JP4888356B2 - Transmission system - Google Patents

Description

  The present invention relates to a transmission system that performs frequency division multiplexing transmission of a plurality of types of signals between a plurality of terminal devices connected to a transmission path.

2. Description of the Related Art Conventionally, a transmission system that performs frequency division multiplex transmission of a plurality of types of signals between a plurality of terminal devices connected to a transmission path is disclosed in Patent Document 1. In this conventional system, a plurality of terminal devices connected to a signal line (transmission path) frequency-division multiplex-transmit three types of signals (audio signal, control signal, video signal) to each terminal device. Is provided with a demultiplexing unit for frequency multiplexing and frequency demultiplexing of the audio signal, the control signal, and the video signal transmitted through the transmission path, respectively.
JP 2007-174578 A

  Here, when the audio signal is an analog signal and the video signal is a digital signal, generally the distance (frequency gap) between the audio signal and the video signal band is considerably wide (for example, about several megahertz), so that the low-order band It is possible to demultiplex an audio signal and a video signal with only a pass filter.

  However, in the conventional system described in Patent Document 1, both the audio signal and the video signal are digital signals, and the frequency gap between the band of the audio signal and the video signal is relatively narrow (for example, several hundred kilohertz). Degree). For this reason, since it is difficult to separate the audio signal and the video signal only with the low-order bandpass filter, in order to separate the audio signal and the video signal, both the transmission side and the reception side have a high level after the bandpass filter. The following filters (low pass filter and high pass filter) are required. That is, the conventional demultiplexing unit requires three types of filters, ie, a band-pass filter, a low-pass filter, and a high-pass filter for one type of signal, which increases the circuit scale and cost. There is. In addition, when a large number of terminal devices are connected to the transmission path, there is a possibility that the terminal device becomes a load on the transmission path and the signal is attenuated.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a transmission system capable of frequency division multiplex transmission of a plurality of types of signals while suppressing an increase in circuit scale and cost and signal attenuation. There is.

  In order to achieve the above object, the invention of claim 1 is a plurality of types of signals including a first signal and a second signal whose frequency bands are adjacent to each other between a plurality of terminal devices connected to a transmission line. Each of the terminal devices is provided between a plurality of transmission means for individually transmitting a plurality of types of signals and between the plurality of transmission means and the transmission path. And a demultiplexing means for frequency-multiplexing a plurality of types of signals transmitted from the terminal and frequency-separating a plurality of types of signals transmitted from other terminal devices via a transmission line, and transmitting a first signal. The transmission means includes a first transmission section for transmitting the first signal and a first reception section for receiving the first signal, and the second transmission means for transmitting the second signal is: A second transmitter for transmitting a second signal and a second signal received; A first interference prevention filter having one end side connected to the transmission line and the other end side commonly connected to the first transmission unit and the first reception unit; A first signal separation filter provided between a connection point between the first transmission unit and the first reception unit and the first reception unit, for separating the first signal; a first transmission unit; The first variable impedance element provided between the connection point of the receiving unit and the first transmitting unit, one end side is connected to the transmission line, and the other end side is common to the second transmitting unit and the second receiving unit A second signal separation unit configured to separate the second signal provided between the connected second interference prevention filter, a connection point between the second transmission unit and the second reception unit, and the second reception unit; A filter, a second variable impedance element provided between a connection point between the second transmitter and the second receiver, and the second transmitter; When the transmission unit of 1 is transmitting the first signal, the impedance of the first variable impedance element is set to be equal to or lower than the characteristic impedance of the transmission line, and the second transmission unit is transmitting the second signal The impedance of the second variable impedance element is set to be equal to or lower than the characteristic impedance of the transmission line, and the impedance of the first variable impedance element is set to be lower than the characteristic impedance of the transmission line when the first receiving unit receives the first signal. And an impedance control means for making the impedance of the second variable impedance element higher than the characteristic impedance of the transmission line when the second receiver is receiving the second signal.

  According to the first aspect of the present invention, the impedance control means transmits the impedance of the variable impedance element connected to the transmitting unit when the first and second transmitting units transmit the first and second signals, respectively. Since the characteristic impedance of the first and second interference prevention filters connected to the transmitter is steep and the interference with other signal frequency bands can be prevented. The first and second transmitters do not require a filter for signal separation, so that an increase in circuit scale and cost can be suppressed, and the first and second receivers are respectively connected to the first and second signals. When receiving the signal, the impedance control means attenuates the signal by making the impedance of the variable impedance element connected to the receiving unit higher than the characteristic impedance of the transmission line. It can be obtained. As a result, a plurality of types of signals can be frequency division multiplexed while suppressing an increase in circuit scale and cost and signal attenuation.

