JP2006325141A - Video transmission system - Google Patents

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JP2006325141A
JP2006325141A JP2005148527A JP2005148527A JP2006325141A JP 2006325141 A JP2006325141 A JP 2006325141A JP 2005148527 A JP2005148527 A JP 2005148527A JP 2005148527 A JP2005148527 A JP 2005148527A JP 2006325141 A JP2006325141 A JP 2006325141A
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impedance
video
unit
transmission line
master unit
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Hiroko Maeda
裕子 前田
Hideo Sakamoto
英雄 阪本
Mitsuharu Ikeda
光治 池田
Satoshi Sugimoto
敏 杉本
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Panasonic Electric Works Co Ltd
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Matsushita Electric Works Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To simplify circuit configuration and to reduce costs of a sub-master unit while suppressing deterioration of video quality. <P>SOLUTION: The video transmission system is constituted of a slave unit 10 installed outside a dwelling unit, a master unit 20 installed inside the dwelling unit and connected to the slave unit 10 via a signal line Ls, one or more sub-master units 30 installed inside the dwelling unit, transmitted and wired to the master unit 20 by a transmission line Ld composed of two-wire balanced cables and a terminating device 40 which terminates the transmission line Ld. Synthetic impedance between input impedance Z of the sub-master unit 30 and terminating resistance R of the terminating device 40 is set so that it becomes ±a% to characteristic impedance of the transmission line Ld. Therefore, it is unnecessary to set the input impedance Z of the sub-master unit 30 to higher enough than the characteristic impedance of the transmission line Ld like in the conventional example, the circuit configuration of the sub-master unit 30 is simplified and the costs of the sub-master unit 30 are reduced while suppressing deterioration of the video quality. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、子器において撮像された映像を親機並びに副親機に伝送して表示する映像伝送システムに関するものである。   The present invention relates to a video transmission system that transmits and displays video captured by a slave unit to a master unit and a secondary master unit.

この種の映像伝送システムは、例えば、住戸の外玄関等に設置されるカメラ付きのドアホン子器と、住戸内に設置され信号線を介してドアホン子器と接続される親機と、住戸内における親機と別の場所にそれぞれ設置され伝送線で送り配線される１乃至複数台の副親機とで構成され、ドアホン子器と親機又は副親機との間におけるドアホン通話や親機と副親機との間における内線通話を行うとともに、ドアホン子器のカメラで撮像された来訪者の映像を親機又は副親機のモニタ画面に表示するようにしたインターホンシステムに組み込まれている（特許文献１参照）。   This type of video transmission system includes, for example, a door phone slave unit with a camera installed at a front door of a dwelling unit, a master unit installed in the dwelling unit and connected to the door phone sub unit via a signal line, Door phone communication between the door phone slave unit and the master unit or the sub master unit, and one or more sub master units that are installed at different locations from the master unit and are sent and wired by transmission lines. Is built into an interphone system that performs extension calls between the mobile phone and the secondary master unit, and displays a visitor image captured by the camera of the door phone slave unit on the monitor screen of the master unit or secondary master unit (See Patent Document 1).

図４は上記インターホンシステムに組み込まれた映像伝送システムの一例を示し、住戸の外玄関等に設置されるカメラ付きのドアホン子器１０と、住戸内に設置され信号線Ｌｓを介してドアホン子器１０と接続される親機２０と、住戸内における親機２０と別の場所にそれぞれ設置され伝送線Ｌｄで送り配線される複数台の副親機３０と、伝送線Ｌｄを終端する終端装置４０とで映像伝送システム（インターホンシステム）が構成されている。ドアホン子器１０ではカメラで撮像した来訪者の映像（映像信号）を周波数変調して信号線Ｌｓに送出し、信号線Ｌｓを介して伝送されてくる周波数変調された映像信号が親機２０において周波数復調され、復調された映像信号によって親機２０のモニタ画面に来訪者の映像が表示される。また親機２０では２線式の平衡ケーブルからなる伝送線Ｌｄを介して周波数変調された映像信号を副親機３０に中継しており、伝送線Ｌｄを介して伝送されてくる周波数変調された映像信号が副親機３０において周波数復調され、復調された映像信号によって副親機３０のモニタ画面にも来訪者の映像が表示される。   FIG. 4 shows an example of a video transmission system incorporated in the above intercom system. A doorphone slave unit 10 with a camera installed at an exterior entrance of a dwelling unit and a doorphone subunit set via a signal line Ls installed in the dwelling unit. 10, a master unit 20 connected to the master unit 10, a plurality of sub-master units 30 installed in different locations from the master unit 20 in the dwelling unit and routed by the transmission line Ld, and a termination device 40 for terminating the transmission line Ld. A video transmission system (interphone system) is configured. The intercom unit 10 frequency-modulates a visitor's video (video signal) captured by the camera and sends it to the signal line Ls. The frequency-modulated video signal transmitted through the signal line Ls is transmitted to the base unit 20. The video of the visitor is displayed on the monitor screen of the master unit 20 by the frequency demodulated video signal. Further, the base unit 20 relays the frequency-modulated video signal to the sub-base unit 30 via the transmission line Ld formed of a two-wire balanced cable, and the frequency-modulated signal transmitted via the transmission line Ld is transmitted. The video signal is frequency-demodulated in the sub-master unit 30, and the video of the visitor is also displayed on the monitor screen of the sub-master unit 30 by the demodulated video signal.

