JP2002064342A - Voltage-current conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage-current conversion circuit, by which the current signals of multiple channels are generated with high accuracy and power consumption is reduced. SOLUTION: Operational amplifiers A1-A3 and transistors Q1 and Q2 are designed to operate at a low operating voltage. A D/A converter 4 inputs a voltage signal 101 to a voltage signal input circuit composed of the operational amplifier A1 and performs voltage-current conversion. A level converting circuit composed of the transistor Q1 and resistors R1 and R2 generates a level converting signal 102. A buffer circuit composed of the operational amplifier A2 inputs the level converting signal 102 through a multiplexer U1 to a capacitor C1 for sample-and-hold. A current output circuit composed of the operational amplifier A3, the transistor Q2 and a resistor R3 generate a current signal 104 from the held signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a voltage-current conversion circuit, and more particularly, to a voltage-current conversion circuit mounted on a measuring device and outputting a multi-channel current signal.

[0002]

2. Description of the Related Art An apparatus for processing measurement data has a voltage-current conversion circuit for converting a multi-channel voltage signal into a current signal and outputting a current signal for each channel. Some are used for communication between them.

FIG. 3 shows a circuit of a conventional voltage-current conversion circuit. The D / A converter 4 converts the digital voltage signal into a voltage signal 101, and outputs the voltage signal 10 via an operational amplifier A6.
1 is input to the signal input terminal of the multiplexer U3. The multiplexer U3 has a switch function of one input and four outputs, and connects an input terminal to one of output terminals of a corresponding channel based on a channel selection control signal 103 from a control unit (not shown), and outputs a voltage. The signal 101 is input to a sample and hold capacitor C3. The voltage signal input circuit including the operational amplifier A7 includes resistors R9 and R1.
0, and the signal held in the level conversion circuit comprising the NPN transistor Q3 is input to the level conversion signal 10
Convert to 2. Resistor R12 and PNP transistor Q4
Output a current signal 104 based on the level conversion signal 102.

Since the operating ranges of the voltage signal input circuit, the level conversion circuit, and the current signal output circuit are lower than the power supply voltage of 24 V, the Zener diode D1 and the resistor R1
The power supply voltage is kept low by a constant voltage circuit made up of 1.
The voltage signal input circuit, the level conversion circuit, the constant voltage circuit, and the current signal output circuit are provided by the number of channels of the multiplexer.

[0005]

In the above-described conventional voltage-current conversion circuit, the voltage signal input circuit, the level conversion circuit, and the current signal output circuit are provided for each channel, so that the resistors R9 and R10 are provided. , And the value of R12 vary among the channels, which causes an error in the accuracy of the current signal.

Further, since the constant voltage circuit is provided for each channel, when the number of channels is increased, the operating current is increased, and the power consumption of the voltage-current conversion circuit is increased.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems of the prior art, and a voltage-current conversion circuit which generates a multi-channel current signal with high accuracy and consumes less power. The purpose is to provide.

[0008]

In order to achieve the above object, a voltage-current conversion circuit according to the present invention converts a voltage signal for a plurality of channels into a current signal and supplies the current signal to each channel. In the circuit, a first voltage source that outputs a first voltage, and a second terminal that has a negative terminal connected to a negative terminal of the first voltage source and outputs a second voltage lower than the first voltage A voltage source, a third voltage source having a positive terminal connected to the first voltage source and outputting a third voltage lower than the first voltage, and a third voltage source that operates at the second voltage and operates at the second voltage; Signal input circuit for sequentially inputting voltage signals for operating the first voltage, a level conversion circuit which operates at the first voltage, converts a level of the voltage signal to output a level conversion signal, and performs level conversion from the level conversion circuit. Input a signal, and select from multiple output terminals. In response to the tunnel selection control signal 1
A multiplexer for selecting one of the output terminals and outputting the level conversion signal to the selected output terminal; and a multiplexer connected to each output terminal of the multiplexer for operating at the third voltage and output from the output terminal of the multiplexer. And a current signal output circuit for converting the level conversion signal into a current signal and outputting the current signal.

In the voltage-current conversion circuit of the present invention, the voltage signal input circuit and the level conversion circuit are shared between channels, and only the current signal output circuit is required for each channel, thereby reducing the number of parts of the entire circuit. Therefore, the generated current signal becomes highly accurate and the power consumption is reduced.