  According to a second aspect of the present invention, in the first aspect of the invention, the first interference prevention filter includes a frequency band of the first signal in the pass band and a frequency band of the second signal in the stop band. The second interference prevention filter includes a band rejection filter including the frequency band of the second signal in the passband and including the frequency band of the first signal in the stopband.

  According to the second aspect of the present invention, the signals received by the first and second receivers are already multiplexed after preventing interference in the terminal device on the transmission side. The signal can be separated by a signal separation filter composed of a pass filter, and the circuit scale and cost can be reduced.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the first transmission means transmits the first signal in a relatively narrow band, and the second transmission means is in a relatively wide band. Two signals are transmitted.

  According to the present invention, it is possible to perform frequency division multiplexing transmission of a plurality of types of signals while suppressing an increase in circuit scale and cost and signal attenuation.

  Hereinafter, an embodiment in which the present invention is applied to an intercom system for a detached house will be described in detail with reference to the drawings. However, the transmission system to which the technical idea of the present invention can be applied is not limited to the intercom system.

  As shown in FIG. 2, the intercom system of this embodiment includes an interphone master unit (hereinafter abbreviated as “master unit”) 1 installed in a dwelling unit and a plurality of units (3 in the illustrated example) installed outside the dwelling unit. Doorphone handsets 2A, 2B, 2C, a plurality of camera handsets 3A, 3B, 3C (in the illustrated example) that are also installed outside the dwelling unit, and a plurality of units installed inside the dwelling unit (see FIG. In the example shown, four interphone sub-master units (hereinafter abbreviated as “sub-master units”) 4A, 4B, 4C, and 4D are provided, and the doorphone sub unit 2A and the camera sub unit 3A transmit balanced two-wire transmission. The transmission is connected to the main unit 1 via the path Ls1, and the doorphone sub unit 2B and the camera sub unit 3B are connected to the main unit 1 via the balanced two-wire transmission path Ls2, and the intercom sub unit 2C and the camera sub unit 3C are connected. It is connected to the master unit 1 via the balanced two-wire transmission line Ls3, and the sub master units 4A to 4D are connected. It is configured by connecting the feed to the parent device 1 in the transmission path Ls4 of 衡 2-wire. In the present embodiment, the master unit 1, the door phone slave units 2A to 2C, and the sub master units 4A to 4D each correspond to a terminal device according to the present invention.

  The doorphone sub-units 2A to 2C all have a common configuration. The microphone 20a, the speaker 20b, and the audio signal output from the microphone 20a are encoded, digitally modulated in a relatively low frequency band, and a transmission line. An audio signal processing unit 20 that digitally demodulates and decodes a modulated audio signal transmitted via Ls1, Ls2, and Ls3 and generates sound from the speaker 20b, an individual imaging element such as a CCD or CMOS, and a lens A camera unit 21 having an optical system for imaging a visitor, a video signal output from the camera unit 21 is encoded, and digitally modulated in a frequency band relatively higher than an audio signal, and the modulated video signal is transmitted through a transmission path The audio signal output from the video signal transmission unit 22 and the audio signal processing unit 20 transmitted via Ls1,. The video signal output from the video signal transmission unit 22 is frequency-multiplexed and sent to the transmission lines Ls1, Ls2, and Ls3, and transmitted from the master unit 1 and the sub-master units 4A to 4D via the transmission lines Ls1, Ls2, and Ls3. A demultiplexing unit 23 for separating the voice signal, a paging signal transmitting unit 24 for transmitting a paging signal via the transmission lines Ls1, Ls2, and Ls3, and a control unit 25 for controlling the entire operation using a microcomputer as a main component. An operation input receiving unit 26 that receives an operation input of a call button (not shown) and outputs an operation signal to the control unit 25, and a parent device 1 via transmission lines Ls1, Ls2, and Ls3 as will be described later. And a power supply unit 27 that creates an operating power supply for each unit using supplied power.

