JP2010263516A - Two-way amplification device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain sufficient isolation even when electric power is not applied. <P>SOLUTION: A two-way AMP 1 includes a squelch circuit 16 at an up-line portion between a second branch circuit 14 and a first branch circuit 11. The squelch circuit 16 includes a PIN diode, attenuating an up-signal in the absence of applied electric power, the PIN diode being inserted in series between an input and an output. Consequently, a changeover SW 19 is switched to an amplification mode side to obtain sufficient isolation even when no electric power is applied to the two-way AMP 1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a bidirectional amplifying apparatus installed in a subscriber's house in a cable television facility that provides a bidirectional service.

  FIG. 11 shows a schematic configuration of a cable television (CATV) facility that is a system for hearing. In the CATV facility shown in FIG. 11, the CATV station 110 includes a TV broadcasting device 111 and a cable internet center modem (CMTS) 112. The CATV station 110 sends a television signal received from the TV receiving antenna (TV ANT) 101 by the TV broadcasting device 111 to the transmission line 114 as a downlink signal via the demultiplexer 113, and the demultiplexer from the transmission line 114. An upstream signal arriving at the center modem 112 via the Internet 113 is sent to the Internet line. The transmission line 114 is laid using a plurality of utility poles 115, and the downlink signal branched by the tap-off 116 provided in the transmission line 114 is drawn into each subscriber home 120. Downlink signals are drawn into the subscriber's home 120 via the protector 117, and the downlink signals amplified by the bidirectional AMP 121 are distributed by the distributor 122 and output from the TV outlet 123 provided in each room. It becomes like this. Thus, by connecting the antenna input terminal of the TV 126 to the TV outlet 123, it becomes possible to view the television broadcast on the TV 126, and the personal computer 125 is connected to the TV outlet 123 via the cable modem 124. 125 is connected to the Internet and can receive Internet services. The upstream signal sent from the personal computer 125 is sent to the transmission line 114 via the cable modem 124 -TV outlet 123 -bidirectional AMP 121 -protector 117.

The bidirectional AMP 121 is an amplifier that compensates for loss due to in-house signal distribution, and amplifies the downstream signal level and the upstream signal level to the rated level. An example of a conventional bidirectional AMP 121 circuit is shown in FIG. The upstream frequency band in the CATV network is slightly different depending on the cable modem 124, but is 5 to 55 MHz, and the downstream frequency band is 70 to 770 MHz.
The bi-directional AMP 121 shown in FIG. 12 includes a first terminal 201 that receives a downlink signal and outputs an uplink signal, and a second terminal 206 that outputs a downlink signal and receives an uplink signal. The downlink signal input from the first terminal 201 is demultiplexed by the demultiplexing circuit 202, level-adjusted by the attenuator (ATT) 203, amplified by the down AMP 204, and passed through the demultiplexing circuit 205 to the second terminal 206. A down signal with a rated level is output from. Further, the upstream signal input from the second terminal 206 is demultiplexed by the demultiplexing circuit 205, level-adjusted by the attenuator 207, and amplified by the upstream AMP 208 to be a rated level upstream signal. The upstream signal output from the upstream AMP 208 is input to a switch SW209 that is switched between an amplification mode in which the upstream signal is amplified and output and a cut mode in which the upstream signal is stopped. When the switching SW 209 is switched to the illustrated amplification mode side, the movable contact c2 is connected to the fixed contact a2, the movable contact c1 is connected to the fixed contact a1, and the upstream signal is c2-a2- The signal is output from the switching SW 209 through the route a1-c1. As a result, an upstream signal is output from the first terminal 201 via the branching circuit 202. When the switching SW 209 is switched to the cut mode side, the movable contact c2 is connected to the fixed contact b2, and the movable contact c1 is connected to the fixed contact b1. Thus, the upstream signal is terminated by the resistor R2 connected to the fixed contact b2, and the movable contact a1 is terminated by the resistor R1 connected to the fixed contact b1, so that the upstream signal is not output from the first terminal 201. become.

