JP2001157180A - Private catv system, down converter and up converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a down converter to accurately restore an up signal in a private CATV system, with which the frequency of the up signal is converted to a private up signal by an up converter on the side of a terminal, and the frequency-converted private up signal is outputted to an external system while using the down converter. SOLUTION: In this private CATV system for transmitting the up signal, while using an up converter 20 and a down converter 10, high-frequency signals for frequency conversion leaked from respective up converters 20 on the terminal side are combined and inputted to the down converter 10. Then, the frequency of the high-frequency signal for frequency conversion is set lower than that of the private incoming signal and that high-frequency signal can be reduced by HPF 34 and 64 inside the respective converters 10 and 20. As a result, in the down converter 10, the input of the high-frequency signal to a mixer 38 is suppressed and the incoming signal can be restored accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an external bidirectional CA.
A service line from the TV system is drawn into the building, a down signal input from the bidirectional CATV system is transmitted to a plurality of terminal devices in the building via a transmission line in the building, and output from each terminal device. The present invention relates to an in-building CATV system for transmitting an upstream signal transmitted to a drop-in line and transmitting the signal to an external bidirectional CATV system.

[0002]

2. Description of the Related Art In this type of in-building CATV system, noise generated in each part of a building is superimposed on a transmission line via a terminal terminal or the like on a subscriber side. Then, of these noises, those having the same frequency component as the upstream signal are output to the external bidirectional CATV system together with the upstream signal as ingress noise.

Therefore, conventionally, an external bidirectional CATV is used.
In order to reduce ingress noise flowing into the system, an upstream signal (a signal in a frequency band (for example, 10 MHz to 55 MHz) that can be transmitted in a bidirectional CATV system) generated by a subscriber terminal device such as a cable modem is upgraded. In the converter, the UHF band (for example, 821 MHz to 866) which is higher than the original frequency and does not overlap with the transmission frequency of the downlink signal (for example, 70 MHz to 770 MHz).
MHz), the signal is converted to an upstream signal (hereinafter referred to as an in-building up signal), transmitted to the service line, and immediately before the upstream signal is output from the transmission line in the building to the service line, the up signal in the building is converted to a down converter It has been considered to convert the signal to the original frequency (in other words, the transmission frequency of the uplink signal in the bidirectional CATV system).

In this type of in-building CATV system, an up-converter and a down-converter are respectively provided.
If each signal is frequency-converted using a high-frequency signal having a different frequency, the down-converter cannot restore the original uplink signal output from the terminal device from the in-building uplink signal. It is necessary to match the frequency of the high-frequency signal used for conversion.

[0005] For this reason, conventionally, for example, a local oscillator circuit for generating a high-frequency signal for frequency conversion using a reference signal generated by each oscillator is provided in each converter with an oscillator having the same configuration and a small frequency variation. Control of the oscillating frequency of a local oscillation circuit that generates a high-frequency signal for frequency conversion in each converter, or a common reference signal (for example, level adjustment of a downstream signal in a bidirectional CATV system, etc.). Control using a pilot signal used for this purpose, such as a signal of a fixed frequency flowing through a transmission line.

In other words, if the up-converter and the down-converter perform frequency conversion of each signal using the high-frequency signal of the same frequency, the down-converter has an element before the up-converter performs frequency conversion. The uplink signal output from the terminal device of each subscriber can be transmitted as it is from the in-building CATV system to the external bidirectional CATV system. Become.

[0007]

However, when the present inventor conducted an experiment, it was found that, when the above-mentioned in-building CATV system was actually constructed, a large-scale in-building CATV system having a large number of up-converters had a down converter side. It was found that the original upstream signal could not be accurately restored. Then, in order to elucidate this problem, the present inventor performed various experiments, and the following was found.

That is, first, an upstream signal of 10 MHz to 55 MHz is converted by an up converter into a signal of 821 MHz to 86 MHz.
In the case where the frequency is converted into a 6 MHz ridge upstream signal, the down converter converts the ridge upstream signal into the upstream signal of the original frequency band (10 MHz to 55 MHz). The frequency of the high frequency signal used for frequency conversion of each signal may be set to 811 MHz or 876 MHz. In the above-mentioned conventional building CATV system, the frequency of the high frequency signal for frequency conversion is lower than the frequency of the high frequency signal for frequency conversion because the upstream signal has a lower frequency than the downstream signal and the upstream signal has a higher frequency than the downstream signal. The frequency is set higher (876 MHz) than the down signal or the up signal in the ridge so as not to affect the signal.