ここで、映像信号を伝送する搬送波の波長が伝送線Ｌｄの配線長よりも短くなるため、伝送線Ｌｄと終端抵抗との間でインピーダンスの不整合が大きくなると、映像信号の反射が生じ、モニタに表示する画質が劣化してしまうことになる。従って、上記従来例においては、終端装置４０のインピーダンスを伝送線Ｌｄの特性インピーダンスに等しくするとともに、伝送線Ｌｄに接続される各副親機３０の入力インピーダンス（伝送線Ｌｄから副親機３０側を見たインピーダンス）を伝送線Ｌｄの特性インピーダンスよりも十分に高い値に設定することで副親機３０の入力インピーダンスの影響が実質的に無視できるようにしている。
特開平１０−５１５６１号公報 Here, since the wavelength of the carrier wave for transmitting the video signal is shorter than the wiring length of the transmission line Ld, if the impedance mismatch between the transmission line Ld and the terminating resistor increases, reflection of the video signal occurs, and the monitor The image quality displayed on the screen will deteriorate. Therefore, in the above conventional example, the impedance of the terminating device 40 is made equal to the characteristic impedance of the transmission line Ld, and the input impedance of each sub-master unit 30 connected to the transmission line Ld (from the transmission line Ld to the sub-master unit 30 side). Is set to a value sufficiently higher than the characteristic impedance of the transmission line Ld, so that the influence of the input impedance of the secondary master unit 30 can be substantially ignored.
JP-A-10-51561

しかしながら、副親機３０において伝送線Ｌｄが送り配線される端子間や、あるいは副親機３０の内部回路に形成された配線パターン間に生じる浮遊容量や各種の寄生容量等の影響によって副親機３０の入力インピーダンスを伝送線Ｌｄの特性インピーダンスよりも十分に高い値に設定することが難しく、ひいては副親機３０の回路構成の複雑化やコストアップを招いていた。   However, in the secondary master unit 30, the secondary master unit is affected by stray capacitance and various parasitic capacitances generated between terminals to which the transmission line Ld is sent and wired, or between wiring patterns formed in the internal circuit of the secondary master unit 30. Thus, it is difficult to set the input impedance of 30 to a value sufficiently higher than the characteristic impedance of the transmission line Ld, which in turn causes the circuit configuration of the secondary master unit 30 to be complicated and costly.

本発明は上記事情に鑑みてなされたものであり、その目的は、映像品質の劣化を抑えつつ副親機の回路構成の簡素化やコストダウンが図れる映像伝送システムを提供することにある。   The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a video transmission system capable of simplifying the circuit configuration of the secondary master unit and reducing the cost while suppressing deterioration of video quality.

