JP2003224834A - Catv system and frequency converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a CATV system, in which a pair of up- and down converters to apply frequency conversion to a transmission signal in order to assure the quality of the transmission signal are employed and which can reduce phase noise included in the transmission signal after passing through both converters. <P>SOLUTION: In an in-building CATV system where an in-building incoming signal is transmitted in a building by using an up-converter 70 to convert an incoming signal into the in-building incoming signal with a frequency higher than that of an outgoing signal and the original incoming signal is outputted to a two-way system at the outside of the building by using the down-converter 10 to convert the frequency of the in- building incoming signal into the frequency of the original incoming signal, each of the converters 70, 40 is provided with PLL circuits 80, 50 for using a common reference signal to generate a high frequency signal for frequency conversion. Each of the PLL circuits 80, 50 is provided with frequency divider circuits having identical frequency division values to each other as frequency divider circuits 82, 54 for the reference signal and frequency divider circuits 84, 54 for the high frequency signal so as to make the phase comparison frequency of the PLL circuits 80, 50 coincident with each other. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention includes a pair of up / down converters for converting the frequency of a transmission signal in a predetermined frequency band on a transmission line, and the transmission signal is transmitted between the converters at a frequency different from the original frequency. By doing
The present invention relates to a CATV system that ensures the transmission quality of the transmission signal, and a frequency conversion device used as an up / down converter in this CATV system.

[0002]

2. Description of the Related Art For example, in a CATV system that retransmits satellite broadcasting from a broadcasting satellite (BS) or communication satellite (CS) in addition to terrestrial broadcasting, a satellite reception signal (from a receiving antenna for receiving satellite broadcasting ( BS-IF signal, CS
-IF signals, etc.) are transmitted as they are onto the transmission line, the satellite reception signal has a higher frequency than the ground wave, which causes a problem that the transmission loss of the satellite reception signal on the transmission line increases. It was

Therefore, conventionally, in this type of CATV system, a down converter is provided on the head end side to convert the satellite reception signal into a UHF band lower than the original frequency and send it out onto a transmission line. Before the distribution of the transmission signal to the subscriber's house or at each subscriber's side, an up converter is used to restore the satellite reception signal to the original frequency band to reduce the transmission loss of the satellite reception signal. is there.

Further, for example, in a bidirectional CATV system in which bidirectional communication can be performed between the center device of the CATV system and the subscriber side terminal device, the subscriber side terminal device sends the data to the center device. The frequency (for example, 10 MHz to 55 MHz) of the upstream transmission signal (upstream signal) is lower than the frequency (for example, 70 to 770 MHz) of the downstream transmission signal (downstream signal) transmitted from the center device to the terminal side. Since it is set to, the high frequency noise generated in various electric appliances is likely to be superposed on the upstream signal, especially from the housing where many terminal terminals are installed to the transmission line (main line etc.) of the bidirectional CATV system. In some cases, high-frequency noise input from each terminal terminal is transmitted as ingress noise, and therefore transmission quality of upstream signals may not be ensured. .

Therefore, conventionally, this type of bidirectional CA has been used.
In the TV system, the upstream signal output from the terminal device is transmitted to each subscriber side at a frequency higher than that of the downstream signal (for example, 8
21 MHz to 866 MHz) by providing an up converter for frequency conversion, and by providing a down converter for returning the upstream signal to the original frequency in the route from the subscriber facility such as an apartment house to the trunk line of the bidirectional CATV system, There are some that are designed to ensure the transmission quality of.

By the way, in the CATV system in which the transmission signal is frequency-converted by using the pair of up / down converters as described above, in order to normally operate the device for receiving the transmission signal, it is necessary to pass through these converters. The transmitted signal must be exactly the same as the original transmitted signal before passing through both converters. To do this, the frequency of the high-frequency signal used to frequency convert the transmitted signal in each converter must be Must be matched between each converter.

Therefore, conventionally, in the CATV system, a reference signal serving as a reference for the frequency conversion high-frequency signal is passed through the transmission line, and each converter uses the reference signal to generate the frequency conversion high-frequency signal. Thus, the frequencies of the high-frequency signals for frequency conversion are made to match between the converters.

Specifically, each converter includes a local oscillator that generates a high-frequency signal for frequency conversion, and a PLL circuit that controls the oscillation frequency of the local oscillator to a predetermined constant frequency using a reference signal. By the operation of this PLL circuit, each converter can generate a high frequency signal for frequency conversion of the same frequency by using a common reference signal.

[0009]

By the way, when the high frequency signal for frequency conversion is generated by using the PLL circuit in each converter as described above, the P of each converter is increased.
If the frequency (phase comparison frequency) with which the phase comparison circuit that constitutes the LL circuit performs phase comparison differs, the phase noise included in the transmission signal that has passed through both converters becomes large,
If the transmission signal is a digital transmission signal (digital broadcasting signal, data communication signal, etc.) that is a modulation of digital data, the device that receives it can accurately restore the digital data from the received transmission signal. I realized that I couldn't do it.

That is, the PLL circuit divides or multiplies the high frequency signal output from the local oscillator to be controlled and the reference signal, respectively, and inputs them to the phase comparison circuit, and the phase comparison circuit outputs these input signals. By generating a signal corresponding to the phase difference and inputting the generated signal to the local oscillator through a loop filter (low-pass filter), the oscillation frequency of the local oscillator is controlled. Since they are designed individually, even if the frequency of the reference signal flowing through the transmission line is the same, the phase comparison frequency in the phase comparison circuit that constitutes the PLL circuit in each converter (specifically, the frequency division value or multiplication factor of the frequency division circuit) The circuit multiplication value) may be different.