  The power supply voltage (DC voltage) from the base unit 1 to the door phone sub-units 2A to 2C is intended to reduce the power consumption of the system when the door phone sub-unit 2A is not in a talking state or a monitor state (described later). Therefore, the state is relatively low, and the state is relatively high in the call state and the monitor state. Hereinafter, a state where the power supply voltage is low is referred to as a standby power supply state, and a state where the power supply voltage is high is referred to as an operation power supply state. In the intercom sub-units 2A to 2C, when in the standby power supply state, the microcomputer of the control unit 25 is in a standby state and waits for an operation signal to be output from the operation input receiving unit 26. When the operation signal is output from the input reception unit 26, the control unit 25 controls the call signal transmission unit 24 to reduce the line voltage of the transmission lines Ls1, ... to a voltage lower than that in the standby power supply state. A call signal is transmitted to the base unit 1. When the base unit 1 that has received the calling signal shifts the power supply voltage from the standby power supply state to the operation power supply state, the microcomputer of the control unit 25 returns from the standby state to the normal state, and the camera unit 21 and the video signal transmission unit 22 are turned on. The video signal is activated to transmit the video signal to the master unit 1 via the transmission lines Ls1,... And the audio signal processing unit 20 is activated to enable transmission / reception of the audio signal, that is, a state where a call is possible. Further, as will be described later, when the master unit 1 accepts an operation input for setting the door phone slave units 2A,. The camera unit 21 of the door phone slave unit 2A,... Is restored by returning from the normal state to starting the camera unit 21 and the video signal transmission unit 22 and transmitting the video signal to the base unit 1 via the transmission lines Ls1,. The video imaged at can be monitored by the master unit 1.

  The camera sub-units 3A to 3C all have a common configuration. The camera unit 30 includes an individual imaging element such as a CCD and a CMOS and an optical system such as a lens. Transmission channel Ls1 between base unit 1 and video signal transmission unit 31 that modulates the video signal to be output at a frequency higher than that of the audio signal and transmits the frequency-modulated video signal via transmission channels Ls1,. ,..., And a human body detection that detects the presence of a person in the monitoring area and outputs a human body detection signal by detecting a heat ray radiated from the human body with a pyroelectric element. And a control unit 34 that controls the entire operation using a microcomputer as a main component. However, the operating power sources of the camera units 3A to 3C are created from a commercial power source by a power circuit (not shown).

  The control signal transmission unit 32 transmits the control signal by frequency shift keying (FSK) using a carrier wave having a frequency sufficiently lower than that of the audio signal. In addition, a unique ID is assigned to each of the camera slave units 3A to 3C by a dip switch (not shown), and the base unit 1 and each of the camera slave units 3A are set by using this ID as the transmission destination or transmission source address of the control signal. Control signals are individually transferred to and from 3C.

  In the camera subunits 3A to 3C, the control unit 34 that has received the human body detection signal output from the human body detection unit 33 activates the camera unit 30 and the video signal transmission unit 31 to transmit the video signal obtained by capturing the monitoring area to the transmission path Ls1. The control unit 34 activates the camera unit 30 and the video signal transmission unit 31 to pick up an image of the monitoring area when a control signal requesting transmission of the video signal is received. The video signal is transmitted to the main unit 1 via the transmission lines Ls1,.

  On the other hand, the base unit 1 encodes the audio signal output from the microphone 10a and the speaker 10b and the microphone 10a, digitally modulates the audio signal in a relatively low frequency band, and transmits the modulated signal via the transmission lines Ls1, Ls2, and Ls3. The audio signal processing unit 10 that digitally demodulates and decodes the received audio signal and generates sound from the speaker 10b, the monitor unit 11 having a display device such as a liquid crystal display, and the transmission line Ls1,. A video signal processing unit 12 that digitally demodulates and decodes the modulated video signal and displays it on the monitor unit 11 and displays various videos based on screen data prepared in advance on the monitor unit 11, and a transmission line Ls1, A call for monitoring a line voltage of ... and receiving a call signal transmitted from the intercom 2A, ... Control signal transmission unit 14 for transmitting a control signal by the FSK method between the signal reception unit 13 and the camera slave units 3A to 3C and the sub master units 4A to 4D, and frequency-multiplexing the audio signal, the video signal, and the control signal And a demultiplexer 15 for separating and separating, a plurality of pushbutton switches (not shown), and a touch panel (not shown) disposed on the screen of the liquid crystal display of the monitor unit 11 to receive operation inputs. An operation input receiving unit 16 that outputs an operation signal corresponding to the received operation input, and a control unit 17 that performs overall operation control using a microcomputer as a main component are provided. In addition, although not shown in figure, the power supply circuit which produces the operation power supply of each part from a commercial power supply and supplies electric power to the door phone sub-units 2A-2C via transmission line Ls1, Ls2, Ls3 is also provided.