請求項１の発明は、上記目的を達成するために、住戸外に設置される子器と、住戸内に設置され信号線を介して子器と接続される親機と、住戸内に設置され親機に対して２線式の平衡ケーブルからなる伝送線で送り配線される１乃至複数台の副親機と、伝送線を終端する終端装置とからなり、子器は、来訪者を撮像する撮像手段と、撮像手段から出力される映像信号を周波数変調し信号線を介して親機に伝送する映像伝送手段とを備え、親機は、信号線を介して伝送されてくる映像信号を復調する映像復調手段と、映像復調手段で復調された映像信号によって映像を表示する表示手段と、信号線を介して伝送されてくる周波数変調された映像信号を伝送線を介して副親機に中継する映像中継手段とを備え、副親機は、伝送線を介して伝送されてくる映像信号を復調する映像復調手段と、映像復調手段で復調された映像信号によって映像を表示する表示手段とを備えた映像伝送システムにおいて、伝送線に接続される副親機並びに終端装置のインピーダンスと伝送線の特性インピーダンスとの整合度合いに対する許容範囲を伝送線の特性インピーダンスに対して±ａ％としたときに、副親機の入力インピーダンスと終端装置のインピーダンスの合成インピーダンスが伝送線の特性インピーダンスに対して±ａ％の範囲となるように設定されたことを特徴とする。   In order to achieve the above object, the first aspect of the present invention provides a slave unit installed outside the dwelling unit, a master unit installed inside the dwelling unit and connected to the slave unit via a signal line, and installed in the dwelling unit. Consists of one or more sub-master units that are sent and wired with a transmission line consisting of a two-wire balanced cable to the master unit, and a termination device that terminates the transmission line, and the slave unit images the visitor An image pickup means and a video transmission means for frequency-modulating a video signal output from the image pickup means and transmitting the image signal to a master unit via a signal line, the master unit demodulates the video signal transmitted via the signal line The video demodulating means, the display means for displaying the video by the video signal demodulated by the video demodulating means, and the frequency-modulated video signal transmitted via the signal line is relayed to the sub-master via the transmission line. The secondary master unit is transmitted via a transmission line. In a video transmission system comprising a video demodulating means for demodulating an incoming video signal and a display means for displaying video by the video signal demodulated by the video demodulating means, the impedance of the sub-master unit and the terminating device connected to the transmission line When the allowable range for the degree of matching between the transmission line characteristic impedance and the transmission line characteristic impedance is ± a% with respect to the transmission line characteristic impedance, the combined impedance of the input impedance of the secondary master unit and the impedance of the terminating device is the characteristic impedance of the transmission line. Is set to be in a range of ± a%.

請求項２の発明は、請求項１の発明において、副親機の入力インピーダンスと終端装置のインピーダンスの合成インピーダンスが、１台分の副親機の入力インピーダンスと終端装置のインピーダンスの合成インピーダンスが伝送線の特性インピーダンスに対してプラスａ％となり、且つ複数台分の副親機の入力インピーダンスと終端装置のインピーダンスの合成インピーダンスが伝送線の特性インピーダンスに対してマイナスａ％となるように設定されたことを特徴とする。   According to a second aspect of the invention, in the first aspect of the invention, the combined impedance of the input impedance of the secondary master unit and the impedance of the terminating device is transmitted as the combined impedance of the secondary master unit for one unit and the impedance of the terminating device. The characteristic impedance of the line is set to plus a%, and the combined impedance of the input impedances of a plurality of sub-master units and the impedance of the terminating device is set to be minus a% with respect to the characteristic impedance of the transmission line. It is characterized by that.

請求項３の発明は、請求項１又は２の発明において、副親機は、入力インピーダンスを相対的に高いインピーダンスと相対的に低いインピーダンスとに切り替える切替手段を備えたことを特徴とする。   The invention of claim 3 is characterized in that, in the invention of claim 1 or 2, the sub-master unit includes a switching means for switching the input impedance between a relatively high impedance and a relatively low impedance.

請求項４の発明は、請求項３の発明において、終端装置は、インピーダンスを相対的に高いインピーダンスと相対的に低いインピーダンスとに切り替える切替手段を備えたことを特徴とする。   The invention of claim 4 is characterized in that, in the invention of claim 3, the termination device comprises switching means for switching the impedance between a relatively high impedance and a relatively low impedance.

請求項５の発明は、請求項１〜４の何れかの発明において、親機の映像中継手段の伝送線に対する出力インピーダンスが伝送線の特性インピーダンスよりも低く設定されたことを特徴とする。   A fifth aspect of the invention is characterized in that, in any one of the first to fourth aspects of the invention, the output impedance of the video relay means of the master unit to the transmission line is set lower than the characteristic impedance of the transmission line.

請求項６の発明は、請求項１〜５の何れかの発明において、親機の映像中継手段は、複数系統の伝送線に映像信号を伝送することを特徴とする。   According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the video relay means of the master unit transmits a video signal to a plurality of transmission lines.

請求項１の発明によれば、副親機の入力インピーダンスを従来例よりも低い値に設定することができて映像品質の劣化を抑えつつ副親機の回路構成の簡素化やコストダウンが図れるという効果がある。   According to the first aspect of the present invention, the input impedance of the secondary master unit can be set to a value lower than that of the conventional example, and the circuit configuration of the secondary master unit can be simplified and the cost can be reduced while suppressing the deterioration of the video quality. There is an effect.

請求項２の発明によれば、請求項１と同様に映像品質の劣化を抑えつつ副親機の回路構成の簡素化やコストダウンが図れるという効果がある。   According to the second aspect of the present invention, as in the first aspect, there is an effect that the circuit configuration of the secondary master unit can be simplified and the cost can be reduced while suppressing the deterioration of the video quality.