In the voltage-current conversion circuit according to the present invention, it is preferable that the level conversion circuit and the current signal output circuit are circuits having a rail-to-rail type operational amplifier. In this case, since the change range of the output voltage with respect to the supply voltage of each circuit is expanded, the supply voltage can be suppressed and the power consumption can be reduced.

A self-diagnosis circuit having a detection circuit for converting the current signal and outputting it as a voltage conversion detection signal; and a comparison circuit for comparing the voltage conversion detection signal with a voltage signal input to the voltage signal input circuit. Is a preferred embodiment of the present invention. In this case, since the self-diagnosis circuit monitors the operation state, failure detection becomes easy.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a voltage-current conversion circuit according to the present invention will be described based on an embodiment of the present invention with reference to the drawings. FIG. 1 is a circuit diagram of a voltage-current conversion circuit according to a first embodiment of the present invention. Voltage of the present embodiment-
The current conversion circuit includes an output circuit 1 for four channels, a control unit 2, a level converter 3, a DA converter 4, a voltage signal input circuit, a level conversion circuit, a buffer circuit, a sample and hold circuit, a current signal output circuit, 24 It comprises a first voltage power supply of [V], a third voltage power supply of 5 [V], and a second voltage power supply of 5 [V]. The second voltage power supply has a negative terminal connected to the first
The second voltage power supply and the first voltage power supply are connected to the negative terminal of the voltage power supply.
The negative terminals of the voltage power supplies are commonly connected, the positive terminal of the third voltage power supply is connected to the positive terminal of the first voltage power supply, and the positive terminals of the third voltage power supply and the first voltage power supply are commonly connected. You.

The voltage signal input circuit includes an operational amplifier A1, and the level conversion circuit includes an N-channel MOS transistor Q1, resistors R1, and R2. The operational amplifier A1 has a non-inverting input terminal serving as an input terminal of the voltage signal input circuit, an inverting input terminal connected to the source of the transistor Q1, and one end of the resistor R1, an output terminal connected to the gate of the transistor Q1, Power is supplied from a voltage source. The other end of the resistor R1 is connected to a negative terminal of the second voltage power supply. The drain of the transistor Q1 is
It is connected to one end of the resistor R2 and serves as an output terminal of the level conversion circuit. The other end of the resistor R2 is connected to the positive terminal of the third voltage power supply.

The buffer circuit is a voltage follower including an operational amplifier A2. The operational amplifier A2 has a non-inverting input terminal serving as an input terminal of a buffer circuit, an inverting input terminal connected to an output terminal, an output terminal serving as an output terminal of the buffer circuit, and power supplied from a third voltage power supply.

The output circuit 1 is composed of a sample and hold capacitor C1 and a current signal output circuit.
The current signal output circuit includes an operational amplifier A3, a P-channel MO
It comprises an S-transistor Q2 and a resistor R3. The operational amplifier A3 has a non-inverting input terminal serving as an input terminal of the output circuit 1, an inverting input terminal serving as a source of the transistor Q2,
The output terminal is connected to one end of the resistor R3, the output terminal is connected to the gate of the transistor Q2, and power is supplied from the third voltage power supply. The other end of the resistor R3 is connected to the positive terminal of the third voltage power supply. The drain of the transistor Q2 becomes one output terminal of the output circuit 1. The other output terminal of the output circuit 1 is connected to the negative terminal of the second voltage power supply.

The multiplexer U1 has a switch function of one input and four outputs, and switches the signal input terminal and any one of the signal output terminals of the corresponding channel based on the channel selection control signal 103 from the control input terminal. Connecting.
The multiplexer U1 has a signal input terminal connected to an output terminal of an operational amplifier A2 which is an output terminal of the buffer circuit,
Output circuit 1 of channel corresponding to four signal output terminals
Are connected respectively to the input terminals. The capacitor C1 is connected between the non-inverting input terminal of the operational amplifier A3 and the positive terminal of the third voltage power supply.

As the operational amplifiers A2 and A3, rail-to-rail type operational amplifiers that swing the output voltage to the full power supply voltage are used. Transistors Q1 and Q
The MOS transistor 2 has a lower gate-source voltage and lower drain-source voltage than the base-emitter voltage and the collector-emitter voltage of the bipolar transistor. In this case, the voltage signal input circuit and the current signal output circuit can be designed with a low power supply voltage.

