JP2005045729A - Communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication system for reducing spurious radiation while a decrease in the impedance of a communication line is restricted even when a plurality of communication systems are connected to the communication line. <P>SOLUTION: A preprocessing unit 3 for generating a preprocessing signal Cv<SP>+</SP>according to data generated from a control unit 2, a signal generating unit 4 for generating a signal Rx<SP>+</SP>, and a signal Rx<SP>-</SP>to communication lines 5H, 5L according to the preprocessing signal Cv<SP>+</SP>, are provided. The control unit 2 makes a switch SW1 and a switch SW2 turned on when data are outputted and makes the switch SW1 and switch SW2 turned off when the data are not outputted. The preprocessing unit 3 includes a charging circuit 7 for charging a capacitor C1 with a current I<SB>11</SB>for generating the preprocessing signal Cv<SP>+</SP>, and a discharging circuit 6 for discharging the capacitor C1 with a current I<SB>21</SB>. In the preprocessing unit 3, a charged voltage generated in the capacitor C1 is generated as the preprocessing signal Cv<SP>+</SP>by causing charging operation by the charging circuit 7 or discharging operation by the discharging circuit 6 in accordance with the data. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a communication apparatus that transmits a communication signal representing predetermined data via a two-wire communication line.

  11 and 12 are block diagrams for explaining the background art. Referring to FIG. 11, a plurality of communication devices 102 are connected to a two-wire communication line 101 made of, for example, a twisted pair cable, and communication signals representing predetermined data can be transmitted and received between the communication devices 102. Has been. Further, a termination resistor 103 equal to the characteristic impedance is connected to the termination of the communication line 101 so that the impedance of the communication line is matched.

  However, when the number of communication devices 102 connected to the communication line 101 increases, the impedance of the communication line 101 decreases and the level of the communication signal transmitted decreases, or the frequency of the communication signal output from the communication device 102 decreases. There arises a disadvantage that the component is radiated from the communication line 101 as unnecessary radiation.

Therefore, for example, like the communication device 102 shown in FIG. 12, by outputting the communication signal to the communication line 101 via the transformer 104, the noise component of the communication signal is removed to reduce unnecessary radiation, or to the signal output unit. There is known a switch that includes a switch 105 and suppresses a decrease in impedance of the communication line 101 by turning off the switch 105 except during signal transmission (see, for example, Patent Document 1).
JP-A-7-231324

  However, as described above, when a large component such as a transformer is used as a noise filter for removing a noise component of a communication signal, it is difficult to reduce the size of the communication device because the noise filter is large. There was an inconvenience.

  The present invention has been made in view of such a problem, and provides a communication device capable of reducing unnecessary radiation while suppressing a decrease in impedance of the communication line even when a plurality of communication devices are connected to the communication line. Objective.

  In order to achieve the above object, a communication apparatus according to the first means of the present invention outputs the data in a communication apparatus that transmits a communication signal representing predetermined data via a two-wire communication line. A control unit that generates a preprocessing signal for generating the communication signal according to data output from the control unit, and a preprocessing output from the preprocessing signal generation unit A signal output unit that outputs the communication signal to the communication line in response to a signal; and an output switch that turns on and off the connection between the signal output unit and the communication line, and the control unit includes: When outputting data, the output switch is turned on, and when the data is not output, the output switch is turned off, and the preprocessing signal generation unit generates the preprocessing signal. Charge for A charging circuit for charging the capacitor for charging with a predetermined current; and a discharging circuit for discharging the charging capacitor with a predetermined current; and charging operation by the charging circuit and discharging operation by the discharging circuit according to the data; The charging voltage generated in the charging capacitor by performing any of the above is generated as the preprocessing signal.

  In the above-described communication device, the signal output unit is connected to the communication line via an output capacitor.

  In the above communication apparatus, the preprocess signal generation unit further includes a voltage limiting circuit that limits a voltage of the preprocess signal to a predetermined voltage range.

  In the above-described communication device, a first resistor is interposed between the voltage limiting circuit and the charging capacitor.

  In the communication device described above, the charging circuit is connected to a first constant current source that outputs a predetermined current, a first transistor connected to the first constant current source, and the charging capacitor. And a first current mirror circuit including a second transistor, and a first capacitor is connected between output terminals of the first transistor.

  In the above communication device, the discharge circuit is connected to a second constant current source that outputs a predetermined current, a third transistor connected to the second constant current source, and the charging capacitor. And a second current mirror circuit composed of a fourth transistor, and a second capacitor is connected between the output terminals of the third transistor.

  In the above communication device, the preprocessing signal generation unit further includes an intermediate voltage setting circuit capable of charging and discharging the charging capacitor so that the voltage of the preprocessing signal is an intermediate voltage within the predetermined voltage range. When the data is not output, the control unit causes the intermediate voltage setting circuit to set the voltage of the preprocess signal to the intermediate voltage.

  In the above communication device, the signal output unit is connected to the output capacitor via the output switch, and the control unit is configured to output the data after a predetermined time has elapsed after the output of the data. The output switch is turned off.

  In the above communication device, the output switch is an analog switch whose resistance value can be changed, and when the control unit starts outputting the data, the output switch is gradually turned off from an off state. It is characterized in that it is shifted to the on state by reducing the resistance value.

