JP2005159668A - Reception amplifier exclusively used for channel and catv system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reception amplifier exclusively used for a channel for a CATV system capable of extracting a television broadcast signal to be amplified with high accuracy and amplifying the signal without incurring a cost increase in the reception amplifier even when the television broadcast signal is a signal broadcast on an adjacent channel together with other television broadcast signal. <P>SOLUTION: The reception amplifier 20 uses a down-converter 40 to convert a television broadcast signal received via an input circuit 30 into an intermediate frequency signal and passes the intermediate frequency signal after the conversion through a band pass filter 46 comprising a SAW filter and a notch filter to extract a signal component of a particular broadcast channel, and an AGC circuit 49 automatically adjusts a gain of an amplifier circuit 44 so that the signal level reaches a desired level. Further, the signal extracted by the band pass filter 46 is frequency-converted into a transmission television broadcast signal by an up-converter 50 and when an AGC output is high, a squelch circuit 58 stops the operation of an amplifier circuit 56. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a channel-specific reception amplifier that extracts a television broadcast signal of a specific broadcast channel to be transmitted to a terminal side from a reception signal from a reception antenna at a head end of a CATV system, amplifies it to a predetermined level, and outputs it. And a CATV system.

  Conventionally, the head end of a CATV system extracts a TV broadcast signal of a specific broadcast channel from reception signals from a reception antenna that receives a TV broadcast signal, and amplifies the signal to a predetermined level and outputs it. A receiving amplifier is provided.

  In addition, this channel dedicated receiving amplifier does not simply amplify a television broadcast signal of a specific broadcast channel, but temporarily converts (down-converts) the received signal from the receiving antenna into an intermediate frequency signal. The TV broadcast signal of a specific broadcast channel is extracted by passing through a band-pass filter composed of a SAW filter (surface acoustic wave filter), the extracted TV broadcast signal is amplified to a predetermined level, and then set for transmission in advance. When it is configured to perform frequency conversion (up-conversion) to a TV broadcast signal of a broadcast channel, and the TV broadcast signal of a specific broadcast channel to be amplified is not included in the received signal, the TV broadcast signal is amplified. There is also known one that stops (see, for example, Patent Document 1).

  That is, for example, as shown in FIG. 6A, a channel 21 (hereinafter referred to as “CH”) TV broadcast signal that is a UHF band TV broadcast signal is transmitted as CH9 and CH11 broadcast in the VHF band. When the channel is converted to a TV broadcast signal of CH10, which is an empty channel between the channels and transmitted to the terminal side, the channel dedicated receiving amplifier is provided with a downconverter and an upconverter for channel conversion.

Further, when the CH21 television broadcast signal is channel-converted to the VHF band vacant channel CH10 and transmitted to the terminal side in this way, the CH9 and CH11 television broadcasted in the VHF band on the CATV system transmission path. In addition to the broadcast signal, the CH10 television broadcast signal obtained by channel conversion of the CH21 television broadcast signal is transmitted simultaneously. In this case, for example, when the CH21 television broadcast is stopped, the CH21 channel dedicated reception is performed. In the amplifier, the automatic gain adjustment circuit operates in spite of the absence of the CH21 television broadcast signal, and the gain of the amplifier is increased to the maximum value. A signal obtained by amplifying noise is output as a broadcast signal, and the TV broadcast signal of CH10 Since there is a problem that the TV broadcast signals of adjacent channels (CH9, CH11) that are transmitted through the transmission path both deteriorate due to the influence of the noise signal, conventionally, such adjacent channel transmission is performed in the CATV system. When performing, a so-called squelch circuit is provided in a channel-dedicated reception amplifier that outputs a television broadcast signal transmitted on the adjacent channel, and a reception signal of a specific broadcast channel to be amplified is included in the reception signal from the reception antenna. If not, the operation of the amplifier circuit is stopped to prevent the noise signal from being output from the channel dedicated receiving amplifier.
Japanese Utility Model Publication No. 6-5278

  By the way, in conventional television broadcasting (analog broadcasting) using terrestrial waves, in order to prevent interference between signals, the broadcasting channels of each television broadcasting signal in the same region are allocated with at least one channel of the television broadcasting signal. However, in terrestrial digital broadcasting that is currently being put into practical use, an orthogonal frequency division multiplexing (OFDM method: Orthogonal Frequency Division Multiplexing) method is used as a method for modulating a television broadcast signal (in this case, digital data). Adjacent channels adjacent to each other are assigned to a plurality of television broadcast signals broadcast in the same area (see FIG. 6B).

  Therefore, in order to amplify a terrestrial digital broadcast television broadcast signal using the above-described conventional channel-dedicated receiver amplifier, the intermediate frequency signal obtained by frequency-converting (down-converting) the received signal is specified. The band-pass filter used for extracting the signal component of the broadcast channel is made to have a bandwidth equivalent to one channel of the TV broadcast signal, and attenuation at the cut-off frequency on the low-frequency side and the high-frequency side of the band-pass filter. It has been necessary to make the rising and falling characteristics of the quantity steep so that signal components other than the specific broadcast channel (that is, signal components of adjacent channels) can be sufficiently attenuated.