JP 2001-128135 A

  The service content of CATV is not only television broadcasting but also communication services such as an Internet service and an IP telephone service utilizing an upstream band, and is diversified. Since Internet services and IP telephone services are public communication services, CATV operators are always required to provide stable services. For this reason, the current situation is that CATV operators are focusing on maintaining and managing transmission lines and always ensuring the quality of transmission signals. The switching SW 209 provided in the bidirectional AMP 121 is provided in order to prevent infusion noise that causes deterioration of the quality of the upstream transmission signal. Infusion noise is a noise distributed in the vicinity of 0-30 MHz in the CATV upstream band, and power supply noise of electric products, noise generated from electric motors, electric tools, etc., flow into the signal line via ground etc., or directly connector terminals It is generated by jumping into.

  The generation process of inflow noise will be described with reference to FIG. The noise in the upstream band, which becomes inflow noise generated at the subscriber's home 120, goes up the branch trunk line while being amplified by the branch amplifier 103 provided in the branch trunk line through the tap-off 116. Furthermore, the CATV station 110 is reached while being amplified by the main line amplifier 102 provided on the main line that bundles the branch main lines. In this case, since the CATV network has a tree structure as shown in FIG. 13, noise generated at a large number of subscriber homes 120 is concentrated on the CATV station 110 so that inflow noise is generated. Become. An example of the frequency characteristic of infusion noise is shown in FIG. As shown in FIG. 14, it can be seen that the inflow noise is at a large level in the CATV upstream band. For this reason, when inflow noise occurs, the C / N (signal-to-noise ratio) of the upstream signal deteriorates, and if the predetermined C / N for operating the equipment of the CATV station 110 cannot be ensured, the system will go down. It becomes like this. In order to prevent inflow noise, the unused TV outlet 123 in the subscriber's house 120 is terminated with a dummy resistor so that noise does not jump in, or when the Internet service or IP telephone service is not received, both The upstream band may be stopped in the direction AMP 121.

  The bi-directional AMP 121 shown in FIG. 12 has a function of stopping the upstream band and preventing inflow noise from occurring, and this function is achieved by switching the switch SW 209 to the cut mode side. The frequency characteristics of the output level of the bidirectional AMP 121 are shown in FIG. As shown in FIG. 15, when the switch 209 is switched to the amplification mode side with the bidirectional AMP 121 turned on, a gain of about 15 dB or more is obtained in the upstream band of about 5 MHz to about 60 MHz. Further, when the switching SW 209 is switched to the cut mode side, an attenuation of −50 dB or more is obtained over the entire upstream band, and an attenuation of about −55.196 dB is obtained at 60 MHz. As described above, when the switching SW 209 is switched to the cut mode side, the isolation between the input and output of the upstream band can be secured about 50 to 60 dB, so that noise generated from electronic devices installed in the home is sufficiently attenuated. Inflow to the CATV main line can be prevented.

  By the way, when the bidirectional AMP 121 or the like is in the middle of construction, the bidirectional AMP 121 or the like is often left in a state where the power is not turned on even though the connection work to the CATV main line has been completed. Further, the coaxial cable connected to the bidirectional AMP 121 may be left undisconnected for a while in a state in which the coaxial cable is not wired or is not terminated with a dummy resistor. FIG. 16 shows the frequency characteristics of the output level when no power is applied to the bidirectional AMP 121. As shown in FIG. 16, when the switching SW 209 is switched to the cut mode side, an attenuation of -50 dB or more is obtained over the entire upstream band, but the switching SW 209 of the bidirectional AMP 121 is switched to the amplification mode side. When switched, only an attenuation of about −20 dB is obtained in the upstream band of about 5 MHz to about 60 MHz. This is because a normal voltage is not applied to the transistor circuit in the bidirectional AMP 121 and the isolation characteristic is about 15 to 20 dB due to the influence of the stray capacitance. That is, when the bidirectional AMP 121 is not operated without applying power while the switching SW 209 of the bidirectional AMP 121 is switched to the amplification mode, the power is applied and bidirectional as shown in the frequency characteristic of the output level shown in FIG. Compared with 50-60 dB, which is the upstream isolation between the input and output when the AMP 121 is operated, the isolation in the upstream is only about 15-20 dB, which is approximately 40 dB or more less, and the inflow of inflow noise is reduced. It cannot be prevented sufficiently.

For this reason, if noises jump in due to the operation of a tool used for construction near the bidirectional AMP 121 having such an isolation characteristic, it cannot be sufficiently attenuated, and noise is caused to the CATV main line. There is a problem in that inflow noise occurs due to the inflow, and the communication is disturbed.
Accordingly, an object of the present invention is to provide a bidirectional amplifying device capable of obtaining sufficient isolation even when no power is applied.