Even if the phase comparison frequency in the PLL circuit is different as described above, if the local oscillator controlled by the PLL circuit has the same oscillation frequency, a high frequency signal of the same frequency is used in each converter. However, in practice, the high frequency signal output from the local oscillator has a slight frequency fluctuation (very small fluctuation) caused by the control operation of the PLL circuit, and the phase comparison frequency , The frequency fluctuations are different, and thus the difference in the frequency fluctuations causes relatively large phase noise to be superimposed on the transmission signal that has passed through both converters.

When the phase noise becomes large in this way, and when the transmission signal is an analog broadcasting signal,
Although not a serious problem, if the transmission signal is a digital transmission signal (digital broadcasting signal or signal for data communication), the error rate of the received data increases on the receiving side of the transmission signal, and in some cases it cannot be received. It becomes.

The present invention has been made in view of these problems, and in a CATV system in which a transmission signal is frequency-converted using a pair of up / down converters in order to secure the quality of the transmission signal, the signal after passing through both converters is used. The purpose is to reduce phase noise included in a transmission signal.

[0014]

In a CATV system according to claim 1, which is made to achieve the above object, a transmission signal of a predetermined frequency band is transmitted on a transmission line different from the original frequency band and other transmission. A first converter that performs frequency conversion into a frequency band that does not overlap with the signal is provided, and the transmission signal that has been frequency-converted by the first converter is provided on the transmission line on which the transmission signal frequency-converted by the first converter flows. A second converter that performs frequency conversion into a frequency band is provided.

Each of these converters has a first local oscillator for generating a high frequency signal for frequency conversion, and
A frequency conversion means for frequency converting the transmission signal by mixing the high frequency signal generated by the first local oscillator and the transmission signal in the predetermined frequency band to be frequency converted, and a common reference signal flowing through the transmission line are used. And a PLL circuit that controls the oscillation frequency from the first local oscillator, and the PLL circuit of each converter is
The reference signal in the LL circuit is fetched by using the first frequency dividing or multiplying circuit having the same frequency dividing value or frequency multiplying value so that the phase comparison frequencies of the high frequency signal and the first local oscillator are the same. Generated high frequency signal,
A control signal of the first local oscillator is obtained by using a second frequency division or multiplication circuit having the same frequency division value or multiplication value, and comparing the phase of the reference frequency signal after the frequency division or frequency multiplication with the high frequency signal. To generate.

As a result, according to the CATV system of the present invention, the phase comparison frequency in the PLL circuit provided in each converter (further, the fluctuation of the high frequency signal for frequency conversion generated in the first local oscillator) is detected. By making them coincident, it is possible to reduce the phase noise included in the transmission signal that has passed through both converters.

Therefore, according to the present invention, even if the transmission signal whose frequency is converted by each converter is a digital transmission signal obtained by modulating digital data, the error rate of the reception data generated on the receiving side of the transmission signal is reduced. Then, the digital data can be accurately restored.

Next, in the CATV system according to the second aspect, the present invention is such that a service line from an external two-way CATV system is introduced into a building and is input from the service line through a transmission line in the structure. In-building CATV, which transmits the down signal to the terminal terminal in the building, and also transmits the up signal input from the terminal device on the subscriber side to the terminal line to the drop line and sends it to the external bidirectional CATV system from the drop line.
It is applied to the system.

In this in-building CATV system, the up-converter as the first converter is provided at one or a plurality of terminal terminals to which an upstream signal from the subscriber side terminal device is input, and the subscriber side terminal is provided. The upstream signal output from the device is frequency-converted into an in-building upstream signal having a frequency higher than that of the downstream signal, and the upstream signal is transmitted onto the transmission line. The in-building upstream signal transmitted to the service line via the service line is frequency-converted into an upstream signal in the original frequency band output by the terminal device on the subscriber side, and sent from the service line to an external bidirectional CATV system.

Therefore, according to the CATV system (in-building CATV system) of claim 2, high-frequency noise in the same frequency band as the upstream signal input to each terminal terminal in the building becomes inflow noise. Of the external bidirectional CATV system and the phase noise contained in the upstream signal passing through the up-converter and the down-converter can be reduced.
On the center side of the system, digital data can be accurately restored from the upstream signal transmitted by the subscriber side terminal device in the building.

Next, a CATV system according to a third aspect is the in-building CATV system according to the second aspect.
A second local oscillator that generates a reference signal is provided in the down converter, and the reference signal generated by the second local oscillator is input to the PLL circuit in the down converter and is transmitted to the transmission line on the up converter side. On the up converter side, the reference signal sent out from the down converter on the transmission line is taken in through the filter circuit,
The input is made to the internal PLL circuit.

Therefore, according to the invention described in claim 3, in constructing the in-building CATV system according to claim 2, the PLL circuit in each converter controls the oscillation frequency of the first local oscillator. It is not necessary to separately provide a dedicated device for flowing the reference signal on the transmission line in order to share the reference signal used for the above, and the system configuration can be simplified.