  That is, in the conventional channel-dedicated receiving amplifier that amplifies an analog television broadcast signal, the received signal does not include the television broadcast signal of the adjacent channel adjacent to the specific broadcast channel. Even if the pass band width of the bandpass filter used to extract the signal component of the specific broadcast channel from the TV broadcast signal is wider than that of one channel of the TV broadcast signal, the falling characteristics at the cut-off frequency on the low frequency side and the high frequency side Even if it is moderate, there is no particular problem, but as with terrestrial digital broadcasting, a channel-dedicated receiving amplifier is used to amplify TV broadcast signals in which multiple TV broadcast signals are broadcast on adjacent channels. When using the filter, reduce the passband bandwidth of the bandpass filter to the minimum necessary. , In the steep rise and fall characteristics, it is the need to be able reliably cut off the television broadcasting signal of an adjacent channel adjacent to a particular broadcast channel.

  However, for this purpose, a general SAW filter as disclosed in Patent Document 1 cannot be used as the bandpass filter, and the specific broadcast channel and the adjacent channel are separated and the adjacent channel is separated. There is a problem that an expensive filter capable of suppressing the signal component has to be used, leading to an increase in the cost of the channel dedicated receiving amplifier.

  Also, in this way, in order to pass the signal component of the specific broadcast channel by the band pass filter and block the signal component of the adjacent channel adjacent thereto, the frequency of the TV broadcast signal of the specific broadcast channel after frequency conversion is It is necessary to make the frequency of the high-frequency signal used for down-converting the received signal constant so that the frequency is always constant.

  For this purpose, it is necessary to use an expensive oscillator that can always oscillate at a constant frequency without being affected by changes in the surrounding environment, as a local oscillator that generates a high-frequency signal for frequency conversion. There arises a problem that the cost of the channel dedicated receiving amplifier is increased.

  The present invention has been made in view of these problems, and in a channel-dedicated reception amplifier that extracts and amplifies a television broadcast signal of a specific broadcast channel by frequency-converting the received signal, the television broadcast signal of the specific broadcast channel to be extracted However, it is an object of the present invention to make it possible to accurately extract signals that are broadcast on adjacent channels together with other television broadcast signals without causing an increase in the cost of the receiving amplifier.

  In the channel-dedicated receiving amplifier according to claim 1, which is made to achieve the object, first, the first frequency converting means converts the received signal from the receiving antenna into an intermediate frequency signal having a frequency lower than the original frequency. The frequency conversion is performed, and the intermediate frequency signal amplifying means amplifies the frequency converted intermediate frequency signal. Then, the filter means selectively passes the intermediate frequency signal corresponding to the television broadcast signal of the preset specific broadcast channel among the amplified intermediate frequency signals, and the gain adjusting means passes the filter means. The gain of the intermediate frequency signal amplification means is adjusted so that the signal level of the intermediate frequency signal becomes a preset signal level. Further, the intermediate frequency signal that has passed through the filter means is frequency-converted by the second frequency conversion means to a television broadcast signal of a preset transmission broadcast channel and output to the outside.

  By the way, in the channel-dedicated receiving amplifier of the present invention, as in the prior art, the filter means is composed of only a bandpass filter, and this bandpass filter alone is used for a plurality of television broadcast signals broadcast on adjacent channels. In order to extract only the television broadcast signal of a specific broadcast channel from the band, the cost of the band-pass filter, and thus the receiving amplifier, is increased.

  Therefore, in the present invention, the filter means includes a bandpass filter in which a signal pass bandwidth is set wider than a bandwidth of a television broadcast signal, and a signal component of an adjacent channel adjacent to the television broadcast signal of a specific broadcast channel. And a notch filter for removing a signal component that can pass through the band-pass filter, even if the frequency of the intermediate frequency signal frequency-converted by the first frequency converting means fluctuates, the specific broadcast channel Is surely passed through the band-pass filter, and the signal component of the adjacent channel included in the passed intermediate frequency signal is removed by the notch filter.

  Therefore, according to the present invention, the function as the filter means for passing only the signal component of the specific broadcast channel is a bandpass filter having a relatively wide band and a gentle filter characteristic, and a notch that complements the filter characteristic of the bandpass filter. It can be realized using a filter, and only the TV broadcast signal of the characteristic broadcast channel is accurately selected from the plurality of TV broadcast signals broadcast on the adjacent channel without incurring the cost increase of the filter means. Thus, a channel-dedicated receiving amplifier that can be extracted and amplified can be realized.

  Further, according to the present invention, even if the frequency of the intermediate frequency signal frequency-converted by the first frequency converting means varies, by making the pass band width of the band pass filter wider than the bandwidth of the television broadcast signal. Since the signal component of the specific broadcast channel can be passed through the band pass filter, the frequency of the local oscillator that generates the high frequency signal necessary for frequency conversion of the received signal by the first frequency conversion means is There is no need to use an expensive oscillator that does not fluctuate. Therefore, the local oscillator can realize a channel-dedicated receiving amplifier at a low cost without increasing the cost of the receiving amplifier.

