JP2023074462A - Communication terminal and communication system - Google Patents

Abstract

To provide a communication terminal and a communication system that can prevent voltage signal attenuation and are less susceptible to reflected waves in communication systems each having a plurality of communication terminals.SOLUTION: A communication terminal 100 transmits, via a signal line 60, a voltage signal in which a voltage is superimposed on a predetermined first reference voltage. The communication terminal 100 includes an impedance adjustment circuit 120 that switches an output impedance of the communication terminal 100 during a period T0 during which data is transmitted by the voltage signal in which the voltage is superimposed on the predetermined first reference voltage.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to communication terminals and communication systems.

2. Description of the Related Art Conventionally, communication systems that perform load control using two-wire signal lines have been widely used. This communication system is configured by connecting a transmitting terminal, which is a master unit as a central control unit, and a communication terminal such as a switch with two-wire signal lines. This communication system has a feature (called a free topology) that the connection and branching of two-wire signal lines and the arrangement of communication terminals are free, and a flexible system configuration is possible. According to this communication system, a communication system can be realized with a small amount of wiring in a large-scale building. Patent Literature 1 discloses an example of a communication system.

JP 2019-204638 A

2. Description of the Related Art In communication systems, there is a demand for an increase in the number of communication terminals and for high-speed, large-capacity communication. However, as the signal frequency becomes higher, the influence of reflected waves cannot be ignored due to impedance mismatch between the signal line and the transmitting terminal or communication terminal. Due to the influence of the reflected wave, a signal reading error occurs in the communication terminal.

Impedance matching is usually used to suppress reflected waves in high-frequency signals. Specifically, an impedance equivalent to the characteristic impedance of the transmission line is connected (terminated) to the receiving terminal to suppress the influence of the reflected wave. However, since the communication system has a plurality of receiving terminals, if each device connected to the communication system performs termination, the voltage signal may be attenuated and the signal may not be read.

An object of the present disclosure is to provide a communication terminal and a communication system that can prevent voltage signal attenuation and are less susceptible to reflected waves in a communication system having a plurality of communication terminals.

A communication terminal according to the present disclosure transmits, via a signal line, a voltage signal in which a voltage is superimposed on a predetermined first reference voltage. The communication terminal is characterized by having an impedance adjustment circuit that switches the output impedance of the communication terminal during a period in which data is transmitted by a voltage signal in which a voltage is superimposed on a predetermined first reference voltage.

According to the communication terminal of the present disclosure, in a communication system having a plurality of communication terminals, it is possible to realize a communication terminal and a communication system that can prevent attenuation of voltage signals and are less susceptible to reflected waves.

1 is a configuration diagram of a communication system according to an embodiment; FIG. 1 is a configuration diagram of a communication system having a communication terminal of an embodiment; FIG. 1 is a circuit diagram of an example of an impedance adjustment circuit according to an embodiment; FIG. 4 is a diagram illustrating operation timings of an impedance adjustment circuit in the communication terminal of the embodiment; FIG.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following description, specific shapes, materials, directions, numerical values, etc. are examples for facilitating understanding of the present disclosure, and can be changed as appropriate according to usage, purpose, specifications, and the like. In addition, it is assumed from the beginning to selectively combine the constituent elements of the embodiments and modifications described below.

First, the overall configuration and schematic operation of a communication system using the communication terminal of the present disclosure will be described.

FIG. 1 is a configuration diagram of a communication system 10. As shown in FIG. The communication system 10 includes a transmission unit 20 , a switch 31 as a communication terminal 30 and a terminal unit 32 . Lighting fixtures 50a-50d are connected to the terminal unit 32 via relays 40a-40d. The lighting fixtures 50a to 50d are controlled objects in the communication system 10. FIG. In addition to these devices, the communication system 10 may be connected to other switches, other terminal units, other controlled objects, etc., but they are omitted from the drawing. The communication system 10 is a system capable of controlling lighting fixtures 50a to 50d, etc., which are controlled objects in the communication system 10, mainly by the transmission unit 20. FIG. The control of lighting equipment includes on/off control of lighting equipment, dimming control, scene control, monitoring control, and the like. Scene control refers to the dimming and toning of the lighting fixtures according to the lighting fixtures installation location such as Japanese-style room, Western-style room, bedroom, study, etc., morning, noon, night, meal time, gathering time, etc. It is to control. Supervisory control refers to monitoring the control state of lighting fixtures. Note that these controls can be performed by operating the switch 31 .