  In the above communication apparatus, the first and second preprocessing signal generation units, the first and second signal output units, the first and second output switches, the first and second 2, the first preprocessing signal generation unit performs a charging operation by a charging circuit included in the first preprocessing signal generation unit when the logical value of the data is 1 On the other hand, when the logical value of the data is 0, the charge generated in the charging capacitor of the first preprocess signal generator by causing the discharge operation of the discharge circuit included in the first preprocess signal generator to be performed. A voltage is generated as the first preprocessing signal, and the first signal output unit outputs the communication signal to the first output switch and the first output according to the first preprocessing signal. Output to one of the communication lines through the capacitor for The second preprocessing signal generation unit causes the discharge operation of the discharge circuit included in the second preprocessing signal generation unit to be performed when the logical value of the data is 1, while the logical value of the data is 0. A charging voltage generated in the charging capacitor of the second preprocessing signal generation unit is generated as the second preprocessing signal by performing a charging operation by the charging circuit included in the second preprocessing signal generation unit. The second signal output unit sends the communication signal to the other of the communication lines via the second output switch and the second output capacitor in accordance with the second preprocessing signal. It is characterized by output.

  In the above-described communication device, the intermediate voltage setting circuit includes a third and a fourth constant current sources that output a predetermined same current, two diodes connected in series, and a connection point of the diodes The first diode pair set to the intermediate voltage and the two diodes are connected in series, and the connection point of the diodes is connected to be able to charge and discharge the charging capacitor of the first preprocessing signal generation unit A second diode pair, a third diode pair in which two diodes are connected in series, and a connection point of the diodes is connected to charge and discharge the charging capacitor of the second preprocessing signal generation unit; And a diode bridge formed by connecting the first, second, and third diode pairs in parallel is interposed between the third and fourth constant current sources. .

  In the communication device having such a configuration, when data is not output from the control unit, the output switch is turned off, and the impedance of the communication device viewed from the communication line is set to a high impedance state. It is possible to suppress a decrease in impedance of the communication line due to being connected to the communication line.

  In the communication device having such a configuration, the charging capacitor is charged / discharged by a predetermined current according to the data output from the control unit, and the preprocessing signal as the charging voltage is gradually increased or decreased. The Then, as a result of the communication signal being gradually raised and lowered according to the preprocessing signal, unnecessary high frequency components of the communication signal are removed, so unnecessary radiation due to the communication signal transmitted to the communication line is eliminated. Can be reduced.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

(First embodiment)
FIG. 1 is a diagram for explaining an example of a configuration of a communication apparatus according to the first embodiment of the present invention. The communication device 1 illustrated in FIG. 1 includes a control unit 2, a preprocessing unit 3, and a signal output unit 4. The signal output unit 4 is connected to a twisted pair cable 5 composed of communication lines 5H and 5L. The preprocessing unit 3 includes a discharge circuit 6, a charging circuit 7, a voltage limiting circuit 8, and a charging capacitor C1.

  The signal output unit 4 includes output buffers 41 and 42, switches SW1 and SW2, and capacitors C2 and C3. The output terminal of the output buffer 41 is connected to the communication line 5H via the switch SW1 and the capacitor C2, and the output terminal of the output buffer 42 is connected to the communication line 5L via the switch SW2 and the capacitor C3. Yes. The input terminals of the output buffers 41 and 42 are connected to the ground via the capacitor C1. The switches SW1 and SW2 are turned on / off according to a control signal from the control unit 2.

  Capacitors C2 and C3 cut DC components of signals between output buffers 41 and 42 and communication lines 5H and 5L. Thereby, for example, it is suppressed that the output buffers 41 and 42 are damaged by a voltage such as a ground potential difference or a power supply voltage generated in the communication lines 5H and 5L. Moreover, the fall of the impedance of the communication lines 5H and 5L by connecting the communication apparatus 1 to the communication lines 5H and 5L can be suppressed with respect to direct current.

The voltage limiting circuit 8 includes constant voltage sources E1 and E2 whose output voltages are V ₁ and V ₂ , and diodes D1 and D2, respectively. In this case, the output voltage V ₁ > the output voltage V ₂ , and the upper limit value of the voltage range of the voltage Cv ⁺ of the preprocess signal is V ₁ and the lower limit value is V ₂ . The connection point between the input terminals of the output buffers 41 and 42 and the capacitor C1 is connected to the anode of the diode D1, the cathode of the diode D1 is connected to the positive electrode of the constant voltage source E1, and the negative electrode of the constant voltage source E1 is connected to the ground. It is connected to the. The connection point between the input terminals of the output buffers 41 and 42 and the capacitor C1 is connected to the cathode of the diode D2, the anode of the diode D2 is connected to the positive electrode of the constant voltage source E2, and the negative electrode of the constant voltage source E2 is connected to the ground. It is connected to the.

As a result, the voltage at the connection point between the input terminals of the output buffers 41 and 42 and the capacitor C1, that is, the voltage Cv ^{+ of the} preprocess signal is limited to a voltage range of V ₁ ≧ Cv ⁺ ≧ V ₂ .

The charging circuit 7 includes a constant current source CS1 for outputting a predetermined current I _1, a collector connected to the constant current source CS1 through the switch SW3, a transistor Tr1 having an emitter connected to the circuit power supply, the collector is a capacitor C1 And a transistor Tr2 whose emitter is connected to a circuit power supply, and a current mirror circuit 71 including transistors Tr1 and Tr2. The switch SW3 is composed of, for example, a semiconductor switch using a transistor or the like, and is turned on when, for example, data Tx is output from the control unit 2 at a high level and indicates a logical value “1”.