In addition to the in-building CATV system according to the second and third aspects, the present invention may be a system that frequency-converts a transmission signal flowing through a transmission line by using a pair of up / down converters. For example, the present invention can be applied to a system in which a pair of converters (down converter and up converter) are provided on a transmission line in order to reduce the transmission loss of satellite reception signals described in the section of the prior art.

On the other hand, the inventions described in claims 4 to 6 relate to a frequency conversion device used as a first converter or an up converter in the CATV system described in claims 1 to 3, respectively. The frequency conversion device according to claim 4 includes a first local oscillator that generates a high-frequency signal for frequency conversion, a high-frequency signal generated by the first local oscillator, and a transmission of a predetermined frequency band that is a target of frequency conversion. By mixing the signal with the frequency conversion means for frequency converting the transmission signal and the reference signal common to the second converter which is another frequency conversion device constituting the CATV system, the first local oscillator is used. And a PLL circuit for controlling the oscillation frequency, and the PLL circuit takes in a reference signal by using the same first frequency dividing or multiplying circuit as the PLL circuit in the second converter, and the PLL circuit in the second converter. A high frequency signal generated by the first local oscillator is captured by using the same second frequency division or multiplication circuit as the circuit, and the obtained reference signal after frequency division or multiplication is acquired. It is configured to phase comparison and a high-frequency signal. Therefore, the frequency conversion device according to claim 4 is
CATV according to claim 1, when used as a converter
You can build a system.

A frequency converter according to a fifth aspect is provided with the frequency converter according to the fourth aspect at a terminal terminal to which an upstream signal from a subscriber side terminal device is input,
It is configured as an up-converter that frequency-converts an upstream signal output from the subscriber-side terminal device into an in-building upstream signal having a higher frequency than the downstream signal and sends out to the transmission line in the building. Therefore, if the frequency conversion device according to claim 5 is used as the first converter in the CATV system according to claim 1, the in-building CATV system according to claim 2 can be constructed.

The frequency converter according to a sixth aspect of the present invention further includes, in the frequency converter according to the fifth aspect, a reference signal transmitted to a terminal terminal via a transmission line selectively. A filter circuit for inputting to a PLL circuit in the frequency conversion device is provided. Therefore, if the frequency conversion device according to claim 6 is used as an up-converter in the in-building CATV system according to claim 2, the in-building CATV system according to claim 3 can be constructed.

Next, the inventions described in claims 7 to 9 relate to a frequency converter used as a second converter or a down converter in the CATV system described in claims 1 to 3, respectively. . The frequency converter according to claim 7 includes a first local oscillator that generates a high-frequency signal for frequency conversion, a high-frequency signal generated by the first local oscillator, and a transmission of a predetermined frequency band that is a target of frequency conversion. A signal from the first local oscillator is mixed by using a reference signal common to the frequency conversion means for frequency-converting the transmission signal by mixing the signal and the first converter which is another frequency conversion device constituting the CATV system. And a PLL circuit for controlling the oscillation frequency, and the PLL circuit takes in a reference signal by using the same first frequency dividing or multiplying circuit as the PLL circuit in the first converter, and the PLL circuit in the first converter. A high frequency signal generated by the first local oscillator is captured by using the same second frequency division or multiplication circuit as the circuit, and the obtained reference signal after frequency division or multiplication is acquired. It is configured to phase comparison and a high-frequency signal. Therefore, the frequency conversion device according to claim 7
CATV according to claim 1, when used as a converter
You can build a system.

The frequency converter according to claim 8 is the same as the frequency converter according to claim 7, except that the first converter is an up-converter provided on the terminal side via a service line in the building. The upstream signal in the building that has been transmitted to the side is frequency-converted into an upstream signal in the original frequency band before the frequency conversion by the up-converter, and external bidirectional C
It is configured as a down converter for sending to the ATV system. Therefore, if the frequency conversion device according to claim 8 is used as the second converter in the CATV system according to claim 1, the in-building CATV system according to claim 2 can be constructed.

A frequency converter according to a ninth aspect is the frequency converter according to the eighth aspect, further comprising a second local oscillator for generating a reference signal, and a reference generated by the second local oscillator. The signal is transferred to the PL in the frequency conversion device.
It is configured such that it is input to the L circuit and is sent out on the transmission line on the up-converter side. Therefore, if the frequency conversion device according to claim 9 is used as a down converter in the in-building CATV system according to claim 2, the in-building CATV system according to claim 3 can be constructed.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the entire interactive CATV system of the embodiment. In this bidirectional CATV system, a headend device (so-called reception point equipment) 2 that receives various broadcast radio waves such as television broadcasting and FM radio broadcasting, and a voluntary frequency different from the broadcast signal output from the headend device 2 The center device 4 that outputs a broadcast signal for broadcasting is provided.

Further, the center device 4 is provided with a communication device (so-called internet server) (not shown) connected to the Internet via a dedicated line, and this communication device is connected to a cable modem on the terminal side. By performing data communication, the subscriber-side communication device connected to the cable modem on the terminal side and another communication device on the Internet are relayed.

The broadcast signal output from the head end device 2 and the center device 4 and the data communication signal output from the center device 4 are combined by the mixer 6.
Predetermined frequency band (70 MHz to 770 MH in this embodiment)
z) is transmitted to the terminal side as a downlink signal.

The downlink signal output from the mixer 6 to the terminal side is transmitted to a predetermined area through the optical transceiver 8, the optical fiber cable, and the node type optical transceiver 10, and the node type optical transceiver 10 Is further transmitted to the terminal side via the coaxial cable wired in the area.

