Signal output device

Abstract

To provide a signal output device that can improve the convenience of communication.SOLUTION: A signal output device 10 outputs a communication signal to a propagation line 30. The signal output device 10 includes a modem 11 that generates one of a first AC signal having a first frequency and a second AC signal having a second frequency as a communication signal, and an amplifier circuit 20 that amplifies the communication signal on the basis of the attenuation of the communication signal in the propagation line 30.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a signal output device.

Background Art

[0002] Conventionally, there is known a signal output device that communicates with a HART communication signal generated by superimposing an AC signal obtained by converting a digital signal into a frequency signal between 1200 Hz and 2200 Hz on a 4 - 20 mA DC signal (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Communication signals attenuate while propagating through a transmission line. Communication signals having different frequencies attenuate at different attenuation rates. The longer the transmission line, the greater the difference in the attenuation rates of communication signals having different frequencies. As the difference in the attenuation rates increases, amplitude control becomes difficult. As a result, the convenience of communication may decrease. An improvement in the convenience of communication is required.

[0005] The present disclosure has been made in view of the above points, and an object thereof is to provide a signal output device capable of improving the convenience of communication.

Means for Solving the Problems

[0006] A signal output device according to some embodiments outputs a communication signal to a transmission line. The signal output device includes a modem that generates one of a first AC signal having a first frequency and a second AC signal having a second frequency as the communication signal, and an amplifier circuit that amplifies the communication signal based on an attenuation rate of the communication signal in the transmission line. By doing so, regardless of whether the communication signal is the first AC signal or the second AC signal, the amplitude when received by a load via the transmission line can be made close to a predetermined value. Also, the degree of freedom in the length of the transmission line is improved. Also, the noise tolerance of the communication signal is improved. As a result, the convenience of communication is improved.

[0007] In a signal output device according to an embodiment, when the attenuation rate of the first AC signal in the transmission line is smaller than the attenuation rate of the second AC signal, the amplifier circuit may make the amplification factor when the communication signal is the first AC signal smaller than the amplification factor when the communication signal is the second AC signal. By doing so, regardless of whether the communication signal is the first AC signal or the second AC signal, the amplitude when received by a load via the transmission line can be made close to a predetermined value. Also, the degree of freedom in the length of the transmission line is improved. Also, the noise tolerance of the communication signal is improved. As a result, the convenience of communication is improved.

[0008] In a signal output device according to an embodiment, when the second frequency is greater than the first frequency, the amplifier circuit may make the amplification factor when the communication signal is the second AC signal greater than the amplification factor when the communication signal is the first AC signal. By doing so, regardless of whether the communication signal is the first AC signal or the second AC signal, the amplitude when received by a load via the transmission line can be made close to a predetermined value. Also, the degree of freedom in the length of the transmission line is improved. Also, the noise tolerance of the communication signal is improved. As a result, the convenience of communication is improved.

[0009] The signal output device according to an embodiment may further include a control unit. The amplification circuit may include a first amplification circuit that amplifies the communication signal at a first amplification factor, a second amplification circuit that amplifies the communication signal at a second amplification factor, and a selection circuit that selects one of the outputs of the first amplification circuit and the output of the second amplification circuit. The control unit may control which output of the output of the first amplification circuit and the output of the second amplification circuit the selection circuit selects based on the attenuation rate of the communication signal in the propagation line. By doing so, it becomes easy to individually control the amplification factors of the first AC signal and the second AC signal. As a result, the convenience of communication is improved.

[0010] In the signal output device according to an embodiment, the control unit may control the selection of the selection circuit based on information obtained from the modem that identifies which of the first AC signal and the second AC signal the communication signal is. By doing so, it becomes easy to individually control the amplification factors of the first AC signal and the second AC signal. As a result, the convenience of communication is improved.

[0011] In the signal output device according to an embodiment, the control unit may control the selection of the selection circuit based on the detection result of the frequency of the communication signal. By doing so, it becomes easy to individually control the amplification factors of the first AC signal and the second AC signal. As a result, the convenience of communication is improved.