Discharge circuit 6 includes a constant current source CS2 for outputting a predetermined current I _2, the collector is connected through a switch SW4 to the constant current source CS2, and the transistors Tr3 whose emitter is connected to ground, collector to the capacitor C1 The transistor Tr4 is connected, and the emitter is connected to the ground. The current mirror circuit 61 includes transistors Tr3 and Tr4. The switch SW4 is composed of, for example, a semiconductor switch using a transistor or the like, and is turned on when, for example, data Tx is output from the control unit 2 at a low level and indicates a logical value “0”.

  The control unit 2 outputs serial communication data Tx for communication or outputs a control signal En indicating that the data Tx is being output. For example, a general-purpose USART (Universal Synchronous Asynchronous Receiver Transmitter) The communication IC (Integrated Circuit) is used. The control unit 2 outputs the data Tx to the switch SW3, turns on the switch SW3 when the data Tx is at a high level, and causes the charging circuit 7 to charge the capacitor C1. Further, the control unit 2 outputs the data Tx to the switch SW4 via the inverter 62, turns on the switch SW4 when the data Tx is at a low level, and causes the discharge circuit 6 to perform the discharging operation from the capacitor C1. .

  Further, the control unit 2 outputs the control signal En at, for example, a high level while outputting the data Tx, thereby turning on the switches SW1 and SW2. When data Tx is not output, the switches SW1 and SW2 are turned off by outputting the control signal En at, for example, a low level.

  Next, the operation of the communication apparatus 1 shown in FIG. 1 will be described. FIG. 2 is a diagram illustrating signal waveforms of respective units when the communication device 1 transmits a communication signal. First, data transmission is started by the control unit 2, the control signal En is set to high level, and data Tx is output. In FIG. 2, the first bit of the data Tx indicates a logical value “1” and is set to a high level. When the control signal En is set to the high level, the switches SW1 and SW2 are turned on, and the output buffers 41 and 42 are connected to the communication lines 5H and 5L via the capacitors C2 and C3, respectively. Data is transmitted from 42 to the communication lines 5H and 5L.

Next, the data Tx is at a high level, as a result of the charging circuit 7 switch SW3 is turned on, a current I ₁ to the transistor Tr1 flows by a constant current source CS1, the transistors constituting the current mirror circuit 71 together with transistors Tr1 A constant current I ₁₁ substantially equal to the current I ₁ is output from Tr2, and the capacitor C1 is charged by the current I ₁₁ . Then, the voltage Cv ⁺ pretreatment signal is a charging voltage of the capacitor C1 is greater than V ₁ gradually rises as the waveform shown in FIG. 2, the voltage Cv ⁺ is V ₁ diode D1 is turned on Limited.

On the other hand, the output buffer 41 outputs a signal Rx ⁺ that gradually increases according to the voltage Cv ⁺ that is the preprocess signal, to the communication line 5H via the capacitor C2. Further, the inverted output buffer 42 outputs a signal Rx ⁻ having a polarity opposite to that of the signal Rx ⁺ , which gradually decreases according to the voltage Cv ⁺ that is the preprocess signal, to the communication line 5L via the capacitor C3. Further, since the voltage Cv ⁺ peak voltage is limited to V _1, the signal for communication Rx ^+, signal Rx ^- also limited to a predetermined voltage range.

The waveforms of the communication signals Rx ⁺ and Rx ⁻ transmitted from the communication device 1 to the communication lines 5H and 5L at the rising edge of the data Tx are gradually increased and decreased, and as a result, the communication signal Unnecessary high frequency components are removed. Further, since the communication signals Rx ⁺ and Rx ⁻ are limited to a predetermined voltage range, occurrence of waveform disturbance such as overshoot is suppressed.

  Thereby, the unnecessary radiation by the communication signal transmitted from the communication device 1 to the communication lines 5H and 5L at the rising edge of the data Tx is reduced.

Next, the data Tx is at a low level by the control unit 2, the discharge circuit switch SW4 is turned on at 6, results current I ₂ to the transistor Tr3 by the constant current source CS2 is flowing, the current mirror circuit 61 together with transistor Tr3 A constant current I ₂₁ substantially equal to the current I ₂ is output from the transistor Tr4 constituting the capacitor C1, and the capacitor C1 is discharged by the current I ₂₁ . Then, the voltage Cv ⁺ is preprocessed signal is charged voltage of the capacitor C1, below the V ₂ gradually lowered as the waveform shown in FIG. 2, the voltage Cv ⁺ is V ₂ or more diodes D2 is turned on Maintained.

On the other hand, the output buffer 41 outputs a signal Rx ⁺ that gradually decreases in accordance with the voltage Cv ⁺ that is the preprocess signal to the communication line 5H via the capacitor C2. Further, the output buffer 42 outputs a signal Rx ⁻ having a polarity opposite to that of the signal Rx ⁺ that gradually increases according to the voltage Cv ⁺ that is the preprocess signal, to the communication line 5L via the capacitor C3. Further, since the voltage Cv ⁺ the lower limit voltage is limited to V _2, the signal for communication Rx ^+, signal Rx ^- also limited to a predetermined voltage range.

The communication signals Rx ⁺ and Rx ⁻ transmitted from the communication device 1 to the communication lines 5H and 5L at the fall of the data Tx are gradually lowered and raised, resulting in a signal waveform for communication. Unnecessary high frequency components are removed. Further, since the communication signals Rx ⁺ and Rx ⁻ are limited to a predetermined voltage range, occurrence of waveform disturbance such as undershoot is suppressed.

  Thereby, the unnecessary radiation by the signal for communication transmitted from the communication apparatus 1 to the twisted pair cable 5 at the fall of the data Tx is reduced.