The communication system 10 employs, for example, a time-division multiplex transmission system, and the signal line 60 is a two-wire cable. In the signal line 60, a signal (information) is transmitted by a pulse signal due to a potential difference between two lines. Further, in the communication system 10 , for example, a cyclic transmission method is adopted, and the signal transmitted from the transmission unit 20 passes through all devices connected to the signal line 60 . Each device confirms the content of the signal, and depending on the content, the device that needs the signal receives the signal. For example, each device receives the signal if the signal contains its own address information, and ignores the signal if the signal does not contain its own address information. In this way, the device connected to the signal line 60 can confirm the contents of even a signal transmitted from the transmission unit 20 whose destination is not itself.

The transmission unit 20 is a base controller that operates centrally in the communication system 10 . The transmission unit 20 transmits the signal from the switch 31 connected to the signal line 60 to the terminal unit 32 . The switch 31 and the terminal unit 32 in FIG. 1 are the communication terminal 30 in the present disclosure. Incidentally, the transmission unit 20 may further have an adapter function for connecting with a host system. Subordinate devices may be controlled based on signals from the host system.

The switch 31 is a wall switch or the like provided for the user to control (on, off, dimming, etc.) the lighting fixtures 50a to 50d. For example, the switch 31 has four operating portions 31a to 31d as shown in FIG. Each operation unit has two states, for example, an ON state and an OFF state, and can be turned on and off by the user's operation.

For example, address information is assigned to each operation unit, and the address information and the lighting fixture are associated in a one-to-one correspondence.

The terminal unit 32 is a device that transmits the signal transmitted from the transmission unit 20 to the relays 40a-40d. The terminal unit 32 has a plurality of terminals, and relays 40a to 40d are connected to the plurality of terminals.

The relays 40a-40d are switches for switching on and off power supply to the lighting fixtures 50a-50d connected thereto. For example, when each relay receives an instruction to turn on the power supply from the terminal unit 32, it turns on the power supply to the lighting fixture connected to itself, and when it receives an instruction to turn off the power supply, it connects to itself. Turn off the power supply to the luminaire that has been turned off. Note that the terminal unit 32 and the relays 40a to 40d may be integrally formed.

Also, instead of the terminal unit 32 and the relays 40a to 40d, a DALI (registered trademark) protocol conversion adapter is used, and the protocol conversion adapter and the plurality of lighting fixtures 50a to 50d are connected via communication lines. good too.

The lighting fixtures 50a to 50d are installed, for example, on the ceiling of the floor in the facility. Each lighting fixture can be switched on and off, and can change the dimming rate (brightness), for example, by a signal from the transmission unit 20 . The light source of the lighting fixture includes LEDs, fluorescent lamps, and the like, but is not particularly limited.

According to such a communication system 10, wiring for connecting the controlled object and the switch 31 one-to-one is unnecessary. In the communication system 10, only the signal line 60 consisting of two lines is required. This allows, for example, less wiring in the communication system 10 in a large building.

As described above, in the communication system 10, an example in which the controlled object is applied to the lighting equipment has been described, but the controlled object is not limited to the lighting equipment. The communication system 10 may be configured to control other equipment such as air conditioners.

In the communication system 10, when the number of connected terminals is increased or the information of signals between terminals is increased, measures are taken to increase the frequency of signals in order to maintain the response of the system. When the voltage signal transmitted through the signal line is increased in frequency, the influence of the reflected wave becomes apparent.

