverter 52, 53 82, 92, 92A, 104, 104A Current drive circuit 50, 80, 90, 90A, 100, 100A Range switching circuit 51, 81 Range control unit 32, 54, 55 Current booster 56, 57, 131, 132, 143, 144 Constant voltage source 93, 93A, 101, 101A, 121, 141 Dead band circuit 102, 102A Limit times 103,103A adder 122,133,142 inverting amplifier 120,120A, 130,140,140A switch circuit
150 resistance series current / voltage conversion circuit

Claims (3)

  A second operational amplifier having a first operational amplifier capable of performing an error amplification operation and capable of performing I / V conversion using an I / V conversion resistor as a negative feedback resistor; a current on / off semiconductor switch; A first type I / V conversion unit including an off-state semiconductor switch, wherein one terminal of the current on / off semiconductor switch is connected to an input unit of a current to be measured of the current / voltage conversion circuit and the first The other operational amplifier is connected to the inverting input terminal of the second operational amplifier, and the non-inverting input terminal of the second operational amplifier is connected by the range on / off semiconductor switch. The connection destination can be selected from the output of the first operational amplifier or the ground potential, and the on / off control of the current flowing through the I / V conversion resistor is possible. The output voltage of the second operational amplifier Inversion Current / voltage conversion circuit a potential difference of the force terminal voltage, characterized in that it consists in voltage proportional to the current value flowing through the I / V conversion resistor. 2. The current / voltage conversion circuit according to claim 1, wherein the first type of I / V conversion unit is provided in parallel for a plurality of ranges, and on / off control of a current flowing through the I / V conversion resistor for each I / V conversion unit is provided. The potential difference between the output voltage of the second operational amplifier and the non-inverting input terminal voltage for each I / V converter is a voltage proportional to the current value flowing through the I / V conversion resistor. Current / voltage conversion circuit. 3. The current / voltage conversion circuit according to claim 2, wherein the current / voltage conversion circuit includes a current-to-measurement current input section and a current on / off semiconductor switch in the first type I / V conversion section in an arbitrary range. Alternatively, a resistor is inserted between the current on / off semiconductor switch and the inverting input terminal of the second operational amplifier of the I / V converter , or a dead band is provided in the range on / off semiconductor switch. Current / voltage conversion circuit characterized by this.

Images