  The bidirectional amplifying device of the present invention includes a first terminal to which a downstream signal is input and an upstream signal is output, a second terminal to which a downstream signal is output and an upstream signal is input, and the first terminal A first branching circuit for supplying a downstream signal input from the terminal to the downstream amplification unit and outputting an upstream signal supplied from the upstream amplification unit to the first terminal; and an upstream signal input from the second terminal A signal is supplied to the upstream amplifying unit, and a downstream signal from the downstream amplifying unit is output to the second terminal. Between the second branching circuit and the upstream amplifier, An inserted squelch circuit, an amplification mode that is inserted between the upstream amplifier and the first branching circuit and outputs an upstream signal amplified by the upstream amplifier, and terminates and stops the upstream signal Changeover switch that can be switched to cut mode Wherein the squelch circuit, circuit component upstream signal in a state where power is not applied is attenuated, and the most important features in that it is inserted in series between the input and the output.

  According to the present invention, in a state where no power is applied to the bidirectional amplifying device, the upstream signal is attenuated by the circuit components, so that sufficient isolation can be obtained even when no power is applied. Become.

It is a circuit diagram which shows the circuit structure of bidirectional | two-way AMP which is the Example of the bidirectional | two-way amplifier of this invention. It is a circuit diagram which shows an example of the squelch circuit in bidirectional | two-way AMP of the Example of this invention. It is a circuit diagram which shows an example of the upstream amplification part in bidirectional | two-way AMP of the Example of this invention. It is a circuit diagram which shows the other example of the squelch circuit in bidirectional | two-way AMP of the Example of this invention. It is a circuit diagram which shows the further another example of the squelch circuit in bidirectional | two-way AMP of the Example of this invention. It is a part of circuit diagram which shows the other circuit example in bidirectional | two-way AMP of the Example of this invention. It is a figure which shows the frequency characteristic of the output level of the upstream band in bidirectional | two-way AMP of the Example of this invention. It is a figure which shows the frequency characteristic of the output level of the upstream band in the state where a power supply is not applied in bidirectional | two-way AMP of the Example of this invention. It is a figure for demonstrating the influence of the squelch circuit in bidirectional | two-way AMP of the Example of this invention. It is another figure for demonstrating the influence of the squelch circuit in bidirectional | two-way AMP of the Example of this invention. It is a figure which shows schematic structure of the cable television (CATV) facility which is a system for common hearing. It is a circuit diagram which shows the circuit structure of the conventional bidirectional | two-way AMP. It is a figure for demonstrating the generation | occurrence | production process of inflow noise. It is a figure which shows the frequency characteristic of infusion noise. It is a figure which shows the frequency characteristic of the output level of the upstream zone | band in the conventional bidirectional | two-way AMP. It is a figure which shows the frequency characteristic of the output level of an upstream band in the state where a power supply is not applied in the conventional bidirectional AMP. It is a figure which compares and shows the frequency characteristic of the output level of the upstream band of the state where the power supply is applied in the conventional bidirectional AMP, and the state where it is not applied.

FIG. 1 shows a circuit configuration of a bidirectional AMP1, which is an embodiment of the bidirectional amplification apparatus of the present invention. The bidirectional AMP1 is used in place of the bidirectional AMP 121 shown in FIG.
The bidirectional AMP 1 according to the present invention shown in FIG. 1 is an amplifier that compensates for loss due to in-house signal distribution, and amplifies the downstream signal level and the upstream signal level to rated levels. The upstream frequency band in the CATV network is about 5 to 55 MHz, and the downstream frequency band is 70 to 770 MHz. The bidirectional AMP1 includes a first terminal 10 to which a downstream signal is input and an upstream signal is output, and a second terminal 15 to which a downstream signal is output and an upstream signal is input. The downlink signal input from the first terminal 10 is demultiplexed to the downlink line unit by the first demultiplexing circuit 11, and the level is adjusted by the attenuator (ATT) 12 provided in the downlink line unit, and the downlink amplification unit Amplified by (downlink AMP) 13. And the down signal made into the rated level is output from the 2nd terminal 15 via the 2nd branching circuit 14 to which the down line part is connected. The bidirectional AMP1 includes a power supply unit 20. The power supply unit 20 converts commercial alternating current (AC100V) into a predetermined DC voltage, and supplies power to the downstream AMP13, the squelch circuit 16 and the upstream AMP18 described later. It is supplied as Vcc.