請求項３の発明によれば、副親機の入力インピーダンスと終端装置のインピーダンスの合成インピーダンスが伝送線の特性インピーダンスに対して±ａ％を超えるような台数の副親機が接続された場合でも切替手段により副親機の入力インピーダンスを相対的に高いインピーダンスに切り替えることで伝送線の特性インピーダンスに対して±ａ％の範囲に収めることができ、副親機の接続台数の増加に柔軟に対応することが可能になるという効果がある。   According to the invention of claim 3, even when a number of secondary master units are connected such that the combined impedance of the input impedance of the secondary master unit and the impedance of the terminating device exceeds ± a% with respect to the characteristic impedance of the transmission line. By switching the input impedance of the secondary master unit to a relatively high impedance by the switching means, it can be kept within the range of ± a% relative to the characteristic impedance of the transmission line, flexibly responding to the increase in the number of secondary master units connected There is an effect that it becomes possible to do.

請求項４の発明によれば、副親機の接続台数が増えた場合における合成インピーダンスの整合がより確実に行えるという効果がある。   According to the invention of claim 4, there is an effect that the combined impedance can be more reliably matched when the number of connected sub-master units is increased.

請求項５の発明によれば、親機から伝送線に送出する映像信号の出力損失を小さくして回路の低消費電力化や小型化が図れるという効果がある。   According to the fifth aspect of the present invention, there is an effect that the output loss of the video signal transmitted from the master unit to the transmission line can be reduced to reduce the power consumption and the size of the circuit.

請求項６の発明によれば、施工性が向上するという効果がある。   According to invention of Claim 6, there exists an effect that workability improves.

以下、本発明を従来例で説明したインターホンシステムに適用した実施形態により詳細に説明する。   Hereinafter, embodiments of the present invention applied to an intercom system described in the related art will be described in detail.

（実施形態１）
本実施形態の映像伝送システムは、図１に示すように住戸外に設置される子器１０と、住戸内に設置され信号線Ｌｓを介して子器１０と接続される親機２０と、住戸内に設置され親機２０に対して２線式の平衡ケーブルからなる伝送線Ｌｄで送り配線される１乃至複数台の副親機３０と、伝送線Ｌｄを終端する終端装置４０とからなる。 (Embodiment 1)
As shown in FIG. 1, the video transmission system of the present embodiment includes a slave unit 10 installed outside a dwelling unit, a master unit 20 installed inside the dwelling unit and connected to the slave unit 10 via a signal line Ls, and a dwelling unit. It comprises one or a plurality of sub-master devices 30 that are installed inside and are sent and wired by a transmission line Ld consisting of a two-wire balanced cable to the master device 20, and a termination device 40 that terminates the transmission line Ld.

子器１０は、来訪者を撮像するカメラ部１１と、カメラ部１１から出力される映像信号を周波数変調する映像信号処理部１２と、平衡−不平衡変換などを行って映像信号処理部１２で周波数変調された映像信号を信号線Ｌｓを介して親機２０に送信する映像送信回路部１３とを備え、カメラ部１１が撮像手段、映像信号処理部１２と映像送信回路部１３が映像伝送手段に相当する。   The slave unit 10 includes a camera unit 11 that images a visitor, a video signal processing unit 12 that modulates the frequency of the video signal output from the camera unit 11, and balanced-unbalanced conversion. A video transmission circuit unit 13 for transmitting the frequency-modulated video signal to the main unit 20 via the signal line Ls, the camera unit 11 being an imaging unit, and the video signal processing unit 12 and the video transmission circuit unit 13 being a video transmission unit. It corresponds to.

親機２０は、平衡−不平衡変換などを行って信号線Ｌｓを介して子器１０から伝送されてくる映像信号を受信する映像受信回路部２１と、映像受信回路部２１で受信した映像信号を復調する映像信号処理部２２と、映像信号処理部２２で復調された映像信号によって映像を表示するモニタテレビ２３と、映像受信回路部２１で受信した映像信号（周波数変調された映像信号）を２線式の平衡ケーブルからなる伝送線Ｌｄを介して副親機３０に送信（中継）する映像送信回路部２４とを備える。   The master unit 20 performs a balanced-unbalanced conversion and the like, receives a video signal transmitted from the slave unit 10 via the signal line Ls, and a video signal received by the video receiving circuit unit 21. A video signal processing unit 22 that demodulates the video signal, a monitor television 23 that displays video using the video signal demodulated by the video signal processing unit 22, and a video signal (frequency-modulated video signal) received by the video reception circuit unit 21. And a video transmission circuit unit 24 that transmits (relays) the secondary master unit 30 via a transmission line Ld formed of a two-wire balanced cable.