  As described above, the capacitor C1 is charged and discharged according to the logical value of the data Tx, and communication signals are transmitted to the communication lines 5H and 5L. When the transmission of the data Tx ends, the control unit 2 sets the control signal En to the low level and the switches SW1 and SW2 are turned off. Thereby, since the impedance when the communication device 1 is viewed from the communication lines 5H and 5L is in a high impedance state, a reduction in impedance of the communication lines 5H and 5L due to the communication device 1 being connected to the communication lines 5H and 5L is suppressed. be able to.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. FIG. 3 is a diagram for explaining an example of a configuration of a communication apparatus according to the second embodiment of the present invention. The communication device 1a shown in FIG. 3 differs from the communication device 1 shown in FIG. 1 in the following points. That is, in the communication device 1 a shown in FIG. 3, the resistor R <b> 1 is interposed between the capacitor C <b> 1 and the discharging circuit 6, the charging circuit 7, and the voltage limiting circuit 8.

Since the other configuration is the same as that of the communication apparatus 1 shown in FIG. 1, the operation of the communication apparatus 1a will be described below with respect to the characteristic points of the present embodiment. FIG. 4 is a diagram illustrating signal waveforms of the respective units when the communication device 1a transmits a communication signal. First, as in the case of the communication device 1 shown in FIG. 1, when the data Tx is set to a high level by the control unit 2, the capacitor C <b> 1 is charged with the current I ₁₁ from the charging circuit 7. During this charging, the communication device 1a, just before reaching the charging voltage Cv ⁺ is V ₁ of the capacitor C1, since rounding by a resistor R1 to the voltage Cv ⁺ charging waveform occurs, the voltage Cv ⁺ reached V ₁ A sudden change in current when the diode D1 is turned on is eliminated.

In addition, a signal Rx ⁺ that gradually rises according to the signal waveform of the voltage Cv ⁺ in which the rounding has occurred is output from the output buffer 41 to the communication line 5H via the capacitor C2. Further, the output buffer 42 outputs a signal Rx ⁻ having a polarity opposite to that of the signal Rx ⁺ that gradually decreases according to the signal waveform of the voltage Cv ⁺ in which the rounding occurs, to the communication line 5L via the capacitor C3. . As a result, the signal waveforms of the signals Rx ⁺ and Rx ⁻ are also rounded, and unnecessary high frequency components of the communication signal are removed.

  Thereby, unnecessary radiation due to a communication signal transmitted from the communication device 1 to the twisted pair cable 5 at the rising edge of the data Tx is reduced.

Next, as in the case of the communication device 1 shown in FIG. 1, when the data Tx is set to a low level by the control unit 2, the capacitor C <b> 1 is discharged with the current I ₂₁ by the discharge circuit 6. During the discharge, in the communication device 1a is so accent voltage Cv ⁺ of the discharge waveform by the resistor R1 immediately before ^{the +} charging voltage Cv of the capacitor C1 reaches V ₂ occurs, the voltage Cv ⁺ reaches V ₂ diodes A sudden change in current when D2 is turned on is eliminated.

In addition, a signal Rx ⁺ that gradually decreases in accordance with the signal waveform of the voltage Cv ⁺ in which the rounding has occurred is output from the output buffer 41 to the communication line 5H via the capacitor C2. Further, the output buffer 42 outputs a signal Rx ⁻ having a polarity opposite to that of the signal Rx ⁺ , which gradually increases according to the signal waveform of the voltage Cv ⁺ in which the rounding occurs, to the communication line 5L via the capacitor C3. . As a result, the signal waveforms of the signals Rx ⁺ and Rx ⁻ are also rounded, and unnecessary high frequency components of the communication signal are removed.

  Thereby, the unnecessary radiation by the signal for communication transmitted from the communication apparatus 1 to the twisted pair cable 5 at the fall of the data Tx is reduced.

(Third embodiment)
Next, a third embodiment of the present invention will be described. FIG. 5 is a diagram for explaining an example of the configuration of a communication apparatus according to the third embodiment of the present invention. The communication device 1b shown in FIG. 5 is different from the communication device 1a shown in FIG. 3 in the following points. That is, in the communication device 1b shown in FIG. 5, the capacitor C4 is connected between the collector and emitter of the transistor Tr1, and the capacitor C5 is connected between the collector and emitter of the transistor Tr3.

Since the other configuration is the same as that of the communication device 1a shown in FIG. 3, the operation of the communication device 1b will be described below with respect to the characteristic points of the present embodiment. FIG. 6 is a diagram illustrating signal waveforms of the respective units when the communication device 1b transmits a communication signal. First, as in the case of the communication device 1 shown in FIG. 1, when the data Tx is set to a high level by the control unit 2, the switch SW3 is turned on in the charging circuit 7, and the current I is supplied to the transistor Tr1 by the constant current source CS1. ₁ is washed away.

In the communication device 1b, a part of the current I ₁ passed by the constant current source CS1 immediately after the switch SW3 is turned on transiently bypasses the transistor Tr1 and flows through the capacitor C4. Therefore, the current flowing through the transistor Tr1 is gradually increases immediately after oN of the switch SW3, so that the gradually increasing also the charging current I ₁₁ of the capacitor C1 by the current mirror circuit 71.

As a result, the waveform at the start of increase in the charging voltage Cv ⁺ of the capacitor C1 is rounded. As a result, the signal waveforms of the signal Rx ⁺ and the signal Rx ⁻ are also rounded, unnecessary high frequency components of the communication signal are removed, and unnecessary radiation due to the communication signal is reduced.