  Further, the upstream signal input from the second terminal 15 is demultiplexed to the upstream line section by the second branching circuit 14 and is supplied to the squelch circuit 16 provided in the upstream line section. The squelch circuit 16 outputs the upstream signal as it is without being attenuated when the operation power is supplied from the power supply unit 20, and greatly attenuates the upstream signal when the operation power is not supplied from the power supply unit 20. Giving. In the upstream line section, an attenuator 17, an upstream AMP 18, and a switching SW 19 are cascaded downstream of the squelch circuit 16. The upstream signal output from the squelch circuit 16 is level-adjusted by an attenuator (ATT) 17 and amplified by an upstream amplifier (upstream AMP) 18 to be an upstream signal of a rated level. The upstream signal output from the upstream AMP 18 is input to the switch SW 19 that is switched between an amplification mode for amplifying and outputting the upstream signal and a cut mode for stopping the upstream signal. When the switch SW19 is switched to the illustrated amplification mode side, the movable contact c2 is connected to the fixed contact a2, the movable contact c1 is connected to the fixed contact a1, and the upstream signal is c2-a2- The signal is output from the switch SW19 through the route a1-c1. As a result, the upstream signal is output from the first terminal 10 via the first branching circuit 11. When the switching SW 19 is switched to the cut mode opposite to the illustrated side, the movable contact c2 is connected to the fixed contact b2, and the movable contact c1 is connected to the fixed contact b1. Thus, the upstream signal is terminated by the resistor R2 connected to the fixed contact b2, and the movable contact a1 is terminated by the resistor R1 connected to the fixed contact b1, and the upstream signal is stopped by the switch SW19. As a result, the upstream signal is not output from the first terminal 10.

  A circuit as an example of the squelch circuit 16 is shown in FIG. In the squelch circuit 16 shown in FIG. 2, a series circuit of a choke coil L1, a PIN diode, and a resistor R1 is connected between the operating power supply Vcc supplied from the power supply unit 20 and the ground. The anode of the PIN diode is connected to the second branching circuit 14 that is input via the capacitor C1, and the cathode of the PIN diode is connected to the ATT 17 that is output via the capacitor C2. When the operating power supply Vcc is supplied from the power supply unit 20, a current flows through the series circuit of the choke coil L1-PIN diode-resistor R1, and the PIN diode is turned on. Therefore, the upstream signal input through the capacitor C1 is output through the capacitor C2 without being attenuated by the PIN diode having a low impedance. When the operating power supply Vcc is not supplied from the power supply unit 20, no current flows through the series circuit of the choke coil L1-PIN diode-resistor R1, and the PIN diode is turned off. For this reason, the upstream signal input through the capacitor C1 is attenuated by about 30 to 40 dB by the PIN diode having a large impedance, and is output through the capacitor C2. Thereby, when the power of the bidirectional AMP1 is turned off or no power is applied, the noise input to the bidirectional AMP1 is blocked by the squelch circuit 16 to prevent the occurrence of inflow noise. become able to.

  Next, FIG. 3 shows a circuit example of the upstream AMP 18 in the bidirectional AMP1. In the upstream AMP 18 shown in FIG. 3, the upstream signal from the ATT 17 is input to the input transformer T1. In the upstream AMP 18, a transistor TR1 and a transistor TR2 form a push-pull amplifier circuit, and upstream signals whose phases are inverted from the secondary side of the input transformer T1 to the bases of the transistors TR1 and TR2 are passed through capacitors C3 and C7, respectively. Have been entered. The collectors of the transistors TR1 and TR2 are connected to both ends of the primary side of the output transformer T2, and the upstream signal amplified by the transistors TR1 and TR2 is output from the secondary side of the output transformer T2 to the switch SW19. The resistors R2, R3, R4, and R5 are bias resistors that apply a bias to the transistor TR1, L2 is a choke coil that supplies the power source Vcc to the transistor TR1, C6 is a bypass capacitor, and C5 is a DC cut capacitor. . The resistors R6, R7, R8, and R9 are bias resistors that apply a bias to the transistor TR2, L3 is a choke coil that supplies the power source Vcc to the transistor TR2, C9 is a bypass capacitor, and C10 is a DC cut capacitor. .