副親機３０は、平衡−不平衡変換などを行って信号線Ｌｓを介して子器１０から伝送されてくる映像信号を受信するとともに受信した映像信号を復調する映像受信処理部３１と、映像受信処理部３１で復調された映像信号によって映像を表示するモニタテレビ３２と、伝送線Ｌｄの線間を終端抵抗で終端する状態と終端しない状態をスイッチのオン・オフで択一的に切り替える終端装置４０とを備える。但し、図示は省略しているが、子器１０、親機２０、副親機３０はそれぞれマイクロホン及びスピーカや、信号線Ｌｓ並びに伝送線Ｌｄを介して音声信号を送受信する音声送受信回路などの通話用の回路を備えており、子器１０と親機２０又は副親機３０との間でドアホン通話を行うとともに親機２０と副親機３０若しくは副親機３０同士の間で内線通話を行うことができる。   The secondary master unit 30 performs balanced-unbalanced conversion and the like, receives a video signal transmitted from the slave unit 10 via the signal line Ls, and demodulates the received video signal, and a video A monitor television 32 that displays an image by a video signal demodulated by the reception processing unit 31, and a termination that selectively switches between a state in which a transmission line Ld is terminated with a termination resistor and a state in which the transmission line Ld is not terminated by turning on and off the switch. Device 40. However, although illustration is omitted, each of the handset 10, the base unit 20, and the sub base unit 30 is a call such as a microphone and a speaker, and a voice transmission / reception circuit that transmits and receives a voice signal via the signal line Ls and the transmission line Ld. Circuit for performing intercom calls between the slave unit 10 and the master unit 20 or the secondary master unit 30 and performing extension calls between the master unit 20 and the secondary master unit 30 or the secondary master unit 30 be able to.

ここで、終端装置４０の終端抵抗（インピーダンス）をＲ、伝送線Ｌｄの特性インピーダンスをＺｏ、伝送線Ｌｄから映像受信処理部３１をみた入力インピーダンス（以下、このインピーダンスを「副親機３０の入力インピーダンス」と呼ぶ。）をＺとしたとき、本実施形態においては、それぞれ下記の不等式（１）〜（３）を満足するように終端抵抗Ｒ並びに副親機３０の入力インピーダンスＺが設定されている。なお、式（３）におけるｎは伝送線Ｌｄに送り配線される副親機３０の台数である。   Here, the termination resistance (impedance) of the termination device 40 is R, the characteristic impedance of the transmission line Ld is Zo, and the input impedance when the video reception processing unit 31 is viewed from the transmission line Ld (hereinafter, this impedance is referred to as “input of the sub master unit 30”). In this embodiment, the terminating resistance R and the input impedance Z of the sub-master unit 30 are set so as to satisfy the following inequalities (1) to (3), respectively. Yes. In Expression (3), n is the number of sub-master devices 30 that are sent and wired to the transmission line Ld.

Figure 2006325141
Figure 2006325141

すなわち、終端抵抗Ｒ及び副親機３０の入力インピーダンスＺは何れも伝送線Ｌｄの特性インピーダンスＺｏに対して＋ａ％の値（＝Ｚｏ×（１＋ａ／１００））よりも高い値であり（式（１）及び（２）参照）、且つ副親機３０の入力インピーダンスＺと終端装置４０の終端抵抗Ｒの合成インピーダンス（１／Ｒ＋ｎ／Ｚの逆数）が伝送線Ｌｄの特性インピーダンスに対して±ａ％の範囲となるように設定されている（式（３）参照）。ここで、ａ［％］の値は、副親機３０の入力インピーダンスＺと終端抵抗Ｒの合成インピーダンスが伝送線Ｌｄの特性インピーダンスＺｏに対して±ａの値（＝Ｚｏ×（１＋ａ／１００））であるときに副親機３０のモニタテレビ３２に映し出される映像の品質が許容限界となる値（例えば、２０［％］）と規定され、例えば、試験を行うことで決定される値である。   That is, both the terminating resistance R and the input impedance Z of the secondary master unit 30 are higher than the value of + a% (= Zo × (1 + a / 100)) with respect to the characteristic impedance Zo of the transmission line Ld (formula ( 1) and (2)), and the combined impedance (reciprocal of 1 / R + n / Z) of the input impedance Z of the secondary master unit 30 and the termination resistor R of the termination device 40 is ± a with respect to the characteristic impedance of the transmission line Ld. % Range (see formula (3)). Here, the value of a [%] is the value of ± a with respect to the characteristic impedance Zo of the transmission line Ld (= Zo × (1 + a / 100)). ) Is defined as a value (for example, 20 [%]) at which the quality of the video displayed on the monitor television 32 of the secondary master unit 30 becomes an allowable limit, and is a value determined by performing a test, for example. .

さらに、不等式（１）〜（３）を変形することで下記の不等式（４），（５）が導き出される。   Further, the following inequalities (4) and (5) are derived by modifying the inequalities (1) to (3).