  Note that the channel-dedicated receiving amplifier of the present invention determines whether or not the received signal includes a TV broadcast signal of a specific broadcast channel in the received signal, and does not include the TV broadcast signal of the specific broadcast channel in the received signal. In addition, an amplification operation stop means for stopping the amplification operation in the reception amplifier is provided. This amplification operation stop means corresponds to the squelch circuit described above.

  That is, also in the present invention, when the received signal does not include a TV broadcast signal of a specific broadcast channel, the reception operation is stopped by stopping the amplification operation of the reception amplifier by the amplification operation stopping means having a squelch function. A signal obtained by amplifying noise is output from the amplifier to prevent other television broadcast signals flowing through the transmission line of the CATV system from being adversely affected.

  Further, as the amplification operation stopping means, as described in claim 2, a television of a specific broadcast channel is used as a reception signal based on the signal level of the gain adjustment signal output from the gain adjustment means to the intermediate frequency signal amplification means. What is necessary is just to comprise so that it may be determined whether the broadcast signal is contained.

  On the other hand, since the functions as the first frequency converting means, the intermediate frequency signal amplifying means, and the filter means are incorporated in a general tuner unit for receiving a television broadcast signal, the channel-dedicated receiving amplifier of the present invention can also be used. The functions of these means may be realized using a tuner unit.

  In other words, as described in claim 3, the first frequency converting means, the intermediate frequency signal amplifying means, and the filter means are televisions of a specific broadcast channel set in advance from the received signals input from the receiving antenna. A broadcast signal is selected, and the selected television broadcast signal is output as an intermediate frequency signal in a predetermined frequency band, and the output level of the intermediate frequency signal is integrated as a tuner unit that can be adjusted from the outside. It may be.

  Further, the filter characteristics of the filter means composed of the band pass filter and the notch filter include the signal component of the specific broadcast channel that is the desired wave in the intermediate frequency signal that has passed through the filter means and the adjacent channel that is the interference wave. The specific broadcast so that the level difference from the signal component of the signal is equal to or greater than the minimum level difference required to determine whether the received signal contains a television broadcast signal of the specific broadcast channel in the amplification operation stop means. What is necessary is just to set so that the signal component of an adjacent channel may be attenuate | damped with respect to the signal component of a channel.

  For this purpose, as described in claim 4, the filter means includes an input level of a television broadcast signal of a specific broadcast channel and an input level of a television broadcast signal of an adjacent channel adjacent to the specific broadcast channel. The allowable value of the difference is set as an input level difference, and the minimum malfunction prevention D / U required to determine whether or not the received signal contains a television broadcast signal of a specific broadcast channel by the amplification operation stop means. And the signal component of the adjacent channel is attenuated more than the signal component of the specific broadcast channel more than the attenuation obtained by adding these parameters (input level difference and malfunction prevention D / U). do it.

  That is, if the filter means is configured in this way, when the TV broadcast signal of the specific broadcast channel is stopped (in other words, when the broadcast is interrupted), the TV of the adjacent channel adjacent to the specific broadcast channel. Without being affected by the broadcast signal, the amplification operation stopping means can accurately detect that fact and the amplification operation at the channel dedicated receiving amplifier can be stopped. Therefore, it is possible to reliably prevent malfunction of the channel dedicated receiving amplifier.

  The malfunction prevention D / U of the amplifying operation stop means is a level difference between signals when a television broadcast signal of a specific broadcast channel is a desired wave (D) and a television broadcast signal of an adjacent channel is an interference wave (U). Is a value (DU ratio).

  On the other hand, the invention according to claim 5 receives a television broadcast signal of a plurality of broadcast channels including a television broadcast signal broadcast on an adjacent channel with one or a plurality of reception antennas, and receives from the reception antennas. By receiving the received signal into a dedicated channel receiving amplifier provided for each broadcasting channel, each channel dedicated receiving amplifier amplifies the television broadcasting signal of each broadcasting channel to a predetermined level, and each television broadcasting signal. In addition, the present invention relates to a CATV system configured to frequency-convert signals to transmission broadcast channels adjacent to each other, and further mix and transmit each television broadcast signal amplified and frequency-converted by a dedicated receiving amplifier for each channel to the terminal side. In this CATV system, the channel-dedicated receiving amplifier according to any one of claims 1 to 4 is used as at least a part of the plurality of channel-dedicated receiving amplifiers.

  Therefore, according to the fifth aspect of the present invention, television broadcast signals broadcast on adjacent channels by terrestrial digital broadcasting or the like are received, and the television broadcast signals of each channel are adjacent on the transmission path in the system. A CATV system capable of transmitting a television broadcast signal of each broadcast channel to an appropriate level without being affected by adjacent channels and transmitting it to the terminal side at the time of channel transmission can be realized at a low cost without causing an increase in cost. Become.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a head end 4 which is a reception point facility of a CATV system according to an embodiment to which the present invention is applied.