Next, one or a plurality of trunk line branch amplifiers 12 are provided on the coaxial cable from the node type optical transceiver 10 to the terminal side, and a branch amplifier 14 is provided at the final end thereof. Each of the amplifiers 12 and 14 not only amplifies the broadcast signal and the data communication signal from the head end device 2 and the center device 4 and outputs them to the terminal side,
A bidirectional amplifier is configured so that an upstream signal in a predetermined frequency band for data communication (10 MHz to 55 MHz in this embodiment) transmitted from the terminal side can be amplified and output to the center device 4 side. .

Further, the main branch amplifier 12 and the branch amplifier 1
On the branch line from 4 is a tap-off (so-called branch device) 1 for connecting the branch line (in other words, the transmission line of the external bidirectional CATV system) and the transmission line in the subscriber-side building.
6 is provided, and the tap-off 16 and the transmission line in the subscriber-side building (a housing complex 20 in FIG. 1) are connected via a service line 17 and a protector 18. The branch line and the drop line 17 are all coaxial cables.

The in-building CATV system to which the present invention is applied is constructed in the housing complex 20 shown in FIG. Hereinafter, the in-building CATV system in the housing complex 20 will be described with reference to FIG.

The in-building CATV system built in the housing complex 20 is connected to the transmission line of the external bidirectional CATV system via the service line 17 and the protector 18.
Through the transmission line (coaxial cable) L in 0, the bidirectional amplifier 22, the branching device 24, the distributor 26, etc. provided in this transmission line L, the downlink signal of the bidirectional CATV system is transferred in the housing complex 20. A plurality of terminal terminals 28 installed in each subscriber's house
The in-building upstream signal that has been transmitted to the terminal device on the subscriber side via the up-converter 70, which will be described later, from the terminal device on the subscriber side to the incoming line 17 (and thus the external bidirectional CA).
It is for transmission to the transmission line of the TV system).

In the CATV system in this building,
When a subscriber enjoys the Internet via a center device of an external bidirectional CATV system, or when transmitting data for viewing reservation of a pay program or TV shopping, etc. to the center device, the subscriber joins the service. The up-converter 70 as the first converter is connected to the terminal terminal 28 on the user side.
Also, an information terminal device (personal computer or the like) 34 for data communication is connected via the cable modem 32.

As a result, the transmission data for data communication output from the information terminal device 34 can be transmitted by the cable modem 32 in a predetermined frequency band (10 MHz to 55 MHz in this embodiment) that can be transmitted by the external bidirectional CATV system. ), And the up-converter 70 frequency-converts the upstream signal into an in-building upstream signal in a predetermined frequency band (821 MHz to 866 MHz in this embodiment) having a higher frequency than the downstream signal. And is input to the terminal 28.

Therefore, the transmission line L of the in-building CATV system and the service line 17 from the external bidirectional CATV system.
At the connection portion with the terminal, the in-building upstream signal transmitted from each terminal terminal 28 via the transmission line L is supplied to the external bidirectional CAT.
In order to frequency-convert the original upstream signal that can be transmitted by the V system, the down converter 40 as the second converter
Is provided.

In FIG. 2, reference numeral 36 is connected to the terminal terminal 28 to which the up converter 70 is not connected,
External bidirectional CATV transmitted via the transmission line L
A television receiver that receives a downlink signal from the system and demodulates and reproduces a television broadcast of a desired channel.

In the in-building CATV system of this embodiment, a cable from an external cable broadcasting system is also drawn in (see FIG. 1), and this cable is placed on the transmission line L near the down converter 40. A mixer 29 is provided which mixes a cable broadcasting signal (frequency: 26 MHz to 70 MHz) input via the terminal and a downlink signal from an external bidirectional CATV system and sends the mixed signal to the terminal side.

Therefore, not only the downlink signal from the external bidirectional CATV system but also the cable broadcasting signal is transmitted to the terminal terminal 28 on the side of each subscriber, and among the subscribers of the in-building CATV system, it is wired. A subscriber who wants to enjoy broadcasting can connect the cable broadcasting receiver 38 to the terminal terminal 28.

Next, the configurations of the down converter 40 and the up converter 70 used in the in-building CATV system of this embodiment will be described with reference to FIG. As shown in FIG. 3, the down converter 40 includes an external bidirectional CATV.
An external connection terminal T1 for connecting the service line 17 from the system through the protector 18 and an internal connection terminal T2 for connecting the transmission line L in the building (that is, the housing complex 20).
And are provided.

Then, the downstream signal input to the external connection terminal T1 is taken into the down converter 40 through the high-pass filter (hereinafter referred to as HPF) 41, and the low-pass filter (hereinafter referred to as LPF). 42
And is transmitted to the transmission line L on the terminal side via the internal connection terminal T2. In addition, the HPF 41 allows the downlink signal to pass,
The cutoff frequency is set to 70 MHz, for example, to prevent passage of the upstream signal after frequency conversion. Further, the LPF 42 allows the downlink signal to pass,
The cut-off frequency is set to 770 MHz, for example, to prevent passage of an in-building upstream signal input to the internal connection terminal T2 via the transmission line L.