Figure 2006325141
Figure 2006325141

従って、不等式（４）を満たすように終端抵抗Ｒの値を設定した後、その終端抵抗Ｒの値において不等式（５）を満たすように副親機３０の入力インピーダンスＺを設定すればよい。但し、副親機３０の接続台数が増えるにつれて副親機３０の入力インピーダンスＺと終端抵抗Ｒの合成インピーダンスが低下するから、伝送線Ｌｄに接続される副親機３０の台数が１台の場合は副親機３０の入力インピーダンスＺと終端抵抗Ｒの合成インピーダンスが伝送線Ｌｄの特性インピーダンスに対して＋ａ％以下となるように設定し、伝送線Ｌｄに接続される副親機３０の台数が複数台の場合は複数台分の副親機３０の入力インピーダンスＺと終端抵抗Ｒのインピーダンスの合成インピーダンスが伝送線Ｌｄの特性インピーダンスに対して−ａ％以上となるように設定すればよい。   Therefore, after setting the value of the termination resistor R so as to satisfy the inequality (4), the input impedance Z of the sub-master device 30 may be set so as to satisfy the inequality (5) in the value of the termination resistance R. However, since the combined impedance of the input impedance Z and the termination resistance R of the secondary master unit 30 decreases as the number of secondary master units 30 connected increases, the number of secondary master units 30 connected to the transmission line Ld is one. Is set so that the combined impedance of the input impedance Z and the terminating resistor R of the secondary master unit 30 is + a% or less with respect to the characteristic impedance of the transmission line Ld, and the number of secondary master units 30 connected to the transmission line Ld is In the case of a plurality of units, the combined impedance of the input impedance Z and the impedance of the terminating resistor R of the sub-master unit 30 for the plurality of units may be set to be −a% or more with respect to the characteristic impedance of the transmission line Ld.

上述のように本実施形態によれば、副親機３０の入力インピーダンスＺと終端装置４０の終端抵抗Ｒの合成インピーダンスが伝送線Ｌｄの特性インピーダンスに対して±ａ％の範囲となるように設定しているため、従来例のように副親機３０の入力インピーダンスＺを伝送線Ｌｄの特性インピーダンスよりも十分に高い値に設定する必要が無く、映像品質の劣化を抑えつつ副親機３０の回路構成の簡素化やコストダウンが図れるものである。   As described above, according to the present embodiment, the combined impedance of the input impedance Z of the secondary master unit 30 and the termination resistor R of the termination device 40 is set to be in a range of ± a% with respect to the characteristic impedance of the transmission line Ld. Therefore, unlike the conventional example, it is not necessary to set the input impedance Z of the secondary master unit 30 to a value sufficiently higher than the characteristic impedance of the transmission line Ld. The circuit configuration can be simplified and the cost can be reduced.

なお、図２に示すように親機２０の映像送信回路部２４に対して複数系統の伝送線Ｌｄ，Ｌｄを接続してもよく、この場合においても各系統の伝送線Ｌｄ毎に上記不等式（１）〜（５）を満足するように副親機３０の入力インピーダンスＺ及び終端装置４０の終端抵抗Ｒの値を設定すればよい。また、親機２０の映像送信回路部２４から伝送線Ｌｄをみたときのインピーダンス（親機２０の出力インピーダンス）を伝送線Ｌｄの特性インピーダンスよりも低く設定すれば、親機２０から伝送線Ｌｓに送出する映像信号の出力損失を小さくして回路の低消費電力化や小型化が図れるという利点がある。   As shown in FIG. 2, a plurality of transmission lines Ld, Ld may be connected to the video transmission circuit unit 24 of the master unit 20, and in this case also, the inequality ( The values of the input impedance Z of the secondary master unit 30 and the termination resistance R of the termination device 40 may be set so as to satisfy 1) to (5). Further, if the impedance when the transmission line Ld is viewed from the video transmission circuit unit 24 of the parent device 20 (the output impedance of the parent device 20) is set lower than the characteristic impedance of the transmission line Ld, the parent device 20 changes to the transmission line Ls. There is an advantage that the output loss of the video signal to be transmitted can be reduced to reduce the power consumption and the size of the circuit.

（実施形態２）
本実施形態のシステム構成図を図３に示す。但し、本実施形態の基本構成は実施形態１と共通であるから、共通の構成要素には同一の符号を付して説明を省略し、本実施形態の特徴となる構成についてのみ説明する。 (Embodiment 2)
FIG. 3 shows a system configuration diagram of the present embodiment. However, since the basic configuration of the present embodiment is the same as that of the first embodiment, the same components are denoted by the same reference numerals, description thereof is omitted, and only the configuration that is a feature of the present embodiment will be described.