  As described above, for example, when the call signal transmitted from the door phone slave unit 2A is received by the call signal receiving unit 13, the control unit 17 of the base unit 1 operates the power supply voltage to the door phone slave unit 2A from the standby power supply state. The power supply state is shifted and the voice signal processing unit 10 is controlled to ring a ringing tone from the speaker 10b. On the other hand, in the intercom 2A, the microcomputer of the control unit 25 returns from the standby state to the normal state, and the camera unit 21 and the video signal transmission unit 22 are activated to transmit the video signal to the master unit 1 via the transmission lines Ls1,. The audio signal processing unit 20 is activated while transmitting. In the base unit 1, the video signal transmitted from the intercom unit 2 </ b> A is processed by the video signal processing unit 12 to display the visitor's video on the monitor unit 11. If a call button (not shown) formed of a pushbutton switch is pressed by looking at the video of the visitor displayed on the control unit 17, an operation signal is output from the operation input receiving unit 16 and the control unit 17 that has received the operation signal. Activates the audio signal processing unit 10 and exchanges audio signals with the intercom 2A via the transmission line Ls1, so that a visitor and a dweller can talk.

  Further, when the presence of a person is detected in the monitoring area in any of the camera slave units (for example, the camera slave unit 3A), the control unit 34 that receives the human body detection signal output from the human body detection unit 33 performs the camera unit 30. In addition, the video signal transmission unit 31 is activated to transmit a video signal obtained by capturing an image of the monitoring area to the base unit 1 via the transmission line Ls1. In the base unit 1, the video signal transmitted from the camera slave unit 3 </ b> A is signal-processed by the video signal processing unit 12, and the video in the monitoring area is displayed on the monitor unit 11. Further, when a call signal transmitted from any one of the doorphone sub-units 2A,... Is received while displaying an image transmitted from the camera sub-unit 3A, or during a call with the doorphone sub-unit 2A,. When the video signal is transmitted from the camera slave unit 3A,..., The control unit 17 causes the video signal processing unit 12 to perform signal processing so that these two videos are displayed on the screen of the monitor unit 11 at the same time.

  Here, since base unit 1 has only one video signal processing unit 12 that receives and processes video signals for three systems of transmission lines Ls1, Ls2, and Ls3, collision between video signals is avoided. Therefore, the time division multiplex transmission system is adopted. That is, a video synchronization signal (hereinafter abbreviated as “synchronization signal”) digitally modulated in the same frequency band as the video signal is sent from the video signal processing unit 12 of the base unit 1 to the transmission lines Ls1, Ls2, and Ls3. The doorphone sub-units 2A to 2C and the camera sub-units 3A to 3C are individually assigned to a plurality of time slots defined by the synchronization signal, and the sub-units 2A to 2C and 3A to 3C are assigned to the own unit. A video signal (packet including video data) is transmitted, received in each time slot in the video signal processing unit 12 of the base unit 1, and the original video is reconstructed from the video signal demodulated and displayed on the monitor unit 11. ing. That is, in this embodiment, the audio signal transmitted in a relatively low frequency band corresponds to the first signal, and is transmitted in a frequency band adjacent to the frequency band of the audio signal and higher than the frequency band of the audio signal. The video signal and the synchronization signal are equivalent to the second signal. However, the details of the time division multiplex transmission are well known in the art and will not be described.