Further, as described above, the HPF 41 and the LPF 42 are
In order to send the reference signal of a constant frequency (for example, 10 MHz) generated by the local oscillator (second local oscillator) 60 for generating the reference signal to the terminal side on the signal path for the downlink signal formed between Directional coupler 62 is provided.

Therefore, the reference signal generated by the second local oscillator 60 is sent out onto the transmission line L on the terminal side through the LPF 42 and the internal connection terminal T2, similarly to the downlink signal.
Next, the in-building upstream signal from the terminal side input to the internal connection terminal T2 is passed through the HPF 43 to the down converter 4
Captured within 0. The HPF 43 is for preventing the downstream signal output from the LPF 42 from sneaking in and selectively capturing only the indoor upstream signal, and the cutoff frequency is set to 821 MHz, for example.

Further, the in-building upstream signal fetched through the HPF 43 is input to a mixer 44 as a frequency conversion means, and the mixer 44 has a first local oscillator whose oscillation frequency is controlled by a PLL circuit 50 described later. By being mixed with the high frequency signal (for example, 876 MHz) generated by the cable 45, the frequency is converted into the original frequency band (10 MHz to 55 MHz) generated by the cable modem 32.

The upstream signal frequency-converted by the mixer 44 is input to the amplifier circuit 47 via the BPF 46, amplified by the amplifier circuit 47 to a predetermined level, and then L
It is sent to the service wire 17 side through the PF 48 and the external connection terminal T1. The BPF 46 is for removing unnecessary signal components from the signal output from the mixer 44, and the signal pass bandwidth is, for example, 10 MHz to 5 MHz.
It is set to 5 MHz. The LPF 48 is for blocking passage of the downstream signal input to the external connection terminal T1 and for passing only the upstream signal after frequency conversion, and the cutoff frequency is set to 55 MHz, for example.

Next, the PLL circuit 50 divides the output (reference signal) from the second local oscillator 60 and the output (high frequency signal for frequency conversion) from the first local oscillator 45 into frequency dividing circuits 52 and 54, respectively. A signal indicating the phase difference of each signal after the frequency division is generated by the phase comparison circuit 56, and the generated signal is used as a control signal of the first local oscillator 45.
By outputting to the first local oscillator 45 via the LPF (loop filter) 58, the oscillation frequency of the first local oscillator 45 is controlled to a constant frequency (for example, 876 MHz).

In this embodiment, the frequency dividing circuit 52 is
The reference signal is divided by 1/20, and the dividing circuit 54 is formed by dividing the high frequency signal for frequency conversion by 1/1752. Therefore, when the reference frequency is 10 MHz as described above, the phase comparison frequency in the phase comparison circuit 56 is 500 kHz, and the oscillation frequency of the first local oscillator 45 is 175
It is controlled to double the value of 876 MHz (= 500 kHz × 1752).

On the other hand, the up converter 70 has a first connection terminal T3 for connecting to the terminal terminal 28 via a coaxial cable or the like, and a cable modem 3 for outputting an upstream signal.
And a second connection terminal T4 for connecting to 2. Then, the downlink signal input from the terminal terminal 28 to the first connection terminal T3 is passed through the LPF 71 and the up converter 70.
It is taken in and output to the cable modem 32 side via the HPF 72 and the second connection terminal T4. In addition, LPF
71 blocks passage of upstream signals in the building after frequency conversion,
It is for passing the downlink signal input to the first connection terminal T3, and the cutoff frequency is, for example, 770M.
It is set to Hz. The HPF 72 is for blocking passage of an upstream signal input from the terminal side to the second connection terminal T4 and allowing only a downstream signal to pass through, and the cutoff frequency is set to 70 MHz, for example.

Next, the upstream signal input from the cable modem 32 to the second connection terminal T4 is passed through the LPF 73.
It is taken into the up-converter 40. In addition, LPF7
Reference numeral 3 is for preventing the downstream signal output from the HPF 72 from wrapping around and selectively capturing only the upstream signal, and the cutoff frequency is set to 55 MHz, for example.

The upstream signal fetched through the LPF 73 is input to a mixer 74 as a frequency conversion means, and the mixer 74 operates a first local oscillator 75 whose oscillation frequency is controlled by a PLL circuit 80 described later. By being mixed with the generated high frequency signal for frequency conversion (for example, 876 MHz), a predetermined frequency band (821 MHz to 866) is generated.
The frequency is converted to an in-building upstream signal (MHz).

The in-building upstream signal whose frequency has been converted by the mixer 74 is input to the amplifier circuit 77 via the BPF 76, amplified by the amplifier circuit 77 to a predetermined level, and then the HPF 78 and the first connection terminal T3. Via the terminal terminal 28. The BPF 76 is the mixer 74.
The signal pass band width is, for example, 821.
It is set to MHz to 866 MHz. Also, HPF
Reference numeral 78 is for blocking the passage of the downlink signal input to the first connection terminal T3 and for passing only the in-building upstream signal after frequency conversion, and the cutoff frequency is, for example, 82.
It is set to 1 MHz.

Next, on the signal path for the downlink signal formed between the LPF 71 and the HPF 72, a branching device 92 for branching a part of the downlink signal including the reference signal transmitted from the down converter 40 is provided. It is provided. A narrow band BPF 94 for selectively passing only the reference signal is provided on the signal line branched from the branching device 92 as the filter circuit according to claim 3.
The reference signal that has passed through F94 is input to the PLL circuit 80.