Conventionally, each communication terminal connected to a communication system has an impedance matching circuit on the input side to prevent the influence of reflected waves. However, as described in the conventional problem, when the number of communication terminals increases, the voltage signal sent from the transmission unit may be attenuated and the signal may not be read. A communication terminal according to the present disclosure has a configuration that suppresses signal attenuation without being affected by reflected waves.

FIG. 2 shows a configuration diagram of a communication system 10 including the communication terminal 100 of this embodiment. In the following description, of the communication terminals 30 in the communication system 10 shown in FIG. Signal lines connected to 300-1 and 300-2 are described as transmission lines 600-1 and 600-2, respectively. Any of the communication terminals 30 shown in FIG. 1 operates as the communication terminal 100 when transmitting a signal, and operates as the receiving terminal 300-1 or the like when not transmitting a signal. None of the communication terminal 100 and the receiving terminals 300-1 and 300-2 of this embodiment has a terminating resistor at the input. As a result, it is possible to prevent attenuation of the voltage signal, which has been a conventional problem. Although only the receiving terminals 300-1 and 300-2 are shown, it is of course possible to have a plurality of receiving terminals.

In the communication system 10 of the present embodiment, reflected waves are suppressed by adjusting the output impedance of the communication terminal 100 . However, constant impedance adjustment means that a low impedance is always connected to the transmission line, which may affect the transmission line. Therefore, the communication system 10 of this embodiment is configured to adjust the output impedance while the voltage signal Vs1 is being transmitted.

A communication terminal 100 of this embodiment has a transmission circuit 110 and an impedance adjustment circuit 120 . Impedance R1 is the input impedance of communication terminal 100 . Specifically, the impedance R1 corresponds to the impedance of the power supply circuit provided in the communication terminal 100, and is set to a high impedance.

The transmission circuit 110 is a circuit for transmitting the voltage signal Vs1. In the communication system 10, the transmission circuit 110 has the same configuration in all of the transmission unit 20, the communication terminal 100, and the receiving terminals 300-1 and 300-2.

The transmission circuit 110 generates a voltage signal Vs1 by superimposing a voltage on a first reference voltage VH (not shown), and outputs it to the transmission line 600-3 via the output impedance Rtx. The voltage signal Vs1 is, for example, a voltage signal obtained by superimposing a voltage that swings negatively from the first reference voltage VH. Output impedance Rtx is an impedance determined by the configuration of transmission circuit 110 of communication terminal 100 .

The transmission circuit 110 is equivalently composed of a series circuit of an output impedance Rtx and a switching element Tr1. When the transmission circuit 110 transmits the voltage signal Vs1, the voltage signal Vs1 synchronized with the serial signal V_Rx is output to the transmission line 600-3 by turning on and off the switching element Tr1 according to the serial signal V_Rx generated by a microcomputer or the like. be done.

The impedance adjustment circuit 120 includes an impedance adjustment element Ra, a switching element Tr2, and a reference voltage Vup, and is connected in parallel to the transmission circuit 110 . Impedance adjustment circuit 120 is a circuit for connecting impedance adjustment element Ra in parallel to transmission circuit 110 via switching element Tr2 from a predetermined reference voltage Vup in a power supply circuit (not shown) in communication terminal 100 . The reference voltage Vup may be the same value as the first reference voltage VH, or may be another reference voltage within the power supply circuit of the communication terminal 100 . The switching element Tr2 is configured to be turned on by the impedance adjustment control signal Va during the period during which the voltage signal Vs1 is transmitted. As will be described later, the impedance adjustment control signal Va is generated by a microcomputer or the like that constitutes the control circuit of the communication terminal 100 in synchronization with the serial signal V_Rx. The impedance adjustment circuit 120 becomes active (operating state) when the impedance adjustment control signal Va is at high level (high potential), and becomes inactive (stopped state) when it is at low level (low potential). Specifically, when the impedance adjustment control signal Va is at a high level, the switching element Tr2 is turned on, and the reference voltage Vup is connected to one end of the transmission circuit 110 via the impedance adjustment element Ra. 100 output impedance is adjusted.