[0012] In the signal output device according to an embodiment, the amplification circuit may include an amplification factor change unit configured to be able to change the amplification factor of the communication signal. The control unit may further control the amplification factor change unit based on communication distance information that identifies the length of the propagation line. By doing so, even when the length of the propagation line is changed, the amplitude when received by the load via the propagation line can be made to approach a predetermined value. As a result, the degree of freedom in the length of the propagation line is improved.

Advantages of the Invention

[0013] According to the signal output device according to the present disclosure, the convenience of communication can be improved.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0015] Embodiments according to the present disclosure will be described while comparing with comparative examples.

[0016] (Comparative Example) As shown in FIG. 1, a communication system 9 according to a comparative example includes a signal output device 90 and a propagation line 95. The signal output device 90 includes a modem 91, an amplifier circuit 92, and a capacitor 93. The propagation line 95 is represented by an equivalent circuit including a resistor 951 connected in series and a capacitor 952 connected between the ground point 97. The propagation line 95 includes an input terminal 953 connected to the signal output device 90 and an output terminal 954 connected to a load 96.

[0017] The signal output device 90 generates an AC communication signal with the modem 91, amplifies it with the amplifier circuit 92, and outputs it. Further, the amplified AC communication signal is input to the input terminal 953 of the propagation line 95 via the capacitor 93 and propagates through the propagation line 95. The AC communication signal is output from the output terminal 954 of the propagation line 95 and transmitted to a load 96 connected between the propagation line 95 and the ground point 97.

[0018] The modem 91 generates, as an AC communication signal, either a first AC signal having a first frequency or a second AC signal having a second frequency. The AC signal propagating through the transmission line 95 attenuates at an attenuation rate determined based on the frequency of the AC signal. In other words, the first AC signal and the second AC signal attenuate at different attenuation rates while propagating through the transmission line 95. In this comparative example, it is assumed that the attenuation rate of the first AC signal is smaller than the attenuation rate of the second AC signal.

[0019] Here, it is assumed that the upper limit of the amplitude of the AC signal amplified and output by the amplifier circuit 92 is determined. Specifically, when the modem 91 outputs a signal of HART (Highway Addressable Remote Tranducer) communication as an AC communication signal, the upper limit of the amplitude of the HART signal amplified and output by the amplifier circuit 92 is determined based on the HART communication standard.

[0020] When the upper limit of the amplitude of the AC communication signal amplified and output by the amplifier circuit 92 is determined, the greater the attenuation rate at which the communication signal propagating through the transmission line 95 attenuates, the smaller the amplitude of the communication signal received by the load 96. The decrease in the amplitude of the communication signal reduces the signal-to-noise ratio of the communication signal. That is, the decrease in the amplitude of the communication signal reduces the noise tolerance of the communication signal. Also, the longer the transmission line 95, the greater the difference in attenuation rates. From this, it can be seen that the amplitude of the second AC signal that attenuates at a large attenuation rate can become even smaller. As a result, the communication distance achievable by the communication signal is limited.

[0021] <Parentheses> From the above, in the communication system 9 according to the comparative example, when AC signals having different frequencies are propagated through a single transmission line 95, it is difficult to control the amplitude when the AC signal is received by the load 96. Also, the transmission line 95 can have a large impact on the amplitude. As a result, the convenience of communication can be reduced.

[0022] Therefore, the present disclosure will describe a signal output device 10 (see FIG. 2 etc.) that can improve the convenience of communication.

[0023] (One embodiment of the present disclosure) As shown in FIG. 2, a communication system 1 according to one embodiment includes a signal output device 10 and a propagation line 30. The signal output device 10 includes a modem 11, an amplifier circuit 20, and a capacitor 16. The propagation line 30 is represented by an equivalent circuit including a resistor 31 connected in series and a capacitor 32 connected between the resistor 31 and a ground point 80. The propagation line 30 includes an input terminal 33 connected to the signal output device 10 and an output terminal 34 connected to a load 40.

[0024] The signal output device 10 generates an AC communication signal with the modem 11.