The PLL circuit 80 divides the reference signal input through the BPF 94 and the output (high frequency signal for frequency conversion) from the first local oscillator 75 into frequency dividing circuits 82 and 84, respectively.
The phase comparison circuit 86 generates a signal representing the phase difference between the respective signals after the frequency division, and the generated signal is used as a control signal for the first local oscillator 75 by an LPF (loop filter) 88. The output frequency of the first local oscillator 75 is controlled to a constant frequency (for example, 876 MHz) by output to the first local oscillator 75 via the.

Then, in the present embodiment, the frequency dividing circuit 82
Is configured to divide the reference signal by 1/20 like the frequency dividing circuit 52 on the down converter 40 side.
4 is also the same as the frequency dividing circuit 54 on the down converter 40 side.
It is configured to divide a high frequency signal for frequency conversion by 1/1752.

Therefore, the PLL circuit 80 operates similarly to the PLL circuit 50 on the down converter 40 side, and if the reference frequency is 10 MHz, the phase comparison frequency in the phase comparison circuit 86 becomes 500 kHz, and the first local portion. The oscillation frequency of the oscillator 75 is 1752
It will be controlled to the doubled 876 MHz (= 500 kHz × 1752).

As described above, in this embodiment, the up-converter 70 as the first converter is provided at the terminal 28 on the subscriber side for data communication with the center device 4 of the external bidirectional CATV system. By connecting and connecting the transmission line L in the building to the transmission line of the external bidirectional CATV system via the protector 18 and the lead-in line 17, the down converter 40 as the second converter is provided at the connection point. An in-building upstream signal, which is obtained by frequency-converting an upstream signal output from a communication terminal (cable modem or the like) on the subscriber side into a frequency band higher than the downstream signal, is allowed to flow through the transmission line L in the object. Therefore, the CAT in the building of this embodiment
According to the V system, even if the high frequency noise generated in the housing complex 20 enters from the terminal terminal 28, this becomes ingress noise and is sent out to the external bidirectional CATV system together with the upstream signal. It can be prevented.

Further, in this embodiment, the up converter 7
The first local oscillators 75 and 45 that generate high-frequency signals for frequency conversion, and the PLL that controls the oscillation frequencies of the first local oscillators 75 and 45, respectively.
The circuits 80 and 50 are provided, and these PLL circuits 80 and 5 are provided.
A common high frequency signal generated by the second local oscillator 60 provided in the down converter 40 is input to 0 as a reference signal. Therefore, according to the present embodiment, the up-converter 70 and the down-converter 40 can generate high-frequency signals having the same frequency using a common reference signal. In the down-converter 40, the up-converter 70 converts the frequency from the in-building upstream signal. It is possible to accurately recover the upstream signal before the operation.

In particular, in this embodiment, in the PLL circuits 80 and 50 of the converters 70 and 40, the high frequency signals for frequency conversion are frequency-divided using the frequency division circuits 84 and 54 having the same frequency division values. At the same time, the reference signals are frequency-divided using the frequency dividing circuits 82 and 52 having the same frequency division value, and the respective frequency-divided signals are input to the phase comparison circuits 56 and 86, whereby the first local oscillators 75 and 45 To generate the control signal. Therefore, according to the present embodiment, the phase comparison frequency by the phase comparison circuits 56, 86 configuring the PLL circuits 80, 50 in each converter 70, 40 (in other words, output from the first local oscillators 75, 45). It is possible to reduce the phase noise included in the upstream signal that has passed through the up-converter 70 and the down-converter 40 by matching the fluctuations of the high-frequency signal for frequency conversion that are performed.

That is, for example, in FIG. 4, the first connection terminal T3 of the up converter 70 and the internal connection terminal T2 of the down converter 40 are connected by a coaxial cable, and the second connection terminal T4 of the up converter 70 receives an upstream signal. When the carrier wave of the corresponding frequency of 30 MHz is input, the result (phase noise characteristic) of the phase noise of the same carrier wave output from the external connection terminal T1 of the down converter 40 is measured, which is clear from this figure. , Each converter 40, 70
The frequency division values of the frequency division circuits 52 and 82 for reference signal frequency division are set to "1/20", and the frequency division values of the frequency division circuits 54 and 84 for high frequency signal frequency division to "1/1752". In the case of the present embodiment that is set, the phase noise is 10 dB compared to the conventional example in which the frequency dividing values of the frequency dividing circuits 52 and 82 and the frequency dividing values of the frequency dividing circuits 54 and 84 are set to different values. The degree can be reduced.

Therefore, according to the in-building CATV system of the present embodiment, it is possible to reduce the error rate of digital data that occurs when the center device 4 side of the external bidirectional CATV system receives and demodulates the upstream signal. As a result, the communication accuracy of the data communication performed between the communication terminal on the subscriber side and the center device 4 can be improved.