  The head end 4 shown in FIG. 1 takes in a received signal from a receiving antenna 2 that receives radio waves transmitted from a transmitting antenna for digital terrestrial broadcasting via an input terminal Tin, and includes a plurality of (this book) included in the received signal. In the embodiment, the television broadcast signals of the eight broadcast channels are individually amplified by the reception amplifiers 20-1 to 20-8 dedicated to the respective channels, so that the television broadcast signals of the respective broadcast channels are transmitted through the coaxial cable. Are converted into signals suitable for transmission to the terminal side, and further, the respective television broadcast signals after the conversion are mixed by the mixer 22 and output from the output terminal Tout to the coaxial cable on the terminal side. .

  In the head end 4, in order to input the reception signal from the reception antenna 2 to the channel dedicated reception amplifiers 20-1 to 20-8, an input for amplifying the reception signal input through the input terminal Tin. An amplifier 10, a distributor 14 for distributing the received signal amplified by the input amplifier 10 into two systems, a variable attenuator 12 for adjusting the input level of the received signal to the distributor 14, Amplifiers 16 and 17 for amplifying the received signals of the respective systems divided into two by the distributor 14 and distributors 18 for distributing the received signals of the respective systems amplified by the amplifiers 16 and 17 respectively. , 19 and a total of eight received signals distributed by the distributors 18 and 19 are input to the channel dedicated receiving amplifiers 20-1 to 20-8, respectively. It has been.

  In addition, on the output path of the television broadcast signal from the mixer 22 to the output terminal Tout, the television broadcast signal is compensated to compensate for the transmission loss of the television broadcast signal that occurs in the path to the relay amplifier provided in the terminal side coaxial cable. Are also provided, and an output amplifying unit 24 and a variable attenuator 26 for adjusting the level of the television broadcast signal.

  Next, channel-dedicated receiving amplifiers 20-1 to 20-8 (hereinafter, these plural amplifiers are collectively referred to simply as receiving amplifier 20) are set in advance from the received signals input from receiving antenna 2. In this embodiment, the TV broadcast signal of the specific broadcast channel is simply amplified and output. The TV broadcast signal of the specific broadcast channel is extracted and amplified to a predetermined level. Instead, the amplified television broadcast signal is once converted into an intermediate frequency signal (down-converted), and only the signal component corresponding to the television broadcast signal of the specific broadcast channel is accurately extracted from the intermediate frequency signal. At the same time, the signal level of the extracted intermediate frequency signal is amplified to a predetermined level, and the amplified intermediate frequency signal is preset. The television broadcast signal of a broadcast channel for transmission and frequency conversion (up-conversion) is adapted to output.

  That is, as shown in FIG. 2, the receiving amplifier 20 of this embodiment extracts a TV broadcast signal of a preset specific broadcast channel from the received signal input to the input terminal T1 from the distributor 18 or 19. An input circuit 30 that amplifies the TV broadcast signal to a predetermined level, a down converter 40 that down-converts the TV broadcast signal of the specific broadcast channel extracted and amplified by the input circuit 30 into an intermediate frequency signal, and the down converter 40 By up-converting the intermediate-frequency signal down-converted by the up-converter 50, the up-converter 50 for generating the television broadcast signal of the transmission broadcast channel, the TV-broadcast signal up-converted by the up-converter 50 is amplified, and the output terminal T2 And an output circuit 60 for outputting to the subsequent mixer 22 It has been.

  Here, the input circuit 30 is an analog band-pass filter composed of a coil L and a capacitor C in order to selectively pass a television broadcast signal of a specific broadcast channel among reception signals input to the input terminal T1. (BPF) 32, an amplification circuit 34 for amplifying a reception signal (a television broadcast signal of a specific broadcast channel) that has passed through the band-pass filter 32, and a television broadcast signal amplified by the amplification circuit 34 on the down converter 40 side And a gain of the amplifying circuit 34 so that the signal level of the television broadcast signal branched by the branch circuit 36 becomes a preset signal level. And an automatic gain adjustment circuit (AGC circuit) 38 for adjusting.

  For this reason, in the input circuit 30, the received signal (a television broadcast signal of a specific broadcast channel) that has passed through the bandpass filter 32 is amplified to a predetermined level by the amplifier circuit 34 and then output to the down converter 40. Become.

  Next, the down-converter 40 includes an oscillation circuit 41 that generates a high-frequency signal having a constant frequency, a high-frequency signal generated by the oscillation circuit 41, and a reception signal that is input via the input circuit 30 (a television broadcast signal of a specific broadcast channel). ), The mixer 42 that converts the TV broadcast signal of the specific broadcast channel to a predetermined intermediate frequency lower than the original frequency, and the amplification that amplifies the intermediate frequency signal frequency-converted by the mixer 42 A circuit 44, a band-pass filter 46 for selectively allowing only a signal component corresponding to a television broadcast signal of a specific broadcast channel among the intermediate frequency signals amplified by the amplifier circuit 44, and the band-pass filter 46 Is output to the up-converter 50 side and a part of the intermediate frequency signal is branched. The circuit 48 and the intermediate frequency signal branched by the branch circuit 48 are detected by, for example, an average value detection method, and the gain of the amplifier circuit 44 is adjusted so that the detected signal level becomes a preset signal level. And an automatic gain adjustment circuit (AGC circuit) 49.