[0025] In the present embodiment, the modem 11 generates a HART communication signal as an AC communication signal. The modem 11 is not limited to this example and may generate various AC signals.

[0026] Further, the modem 11 generates and outputs one of an AC signal having a first frequency and an AC signal having a second frequency. It is assumed that the first frequency is lower than the second frequency. In the present embodiment, the modem 11 generates a HART communication signal as an AC signal. Therefore, the first frequency and the second frequency are determined based on the HART communication standard. Specifically, the first frequency and the second frequency are 1.2 kHz and 2.2 kHz, respectively.

[0027] The signal output device 10 amplifies the AC communication signal generated by the modem 11 with the amplifier circuit 20.

[0028] The amplified AC communication signal is input to the input terminal 33 of the propagation line 30 via the capacitor 16, propagates through the propagation line 30, is output from the output terminal 34, and is transmitted to the load 40. That is, the load 40 receives the AC signal that has propagated through the propagation line 30 as a communication signal. When the AC communication signal is a HART communication signal, the load 40 acquires information specified by the received HART communication signal.

[0029] <Amplification based on the attenuation rate in the propagation line 30> The alternating current signal attenuates while propagating through the transmission line 30. The attenuation rate of the alternating current signal per unit length of the transmission line 30 is determined based on the circuit characteristics of the transmission line 30 and the frequency of the alternating current signal. The longer the transmission line 30 is, the higher the attenuation rate of the alternating current signal becomes. That is, the longer the transmission line 30 is, the smaller the amplitude of the alternating current signal received by the load 40 becomes.

[0030] The amplification circuit 20 of the signal output device 10 amplifies the communication signal based on the attenuation rate of the alternating current signal in the transmission line 30. Specifically, the amplification circuit 20 determines the amplification factor of the alternating current signal based on the attenuation rate in the transmission line 30 so as to control the amplitude of the alternating current signal received by the load 40 to a predetermined value. The predetermined value that is the target of the amplitude control is the upper limit of the amplitude of the alternating current signal received by the load 40 based on the standard of communication using the communication signal, or a value smaller than the upper limit.

[0031] As described above, the attenuation rate of the alternating current signal in the transmission line 30 is determined based on the frequency of the alternating current signal. In the present embodiment, the modem 11 generates and outputs one of the first alternating current signal and the second alternating current signal having different frequencies. The difference in the attenuation rates of the first alternating current signal and the second alternating current signal that propagate through the same transmission line 30 occurs based on the difference in the frequencies of the first alternating current signal and the second alternating current signal.

[0032] When the first alternating current signal is generated as the communication signal, the amplification circuit 20 amplifies the first alternating current signal based on the attenuation rate of the first alternating current signal in the transmission line 30. When the second alternating current signal is generated as the communication signal, the amplification circuit 20 amplifies the second alternating current signal based on the attenuation rate of the second alternating current signal in the transmission line 30. That is, the amplification circuit 20 amplifies the communication signal based on the attenuation rate of the alternating current signal in the transmission line 30.

[0033] In this embodiment, it is assumed that the attenuation rate of the first AC signal in the propagation line 30 is smaller than the attenuation rate of the second AC signal. That is, when the first AC signal and the second AC signal having the same amplitude are input to the propagation line 30, the amplitude of the first AC signal when received by the load 40 is larger than the amplitude of the second AC signal. Therefore, the amplification circuit 20 can reduce the difference between the amplitude of the first AC signal and the amplitude of the second AC signal when received by the load 40 by making the amplification rate of the first AC signal smaller than the amplification rate of the second AC signal.

[0034] In this embodiment, it is assumed that the first frequency of the first AC signal is lower than the second frequency of the second AC signal. Also, it is assumed that the higher the frequency of the AC signal propagating through the propagation line 30, the larger the attenuation rate of the AC signal in the propagation line 30. In this case, the amplification circuit 20 makes the amplification rate of the AC signal having a lower frequency smaller than the amplification rate of the AC signal having a higher frequency. Specifically, the amplification circuit 20 makes the amplification rate of the first AC signal smaller than the amplification rate of the second AC signal. By doing so, the difference between the amplitude of the first AC signal and the amplitude of the second AC signal when received by the load 40 can be reduced.