Next, as in the case of the communication device 1 shown in FIG. 1, when the data Tx is set to a low level by the control unit 2, the switch SW4 is turned on in the discharge circuit 6, and the current is supplied to the transistor Tr3 by the constant current source CS2. I ₂ is flushed. In the communication device 1b, the portion of the current I ₂ which flows through the constant current source CS2 immediately after the switch SW4 is turned on, since the flow through capacitor C5 to bypass the transiently transistor Tr3, the current flowing through the transistor Tr3 The current gradually increases immediately after the switch SW4 is turned on, and the discharge current I ₂₁ of the capacitor C1 by the current mirror circuit 61 also gradually increases.

As a result, the waveform at the start of the decrease in the charging voltage Cv ⁺ of the capacitor C1 is rounded. As a result, the signal waveforms of the signal Rx ⁺ and the signal Rx ⁻ are also rounded, unnecessary high frequency components of the communication signal are removed, and unnecessary radiation due to the communication signal is reduced.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. FIG. 7 is a diagram for explaining an example of the configuration of the communication apparatus according to the fourth embodiment of the present invention. The communication device 1c shown in FIG. 7 is different from the communication device 1 shown in FIG. 1 in the following points. That is, the communication apparatus 1c shown in FIG. 7, the intermediate voltage setting circuit for keeping the charging voltage Cv ⁺ the intermediate voltage _{V 3 = (V 1 + V} 2) / 2 of the capacitor C1 when not outputting data Tx 9 Is provided. The communication device 1c includes a delay circuit 10 interposed between the control unit 2 and the switches SW1 and SW2. The switches SW1 and SW2 are composed of analog switches whose resistance values can be changed. For example, the switches SW1 and SW2 are switched by a method such as a control signal for turning on and off the switches SW1 and SW2 is smoothed by an integration circuit. When turning on, the resistance value is gradually decreased from the off state to shift to the on state, while when turning off the switches SW1 and SW2, the resistance value is gradually increased from the on state to shift to the off state. Has been.

  Since other configurations are the same as those of the communication apparatus 1 shown in FIG. 1, the characteristic points of the present embodiment will be described below.

Intermediate voltage setting circuit 9 includes a constant current source CS3, CS4 to output a predetermined current I ₃ in the same manner respectively, the diodes D3, D4, D5, D6, a switch SW5, SW6, SW7, and an inverter 91. A diode bridge 92 is configured by connecting the diodes D3 and D4 connected in series and the diodes D5 and D6 connected in series in parallel. The constant current source CS3 is connected to the anodes of the diodes D3 and D5 via the switch SW5, and the cathodes of the diodes D4 and D6 are connected to the constant current source CS4 via the switch SW6.

Further, a connection point between the diode D3 and the diode D4 is connected to a connection point between resistors R2 and R3 connected in series between the positive electrode of the constant voltage source E1 and the positive electrode of the constant voltage source E2. The resistors R2 and R3 have the same resistance value. As a result, the voltage between the output voltage V ₁ of the constant voltage source E1 and the output voltage V ₂ of the constant voltage source E2 is divided by the resistors R2 and R3, and the intermediate voltage V ₃ = (V ₁ + V ₂ ) / 2. Is applied to the connection point between the diode D3 and the diode D4.

  Further, the connection point between the diode D5 and the diode D6 is connected so that the capacitor C1 can be charged and discharged. Further, a switch SW7 is interposed between the capacitor C1, the diodes D5 and D6, and the output buffers 41 and 42, and the discharge circuit 6, the charging circuit 7, and the voltage limiting circuit 8.

  The switch SW7 is turned off when the control signal En from the control unit 2 is at a low level and turned on at a high level. The switches SW5 and SW6 are connected to the control unit 2 via the inverter 91, and the control signal En from the control unit 2 is turned on at a low level and turned off at a high level.

  The delay circuit 10 outputs to the switches SW1 and SW2 a delay signal Enx obtained by delaying the falling timing of the control signal En from the control unit 2 by a predetermined time. Thus, the switches SW1 and SW2 are turned off after a predetermined time has elapsed after the output of the data Tx from the control unit 2 is completed.

Next, a characteristic operation of the communication device 1c shown in FIG. 7 different from that of the communication device 1 shown in FIG. 1 will be described. FIG. 8 is a diagram illustrating signal waveforms of the respective units when the communication device 1c transmits a communication signal. First, in a state where data Tx is not output from the control unit 2, the control signal En is set to a low level by the control unit 2, and the switches SW5 and SW6 are turned on and the switch SW7 is turned off. As a result, the current I ₃ output from the constant current source CS3 flows after being shunted into the series circuit of the diodes D3 and D4 and the series circuit of the diodes D5 and D6, and is then connected to the diode D4 and the diode D6. is the current I ₃ again by a constant current source CS4 in merge to.

Since the intermediate voltage V ₃ = (V ₁ + V ₂ ) / 2 is applied to the connection point between the diode D3 and the diode D4, the voltage at the connection point between the diode D5 and the diode D6 is also the intermediate voltage. V ₃ is set. That is, the voltage Cv ⁺ lower than the intermediate voltage V _3, the capacitor C1 is charged from the constant current source CS3 through the diode D5, the higher the voltage Cv ⁺ than the intermediate voltage V _3, the diode from the constant current source CS4 results capacitor C1 is discharged through D6, the charging voltage of the capacitor C1 Cv ⁺ is kept at an intermediate voltage V _3. Further, the output signals Rx ⁺ and Rx ^{− of} the output buffers 41 and 42 are also set to intermediate voltages according to the voltage Cv ⁺ .