  The secondary master units 4A to 4D all have a common configuration, and encode a voice signal output from the microphone 40a, the speaker 40b, and the microphone 40a, digitally modulate it in a relatively low frequency band, and a transmission path. An audio signal processing unit 40 that digitally demodulates and decodes an audio signal transmitted via Ls4 and generates sound from the speaker 40b, a monitor unit 41 having a display device such as a liquid crystal display, and the base unit 1 Digitally demodulating and decoding the modulated video signal transmitted through the base unit 1 and displaying it on the monitor unit 41, and displaying various videos based on screen data prepared in advance. A control signal is transmitted by the FSK method between the video signal processing unit 42 displayed on the monitor unit 41 and the master unit 1. A control signal transmission unit 43, a demultiplexing unit 44 that frequency-multiplexes and separates audio signals, video signals, and control signals, a plurality of push button switches (not shown), and a monitor unit 41 on a liquid crystal display screen. An operation input receiving unit 45 that includes a touch panel (not shown) and receives an operation input and outputs an operation signal corresponding to the received operation input, and performs overall operation control using a microcomputer as a main component. And a control unit 46. Each secondary master unit 4A to 4D is assigned a unique ID (an ID different from the IDs of the camera slave units 3A to 3C) by a dip switch (not shown), and this ID is assigned to the transmission destination or transmission source of the control signal. By using this address, control signals are individually exchanged between the master unit 1 and the sub-master units 4A to 4D.

  Here, when the master unit 1 receives a call signal from the door phone slave unit 2A,..., It calls the sub master units 4A to 4D from the door phone slave unit 2A,... (Hereinafter referred to as “door phone call”). A control signal for notifying the user is transmitted, and, as will be described later, an operation for performing a one-to-one or one-to-many extension call between the master unit 1 and the sub-master units 4A to 4D has been performed. Sometimes, a control signal for notifying a call to the secondary master units 4A to 4D (hereinafter referred to as "extension call") is transmitted. In the sub master unit 4A,..., When the control signal transmission unit 43 receives the doorphone call control signal transmitted from the base unit 1, the control unit 46 controls the voice signal processing unit 40 to ring the ring tone from the speaker 40b. In addition, the video signal transmitted from the intercom unit 2A,... Via the master unit 1 is signal-processed (digital demodulated and decoded) by the video signal processing unit 42, and the video of the visitor is displayed on the monitor unit 41. If the dweller who hears the ringing tone views the video of the visitor displayed on the monitor unit 41 and presses a call button (not shown) including a push button switch, the operation input receiving unit 45 sends an operation signal. Is output, and the control unit 46 that receives the operation signal activates the audio signal processing unit 40 and exchanges audio signals with the intercom handsets 2A,... Via the transmission lines Ls1 to Ls3 and Ls4. Visitor And dwelling people can call. Alternatively, when the control signal transmission unit 43 receives the extension call control signal transmitted from the base unit 1, the control unit 46 of the secondary base unit 4A,... Controls the voice signal processing unit 40 to generate a ringing tone from the speaker 40b. If the dweller who hears the ringing tone presses a call button (not shown) including a pushbutton switch, an operation signal is output from the operation input receiving unit 45, and the control unit 46 that receives the operation signal The inhabitants can make a call (extension call) by activating the audio signal processing unit 40 and exchanging audio signals with the sub-master units 4A,... Via the transmission lines Ls1 to Ls3 and Ls4.

  Here, in the master unit 1 and the sub master units 4A to 4D, any one of the door phone slave units 2A to 2C or the camera slave units 3A to 3C is selected, and a video signal is transmitted to the selected slave unit to monitor unit 11 , 41 has a function of displaying video (video monitor function). For example, when performing video monitoring of the doorphone slave unit 2 </ b> C, the control unit 17 of the base unit 1 shifts the power supply voltage to the doorphone slave unit 2 </ b> C from the standby power supply state to the operation power supply state, and from the video signal processing unit 12. A synchronization signal is transmitted via the transmission line Ls3. As a result, the microcomputer of the control unit 25 of the door phone sub-unit 2C returns from the standby state to the normal state, activates the camera unit 21 and the video signal transmission unit 22, and transmits the video signal through the transmission line Ls3 in its own time slot. By transmitting to the master unit 1, the video image captured by the camera unit 21 of the door phone slave unit 2C can be displayed on the monitor unit 11 of the master unit 1 for video monitoring. Alternatively, when the video monitoring of the camera slave unit 3C is performed, the control unit 17 of the parent device 1 transmits a control signal including a command requesting the camera slave unit 3C to transmit a video signal from the control signal transmission unit 14. In addition, a synchronization signal is transmitted from the video signal processing unit 12 via the transmission line Ls3. Then, in the camera slave unit 3C that has received this control signal by the control signal transmission unit 32, the control unit 34 activates the camera unit 30 and the video signal transmission unit 31, and transmits the video signal through the transmission line Ls3 in its own time slot. To the master unit 1 via the network. As a result, the base unit 1 can perform video monitoring by displaying the video captured by the camera unit 30 of the camera slave unit 3C on the monitor unit 11. When video monitoring is performed by the secondary master units 4A to 4D, a control signal including a video monitor start request specifying the target doorphone slave units 2A to 2C or the camera slave units 3A to 3C is sent from the secondary master units 4A to 4D. By transmitting to the master unit 1, the master unit 1 transmits the video signal to the designated slave unit, and video is transmitted from the doorphone slave units 2A to 2C or the camera slave units 3A to 3C via the master unit 1. A signal can be received and an image can be displayed on the monitor unit 41 of the sub-master units 4A to 4D. Note that the hardware of the control signal transmission units 14 and 43 that transmit the control signal in the master unit 1 and the sub-master units 4A to 4D may be shared with the audio signal transmission hardware in the audio signal processing units 10 and 40. I do not care.