[0035] <Configuration example of the amplification circuit 20> As shown in FIG. 2, the amplification circuit 20 may include a first amplification circuit 21, a second amplification circuit 22, and a selection circuit 23. When the first AC signal is generated as a communication signal by the modem 11, the first amplification circuit 21 amplifies the first AC signal output from the modem 11 based on the attenuation rate of the first AC signal in the propagation line 30 and outputs it to the selection circuit 23. When the second AC signal is generated as a communication signal by the modem 11, the second amplification circuit 22 amplifies the second AC signal output from the modem 11 based on the attenuation rate of the second AC signal in the propagation line 30 and outputs it to the selection circuit 23.

[0036] The signal output device 10 may further include a control unit 15. The control unit 15 is configured to be able to control the amplification factor of the amplification circuit 20. The control unit 15 may be configured to include a processor such as a CPU (Central Processing Unit). The control unit 15 may realize a predetermined function by causing the processor to execute a predetermined program. The control unit 15 may include a storage unit. The storage unit may store various information used for the operation of the control unit 15, or a program for realizing the function of the control unit 15. The storage unit may function as a work memory of the control unit 15. The storage unit may be configured by, for example, a semiconductor memory. The storage unit may be included in the control unit 15 or may be configured separately from the control unit 15.

[0037] In the configuration example shown in FIG. 2, the control unit 15 acquires from the modem 11 information specifying which of the first AC signal or the second AC signal the modem 11 has generated as a communication signal. The information specifying the AC signal generated by the modem 11 as a communication signal may include information regarding the frequency of the AC signal, and is also referred to as frequency information. The control unit 15 generates control information for the selection circuit 23 based on the frequency information acquired from the modem 11 and outputs it to the selection circuit 23. Specifically, when the control unit 15 acquires from the modem 11 information that the first AC signal has been generated as a communication signal, the control unit 15 generates control information so as to cause the selection circuit 23 to select the output of the first amplification circuit 21. When the control unit 15 acquires from the modem 11 information that the second AC signal has been generated as a communication signal, the control unit 15 generates control information so as to cause the selection circuit 23 to select the output of the second amplification circuit 22.

[0038] The signal output device 10 may further include a frequency detection unit 17 as illustrated in FIG. 3. The frequency detection unit 17 is configured to detect the frequency of the AC signal output as a communication signal from the modem 11. The frequency detection unit 17 outputs the detection result of the frequency to the control unit 15. The control unit 15 acquires the detection result of the frequency. The control unit 15 may acquire the detection result of the frequency as frequency information. Based on the detection result (frequency information) of the frequency detection unit 17, the control unit 15 identifies which of the first AC signal or the second AC signal the modem 11 has generated as the communication signal. When the control unit 15 determines that the first AC signal has been generated as the communication signal, it generates control information to cause the selection circuit 23 to select the output of the first amplification circuit 21. When the control unit 15 determines that the second AC signal has been generated as the communication signal, it generates control information to cause the selection circuit 23 to select the output of the second amplification circuit 22. That is, the control unit 15 may generate the control information of the selection circuit 23 based on the detection result of the frequency detection unit 17.

[0039] The signal output device 10 illustrated in FIGS. 2 and 3 selects and outputs one of the outputs of the first amplification circuit 21 and the second amplification circuit 22 by the selection circuit 23 based on the control information from the control unit 15. By doing so, the amplification circuit 20 can amplify the first AC signal and the second AC signal individually and make the amplification factor of the first AC signal different from that of the second AC signal. As a result, the amplification circuit 20 can amplify each of the first AC signal and the second AC signal based on the attenuation rate in the transmission line 30. That is, the amplification circuit 20 can easily control the amplification factor of each AC signal based on the attenuation rate in the transmission line 30 of the AC signals having different frequencies.

[0040] <Example procedure of signal output method> The signal output device 10 may execute a signal output method including the procedure of the flowchart illustrated in FIG. 4. The signal output method may be realized as a signal output program to be executed by a processor constituting the control unit 15. The signal output program may be stored in a non-transitory computer-readable medium.