  Next, data transmission is started by the control unit 2, the control signal En is set to high level, and data Tx is output. In FIG. 8, the first bit of the data Tx indicates a logical value “1” and is set to the high level. Further, when the control signal En is set to the high level, the switch SW7 is turned on, and the discharging circuit 6, the charging circuit 7, and the voltage limiting circuit 8 are connected to the capacitor C1, and the switches SW5 and SW6 are turned off to turn on the intermediate voltage. Charging / discharging of the capacitor C1 by the setting circuit 9 is stopped.

  Further, since the rise of the control signal En is not delayed in the delay circuit 10, the delay signal Enx is set to the high level by the delay circuit 10, the impedances of the switches SW1 and SW2 are gradually lowered, and the output buffer 41 is turned on. , 42 are connected to the communication lines 5H, 5L via the capacitors C2, C3, respectively, so that data can be transmitted from the output buffers 41, 42 to the twisted pair cable 5.

On the other hand, before the switches SW1 and SW2 are turned on, the capacitors C2 and C3 may be in a state where, for example, the charge due to the communication signal transmitted last time is stored. In such a case, in the communication device 1 shown in FIG. 1, the voltage due to the charge stored in the capacitors C2 and C3 with reference to the output voltage of the output buffers 41 and 42 at the moment when the switches SW1 and SW2 are turned on. May be applied to the communication lines 5H and 5L, and the voltage may be transmitted to the communication lines 5H and 5L as a communication signal. However, in the communication device 1c shown in FIG. 7, since the impedances of the switches SW1 and SW2 gradually decrease and shift to the ON state, even when charges are stored in the capacitors C2 and C3, they are stored. The charged charges are gradually charged and discharged to the voltages of the output signals Rx ⁺ , Rx ⁻ of the output buffers 41, 42, and the voltages due to the charges stored in the capacitors C 2, C 3 are used as communication signals as communication lines 5 H, 5 L. It is suppressed that it is transmitted to.

Further, the control unit 2, the data Tx is at a high level, as in the communication device 1 shown in FIG. 1, the capacitor C1 is charged by the current I _11, pre-processed signal is a charging voltage of the capacitor C1 Voltage Cv ⁺ gradually increases. At this time, in the communication apparatus 1c shown in Fig. 7, since the voltage Cv ⁺ are previously to the intermediate voltage V _3, the voltage change due to charging and discharging of the capacitor C1 decreases, the output signal Rx of the output buffer 41 The voltage change of ⁺ and Rx ⁻ is also reduced. As a result, sudden changes in the waveforms of the signals Rx ⁺ and Rx ⁻ at the start of transmission are suppressed, so that unnecessary radiation due to communication signals is reduced.

Next, when the transmission of the data Tx is completed and the control signal En is set to a low level by the control unit 2, the switches SW5 and SW6 are turned on and the switch SW7 is turned off. , the charging voltage of the capacitor C1 Cv ⁺ is the intermediate voltage V _3, the output signal Rx ⁺ of the output buffer 41 in response to the voltage Cv ^+, Rx ^- are also to an intermediate voltage. As a result, sudden changes in the waveforms of the signals Rx ⁺ and Rx ⁻ at the end of transmission are suppressed, so that unnecessary radiation due to communication signals is reduced.

On the other hand, when the switch SW1 and SW2 are turned off simultaneously with the control signal En being set to the low level as in the communication device 1 shown in FIG. 1, the output signals Rx ⁺ and Rx ⁻ of the output buffers 41 and 42 are turned off. As a result, the switches SW1 and SW2 are turned off before the potentials of the capacitors C2 and C3 are set to the intermediate voltage, and there is a possibility that charges are stored in the capacitors C2 and C3.

  However, in the communication device 1c shown in FIG. 7, the switches SW1 and SW2 are turned off by the delay signal Enx in which the falling timing of the control signal En is delayed by a predetermined time by the delay circuit 10, so that the control signal En is at the low level. The switches SW1 and SW2 are turned off after a lapse of time until the potentials of the capacitors C2 and C3 are changed to the intermediate voltage after being turned on, and the charge is prevented from being stored in the capacitors C2 and C3. It is possible to suppress the voltage due to the electric charge stored in the capacitors C2 and C3 from being transmitted to the communication lines 5H and 5L as a communication signal when starting transmission.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described. FIG. 9 is a diagram for explaining an example of a configuration of a communication apparatus according to the fifth embodiment of the present invention. The communication device 1d shown in FIG. 9 is different from the communication device 1c shown in FIG. 7 in the following points. That is, the communication device 1d shown in FIG. 9 further includes a discharging circuit 6a, a charging circuit 7a, and a voltage limiting circuit 8a configured similarly to the discharging circuit 6, the charging circuit 7, and the voltage limiting circuit 8. Further, instead of the output buffer 42 which is an inverting output buffer, an output buffer 41a similar to the output buffer 41 which does not invert the output is used. Furthermore, instead of the intermediate voltage setting circuit 9, an intermediate voltage setting circuit 9a is provided.

  Since the other configuration is the same as that of the communication device 1c shown in FIG. 7, the characteristic points of the present embodiment will be described below.

  The switch SW4a in the discharge circuit 6a is turned on, for example, when the data Tx is output at a high level from the control unit 2 and indicates a logical value “1”. That is, the switch SW4a in the discharge circuit 6 is turned on and off in reverse. To be. In other respects, the discharge circuit 6a and the discharge circuit 6 are the same.