本実施形態は、入力インピーダンスＺを複数通りに切り替える入力インピーダンス切替回路部３３を副親機３０に備えた点に特徴がある。入力インピーダンス切替回路部３３は、映像受信処理部３１の２つの入力端にそれぞれ一端が並列に接続され且つ互いに抵抗値が異なる各３つの抵抗Ｒ１，Ｒ２，Ｒ３と、伝送線Ｌｄの各線と３つの抵抗Ｒ１，Ｒ２，Ｒ３の他端とを択一的に切替接続する一対のスイッチＳＷとで構成される。但し、これら一対のスイッチＳＷは図示しない操作部を手動で操作することによって連動して切り替えられるものであって、常に同じ抵抗値を有する抵抗Ｒ１又はＲ２又はＲ３に接続される。   The present embodiment is characterized in that the sub-master unit 30 includes an input impedance switching circuit unit 33 that switches the input impedance Z in a plurality of ways. The input impedance switching circuit unit 33 includes three resistors R1, R2, and R3 each having one end connected in parallel to the two input ends of the video reception processing unit 31 and having different resistance values, and each line of the transmission line Ld and 3 It comprises a pair of switches SW that selectively switch-connect the other ends of the two resistors R1, R2, and R3. However, the pair of switches SW are switched in conjunction with each other by manually operating an operation unit (not shown), and are always connected to the resistors R1, R2, or R3 having the same resistance value.

すなわち、実施形態１で説明したように副親機３０の入力インピーダンスＺ並びに終端装置４０の終端抵抗Ｒの値は規定台数ｎに応じた値に設定されているが、施工物件の種類等によっては規定台数ｎよりも多い台数Ｎ（≧ｎ＋１）の副親機３０が伝送線Ｌｄに接続される場合があり、かかる場合においても入力インピーダンス切替回路部３３により副親機３０の入力インピーダンスＺを高い値に切り替えることで伝送線Ｌｄの特性インピーダンスＺｏに対して±ａ％の範囲に副親機３０の入力インピーダンスＺと終端装置４０の終端抵抗Ｒの合成インピーダンスを収めることができ、副親機３０の接続台数の増加に柔軟に対応することが可能になる。   That is, as described in the first embodiment, the input impedance Z of the secondary master unit 30 and the termination resistance R of the termination device 40 are set to values corresponding to the specified number n, but depending on the type of construction item, etc. In some cases, the number N (≧ n + 1) of the secondary master unit 30 that is larger than the prescribed number n is connected to the transmission line Ld. In such a case as well, the input impedance Z of the secondary master unit 30 is increased by the input impedance switching circuit 33. By switching to the value, the combined impedance of the input impedance Z of the secondary master unit 30 and the termination resistance R of the termination device 40 can be accommodated within a range of ± a% with respect to the characteristic impedance Zo of the transmission line Ld. It is possible to flexibly cope with an increase in the number of connected devices.

さらに本実施形態では、終端装置４０に互いに抵抗値が異なる３つの終端抵抗Ｒａ，Ｒｂ，Ｒｃを設け、手動で切り替えられるスイッチＳＷによって３つの終端抵抗Ｒａ，Ｒｂ，Ｒｃの何れか１つを択一的に選択できるようにしている。このように副親機３０の入力インピーダンスＺだけでなく終端装置４０の終端抵抗も切り替えられるようにすれば、副親機３０の接続台数が増えた場合における合成インピーダンスの整合がより確実に行えるという利点がある。   Further, in the present embodiment, the termination device 40 is provided with three termination resistors Ra, Rb, Rc having different resistance values, and any one of the three termination resistors Ra, Rb, Rc is selected by a switch SW that is manually switched. You can select one. In this way, if not only the input impedance Z of the secondary master unit 30 but also the termination resistance of the termination device 40 can be switched, the combined impedance can be more reliably matched when the number of secondary master units 30 connected increases. There are advantages.

本発明の実施形態１を示すシステム構成図である。1 is a system configuration diagram showing Embodiment 1 of the present invention. 同上の他のシステム構成図である。It is another system block diagram same as the above. 本発明の実施形態２を示すシステム構成図である。It is a system block diagram which shows Embodiment 2 of this invention. 従来例のシステム構成図である。It is a system configuration diagram of a conventional example.