Here, the frequency characteristics of the output level of the bidirectional AMP1 are shown in FIGS. The frequency characteristics shown in FIG. 7 are frequency characteristics when the switch SW 19 is switched to the amplification mode side in a state where the bidirectional AMP 1 is turned on or not turned on. Referring to FIG. 7, when the bidirectional AMP 1 is powered on, a gain of about 15 dB or more is obtained in the upstream band of about 5 MHz to about 60 MHz. When the bidirectional AMP1 is not turned on, an attenuation of -50 dB or more is obtained over the entire upstream band, and an attenuation of about -60.204 dB is obtained at a frequency of about 59.9931 MHz. As described above, even when the bidirectional AMP 1 is not turned on, isolation between the input and output in the upstream band can be secured by the action of the squelch circuit 16.
FIG. 8 shows the frequency characteristics when the switch SW19 is switched to the amplification mode side when no power is applied to the bidirectional AMP1, and the switch SW19 is set to the cut mode side when the power is supplied to the bidirectional AMP1. The frequency characteristics when switched to. Referring to FIG. 8, when the switch SW 19 is switched to the cut mode side in the state where the power is supplied to the bidirectional AMP 1, an attenuation of −50 dB or more is obtained over the entire upstream band, and the frequency is 60. An attenuation of about −55.659 dB is obtained at 000 MHz. It can also be seen that an attenuation of −50 dB or more is obtained over the entire upstream band even when the switch SW 19 is switched to the amplification mode side in a state where no power is applied to the bidirectional AMP1. As described above, the isolation between the input and output in the upstream band is performed by setting the switch SW 19 to the cut mode side when the power is supplied to the bidirectional AMP1 by the action of the squelch circuit 16 even when the power is not applied to the bidirectional AMP1. Since about 50 to 60 dB, which is the same as the case of switching, can be secured, noise generated from an electronic device installed in the house is sufficiently attenuated and can be prevented from flowing into the CATV main line.

  By the way, the squelch circuit 16 using the PIN diode shown in FIG. 2 cannot be provided after the upstream AMP 18. The reason for this will be described with reference to FIGS. Since the PIN diode is a semiconductor, when an excessive signal is passed, the diode itself causes distortion. In the general specification of the bidirectional AMP1, the rated output level of the upstream signal is about 120 dBμV (voltage level is 1V, 75Ω), and this level reaches the nonlinear region of the PIN diode. Therefore, the upstream signal that has passed through the PIN diode is distorted. FIG. 9 shows the frequency characteristics of the output level of the bidirectional AMP 1 when the squelch circuit 16 is provided at the subsequent stage of the upstream AMP 18. Referring to FIG. 9, it can be seen that the upstream signal having a frequency of 20 MHz is distorted and the rated output level of 120 dBμV is not obtained. Further, it can be seen that the signal having a frequency of 60 MHz is distorted and has a high level, and the D / U ratio of the upstream signal with respect to the signal is not 60 dB. As described above, when the squelch circuit 16 is provided at the subsequent stage of the upstream AMP 18, the performance of the bidirectional AMP1 is deteriorated.

  When the gain of the upstream AMP 18 is set to 20 dB, which is generally used, the input level is 100 dBμV (0.1 V in voltage level), which can be accommodated in the linear region of the PIN diode. For this reason, by providing the squelch circuit 16 in front of the upstream AMP 18, it becomes possible to secure isolation between the input and output without causing distortion in the PIN diode itself. FIG. 10 shows the frequency characteristics of the output level of the bidirectional AMP 1 when the squelch circuit 16 is provided in the upstream of the upstream AMP 18. Referring to FIG. 10, it can be seen that the upstream signal having a frequency of 20 MHz is not distorted and an output level of 120 dBμV of the rated output is obtained. It can also be seen that a signal with a frequency of 60 MHz is not distorted, and the D / U ratio of the upstream signal with respect to the signal is 60 dB or more.