  The switch SW3a in the charging circuit 7a is turned on when, for example, the data Tx is output at a low level from the control unit 2 and indicates a logical value “0”. That is, the switch SW3 in the charging circuit 7 is turned on and off in reverse. To be. In other respects, the discharge circuit 6a and the discharge circuit 6 are the same.

The discharge circuit 6a, the charging circuit 7a, and the voltage limiting circuit 8a are connected in the same manner as the discharging circuit 6, the charging circuit 7, and the voltage limiting circuit 8, and the capacitor C1a is connected via the switch SW7a configured similarly to the switch SW7. It is configured to be chargeable / dischargeable. Further, the output buffer 41a, the charging voltage Cv of the capacitor C1a ^- signals corresponding to Rx ^-, and outputs to the communication line 5L via a switch SW2 and a capacitor C3.

  The intermediate voltage setting circuit 9a differs from the intermediate voltage setting circuit 9 included in the communication device 1c shown in FIG. 7 in the following points. That is, instead of the diode bridge 92 included in the intermediate voltage setting circuit 9, diodes D3 and D4 connected in series, diodes D5 and D6 connected in series, and diodes D7 and D8 connected in series are connected in parallel. A diode bridge 92a is used. The connection point between the diode D5 and the diode D6 is connected so that the capacitor C1 can be charged and discharged as in the case of the intermediate voltage setting circuit 9, while the connection point between the diode D7 and the diode D8 charges the capacitor C1a. It is connected so that it can be discharged.

  Since the other configuration is the same as that of the communication device 1c shown in FIG. 7, a characteristic operation of the communication device 1d shown in FIG. 9 different from that of the communication device 1c shown in FIG. 7 will be described. FIG. 10 is a diagram illustrating signal waveforms of the respective units when the communication device 1d transmits a communication signal.

First, in a state where data Tx is not output from the control unit 2, the control signal En is set to a low level by the control unit 2, and the switches SW5 and SW6 are turned on and the switch SW7 is turned off. Thus, in the intermediate voltage setting circuit 9a, a current I ₃ which is output from the constant current source CS3, a series circuit of diodes D3, D4, a series circuit of diodes D5, D6, to a series circuit of diodes D7, D8 after flowing diverted, it is a current I ₃ again by a constant current source CS4 merges at the junction of diodes D4, D6, D8.

Since the intermediate voltage V ₃ = (V ₁ + V ₂ ) / 2 is applied to the connection point between the diode D3 and the diode D4, the connection point between the diode D5 and the diode D6, and the diode D7 and the diode D8. The voltage at the connection point to is also set to the intermediate voltage V ₃ . Thus, as in the case of an intermediate voltage setting circuit 9 shown in FIG. 7, the charging voltage Cv ⁺ of the capacitor C1, the charging voltage Cv of the capacitor C1a ^- and is kept at an intermediate voltage V _3. Further, the output signals Rx ⁺ and Rx ^{− of} the output buffers 41 and 42 are also set to intermediate voltages according to the voltages Cv ⁺ and Cv ⁻ .

In this case, a signal Rx ⁺ output circuit comprising a discharge circuit 6, a charge circuit 7, a voltage limiting circuit 8, a capacitor C1, and an output buffer 41, a discharge circuit 6a, a charging circuit 7a, a voltage limiting circuit 8a, a capacitor C1a, and Since the intermediate voltage setting circuit 9a can be used in common with the output circuit composed of the output buffer 41a, variations in the intermediate voltage can be suppressed and the number of components can be reduced in order to configure the intermediate voltage setting circuit. .

Further, for example, when an inverted output buffer 42 that inverts and outputs the voltage Cv ⁺ is used as an output buffer for outputting the signal Rx ⁻ as in the communication device 1c shown in FIG. Since the characteristic variation with the output buffer 42 increases, there is a disadvantage that the waveform distortion of the differential signal output between the communication lines 5H and 5L increases. However, in the communication device 1d shown in FIG. 9, the signal Rx ^- as an output buffer 41a for outputting, it is possible to use an output buffer of the same non-inverting output buffer 41 for outputting a signal Rx ^+, Waveform distortion of the differential signal output between the communication lines 5H and 5L is suppressed, and unnecessary radiation due to the communication signal is reduced.

It is a figure for demonstrating an example of a structure of the communication apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the signal waveform of each part of the communication apparatus shown in FIG. It is a figure for demonstrating an example of a structure of the communication apparatus which concerns on the 2nd Embodiment of this invention. It is a figure which shows the signal waveform of each part of the communication apparatus shown in FIG. It is a figure for demonstrating an example of a structure of the communication apparatus which concerns on the 3rd Embodiment of this invention. It is a figure which shows the signal waveform of each part of the communication apparatus shown in FIG. It is a figure for demonstrating an example of a structure of the communication apparatus which concerns on the 4th Embodiment of this invention. It is a figure which shows the signal waveform of each part of the communication apparatus shown in FIG. It is a figure for demonstrating an example of a structure of the communication apparatus which concerns on the 5th Embodiment of this invention. It is a figure which shows the signal waveform of each part of the communication apparatus shown in FIG. It is a figure which shows the communication system structure for demonstrating background art. It is a figure which shows the communication apparatus by background art.