[0041] The control unit 15 acquires frequency information (step S1). The control unit 15 may acquire, from the modem 11, information for specifying an AC signal generated by the modem 11 as a communication signal, as the frequency information. The control unit 15 may acquire, from the frequency detection unit 17, the detection result of the frequency detection unit 17 as the frequency information.

[0042] The control unit 15 determines whether a first AC signal is generated as a communication signal by the modem 11 based on the frequency information (step S2). When the first AC signal is generated as the communication signal (step S2: YES), the control unit 15 selects the output of the first amplifier circuit 21 as the output of the amplifier circuit 20 (step S3). Specifically, the control unit 15 generates control information so that the selection circuit 23 selects the output of the first amplifier circuit 21 and outputs the control information to the selection circuit 23. When the first AC signal is not generated as the communication signal (step S2: NO), the control unit 15 determines that a second AC signal is generated as the communication signal, and selects the output of the second amplifier circuit 22 as the output of the amplifier circuit 20 (step S4). Specifically, the control unit 15 generates control information so that the selection circuit 23 selects the output of the second amplifier circuit 22 and outputs the control information to the selection circuit 23. After executing the procedure of step S3 or S4, the control unit 15 ends the execution of the procedure of the flowchart in FIG. 4.

[0043] <Parentheses> As described above, according to the signal output device 10 and the signal output method according to the present embodiment, the first AC signal that attenuates at a small attenuation rate in the transmission line 30 and the second AC signal that attenuates at a large attenuation rate in the transmission line 30 are each amplified at different amplification rates. Specifically, the amplifier circuit 20 can make the amplification rate of the first AC signal that attenuates at a small attenuation rate in the transmission line 30 smaller than the amplification rate of the second AC signal that attenuates at a large attenuation rate in the transmission line 30. By doing so, the difference in the amplitudes of the first AC signal and the second AC signal when received by the load 40 can be reduced. As a result, regardless of whether the first AC signal or the second AC signal is generated as the communication signal, the amplitude of the AC signal received by the load 40 can be made closer to a predetermined value.

[0044] Here, it is assumed that the upper limit of the amplitude of the AC communication signal output by the amplifier circuit 20 is determined. Specifically, when the modem 11 outputs a HART communication signal as the communication signal, it is assumed that the upper limit of the amplitude of the HART signal output by the amplifier circuit 20 is determined based on the HART communication standard.

[0045] Even if the upper limits of the amplitudes when the first AC signal and the second AC signal are output from the amplifier circuit 20 are determined, the signal output device 10 according to the present embodiment can reduce the difference in the respective amplitudes when received by the load 40. Specifically, the signal output device 10 sets the amplitude when the second AC signal that attenuates at a large attenuation rate in the transmission line 30 is output from the amplifier circuit 20 to the upper limit or a value close to the upper limit. On the other hand, the signal output device 10 makes the amplitude when the first AC signal that attenuates at a small attenuation rate in the transmission line 30 is output from the amplifier circuit 20 smaller than the upper limit. By doing so, the difference in the respective amplitudes when the first AC signal and the second AC signal are received by the load 40 is reduced. When the difference in the respective amplitudes when the first AC signal and the second AC signal are received by the load 40 is reduced, signal processing in the load 40 becomes easy. For example, the first AC signal and the second AC signal may be amplified at the same amplification rate in the load 40.

[0046] Further, even when the attenuation rate in the transmission line 30 increases due to the increase in the length of the transmission line 30, the signal output device 10 according to the present embodiment can reduce the difference in the respective amplitudes when the first AC signal and the second AC signal are received by the load 40 by changing the amplification factor of the amplifier circuit 20. Therefore, even when the transmission line 30 becomes longer, the difference in the respective amplitudes when the first AC signal and the second AC signal are received by the load 40 can be reduced. As a result, the communication possible distance by the communication signal can be increased. That is, the extension of the transmission line 30 becomes possible.