  Next, a squelch circuit 26 which is another circuit is shown in FIG. The squelch circuit 26 shown in FIG. 4 is configured by a relay RY. That is, the operating power supply Vcc from the power supply unit 20 is applied to the relay coil L4 of the relay RY, connected to the second branching circuit 14 to which the movable contact C3 of the relay RY is input, and the relay RY is normally opened. The contact b3 is connected to the ATT 17 that is an output. Further, the normally closed contact a3 of the relay RY is terminated by a resistor R10. In such a squelch circuit 26, when the operating power supply Vcc is supplied from the power supply unit 20, a current flows through the relay coil L4 of the relay RY to drive the movable contact c3 to the normally open contact b3 side. For this reason, the upstream signal input to the movable contact c3 is output without being attenuated via the normally open contact b3. Further, when the operating power supply Vcc is not supplied from the power supply unit 20, since the current does not flow through the relay coil L4 of the relay RY and is not driven, the movable contact c3 is connected to the normally closed contact a3 side. For this reason, the upstream signal input to the movable contact c3 is terminated by the resistor R10, and is not substantially output from the normally open contact b3. Thereby, when the power of the bidirectional AMP1 is turned off or no power is applied, the noise input to the bidirectional AMP1 is blocked by the squelch circuit 26, thereby preventing the inflow noise from being generated. become able to. Isolation between the input and output in the upstream band when using the squelch circuit 26 can be secured from 50 to 60 dB or more even when no power is applied to the bidirectional AMP 1, and thus is generated from an electronic device installed in the house. The incoming noise is sufficiently attenuated and can be prevented from flowing into the CATV main line.

  Since the squelch circuit 26 shown in FIG. 4 uses a relay RY in place of the PIN diode, non-linear distortion does not occur even when the input level increases. Therefore, the squelch circuit 26 can be provided in the subsequent stage of the upstream AMP 18. FIG. 5 shows a part of a circuit example of the bidirectional AMP 1 in which the squelch circuit 26 is provided in the subsequent stage of the upstream AMP 18. In the bidirectional AMP1 shown in FIG. 5, the rated output output from the secondary side of the output transformer T2 of the upstream AMP 18 is input to the movable contact c3 of the relay RY, and the normally open contact b3 is connected to the switch SW19. It is connected to the movable contact c2. Since the operation of the squelch circuit 26 is the same as described above, the description is omitted. However, when the squelch circuit 26 is provided at the subsequent stage of the upstream AMP 18, the isolation between the input and output in the upstream band is performed in a state where no power is applied to the bidirectional AMP1. However, it is possible to secure 50 to 60 dB or more, and noise generated from an electronic device or the like installed in the house is sufficiently attenuated to prevent inflow into the CATV main line.

Next, FIG. 6 shows a part of another circuit example of the bidirectional AMP 1 according to the present invention. The bi-directional AMP1 shown in FIG. 6 includes a switch SW29 whose configuration has been changed. When the switch SW29 is switched to the amplification mode side, power is supplied to the squelch circuit 16 and the upstream AMP18, and the switch SW29 is switched to the cut mode. When switched to the side, power is not supplied to the squelch circuit 16 and the upstream AMP 18.
In the bidirectional AMP1 shown in FIG. 6, the power supply Vcc is supplied from the power supply unit 20 to the fixed contacts a1 and a2 via the choke coil L5. The upstream signal output from the output transformer T2 of the upstream AMP 18 is supplied to the movable contact c2 via the DC cut capacitor C11, and one end of the choke coil L6 is connected to the movable contact c2, and the choke coil L6 is connected. Is connected to the power source of the squelch circuit 16 and the upstream AMP 18. Further, the movable contact c1 is connected to the first branching circuit 11 via a DC cut capacitor C12.

  When the switching SW 29 is switched to the amplification mode shown in the figure, the movable contact c2 is connected to the fixed contact a2, and the movable contact c1 is connected to the fixed contact a1 and is input through the capacitor C11. The signal is output from the switching SW 29 via the capacitor C12 through the path c2-a2-a1-c1. As a result, the upstream signal is output from the first terminal 10 via the first branching circuit 11. Further, the DC power from the power supply unit 20 is supplied as the operation power Vcc to the squelch circuit 16 and the upstream AMP 18 through the path L5-a2-c2-L6, and the squelch circuit 16 and the upstream AMP 18 are in the operating state.