Explanation of symbols

1, 1a, 1b, 1c, 1d Communication device 2 Control unit 3 Preprocessing unit (preprocessing signal generation unit)
4 Signal output section 5 Twisted pair cable 5H, 5L Communication line 6, 6a Discharge circuit 7, 7a Charge circuit 8, 8a Voltage limit circuit 9, 9a Intermediate voltage setting circuit 10 Delay circuit 41, 41a, 42 Output buffer 61 Current mirror circuit ( Second current mirror circuit)
71 Current mirror circuit (first current mirror circuit)
92, 92a Diode bridge C1, C1a Capacitor (charging capacitor)
C2, C3 capacitors (capacitors for output)
C4 capacitor (first capacitor)
C5 capacitor (second capacitor)
CS1 constant current source (first constant current source)
CS2 constant current source (second constant current source)
CS3 constant current source (third constant current source)
CS4 constant current source (fourth constant current source)
D1, D2, D3, D4, D5, D6, D7, D8 Diodes E1, E2 Constant voltage source R1 Resistance (first resistance)
SW1, SW2 switch (switch for output)
SW3, SW4, SW5, SW6, SW7 Switch SW3a, SW4a, SW7a Switch Tr1 Transistor (first transistor)
Tr2 transistor (second transistor)
Tr3 transistor (third transistor)
Tr4 transistor (fourth transistor)

Claims (11)

In a communication device that transmits a communication signal representing predetermined data via a two-wire communication line,
A control unit for outputting the data;
A preprocessing signal generation unit that generates a preprocessing signal for generating the communication signal according to data output from the control unit;
A signal output unit that outputs the communication signal to the communication line according to the preprocess signal output from the preprocess signal generation unit;
An output switch for turning on and off the connection between the signal output unit and the communication line;
The control unit turns on the output switch when outputting the data, and turns off the output switch when not outputting the data.
The preprocessing signal generation unit includes a charging circuit that charges a charging capacitor for generating the preprocessing signal with a predetermined current, and a discharging circuit that discharges the charging capacitor with a predetermined current. The charging voltage generated in the charging capacitor is generated as the preprocessing signal by performing either a charging operation by the charging circuit or a discharging operation by the discharging circuit according to data. Communication device. The communication apparatus according to claim 1, wherein the signal output unit is connected to the communication line via an output capacitor. The communication apparatus according to claim 1, wherein the preprocessing signal generation unit further includes a voltage limiting circuit that limits a voltage of the preprocessing signal to a predetermined voltage range. The communication device according to claim 1, wherein a first resistor is interposed between the voltage limiting circuit and the charging capacitor. The charging circuit includes a first constant current source that outputs a predetermined current, a first transistor connected to the first constant current source, and a second transistor connected to the charging capacitor. A first current mirror circuit;
The communication apparatus according to claim 1, wherein a first capacitor is connected between output terminals of the first transistor. The discharge circuit includes a second constant current source that outputs a predetermined current, a third transistor connected to the second constant current source, and a fourth transistor connected to the charging capacitor. A second current mirror circuit,
The communication apparatus according to claim 1, wherein a second capacitor is connected between output terminals of the third transistor. The preprocessing signal generation unit further includes an intermediate voltage setting circuit capable of charging and discharging the charging capacitor in order to set the voltage of the preprocessing signal to an intermediate voltage in the predetermined voltage range,
7. The communication according to claim 3, wherein, when the data is not output, the control unit causes the intermediate voltage setting circuit to set the voltage of the preprocessing signal to the intermediate voltage. 8. apparatus. The signal output unit is connected to the output capacitor via the output switch,
8. The communication apparatus according to claim 7, wherein the control unit turns off the output switch after a predetermined time has elapsed after the output of the data. The output switch is an analog switch whose resistance value can be changed,
9. The communication according to claim 7, wherein, when starting to output the data, the control unit shifts the output switch to an on state by gradually decreasing a resistance value from the off state. apparatus. The first and second preprocessing signal generation units, the first and second signal output units, the first and second output switches, and the first and second output capacitors. Prepared,
When the logical value of the data is 1, the first preprocessing signal generation unit performs a charging operation by a charging circuit included in the first preprocessing signal generation unit, while the logical value of the data is 0 In this case, the charging voltage generated in the charging capacitor of the first preprocessing signal generation unit by performing the discharging operation by the discharging circuit included in the first preprocessing signal generation unit is used as the first preprocessing signal. Generate
The first signal output unit outputs the communication signal to one of the communication lines via the first output switch and the first output capacitor in accordance with the first preprocessing signal. And
The second preprocessing signal generation unit performs a discharging operation by a discharge circuit included in the second preprocessing signal generation unit when the logical value of the data is 1, while the logical value of the data is 0. In this case, the charging voltage generated in the charging capacitor of the second preprocessing signal generation unit by performing the charging operation by the charging circuit included in the second preprocessing signal generation unit is used as the second preprocessing signal. Generate
The second signal output unit outputs the communication signal to the other of the communication lines via the second output switch and the second output capacitor in accordance with the second preprocessing signal. The communication device according to any one of claims 7 to 9, wherein The intermediate voltage setting circuit includes a third constant current source and a fourth constant current source that output the same predetermined current, two diodes connected in series, and a connection point of the diodes set to the intermediate voltage. A pair of diodes, two diodes connected in series, and a connection point of the diodes connected to be able to charge and discharge the charging capacitor of the first preprocessing signal generator, And a third diode pair in which two diodes are connected in series and a connection point of the diodes is connected so as to be able to charge and discharge the charging capacitor of the second preprocessing signal generation unit. 11. The communication apparatus according to claim 10, wherein a diode bridge formed by connecting two and third diode pairs in parallel is interposed between the third and fourth constant current sources.

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