  Next, the configuration of the demultiplexing units 15, 23, and 44 of the terminal device (base unit 1, door phone sub-units 2A to 2C, sub-base units 4A to 4D) that is the gist of the present invention will be described.

  FIG. 1 is a block diagram showing a main part of base unit 1. The audio signal processing unit 10 includes an audio signal transmission unit 101 that transmits a digitally modulated audio signal and an audio signal reception unit 102 that receives the digitally modulated audio signal. The video signal processing unit 12 includes a digital signal. A synchronization signal transmission unit 121 that transmits a modulated video synchronization signal and a video signal reception unit 122 that receives a digitally modulated video signal are provided.

  The demultiplexing unit 15 has one end connected to the transmission paths Ls1 to Ls3 of the slave units (doorphone slave units 2A to 2C and camera slave units 3A to 3C) and the other end side common to the audio signal transmitting unit 101 and the audio signal receiving unit 102. Audio signal separation that is provided between the connected first handset side interference prevention filter F11, the connection point of the audio signal transmitting unit 101 and the audio signal receiving unit 102, and the audio signal receiving unit 102 to separate the audio signal The filter F12, the first variable impedance element Z1 provided between the connection point of the audio signal transmitting unit 101 and the audio signal receiving unit 102, and the audio signal transmitting unit 101, and the transmission lines Ls1 to Ls3 whose one end is a slave unit Is connected to the synchronization signal transmission unit 121 and the video signal reception unit 122, and the second slave unit side interference prevention filter F21 is connected to the synchronization signal transmission unit 121 and the video signal reception unit 122. A video signal separation filter F22 provided between a connection point of the unit 122 and the video signal receiving unit 122 to separate the video signal and the synchronization signal from the audio signal, and a connection point of the synchronization signal transmitting unit 121 and the video signal receiving unit 122 Is connected to the transmission line Ls4 of the sub-master unit and the other end is common to the audio signal transmitting unit 101 and the audio signal receiving unit 102. The second sub-base unit side interference prevention filter F31 connected to the second sub-base unit is connected to the transmission line Ls4 of the sub-base unit and the other end side is commonly connected to the synchronization signal transmitting unit 121 and the video signal receiving unit 122. When the secondary master unit side interference prevention filter F32 and the audio signal transmission unit 101 are transmitting audio signals, the impedance of the first variable impedance element Z1 is set to the transmission line Lsn (n = 1). 2, 3, 4), and when the synchronization signal transmitter 121 is transmitting a synchronization signal, the impedance of the second variable impedance element Z 2 is less than the characteristic impedance of the transmission line Lsn, and the audio signal receiver The impedance of the first variable impedance element Z1 is set higher than the characteristic impedance of the transmission line Lsn when the audio signal 102 is receiving an audio signal, and the second variable impedance is received when the video signal receiving unit 122 is receiving the video signal. Impedance control means for making the impedance of the variable impedance element Z2 higher than the characteristic impedance of the transmission line Lsn. However, in the present embodiment, the audio signal transmission unit 101 and the synchronization signal transmission unit 121 increase or decrease the impedances of the first variable impedance element Z1 and the second variable impedance element Z2, respectively, to realize the function of the impedance control means. ing.