Further, when the switching SW 29 is switched to the cut mode side opposite to the illustrated side, the movable contact c2 is connected to the fixed contact b2, and the movable contact c1 is connected to the fixed contact b1. As a result, the upstream signal is terminated by the resistor R2 connected to the fixed contact b2, and the movable contact a1 is terminated by the resistor R1 connected to the fixed contact b1, and the upstream signal is stopped by the switch SW29. Since the fixed contacts a1 and a2 are opened, the DC power from the power supply unit 20 is not output from the movable contact c2, and the power Vcc is not supplied to the squelch circuit 16 and the upstream AMP 18. Thus, when the switching SW 29 is switched to the cut mode side, the operations of the squelch circuit 16 and the upstream AMP 18 are stopped, so that the amount of isolation in the upstream band can be further increased.
In the case of the configuration of the switching SW 29 shown in FIG. 6, the squelch circuit 26 shown in FIG. 4 may be used instead of the squelch circuit 16.

  In the bidirectional amplifying device of the present invention described above, a squelch circuit in which an upstream signal is attenuated in a state where no power is applied is inserted in series between an input and an output is connected to the upstream of an upstream amplifier. As a result, sufficient isolation can be obtained even when no power is applied to the bidirectional amplifier. Moreover, it is good also as a squelch circuit which uses a relay instead of a PIN diode. In this case, the movable contact and the normally open contact of the relay are inserted in series between the input and output of the squelch circuit. Since the squelch circuit using the relay does not generate nonlinear distortion even when the input level increases, it can be provided in the subsequent stage of the upstream amplification unit.

DESCRIPTION OF SYMBOLS 1 Bidirectional AMP, 10 1st terminal, 11 branching circuit, 12 attenuator, 13 Down amplification part, 14 Branching circuit, 15 2nd terminal, 16 Squelch circuit, 17 Attenuator, 18 Up amplification part, 19 Switch SW, 20 Power supply unit, 26 squelch circuit, 29 switching SW, 101 TV receiving antenna, 102 trunk amplifier, 103 branch amplifier, 110 CATV station, 111 TV broadcasting device, 112 center modem, 113 duplexer, 114 transmission path, 115 utility pole, 116 Tap-off, 117 Security device, 120 Subscriber's house, 121 Two-way AMP, 122 Distributor, 123 TV outlet, 124 Cable modem, 125 PC, 126 TV, 201 1st terminal, 202 Branching circuit, 203 Attenuator, 204 Down AMP, 205 branching circuit 206 second terminal, 207 an attenuator, 208 uplink AMP, 209 switching SW

Claims (5)

A first terminal that receives a downstream signal and outputs an upstream signal;
A second terminal to which a downstream signal is output and an upstream signal is input;
A first branching circuit that supplies a downstream signal input from the first terminal to a downstream amplification unit and outputs an upstream signal supplied from the upstream amplification unit to the first terminal;
A second branching circuit that supplies an upstream signal input from the second terminal to the upstream amplification unit and outputs a downstream signal from the downstream amplification unit to the second terminal;
A squelch circuit inserted between the second branching circuit and the upstream amplifier;
Switching between an amplification mode that is inserted between the upstream amplifier and the first branching circuit and outputs the upstream signal amplified by the upstream amplifier, and a cut mode that terminates and stops the upstream signal With a switch,
In the squelch circuit, a circuit component in which an upstream signal is attenuated when no power is applied is inserted in series between an input and an output.   2. The bidirectional amplification device according to claim 1, wherein the circuit component is a PIN diode.   2. The bidirectional amplification according to claim 1, wherein the circuit component is a relay, and a movable contact and a normally open contact of the relay are inserted in series between an input and an output of the squelch circuit. apparatus. A first terminal that receives a downstream signal and outputs an upstream signal;
A second terminal to which a downstream signal is output and an upstream signal is input;
A first branching circuit that supplies a downstream signal input from the first terminal to a downstream amplification unit and outputs an upstream signal supplied from the upstream amplification unit to the first terminal;
A second branching circuit that supplies an upstream signal input from the second terminal to the upstream amplification unit and outputs a downstream signal from the downstream amplification unit to the second terminal;
A squelch circuit inserted between the upstream amplifier and the first branching circuit, an amplification mode for outputting the upstream signal amplified by the upstream amplifier, and a cut mode for terminating and stopping the upstream signal And a changeover switch that can be switched to
The squelch circuit is a relay, and a movable contact and a normally open contact of the relay are inserted in series between an input and an output of the squelch circuit.   5. The power supply to the squelch circuit and the upstream amplifying unit is stopped when the changeover switch is switched to the cut mode. 6. Bidirectional amplifier.

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