The control section 2 is supplied with power from the second voltage power supply, inputs a channel selection control signal 103 via the level converter 3 to the multiplexer U1, and selects the output circuit 1 of the corresponding channel. The DA converter 4 converts the digital signal into a voltage signal 101 and inputs the signal to an input terminal of a voltage signal input circuit.

The voltage signal input circuit inputs the voltage signal 101 and supplies it to the level conversion circuit. The level conversion circuit is the third
The level of the signal is shifted so that the circuit supplied with power from the voltage
Is input to the sample and hold capacitor C1 via the buffer circuit. The values of the resistors R1 and R2 of the level conversion circuit are designed so that the voltage signal 101 can be converted to the optimum level conversion signal 102.

The current signal output circuit generates a current signal 104 from the voltage signal of the level conversion signal 102 held, and outputs the current signal 104 from the output terminal pair. The value of the resistor R3 of the current signal output circuit is designed so that the optimum current signal 104 can be generated from the held signal.

According to the above embodiment, the voltage signal input circuit and the level conversion circuit are shared between the channels, and only the current signal output circuit is required for each channel, thereby reducing the number of parts of the entire circuit. In addition, the generated current signal becomes highly accurate and the power consumption is reduced.

FIG. 2 is a diagram showing the voltage-voltage of the second embodiment of the present invention.
It is a circuit diagram of a current conversion circuit. The voltage-current conversion circuit of the present embodiment differs from the previous embodiment in that it has a self-diagnosis function of detecting a failure. The voltage-current conversion circuit of the present embodiment includes second and third voltage signal input circuits, second and third level conversion circuits, and a multiplexer U2 instead of the configuration of the previous embodiment. . Control unit 2A
Has one DA converter and two AD converters. In addition, one DA conversion unit and two AD conversion units can be provided as separate circuits outside the control unit 2A.

The second voltage signal input circuit includes an operational amplifier A
4 and the second level conversion circuit is a P-channel M
It comprises an OS transistor Q3, resistors R4, and R5. The operational amplifier A4 has a non-inverting input terminal serving as an input terminal of the second voltage signal input circuit, an inverting input terminal connected to the source of the transistor Q3, and one end of the resistor R5, and an output terminal connected to the gate of the transistor Q3. ,
Power is supplied from the third voltage power supply. The other end of the resistor R5 is connected to the positive terminal of the third voltage power supply. The drain of the transistor Q3 is connected to one end of the resistor R4,
Output terminal of the level conversion circuit. The other end of the resistor R4 is connected to the negative terminal of the second voltage power supply.

The third voltage signal input circuit includes an operational amplifier A
5 and the third level conversion circuit is a P-channel M
It comprises an OS transistor Q4, resistors R6 and R7. The operational amplifier A5 has a non-inverting input terminal serving as an input terminal of the third voltage signal input circuit, an inverting input terminal connected to the source of the transistor Q4, and one end of the resistor R7, and an output terminal connected to the gate of the transistor Q4. ,
Power is supplied from the third voltage power supply. The other end of the resistor R7 is connected to the positive terminal of the third voltage power supply. The drain of the transistor Q4 is connected to one end of the resistor R6,
Output terminal of the level conversion circuit. The other end of the resistor R6 is connected to the negative terminal of the second voltage power supply.

The output circuit 1A has an RC filter.
The RC filter includes a capacitor C2 in the output circuit 1 and a resistor R8 in the output circuit 1. The multiplexer U2 has a switch function of four inputs and one output, and connects the signal output terminal to any one of the signal input terminals of the corresponding channel based on the channel selection control signal 103 from the control input terminal. Multiplexer U2 is
The signal output terminal is connected to the non-inverting input terminal of the operational amplifier A5, which is the input terminal of the third voltage signal input circuit, and one of the signal input terminals is connected to the second output terminal of the output circuit 1A of the corresponding channel. . The second output terminal of the output circuit 1A is connected to the positive terminal of the third voltage power supply via the capacitor C2, and connected to the inverting input terminal of the operational amplifier A3 via the resistor R8.

In the control section 2A, the first signal input terminal is connected to one end of the resistor R4, which is the output terminal of the second level conversion circuit, and the second signal input terminal is the output terminal of the third level conversion circuit. An operational amplifier A connected to one end of the resistor R6 and having a signal output terminal as an input terminal of the first voltage signal input circuit.
1 non-inverting input terminal.