The impedance adjusting element Ra is set to a value sufficiently larger than the impedance Rtx. Therefore, when the impedance adjustment control signal Va becomes high level and the switching element Tr2 is turned on, the reference voltage Vup is output to the output terminal T1 via the impedance Ra.

The impedance adjustment element Ra is preferably equal to the characteristic impedance R0 of the transmission line 600-3. Reflected waves from receiving terminals 300 - 1 and 300 - 2 are input to communication terminal 100 . Therefore, by matching the impedance adjustment element Ra with the characteristic impedance R0, the communication terminal 100 does not output reflected waves, so normal data transmission is possible without distorting the voltage signal Vs1. However, the impedance adjusting element Ra does not have to match the characteristic impedance R0 completely. Impedance errors are allowed to the extent that they do not affect the reading of the voltage signal Vs1 at each receiving terminal 300-1, 300-2.

When the impedance adjustment circuit 120 of the present embodiment is in an operating state, the output impedance of the communication terminal 100 is the combined impedance of the impedances Rtx, Ra, and R1 when the switching element Tr1 is on, and the impedance Ra when the switching element Tr1 is off. and R1. When the voltage signal Vs1 is not transmitted, the impedance adjustment circuit 120 is brought into a stopped state, thereby disconnecting the impedance adjustment element Ra, so that the output impedance of the communication terminal 100 becomes R1, which is a high impedance.

FIG. 3 shows specific circuit configurations of the transmission circuit 110 and the impedance adjustment circuit 120 of the communication terminal 100 of this embodiment. In communication terminal 100, transmission circuit 110 and impedance adjustment circuit 120 are connected in parallel to output terminals T1 and T2.

The transmission circuit 110 is a circuit that is connected in parallel to the equivalent impedance R1 of the power supply circuit of the communication terminal 100 and outputs a voltage signal Vs1 in which a voltage synchronized with the serial signal V_Rx is superimposed. The serial signal V_Rx is a signal synchronized with the voltage signal Vs1 output to the transmission line. Serial signal V_Rx is generated by a microcomputer (not shown) of communication terminal 100 .

The transmission circuit 110 receives the serial signal V_Rx from the microcomputer, drives the transistor Q1 (hereinafter referred to as Q1) with the signal inverted by the operational amplifier AMP, and supplies the first reference voltage VH between the output terminals T1 and T2. It outputs a voltage signal Vs1 in which a voltage synchronized with the serial signal V_Rx is superimposed. The transmit circuit 110 causes the impedance Rtx to be connected to the output terminals T1-T2 to the transmission line.

The impedance adjustment circuit 120 includes a series circuit of an impedance adjustment element Ra and a capacitor C1 connected to the output terminal T1 via a PMOSFET Q2 (hereinafter referred to as Q2) to the reference voltage Vup, and an NMOSFET for controlling the on/off of Q2. is composed of Q3 (hereinafter referred to as Q3).

A source terminal of Q2 is connected to the reference voltage Vup, and a drain terminal of Q2 is connected to one end of the impedance adjustment element Ra. The gate terminal of Q2 is connected to the other end of a resistor R3, one end of which is connected to the reference voltage Vup, and is further connected to the drain terminal of Q3. The source terminal of Q3 is connected to circuit ground GND. The gate terminal of Q3 receives the impedance adjustment control signal Va of the impedance adjustment circuit 120 generated by the microcomputer.

The impedance adjustment circuit 120 becomes operative while the impedance adjustment control signal Va is at high level. That is, when the impedance adjustment control signal Va becomes high level, Q3 is turned on, the gate terminal of Q2 becomes low potential, and the source-drain terminal of Q2 is turned on. Then, the reference voltage Vup is output to the output terminal T1 through the impedance adjustment element Ra and the capacitor C1. The capacitor C1 is a DC cut capacitor that prevents a DC voltage from flowing into the impedance adjustment circuit 120 from the output terminal T1. The capacitance value of the capacitor C1 is set to a sufficiently small impedance with respect to the impedance adjusting element Ra.