  Further, the first slave unit side interference prevention filter F11 and the first sub-master unit side interference prevention filter F31 include a frequency band of the audio signal in the pass band and a frequency band of the video signal and the synchronization signal in the stop band. The second handset-side interference prevention filter F21 and the second sub-master-side interference prevention filter F32 each include a pass filter that includes the frequency band of the audio signal in the stop band and the pass band of the frequency band of the video signal and the synchronization signal. The audio signal separation filter F12 includes a low-pass filter that includes the frequency band of the audio signal in the pass band and includes the frequency band of the video signal and the synchronization signal in the stop band, and the video signal separation filter F22. Consists of a high-pass filter including the frequency band of the video signal and the synchronizing signal in the pass band and including the frequency band of the audio signal in the stop band. Since the control signal is transmitted in a frequency band sufficiently lower than the frequency band of the audio signal and the video signal, it is easily multiplexed and separated by a low-order low-pass filter or the like as described in the conventional example. be able to. Moreover, although illustration and description are omitted, the demultiplexing units 23 and 44 of the door phone sub-units 2A to 2C and the sub-master units 4A to 4D have the same configuration as the demultiplexing unit 15 of the base unit 1.

  Next, the operation of the demultiplexing unit 15 in the parent device 1 will be described. First, as shown in FIG. 3A, a case where an audio signal is transmitted from the base unit 1 and a video signal transmitted from the intercom handsets 2A to 2C is received at the same time will be described. In this case, the audio signal transmission unit 101 sets the impedance of the first variable impedance element Z1 to be equal to or lower than the characteristic impedance of the transmission line LSn, so that the first slave unit side interference prevention filter F11 (and the first sub master unit side interference) can be obtained. The filter characteristic of the prevention filter F31) is steep, so that interference outside the band of the audio signal can be removed, and the synchronization signal transmission unit 121 uses the impedance of the second variable impedance element Z2 as the characteristic of the transmission line LSn. The attenuation of the video signal can be suppressed by making it higher than the impedance. Since the interference of the audio signal to the frequency band of the video signal is removed by the first slave unit side interference prevention filter F11 (and the first sub master unit side interference prevention filter F31), the master unit 1 (and In the secondary master units 4A to 4D), the video signal can be separated by the video signal separation filter F22 including a low-order high-pass filter.

  Further, as shown in FIG. 3 (b), a case will be described in which a synchronization signal is transmitted from the parent device 1 to the door phone sub-units 2A to 2C and simultaneously, an audio signal is transmitted from the parent device 1 to the door phone sub-units 2A to 2C. In this case, the audio signal transmission unit 101 and the synchronization signal transmission unit 121 make the impedances of the first and second variable impedance elements Z1 and Z2 equal to or lower than the characteristic impedance of the transmission line LSn, respectively. The filter characteristics of the side interference prevention filters F11 and F21 (and the first and second sub-master unit side interference prevention filters F31 and F32) become steep, and the interference of the audio signal and the synchronization signal outside each band is removed. Can do.

  Further, as shown in FIG. 3 (c), the master unit 1 receives the audio signals transmitted from the doorphone slave units 2A to 2C, and simultaneously receives the video signals transmitted from the door phone slave units 2A to 2C. The case where it does is demonstrated. In this case, the audio signal transmission unit 101 and the synchronization signal transmission unit 121 respectively attenuate the audio signal and the video signal by setting the impedances of the first and second variable impedance elements Z1 and Z2 higher than the characteristic impedance of the transmission line LSn. In addition, as described with reference to FIG. 3B, the audio signal and the video signal are multiplexed by removing interference from each other in the demultiplexing unit 23 of the transmission source intercom units 2A to 2C. Therefore, it can be separated by the audio signal separation filter F12 and the video signal separation filter F22 which are low-order low-pass filters.

  Finally, as shown in FIG. 3 (d), a case will be described in which the base unit 1 receives the audio signals transmitted from the intercom handsets 2A to 2C and simultaneously transmits the synchronization signal from the base unit 1. In this case, the audio signal transmitting unit 101 can suppress the attenuation of the audio signal by making the impedance of the first variable impedance element Z1 higher than the characteristic impedance of the transmission line LSn, and the synchronization signal transmitting unit 121 can By setting the impedance of the second variable impedance element Z2 to be equal to or lower than the characteristic impedance of the transmission line LSn, the filter characteristics of the second slave unit side interference prevention filter F21 (and the second secondary master unit side interference prevention filter F32) are steep. Thus, interference outside the band of the synchronization signal can be eliminated. Note that the operations of the demultiplexing units 23 and 43 of the door phone sub-units 2A to 2C and the sub-base units 4A to 4D are basically the same as those of the base unit 1, and thus description thereof is omitted.