  Therefore, in the down converter 40, the television broadcast signal of the specific broadcast channel included in the input signal from the input circuit 30 is frequency-converted into a signal in a predetermined intermediate frequency band set in advance, and the frequency-converted intermediate Only the signal component corresponding to the television broadcast signal of the specific broadcast channel is accurately extracted from the frequency signal, and the extracted intermediate frequency signal is amplified to a predetermined level and output to the up-converter 50. become.

  In the down converter 40, the oscillation circuit 41 and the mixer 42 correspond to first frequency conversion means of the present invention, the amplifier circuit 44 corresponds to intermediate frequency signal amplification means of the present invention, and the AGC circuit 49 This corresponds to the gain adjusting means of the invention. The band-pass filter 46 corresponds to the filter means of the present invention, and includes a band-pass filter 32 in the input circuit 30 comprising a coil L and a capacitor C, and a band-pass filter 64 in an output circuit 60 described later. The details will be described later.

  Next, the up-converter 50 confuses the oscillation circuit 52 that generates a high-frequency signal with a constant frequency, and the high-frequency signal generated by the oscillation circuit 52 with the intermediate-frequency signal that is input from the down-converter 40. A mixer 54 that converts the frequency of the signal into a television broadcast signal of a transmission broadcast channel; an amplifier circuit 56 that amplifies the output from the mixer 54 (a television broadcast signal of the transmission broadcast channel) and outputs the amplified signal to the output circuit 60; A gain adjustment signal (DC voltage) output from the AGC circuit 49 to the amplifier circuit 44 is taken in the down converter 40, and the signal level of the gain adjustment signal is set to a set level (in an operational amplifier constituting a so-called comparator). Specifically, it is determined whether or not the signal level that increases the gain of the amplifier circuit 44 to near the maximum gain is reached. Thus, it is determined whether or not the reception signal input from the reception antenna 2 includes a television broadcast signal of a specific broadcast channel to be amplified by the reception amplifier 20, and the gain adjustment signal is determined from the set level. A squelch circuit 58 that stops the amplification operation of the amplifier circuit 56 by, for example, shutting off the power supply to the amplifier circuit 56 when the received signal does not include a television broadcast signal of a specific broadcast channel; It is composed of

  Therefore, in this up-converter 50, the intermediate frequency signal corresponding to the TV broadcast signal of the specific broadcast channel input from the down converter 40 is upgraded to the TV broadcast signal of the transmission broadcast channel suitable for transmission by the CATV system. In addition to the conversion and output, when the reception signal input from the reception antenna 2 does not include a television broadcast signal of a specific broadcast channel, the amplification operation of the amplification circuit 56 is stopped and the frequency is converted. Can be prevented from being output to the output circuit 60 side (in this case, noise generated by amplifying the noise generated inside the receiving amplifier or the noise input from the outside).

  In the upconverter 50, the oscillation circuit 52 and the mixer 54 correspond to second frequency conversion means of the present invention, and the squelch circuit 58 corresponds to amplification operation stop means of the present invention. In this embodiment, the oscillation circuit 52 can change the oscillation frequency by an external operation in order to enable the broadcast channel of the television broadcast signal after up-conversion by an external operation.

  Finally, the output circuit 60 amplifies the output from the up-converter 50 by the amplifier circuit 62, and the mixer 22 side via the band-pass filter 64 and the output terminal T2 similar to those of the input circuit 30. To be output.

  Thus, each receiving amplifier 20 once converts the TV broadcast signal of a specific broadcast channel extracted and amplified by the input circuit 30 into an intermediate frequency signal (down-convert) by the down-converter 40, The intermediate frequency signal corresponding to the television broadcast signal of the specific broadcast channel is extracted by passing the frequency signal through the band-pass filter 46. In this embodiment, the intermediate frequency signal is input to each reception amplifier 20. In the reception amplifier 20 that amplifies at least the television broadcast signal broadcast on the adjacent channel, the band-pass filter 46 is included. Allows only the signal component of the specific broadcast channel to be amplified to pass and is adjacent to the TV broadcast signal. It is necessary to cut off the signal components of the adjacent channel.

  Therefore, the filter characteristics of the band-pass filter 46 of each receiving amplifier 20 accurately determine the signal level range of the received signal that can be input to the receiving amplifier 20 and the presence or absence of a TV broadcast signal of a specific broadcast channel in the squelch circuit 58. DU ratio (hereinafter referred to as squelch circuit malfunction prevention) between desired wave (D: signal component of specific broadcast channel in intermediate frequency signal) and interference wave (U: signal component of adjacent channel in intermediate frequency signal) D / U) is set as shown in FIG.

  That is, first, as shown in FIG. 3A, in the receiving amplifier 20 of this embodiment, the signal level range of the received signal that can be input is set to 50 dBμ to 80 dBμ by design. For this reason, the level difference between the desired wave (the TV broadcast signal of the specific broadcast channel) and the interference wave (the TV broadcast signal of the adjacent channel) is 30 dB at the maximum.