The control unit 2A converts a set value of digital information to be transmitted into a voltage signal 101 by a DA converter, and inputs the voltage signal 101 from a signal output terminal to a first level conversion circuit. The control unit 2A converts the first voltage conversion inspection signal from the first signal input terminal into a readback value of digital information by an AD conversion unit, and converts the second voltage conversion inspection signal from the second signal input terminal into an AD conversion unit. Then, the digital information is converted into a DA conversion value, and a self-diagnosis is performed by a built-in comparison circuit.

The control unit 2A includes a set value, a readback value,
Then, the D / A conversion value is analyzed to detect "disconnection failure" or "readback error". If the readback value is different from the set value, a “readback error” is notified. D
If the A-converted value is normal and the readback value is equal to or less than a predetermined value (for example, 0.65 [mA]), a "disconnection failure" is notified. If the DA conversion value is abnormal, a "readback error" is notified.

According to the above embodiment, since the self-diagnosis circuit monitors the operation state, the failure detection becomes easy.

Although the present invention has been described based on the preferred embodiment, the voltage-current conversion circuit of the present invention is not limited to the configuration of the above-described embodiment, but is limited to the embodiment. The voltage-current conversion circuit obtained by making various modifications and changes from the configuration described above is also included in the scope of the present invention.

[0031]

As described above, in the voltage-current conversion circuit of the present invention, the voltage signal input circuit and the level conversion circuit are shared between the channels, and only the current signal output circuit is required for each channel. Since the number of components of the entire circuit is reduced, the generated current signal becomes highly accurate and the power consumption is reduced. Further, since the self-diagnosis circuit monitors the operation state, failure detection becomes easy.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a voltage-current conversion circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a voltage-current conversion circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional voltage-current conversion circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Output circuit 2 Control circuit 3 Level converter 4 DA converter 101 Voltage signal 102 Level conversion signal 103 Channel selection control signal 104 Current signal A1 to A8 Operational amplifier U1 to U3 Multiplexer R1 to R12 Resistance C1 to C3 Capacitor Q1 to Q4 Transistor D1 Zener diode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiyuki Miyata 2-9-132 Nakamachi, Musashino-shi, Tokyo Inside Yokogawa Electric Corporation (72) Inventor Yukio Uba 2-9-132 Nakamachi, Musashino-shi, Tokyo Inside Kawa Electric Co., Ltd. (72) Inventor Hiroyasu Ikedo 1-1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture F-term (reference) 2G035 AA20 AB01 AC02 AD03 AD10 AD13 AD20 AD23 AD45 AD48 AD54 5H430 BB01 BB09 BB12 EE06 EE09 EE12 EE17 FF08 FF12 GG01 GG11 HH03 5J091 AA01 CA36 CA97 FA01 HA08 HA10 HA17 HA20 HA25 HA29 HA38 KA00 KA01 KA03 KA11 KA17 KA18 KA19 KA34 KA41 SA13 SA15 5J092 AA01 CA36 KA18 KA19 KA34 KA41 SA13 SA15

Claims (3)

[Claims] 1. A voltage-current conversion circuit for converting a voltage signal for a plurality of channels into a current signal and supplying the current signal to each channel, wherein a first voltage source for outputting a first voltage and a negative terminal are connected to the first voltage source. A second voltage source connected to the negative terminal of the first voltage source and outputting a second voltage lower than the first voltage; and a positive terminal connected to the first voltage source and connected to the first voltage source. Third too low
A third voltage source that outputs a voltage of the second voltage, a voltage signal input circuit that operates at the second voltage and sequentially inputs voltage signals for the plurality of channels, and that operates at the first voltage, A level conversion circuit for level-converting a signal and outputting a level conversion signal, a level conversion signal being input from the level conversion circuit, and selecting one output terminal from a plurality of output terminals in response to a channel selection control signal; A multiplexer for outputting the level-converted signal to the selected output terminal, and a current connected to each output terminal of the multiplexer, operating at the third voltage and outputting the level-converted signal output from the output terminal of the multiplexer. And a current signal output circuit for converting the signal into a signal and outputting the signal. 2. The voltage-current conversion circuit according to claim 1, wherein said level conversion circuit and said current signal output circuit are circuits having a rail-to-rail type operational amplifier. 3. A self-contained circuit comprising: a detection circuit for converting the current signal to output as a voltage conversion detection signal; and a comparison circuit for comparing the voltage conversion detection signal with a voltage signal input to the voltage signal input circuit. The voltage-current conversion circuit according to claim 1, further comprising a diagnosis circuit.