Next, operation timing of the impedance adjustment circuit 120 will be described. FIG. 4 shows operation timings of the impedance adjustment control signal Va and the serial signal V_Rx. The period T0 during which the serial signal V_Rx repeats high level and low level is the period during which the voltage signal Vs1 is transmitted. While the impedance adjustment control signal Va is high level, the impedance adjustment circuit 120 is in an operating state, and in a low level period, the impedance adjustment circuit 120 is in a non-operating state.

The impedance adjustment control signal Va becomes high level earlier by time Td1 than the start of the serial signal V_Rx (start of period T0), and becomes low level later by time Td2 than the end of the serial signal V_Rx (end of period T0). Therefore, the impedance adjustment circuit 120 starts operating a predetermined time Td1 before starting data transmission by the voltage signal Vs1. Also, the impedance adjustment circuit 120 stops operating after a predetermined time Td2 after data transmission by the voltage signal Vs1 is completed.

The reason for starting the operation by the predetermined time Td1 before starting data transmission by the voltage signal Vs1 is that it is effective as a setup time for the impedance adjustment circuit 120 . A capacitor C1 is connected in series to the impedance adjustment circuit 120, and acts as a period for setting the capacitor C1 to the potential of the output terminal T1 of the transmission line before starting data transmission. This can prevent the potential from becoming unstable immediately after the start of data transmission.

The reason why the operation is terminated after the predetermined time Td2 after the data transmission by the voltage signal Vs1 is terminated is to prevent the reflected waves returned from each receiving terminal from remaining. When the impedance adjustment circuit 120 stops operating at the same time as the end of the serial signal V_Rx (end of data transmission), at least the reflected wave of the voltage signal Vs1 corresponding to the last transmitted data matches the characteristic impedance of the transmission line. will be received by the high impedance R1. In this case, the reflected wave remains in the transmission line, which may affect the next data transmission. By extending the operation of the impedance adjustment circuit 12 by an appropriate time Td2, it is possible to suppress the reflected wave from remaining on the transmission line.

It should be noted that the present invention is not limited to the above-described embodiments and modifications thereof, and it goes without saying that various modifications and improvements are possible within the scope of the matters described in the claims of the present application. .

10 communication system, 20 transmission unit, 30, 100 communication terminal, 31 switch, 32 terminal unit, 40 relay, 50 load (lighting fixture), 60 signal line (transmission line), 110 transmission circuit, 120 impedance adjustment circuit

Claims (8)

A communication terminal that transmits, via a signal line, a voltage signal in which a voltage is superimposed on a predetermined first reference voltage,
A communication terminal having an impedance adjustment circuit that switches output impedance during a period of data transmission by the voltage signal. The impedance adjustment circuit stops operating after the transmission of the data is completed.
The communication terminal according to claim 1. The impedance adjustment circuit starts operating before starting transmission of the data.
A communication terminal according to claim 1 or 2. the impedance adjustment circuit switches the output impedance to the characteristic impedance of the signal line;
A communication terminal according to any one of claims 1 to 3. The impedance adjustment circuit is
having an impedance adjustment element,
The impedance adjustment element has one end connected to one of the signal lines and the other end connected to a predetermined voltage of a power supply circuit of the communication terminal via a switch.
A communication terminal according to any one of claims 1 to 4. The impedance adjustment circuit has a DC cut capacitor connected in series with the impedance adjustment element,
A communication terminal according to any one of claims 1 to 5. the predetermined voltage of the power supply circuit is a voltage different from the first reference voltage;
A communication terminal according to any one of claims 1 to 6. A communication terminal according to any one of claims 1 to 7;
one or more receiving terminals that receive the data transmitted from the communication terminal;
communication system.

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