  The squelch circuit 58 operates when the signal level of the desired wave (specific broadcast channel) is 45 dBμ or less, which is 5 dB lower than the minimum input level. As shown in FIG. 3B, the squelch circuit malfunction prevention D / U necessary for accurately determining the presence or absence is designed to be 20 dB.

  In this case, in the band pass filter 46, as shown in FIG. 3C, the squelch circuit malfunction prevention D / U: 20 dB, the maximum level difference between the desired wave and the disturbing wave: 30 dB, and the squelch circuit Difference in operation level: 55 dB or more obtained by adding 5 dB is sufficient so that the interference wave can be attenuated with respect to the desired wave. Therefore, the filter characteristic of the bandpass filter 46 is the signal characteristic of the specific broadcast channel. Thus, other signal components including the signal components of adjacent channels are set to be attenuated by 55 dB or more.

  In addition, it is extremely difficult to realize such filter characteristics with an analog bandpass filter including a coil L and a capacitor C or a single SAW filter (surface acoustic wave filter). In this embodiment, as shown in FIG. 4A, the bandpass filter 46 is a general bandpass filter because the unit price of the device itself is extremely high and the cost of the reception amplifier 20 is increased. The SAW filter 46a and the two notch filters 46b and 46c are used.

  In other words, generally used analog band-pass filters and SAW filters cannot make the filter characteristics of the band-pass filter 46 (specifically, change characteristics of attenuation in the cut-off frequency region) steep, and adjacent channels In this embodiment, the band pass filter 46 is composed of the SAW filter 46a and the notch filters 46b and 46c, as shown in FIG. 4B. The attenuation characteristics of the SAW filter 46a in the low frequency side and high frequency side cutoff frequency regions are corrected to be steep using the notch filters 46b and 46c, respectively. The signal component of the channel can be surely cut off.

  In the case of terrestrial digital broadcasting, the bandwidth for one channel of television broadcasting is 6 MHz as in the conventional case, but the bandwidth of the television broadcasting signal itself is 5.58 MHz. Accordingly, the pass band width of the band pass filter 46 is set to 5.58 MHz corresponding to the bandwidth of the television broadcast signal, considering the change characteristic of the attenuation amount in the cut-off frequency regions on the low frequency side and the high frequency side. However, with this setting, when the oscillation frequency of the oscillation circuit 41, which is a local oscillator in the down converter 40, fluctuates and the frequency of the intermediate frequency signal fluctuates, the signal component of the specific broadcast channel is changed. Some may be removed.

  Therefore, in the present embodiment, the pass band width of the band-pass filter 46 is wider than 5.58 MHz (eg, 5.62 MHz) in consideration of the frequency variation (eg, ± 20 kHz) of the oscillation circuit 41 in the down converter 40. By setting, the signal component of the specific broadcast channel can be surely extracted via the band pass filter 46.

  As described above, in the CATV system of the present embodiment, the television broadcast signal received by the receiving antenna 2 using the channel dedicated receiving amplifiers 20-1 to 20-8 provided in the head end 20, Each channel is amplified to a predetermined level and transmitted to the terminal side. In each receiving amplifier 20, the received signal input through the input circuit 30 is down-converted into an intermediate frequency signal and amplified. After that, a television broadcast signal of a specific broadcast channel is extracted using a bandpass filter 46 including a SAW filter 46a and notch filters 46b and 46c.

  For this reason, according to the CATV system of the present embodiment, even if a plurality of television broadcast signals received by the reception antenna 2 are television broadcast signals broadcast on adjacent channels, each receiving amplifier in the head end 20 20 can accurately extract the television broadcast signal of each broadcast channel and convert it into a television broadcast signal of a transmission broadcast channel of a predetermined level, and a band pass filter 46 for extracting the television broadcast signal, Since it can be realized at a low cost by using a SAW filter and a notch filter that are generally used conventionally, it is possible to transmit a television broadcast signal provided by digital terrestrial broadcasting while suppressing the cost of each receiving amplifier 20. A CATV system can be realized at low cost.

  In each reception amplifier 20, the signal component (intermediate frequency signal) of the specific broadcast channel extracted using the bandpass filter 46 is up-converted by the up-converter 50 into a television broadcast signal of the transmission broadcast channel. The up-converted TV broadcast signal is further amplified and output to the terminal side. In the up-converter 50, the squelch circuit 58 outputs to the output (gain adjustment signal) from the AGC circuit 49 in the down-converter 40. Based on this, it is determined whether or not the reception signal input from the reception antenna 2 includes a TV broadcast signal of a specific broadcast channel. If the reception signal does not include a TV broadcast signal of a specific broadcast channel, Then, the amplification operation of the amplifier circuit 56 is stopped.

  For this reason, in the CATV system of this embodiment, each receiving amplifier 20 in the head end 2 does not include a TV broadcast signal of a specific broadcast channel to be amplified in the received signal input from the receiving antenna 2. In addition, since the own amplification operation is stopped, even if the broadcast channel (transmission broadcast channel) of the television broadcast signal output from each reception amplifier 20 is assigned to the adjacent channels adjacent to each other, It is possible to reliably prevent the television broadcast signal output from the other receiving amplifier 20 from being deteriorated by the output high level noise signal.