  Thus, in the present embodiment, when transmitting the audio signal and the synchronization signal, the impedance of the first and second variable impedance elements Z1 and Z2 is made equal to or lower than the characteristic impedance of the transmission line LSn, so that the audio signal separation filter F12 and Since the filter characteristics of the video signal separation filter F22 are steep and the interference of the audio signal and the synchronization signal outside the band is removed, the audio signal transmission unit 101 and the synchronization signal transmission unit 121 do not need a filter for signal separation. The increase in circuit scale and cost can be suppressed, and when the audio signal receiving unit 102 and the video signal receiving unit 122 receive the audio signal and the video signal, respectively, the impedance control means is connected to the receiving unit. The impedances of the first and second variable impedance elements Z1 and Z2 having the characteristic in the transmission line LSn It is possible to suppress the attenuation of the signal to be higher than-impedance. As a result, it is possible to perform frequency division multiplexing transmission of a plurality of types of signals (audio signal, video signal, and synchronization signal) while suppressing increase in circuit scale and cost and signal attenuation as compared with the conventional example.

It is a principal part block diagram of the main | base station (terminal device) in embodiment of this invention. It is a system configuration | structure figure of an intercom system same as the above. (A)-(d) is operation | movement explanatory drawing same as the above.

Explanation of symbols

1 Interphone main unit (terminal device)
DESCRIPTION OF SYMBOLS 15 Demultiplexing part 101 Audio | voice signal transmission part 102 Audio | voice signal receiving part 121 Synchronization signal transmission part 122 Image | video signal receiving part F11 1st subunit | mobile_unit side interference prevention filter F12 Audio | voice signal separation filter F21 2nd subunit | mobile_unit side interference prevention filter F22 Video signal separation filter

Claims (3)

A transmission system that performs frequency division multiplex transmission of a plurality of types of signals including a first signal and a second signal whose frequency bands are adjacent to each other between a plurality of terminal devices connected to a transmission path,
Each terminal apparatus frequency-multiplexes a plurality of transmission means for individually transmitting a plurality of types of signals, and a plurality of types of signals that are provided between the plurality of transmission means and the transmission path and transmitted from each transmission means. And demultiplexing means for frequency-separating a plurality of types of signals transmitted from other terminal devices via a transmission line,
The first transmission means for transmitting the first signal has a first transmission unit for transmitting the first signal and a first reception unit for receiving the first signal,
The second transmission means for transmitting the second signal has a second transmitter for transmitting the second signal, and a second receiver for receiving the second signal,
The demultiplexing means includes a first interference prevention filter having one end connected to the transmission line and the other end connected in common to the first transmitter and the first receiver, the first transmitter, and the first receiver. A first signal separation filter provided between the connection point of the first and the first reception unit for separating the first signal, a connection point between the first transmission unit and the first reception unit, and the first transmission A first variable impedance element provided between the first transmission line and a second interference prevention filter having one end connected to the transmission line and the other end connected in common to the second transmission unit and the second reception unit; A second signal separation filter provided between a connection point between the second transmission unit and the second reception unit and the second reception unit to separate the second signal; a second transmission unit; A second variable impedance element provided between a connection point of the receiving unit and the second transmitting unit, and the first transmitting unit outputs the first signal The impedance of the first variable impedance element is set to be equal to or lower than the characteristic impedance of the transmission line when transmitting, and the impedance of the second variable impedance element is transmitted when the second transmission unit transmits the second signal. The impedance of the first variable impedance element is made higher than the characteristic impedance of the transmission line when the first receiver is receiving the first signal, and the second receiver is A transmission system comprising: impedance control means for making the impedance of the second variable impedance element higher than the characteristic impedance of the transmission line when receiving the second signal.   The first interference prevention filter includes a band pass filter including the frequency band of the first signal in the pass band and the frequency band of the second signal in the stop band. The second interference prevention filter includes the second interference filter 2. The transmission system according to claim 1, comprising a band rejection filter including a frequency band of the signal in a pass band and including a frequency band of the first signal in a stop band.   3. The first transmission means transmits a first signal in a relatively narrow band, and the second transmission means transmits a second signal in a relatively wide band. The described transmission system.

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