[0047] Also, it can be said that the influence of the transmission line 30 on the amplitude is reduced. It can also be said that the degree of freedom in the design of the transmission line 30 is improved. As a result, the convenience of communication in the communication system 1 is improved.

[0048] (Other embodiments) <Amplification circuit 20 having amplification factor changing unit 28> As shown in FIG. 5, a signal output device 10 according to another embodiment includes a modem 11, an amplification circuit 20 having an amplification factor changing unit 28, a control unit 15, and a capacitor 16. The modem 11 generates an AC communication signal. The amplification factor changing unit 28 is configured to be able to change the amplification factor. The amplification circuit 20 amplifies the AC communication signal generated by the modem 11 at the amplification factor set by the amplification factor changing unit 28. Further, the AC communication signal amplified by the amplification circuit 20 is input to the transmission line 30 via the capacitor 16, propagates through the transmission line 30, and is received by the load 40.

[0049] The amplification factor changing unit 28 may include, for example, a variable resistor as an electric resistor that determines the amplification factor. The amplification factor changing unit 28 may change the amplification factor of the amplification circuit 20 by changing the resistance value of the variable resistor.

[0050] The control unit 15 identifies an AC signal generated by the modem 11 as a communication signal based on the frequency information. The control unit 15 controls the amplification factor changing unit 28 so as to make the amplification factor of the amplification circuit 20 different when the modem 11 generates a first AC signal as a communication signal and when the modem 11 generates a second AC signal as a communication signal. For example, the control unit 15 may control the amplification factor changing unit 28 so that the amplification factor of the amplification circuit 20 becomes a first amplification factor when a first AC signal is generated as a communication signal. The control unit 15 may control the amplification factor changing unit 28 so that the amplification factor of the amplification circuit 20 becomes a second amplification factor when a second AC signal is generated as a communication signal.

[0051] In this embodiment, even when the attenuation rates of the first AC signal and the second AC signal in the propagation line 30 change due to a change in the length of the propagation line 30, the amplification factor can be changed based on further information specifying the length of the propagation line 30. The information specifying the length of the propagation line 30 is also referred to as communication distance information. Specifically, the control unit 15 may control the amplification factor of the amplification circuit 20 based on the frequency information and the communication distance information. By doing so, in the communication system 1, even when the length of the propagation line 30 is changed, the difference in the amplitudes of the first AC signal and the second AC signal when received by the load 40 can be reduced. Therefore, the degree of freedom in designing the propagation line 30 is increased. As a result, the communication convenience of the communication system 1 is improved.

[0052] <Bidirectionality of communication> In this embodiment, the configuration in which the communication signal is transmitted to the load 40 has been described. As another embodiment, the modem 11 and the amplification circuit 20 may be located on the load 40 side of the propagation line 30, and the communication signal may be transmitted from the output terminal 34 to the input terminal 33 of the propagation line 30. Also in this case, the amplification factor of the communication signal in the amplification circuit 20 may be determined based on the attenuation rate of the communication signal in the propagation line 30. When the amplification circuit 20 is provided on the load 40 side, the amplification circuit 20 may determine the amplification factor of the communication signal based on the attenuation rate when the communication signal propagates from the output terminal 34 to the input terminal 33 through the propagation line 30. When bidirectional communication is possible, the input terminal 33 may not only input but also output a signal. The output terminal 34 may not only output but also input a signal. That is, the names of the input terminal 33 and the output terminal 34 are for convenience in distinguishing the terminals.

[0053] <Superposition of DC signal> In the above-described embodiments, the signal output device 10 generates an AC communication signal by the modem 11. The signal output device 10 may further include a circuit that amplifies the AC communication signal by the amplifier circuit 20, passes it through the capacitor 16, and then superimposes a DC signal on the communication signal. The DC signal may be, for example, an instrumentation standard signal used to notify the load 40 of the result measured by an external measuring device. The instrumentation standard signal includes, for example, a current having a magnitude of 4 mA or more and 20 mA or less. That is, the instrumentation standard signal is a DC current signal whose current magnitude is controlled within a predetermined range. The external measuring device may include, for example, a pH measuring device or the like, or may include various other measuring devices. A configuration that converts the measurement result of the measuring device into an instrumentation standard signal is also referred to as a converter or a transmitter or the like. That is, the signal output device 10 can be used in a converter, a transmitter, or the like. The signal output device 10 may be used in a PLC (Programmable Logic Controller) or a DCS (Distributed Control System) or the like. By the signal output device 10 superimposing a DC signal on the AC communication signal and outputting it to the load 40, a plurality of information can be transmitted. As a result, the communication convenience of the communication system 1 is improved.