  Therefore, according to the CATV system of the present embodiment, it is possible to amplify the terrestrial digital broadcast television broadcast signal received by the reception antenna 2 within the head end 4 to a desired level for each broadcast channel. In addition, the amplified television broadcast signal of each broadcast channel can be transmitted to the terminal side without degrading the quality.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various aspect can be taken in the range which does not deviate from the summary of this invention.

  For example, in the above embodiment, each receiving amplifier 20 has been described as including four circuit blocks of the input circuit 30, the down converter 40, the up converter 50, and the output circuit 60. 30 and the portion of the down converter 40 excluding the branch circuit 48 and the AGC circuit 49 can be realized by using a television broadcasting tuner unit that has been incorporated in various receiving apparatuses. As shown in FIG. 5, the amplifier 20 may be composed of a commercially available tuner unit 20a and a signal processing circuit 20b.

  That is, the tuner unit 20 a includes a bandpass filter 32, an amplifier circuit 34, a branch circuit 36, an AGC circuit 38, an oscillation circuit 41, a mixer 42, an amplifier circuit 44, and a bandpass filter 46. The signal processing circuit 20b is composed of a branch circuit 48, an AGC circuit 49, an oscillation circuit 52, a mixer 54, an amplification circuit 56, a squelch circuit 58, an amplification circuit 62, and the like. In addition, each reception amplifier 20 may be configured by configuring the band-pass filter 64 as a signal processing circuit dedicated to the embodiment apparatus assembled on one or a plurality of printed wiring boards and connecting them together.

  In this way, since each receiving amplifier 20 can be realized using a commercially available tuner unit 20a, each receiving amplifier 20, and hence the CATV system can be realized at low cost.

  In the above embodiment, the band-pass filter 46 has been described as a signal that attenuates the signal component of the adjacent channel by 55 dB or more compared to the signal component of the specific broadcast channel. In the terrestrial digital broadcasting that will be put to practical use in the future, the TV broadcast signal of each channel is transmitted so that the input level difference is 10 dB or less. When the channel-dedicated receiving amplifier is used for reception of terrestrial digital broadcasting, the filter characteristics of the bandpass filter 46 include the input level difference of 10 dB and the malfunction prevention D / U (the squelch circuit malfunction prevention D / U described above: 20 dB) plus the attenuation (for example, 30 dB) or more, the signal component of the adjacent channel It suffices to significantly attenuate than the signal component of a constant channels.

  In the above-described embodiment, the band-pass filter 46 is described as being configured by the SAW filter 46a and the two notch filters 46b and 46c. However, the band-pass filter 46 includes a coil L and a capacitor C instead of the SAW filter 46a. An analog filter (LC filter) may be used. In this case, the SAW filter 46a is a single component, whereas the analog filter is composed of a combination of the coil L and the capacitor C, so that the number of components of the reception amplifier 20 increases. In order to reduce the size of the reception amplifier 20, it is desirable that the bandpass filter 46 is composed of a SAW filter and a notch filter.

  In the above embodiment, the notch filters 46b and 46c correct the filter characteristics of the SAW filter 46a, which is a bandpass filter, so that the signal components of the adjacent channels adjacent to the specific broadcast channel that should pass through the bandpass filter 46 are obtained. Therefore, when the signal component of the adjacent channel exists only on the high frequency side or the low frequency side of the specific broadcast channel, one notch filter 46b or 46c corresponding to the adjacent channel is provided. What is necessary is just to provide.

  The notch filters 46b and 46c only need to be connected in series to the SAW filter 46a, and the installation location may be before or after the SAW filter 46a. Alternatively, the SAW filter 46a may be connected to two notch filters. You may arrange | position so that it may be pinched | interposed by 46b and 46c.

  Further, in the above embodiment, it has been described that each receiving amplifier 20 in the head end 4 is the one shown in FIG. 2 to which the present invention is applied, but the channel dedicated receiving amplifiers 20-1 to 20-20 in the head end 4 are described. -8 may be constituted by a part of which is shown in FIG. 2 to which the present invention is applied, and the other receiving amplifiers may be conventional ones.

  That is, the channel-dedicated receiving amplifier of the present invention broadcasts a TV broadcast signal of a specific broadcast channel to be amplified on an adjacent channel together with other TV broadcast signals, and the terminal side receives the amplified TV broadcast signal. In the case where adjacent channels are transmitted together with other TV broadcast signals, the above-described effects specific to the present invention are exhibited. Therefore, in constructing a CATV system, the channel-dedicated receiving amplifier of the present invention exhibits the effects. It may be installed where appropriate.

It is a block diagram showing the schematic structure of the head end of the CATV system of an Example. It is a block diagram showing the structure of the channel exclusive use receiving amplifier 20 of an Example. It is explanatory drawing explaining the characteristic of the band pass filter which comprises the down converter of an Example. It is explanatory drawing explaining the structure of the band pass filter which comprises the down converter of an Example. It is explanatory drawing showing the modification of the channel exclusive use receiving amplifier 20 of an Example. It is explanatory drawing explaining operation | movement of the conventional channel exclusive receiving amplifier, and channel arrangement | positioning of terrestrial digital broadcasting.