In the conventional example shown in FIG. 4, the frequency dividing values of the frequency dividing circuits 52 and 54 in the down converter 40 are the same as those in this embodiment, and the frequency dividing circuit 8 in the up converter 70 is the same.
The frequency division value of 2,84 is a value different from that of this embodiment, that is, "1".
/ 40 "and" 1/3504 "are set, and the phase noise measurement result is shown when the phase noise is measured in the same procedure as described above.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modes can be adopted. For example, in the above embodiment, the PLL circuits 80 and 50 of the up converter 70 and the down converter 40 divide the reference signal and the high frequency signal for frequency conversion into frequency dividing circuits 82, 84 and 52, respectively.
Although it has been described that the frequency is divided by 54 and input to the phase comparison circuits 86 and 56, the frequency dividing circuits 82 and 52 or the frequency dividing circuits 84 and 5 are included in the respective PLL circuits 80 and 50.
Instead of 4, a multiplying circuit for multiplying the reference signal or the high frequency signal may be provided, or in addition to the dividing circuits 82, 52 or the dividing circuits 84, 54,
A multiplying circuit for multiplying the reference signal or the high frequency signal before or after the frequency division may be provided. However, also in this case, in order to obtain the effect of the present invention as in the above-described embodiment, it is necessary to make the multiplication values of the signal frequencies of the multiplication circuits corresponding to each other in the PLL circuits 80 and 50 coincide with each other.

Further, for example, in the above embodiment, the second local oscillator 60, which is the source of the reference signal, is incorporated in the down converter 40, and the reference signal is sent from the down converter 40 onto the transmission line L to raise the reference signal. Although the converter 70 can generate the high frequency signal for frequency conversion by using the same reference signal as that of the down converter 40, the source of the reference signal does not necessarily have to be incorporated in the down converter 40, and the second local oscillator 60 can be used.
Is connected to the transmission line L, the down converter 40 uses a filter circuit such as a BPF to extract the reference signal from the transmission line L, and the down converter 40 outputs the reference signal to the PLL circuit 50. It may be configured to input.

Furthermore, in the above embodiment, the case where the present invention is applied to the in-building CATV system has been described.
Even if the present invention is a system in which a pair of converters (down converter and up converter) are provided on a transmission line in order to reduce the transmission loss of satellite reception signals, as described in the section of the prior art, The same applies as in the example.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing the overall configuration of an interactive CATV system according to an embodiment.

[Fig. 2] In-building CAT constructed in the housing complex of the embodiment
It is a schematic block diagram showing the structure of a V system.

FIG. 3 is a block diagram showing a configuration of a down converter and an up converter provided in the in-building CATV system of the embodiment.

FIG. 4 is an explanatory diagram showing phase noise of an upstream signal transmitted from the in-building CATV system of the embodiment to the outside in comparison with a conventional example.

[Explanation of symbols]

2 ... Headend device, 4 ... Center device, 6, 29 ... Mixer, 8 ... Optical transceiver, 10 ... Node type optical transceiver, 1
2 ... Trunk line branch amplifier, 14 ... Branch amplifier, 16 ... Tap-off, 17 ... Drop line, 18 ... Protector, 20 ... Apartment,
22 ... Bidirectional amplifier, 24 ... Brancher, 28 ... Terminal terminal,
32 ... Cable modem, 34 ... Information terminal device, 40 ... Down converter, 70 ... Up converter, 44, 74
... Mixer, 45,75 ... First local oscillator, 47,77 ...
Amplifier circuit, 50, 80 ... PLL circuit, 52, 54, 8
2, 84 ... Frequency divider circuit, 56, 86 ... Phase comparison circuit, 60
... 2nd local oscillator, 62 ... Directional coupler, 92 ... Brancher, L ... Transmission line.

Claims (9)