符号の説明Explanation of symbols

１０ 子器
２０ 親機
３０ 副親機
４０ 終端装置
Ｌｄ 伝送線 10 slave unit 20 master unit 30 secondary master unit 40 terminator Ld transmission line

Claims (6)

住戸外に設置される子器と、住戸内に設置され信号線を介して子器と接続される親機と、住戸内に設置され親機に対して２線式の平衡ケーブルからなる伝送線で送り配線される１乃至複数台の副親機と、伝送線を終端する終端装置とからなり、
子器は、来訪者を撮像する撮像手段と、撮像手段から出力される映像信号を周波数変調し信号線を介して親機に伝送する映像伝送手段とを備え、
親機は、信号線を介して伝送されてくる映像信号を復調する映像復調手段と、映像復調手段で復調された映像信号によって映像を表示する表示手段と、信号線を介して伝送されてくる周波数変調された映像信号を伝送線を介して副親機に中継する映像中継手段とを備え、
副親機は、伝送線を介して伝送されてくる映像信号を復調する映像復調手段と、映像復調手段で復調された映像信号によって映像を表示する表示手段とを備えた映像伝送システムにおいて、
伝送線に接続される副親機並びに終端装置のインピーダンスと伝送線の特性インピーダンスとの整合度合いに対する許容範囲を伝送線の特性インピーダンスに対して±ａ％としたときに、副親機の入力インピーダンスと終端装置のインピーダンスの合成インピーダンスが伝送線の特性インピーダンスに対して±ａ％の範囲となるように設定されたことを特徴とする映像伝送システム。 A slave unit installed outside the dwelling unit, a master unit installed inside the unit and connected to the slave unit via a signal line, and a transmission line consisting of a two-wire balanced cable installed in the dwelling unit Consisting of one or more sub-master units that are wired in the transmission line, and a terminating device that terminates the transmission line,
The slave unit includes an imaging unit that images a visitor, and a video transmission unit that modulates the frequency of the video signal output from the imaging unit and transmits the video signal to the parent unit via the signal line.
The master unit is transmitted via the signal line, the video demodulating means for demodulating the video signal transmitted through the signal line, the display means for displaying the video by the video signal demodulated by the video demodulating means. Video relay means for relaying the frequency-modulated video signal to the secondary master unit via a transmission line;
In the video transmission system, the secondary master unit includes a video demodulation unit that demodulates a video signal transmitted through a transmission line, and a display unit that displays a video by the video signal demodulated by the video demodulation unit.
When the allowable range for the degree of matching between the impedance of the secondary master unit connected to the transmission line and the terminating device and the characteristic impedance of the transmission line is ± a% with respect to the characteristic impedance of the transmission line, the input impedance of the secondary master unit A video transmission system, wherein the combined impedance of the terminal device and the terminating device is set to be within a range of ± a% with respect to the characteristic impedance of the transmission line. 副親機の入力インピーダンスと終端装置のインピーダンスの合成インピーダンスが、１台分の副親機の入力インピーダンスと終端装置のインピーダンスの合成インピーダンスが伝送線の特性インピーダンスに対してプラスａ％となり、且つ複数台分の副親機の入力インピーダンスと終端装置のインピーダンスの合成インピーダンスが伝送線の特性インピーダンスに対してマイナスａ％となるように設定されたことを特徴とする請求項１記載の映像伝送システム。   The combined impedance of the input impedance of the secondary master unit and the impedance of the terminating device is a plus a% of the combined impedance of the input impedance of the secondary master unit and the terminating device impedance with respect to the characteristic impedance of the transmission line. 2. The video transmission system according to claim 1, wherein the combined impedance of the input impedance of the sub-master device and the impedance of the terminating device is set to be minus a% with respect to the characteristic impedance of the transmission line. 副親機は、入力インピーダンスを相対的に高いインピーダンスと相対的に低いインピーダンスとに切り替える切替手段を備えたことを特徴とする請求項１又は２記載の映像伝送システム。   The video transmission system according to claim 1 or 2, wherein the sub-master unit includes switching means for switching the input impedance between a relatively high impedance and a relatively low impedance. 終端装置は、インピーダンスを相対的に高いインピーダンスと相対的に低いインピーダンスとに切り替える切替手段を備えたことを特徴とする請求項３記載の映像伝送システム。   4. The video transmission system according to claim 3, wherein the termination device includes switching means for switching the impedance between a relatively high impedance and a relatively low impedance. 親機の映像中継手段の伝送線に対する出力インピーダンスが伝送線の特性インピーダンスよりも低く設定されたことを特徴とする請求項１〜４の何れかに記載の映像伝送システム。   5. The video transmission system according to claim 1, wherein the output impedance of the video relay means of the master unit is set lower than the characteristic impedance of the transmission line. 親機の映像中継手段は、複数系統の伝送線に映像信号を伝送することを特徴とする請求項１〜５の何れかに記載の映像伝送システム。   6. The video transmission system according to claim 1, wherein the video relay means of the master unit transmits a video signal to a plurality of transmission lines.
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