Explanation of symbols

2 ... receiving antenna, 4 ... head end, 10 ... input amplifier, 12 ... variable attenuator, 14 ... distributor, 16, 17 ... amplifier, 18, 19 ... distributor, 20-1 to 20-8 ... dedicated channel reception Amplifier (20 ... receiving amplifier), 22 ... mixer, 24 ... output amplifier, 26 ... variable attenuator, 30 ... input circuit, 32 ... band pass filter, 34 ... amplifier circuit, 36 ... branch circuit, 38 ... AGC circuit, DESCRIPTION OF SYMBOLS 40 ... Down converter, 41 ... Oscillator circuit, 42 ... Mixer, 44 ... Amplifier circuit, 46 ... Band pass filter, 48 ... Branch circuit, 49 ... AGC circuit, 50 ... Up converter, 52 ... Oscillator circuit, 54 ... Mixer, 56 ... Amplifier circuit 58 ... Squelch circuit 60 ... Output circuit 62 ... Amplifier circuit 64 ... Bandpass filter 20a ... Tuner unit 20b ... Signal processing circuit 46a SAW filter, 46b, 46c ... notch filter.

Claims (5)

First frequency conversion means for frequency-converting a reception signal from a reception antenna that receives a plurality of television broadcast signals broadcast on adjacent channels to an intermediate frequency signal having a frequency lower than the original frequency;
Intermediate frequency signal amplification means for amplifying the intermediate frequency signal output from the first frequency conversion means;
Filter means for selectively passing an intermediate frequency signal corresponding to a television broadcast signal of a preset specific broadcast channel among the intermediate frequency signals amplified by the intermediate frequency signal amplification means;
Gain adjusting means for adjusting the gain of the intermediate frequency signal amplifying means so that the signal level of the intermediate frequency signal that has passed through the filter means becomes a preset signal level;
Second frequency conversion means for converting the frequency of the intermediate frequency signal that has passed through the filter means into a television broadcast signal of a preset transmission broadcast channel;
It is determined whether or not the received broadcast signal includes the TV broadcast signal of the specific broadcast channel, and when the received signal does not include the TV broadcast signal of the specific broadcast channel, an amplification operation in the reception amplifier Amplifying operation stopping means for stopping
A channel-dedicated receiving amplifier comprising:
The filter means includes
A bandpass filter in which a signal passband width is set wider than a bandwidth of the television broadcast signal;
A notch filter for removing a signal component of an adjacent channel adjacent to a television broadcast signal of the specific broadcast channel and capable of passing through the bandpass filter;
A channel-dedicated receiving amplifier.   The amplifying operation stopping means is based on the signal level of the gain adjusting signal output from the gain adjusting means to the intermediate frequency signal amplifying means, and whether or not the received signal includes a television broadcast signal of the specific broadcast channel. The channel dedicated receiving amplifier according to claim 1, wherein the channel dedicated receiving amplifier is determined. The first frequency converting means, the intermediate frequency signal amplifying means, and the filter means are:
A television broadcast signal of a specific broadcast channel set in advance is selected from the received signals, the selected television broadcast signal is output as an intermediate frequency signal in a predetermined frequency band, and an output level of the intermediate frequency signal is set. Tuner unit adjustable from outside,
The channel-dedicated receiving amplifier according to claim 1, wherein the channel-dedicated receiving amplifier is integrated with the channel-specific receiving amplifier. The filter means includes
An input level difference representing an allowable value of a difference between an input level of the TV broadcast signal of the specific broadcast channel and an input level of the TV broadcast signal of an adjacent channel adjacent to the specific broadcast channel;
The amplifying operation stop means is a DU ratio representing a level difference between signals when the television broadcast signal of the specific broadcast channel is a desired wave (D) and the television broadcast signal of the adjacent channel is an interference wave (U). A malfunction prevention D / U that is at least required to determine whether or not the received signal includes a TV broadcast signal of a specific broadcast channel;
4. The structure according to claim 1, wherein the signal component of the adjacent channel is attenuated more than the signal component of the specific broadcast channel by an amount equal to or greater than an attenuation amount obtained by adding. A dedicated receiver amplifier for channels according to the above. TV broadcast signals of a plurality of broadcast channels including TV broadcast signals broadcast on adjacent channels are received by one or a plurality of reception antennas, and reception signals from the reception antennas are provided for the respective broadcast channels. Each channel dedicated receiver amplifier amplifies the television broadcast signal of each broadcast channel to a predetermined level, and transmits each television broadcast signal to a transmission broadcast channel adjacent to each other. A CATV system configured to perform frequency conversion, mix each television broadcast signal amplified and frequency converted by the dedicated receiving amplifier for each channel, and transmit the mixed signal to the terminal side,
5. A CATV system, wherein the channel-dedicated receiving amplifier according to claim 1 is used for at least a part of the plurality of channel-dedicated receiving amplifiers.

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