[0054] Although the embodiments according to the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications or alterations are included in the scope of the present disclosure. For example, the functions included in each component or each step can be rearranged so as not to be logically contradictory, and a plurality of components or steps can be combined into one or divided.

Explanation of Reference Numerals

[0055] 1 Communication system 10 Signal output device (11: Modem, 15: Control unit, 16: Capacitor, 17: Frequency detection unit) 20 Amplifier circuit (21: First amplifier circuit, 22: Second amplifier circuit, 23: Selection circuit, 28: Amplification factor change unit) 30 Propagation line (31: Resistor, 32: Capacitor, 33: Input terminal, 34: Output terminal) 40 Load 80 Ground point

Claims

1. A signal output device that outputs a communication signal to a transmission line, comprising: a modem that generates, as the communication signal, one of a first AC signal having a first frequency and a second AC signal having a second frequency different from the first frequency; an amplification circuit that amplifies the communication signal with different amplification factors when the first AC signal is input as the communication signal and when the second AC signal is input, and outputs the amplified signal to the transmission line; a control unit; wherein the amplification circuit includes a first amplification circuit that amplifies the communication signal with a first amplification factor, a second amplification circuit that amplifies the communication signal with a second amplification factor, and a selection circuit that selects one of the outputs of the first amplification circuit and the second amplification circuit; the control unit controls which output of the outputs of the first amplification circuit and the second amplification circuit the selection circuit selects based on the detection result of the frequency of the communication signal; a signal output device.

2. A signal output device that outputs a communication signal to a transmission line, comprising: a modem that generates, as the communication signal, one of a first AC signal having a first frequency and a second AC signal having a second frequency different from the first frequency; an amplification circuit that amplifies the communication signal with different amplification factors when the first AC signal is input as the communication signal and when the second AC signal is input, and outputs the amplified signal to the transmission line; a control unit; wherein the amplification circuit includes a first amplification circuit that amplifies the communication signal with a first amplification factor, a second amplification circuit that amplifies the communication signal with a second amplification factor, and a selection circuit that selects one of the outputs of the first amplification circuit and the second amplification circuit; the control unit controls which output of the outputs of the first amplification circuit and the second amplification circuit the selection circuit selects based on information obtained from the modem that specifies which of the first AC signal and the second AC signal the communication signal is; a signal output device.

3. A signal output device that outputs a communication signal to a transmission line, comprising: a modem that generates, as the communication signal, one of a first AC signal having a first frequency and a second AC signal having a second frequency different from the first frequency; an amplification circuit that amplifies the communication signal with different amplification factors when the first AC signal is input as the communication signal and when the second AC signal is input, and outputs the amplified signal to the transmission line; a control unit; wherein The amplification circuit has an amplification factor changing unit configured to be able to change the amplification factor of the communication signal. The control unit controls the amplification factor changing unit to change the amplification factor of the communication signal based on the detection result of the frequency of the communication signal. A signal output device.

4. The signal output device according to claim 3, wherein the control unit further controls the amplification factor changing unit to change the amplification factor of the communication signal based on communication distance information specifying the length of the propagation line.

5. The signal output device according to any one of claims 1 to 4, wherein when the attenuation rate of the first AC signal in the propagation line is smaller than the attenuation rate of the second AC signal, the amplification factor when the communication signal is the first AC signal is made smaller than the amplification factor when the communication signal is the second AC signal.

6. The signal output device according to any one of claims 1 to 5, wherein when the second frequency is higher than the first frequency, the amplification factor when the communication signal is the second AC signal is made larger than the amplification factor when the communication signal is the first AC signal.

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