[Claims] 1. A transmission signal of a predetermined frequency band is transmitted on a transmission line for transmitting various transmission signals including a television broadcast signal to a frequency band different from the original frequency band and not overlapping with other transmission signals. A first converter that performs frequency conversion is provided, and the transmission signal frequency-converted by the first converter is used as an original frequency on a transmission line downstream of the first converter in which the transmission signal frequency-converted by the first converter flows. C equipped with a second converter for frequency conversion into a band
In the ATV system, the first converter and the second converter respectively include a first local oscillator that generates a high frequency signal for frequency conversion, a high frequency signal generated by the first local oscillator, and a predetermined frequency conversion target. The frequency conversion means for frequency-converting the transmission signal by mixing the transmission signal in the frequency band, and the common reference signal flowing through the transmission line are used to generate the first signal.
A PLL circuit that controls the oscillation frequency from the local oscillator; and the PLL circuits of the converters are configured such that the phase comparison frequencies of the reference signal and the high-frequency signal in the respective PLL circuits match each other. In addition, the reference signal is fetched by using a first dividing or multiplying circuit having the same dividing value or multiplying value, and the high frequency signal generated by the first local oscillator is fed to the first dividing or multiplying value having the same dividing value or multiplying value. It is characterized in that the control signal of the first local oscillator is generated by using the frequency division or multiplication circuit of No. 2 and phase-comparing the obtained reference signal after division or multiplication with the high frequency signal. CATV system. 2. The CATV system pulls a drop wire from an external two-way CATV system into a building.
Through the transmission line in the building, while transmitting the downlink signal input from the service line to the terminal terminal in the building,
An uplink signal input from the terminal device on the subscriber side to the terminal terminal is transmitted to the service line, and the bidirectional C external from the service line is provided.
An in-building CATV system for sending to an ATV system, wherein the first converter is provided at a terminal terminal to which an upstream signal from the subscriber side terminal device is input, and an upstream signal output from the subscriber side terminal device. Is an up-converter that converts the frequency of the signal into an in-building upstream signal having a higher frequency than the downstream signal and sends out the signal to a transmission line in the building, wherein the second converter is from the up converter to the transmission line in the building. The in-building upstream signal transmitted to the service line via the service line is frequency-converted into an upstream signal in the original frequency band output by the subscriber side terminal device, and is sent from the service line to an external bidirectional CATV system. The CATV system according to claim 1, wherein the CATV system is a down converter. 3. The down converter includes a second local oscillator that generates the reference signal, inputs the reference signal generated by the second local oscillator to a PLL circuit in the down converter, and supplies the reference signal to the up converter side. The up-converter selectively fetches the reference signal sent on the transmission line from the down-converter,
The CAT according to claim 2, further comprising a filter circuit for inputting to a PLL circuit in the up converter.
V system. 4. A transmission signal of a predetermined frequency band is transmitted on a transmission line for transmitting various transmission signals including a television broadcasting signal into a frequency band different from the original frequency band and not overlapping with other transmission signals. A first converter that performs frequency conversion is provided, and the transmission signal frequency-converted by the first converter is used as an original frequency on a transmission line downstream of the first converter in which the transmission signal frequency-converted by the first converter flows. A second local converter for frequency conversion into a band, wherein the first converter and the second converter respectively generate a high frequency signal for frequency conversion; and a high frequency signal generated by the first local oscillator. And a frequency conversion means for frequency-converting the transmission signal by mixing the frequency-converted transmission signal of a predetermined frequency band. Using a common reference signal flowing through, to control the oscillation frequency from the first local oscillator P
In a CATV system including an LL circuit, which is a frequency converter used as the first converter, the PLL circuit forming the frequency converter has a phase comparison frequency between the reference signal and the high frequency signal. ,
The PLL in the second converter so as to match the phase comparison frequency in the PLL circuit that constitutes the second converter.
The reference signal is captured by using the same first frequency division or multiplication circuit as the circuit, and the first local oscillator is generated by using the same second frequency division or multiplication circuit as the PLL circuit in the second converter. A frequency conversion device, which takes in a high-frequency signal and compares the phase of the taken-in divided or multiplied reference signal with the high-frequency signal. 5. The CATV system pulls a drop wire from an external two-way CATV system into a building.
Through the transmission line in the building, while transmitting the downlink signal input from the service line to the terminal terminal in the building,
An uplink signal input from the terminal device on the subscriber side to the terminal terminal is transmitted to the service line, and the bidirectional C external from the service line is provided.
An in-building CATV system for sending to an ATV system, the frequency conversion device being provided in a terminal terminal to which an upstream signal from the subscriber side terminal device is input, and an upstream signal output from the subscriber side terminal device. 5. The frequency conversion device according to claim 4, wherein the frequency conversion device is an up-converter that frequency-converts the signal into an in-building upstream signal having a frequency higher than that of the downstream signal and sends it out onto a transmission line in a building. 6. A filter circuit for selectively fetching the reference signal transmitted to the terminal terminal via the transmission line and inputting the reference signal to a PLL circuit in the frequency conversion device. Item 5. The frequency conversion device according to item 5. 7. A transmission signal of a predetermined frequency band is transmitted on a transmission line for transmitting various transmission signals including a television broadcast signal to a frequency band different from the original frequency band and not overlapping with other transmission signals. A first converter that performs frequency conversion is provided, and the transmission signal frequency-converted by the first converter is used as an original frequency on a transmission line downstream of the first converter in which the transmission signal frequency-converted by the first converter flows. A second local converter for frequency conversion into a band, wherein the first converter and the second converter respectively generate a high frequency signal for frequency conversion; and a high frequency signal generated by the first local oscillator. And a frequency conversion means for frequency-converting the transmission signal by mixing the frequency-converted transmission signal of a predetermined frequency band. Using a common reference signal flowing through, to control the oscillation frequency from the first local oscillator P
In a CATV system composed of an LL circuit, the frequency converter used as the second converter, wherein the PLL circuit constituting the frequency converter has a phase comparison frequency between the reference signal and the high frequency signal. ,
The PLL in the first converter so as to match the phase comparison frequency in the PLL circuit constituting the first converter.
The reference signal is captured by using the same first frequency division or multiplication circuit as the circuit, and the first local oscillator is generated by using the same second frequency division or multiplication circuit as the PLL circuit in the first converter. A frequency conversion device, which takes in a high-frequency signal and compares the phase of the taken-in divided or multiplied reference signal with the high-frequency signal. 8. The CATV system pulls a drop wire from an external two-way CATV system into the building,
Through the transmission line in the building, while transmitting the downlink signal input from the service line to the terminal terminal in the building,
An uplink signal input from the terminal device on the subscriber side to the terminal terminal is transmitted to the service line, and the bidirectional C external from the service line is provided.
It is an in-building CATV system for sending to an ATV system, and the frequency conversion device is converted into a frequency in an up-converter as the first converter provided on the terminal side of the in-building CATV system, and then in the building. The in-building upstream signal transmitted to the service line side through the transmission line,
8. The frequency converter according to claim 7, wherein the upconverter is a downconverter that performs frequency conversion into an upstream signal in the original frequency band before frequency conversion, and sends the upstream signal to the external bidirectional CATV system from the service line. apparatus. 9. A second local oscillator for generating the reference signal is provided, wherein the reference signal generated by the second local oscillator is input to a PLL circuit in the frequency conversion device, and the transmission line on the up-converter side is provided. The frequency conversion device according to claim 8, wherein the frequency conversion device transmits the frequency.