However, when the frequency of the high-frequency signal for frequency conversion is set to be higher than the frequency of the in-building up signal, the up-converter transmits the frequency-converted building signal on the transmission line of the in-building CATV system. It was found that a high-frequency signal for frequency conversion leaked together with the inbound signal. This is because in a system that frequency-converts an upstream signal having a lower frequency than the downstream signal into a ridge upstream signal having a higher frequency than the downstream signal, the frequency difference between the high-frequency signal for frequency conversion and the ridge upstream signal is It becomes extremely small with respect to the transmission frequency of the inbound signal (10 MH in the above example).
z), even if a filter circuit (such as a band-pass filter) for selectively passing the in-building up signal is provided in the output path of the in-building up signal in the upconverter, the filter circuit is used for frequency conversion. This is because high-frequency signals cannot be satisfactorily removed.

On the other hand, in the CATV system in the building,
Since an upconverter is installed for each terminal device that outputs an uplink signal, the upconverter increases as the number of subscribers who own such terminal devices increases (in other words, as the scale of the CATV system in the building increases). , The number of high-frequency signals leaking out onto the transmission line increases.

On the other hand, since each upconverter performs data communication in a time-division manner with a communication device provided in the center device of the external bidirectional CATV system, in the CATV system in the building, A plurality of upconverters do not output an in-building up signal at the same time.

As a result, the high-frequency signal leaked from each up-converter is synthesized on the transmission line and input to the down-converter, and the input level becomes higher as the CATV system in the building is larger. It turned out that it became larger than the input level of the inbound ridge signal.

The high-frequency signal input to the down-converter via the transmission line as described above has a phase difference when the high-frequency signal leaked from each up-converter is synthesized on the transmission line, and a high-frequency signal for each up-converter. Due to a slight shift in the frequency of the high-frequency signal, the normal frequency (876 MHz)
It was also found that a noise component (hereinafter referred to as phase noise) having a spread in the upper and lower frequency directions around z) was included.

Next, as described above, when the synthesized signal of the high-frequency signal for frequency conversion leaked from each up-converter is input to the down-converter together with the in-building up signal, the down-converter generates the synthesized signal. Is input to a frequency conversion circuit (generally a mixer) together with the in-building up signal.

The frequency of the synthesized signal (specifically, the center frequency) is the same as the high-frequency signal for frequency conversion generated on the down converter side, and the signal level is high. Then, the synthesized signal leaks into the signal path of the high-frequency signal for frequency conversion, and the high-frequency signal including the above-described phase noise is input to the frequency conversion circuit as a signal for frequency conversion.

As a result, in the down converter, the in-building up signal is frequency-converted using a low-purity high-frequency signal in which phase noise is superimposed on a normal high-frequency signal. Including phase noise spreading in the upper and lower frequency directions, especially large C
It has been found that in an ATV system, an upstream signal may be buried in surrounding phase noise.

In order to solve such a problem, the phase of a high-frequency signal generated on each upconverter side is adjusted, or the line length of a transmission line from each upconverter to the junction of the high-frequency signal is adjusted. Thus, high-frequency signals leaked from each up-converter may be canceled out on the transmission line, but it is difficult to actually take such measures.

The present invention has been made in view of such a problem, and the terminal uses an up-converter to convert the frequency of an upstream signal into a high-frequency indoor upstream signal, and is connected to an external bidirectional CATV system. On the drop-in side, in a building CATV system in which a down converter is used to convert the frequency of an in-building up signal to an original up signal, the down converter converts the high-frequency signal leaked from the up converter in the terminal into a high-frequency signal. It is an object of the present invention to accurately restore an original uplink signal without being affected by the above.

[0019]

Means for Solving the Problems and Effects of the Invention In order to achieve the above object, the CA in a building according to claim 1 has been made.
In the TV system, the above-mentioned conventional building CATV
Similarly to the system, a down signal input from an external bidirectional CATV system via a service line is transmitted to a plurality of terminal terminals via a transmission line in a building, and an up converter is transmitted from a terminal device on the subscriber side. The in-building up signal input to each terminal via the transmission line is transmitted to the service line via the transmission line, and the down line provided between the transmission line and the service line from the service line to the external bidirectional CATV system. The upstream signal that has been frequency-converted to the original upstream signal output by the terminal device using the converter is transmitted.

In the CATV system according to the present invention, the frequency of the high-frequency signal used by the up-converter and the down-converter to convert the frequency of the up signal or the up signal in the building is set to the same frequency as in the prior art. This allows the down converter to accurately convert the in-building up signal to the original up signal output by the terminal device, but the frequency of the high-frequency signal is higher than that of the in-building up signal as in the past. Is not set to a high frequency, but set to a lower frequency than the in-building up signal.

Therefore, according to the in-building CATV system of the present invention, the signal level of the high-frequency signal for frequency conversion leaking together with the in-building up signal from each of the up-converters on the subscriber side to the corresponding terminal terminal side, and transmission. The signal level of the high-frequency signal for frequency conversion input together with the in-building up signal from the line to the frequency conversion circuit in the down-converter,
It can be attenuated using a filter for separating the downstream signal and the upstream signal built in each converter, and the above-described phase noise included in the high frequency signal is added to the upstream signal after frequency conversion by the down converter, This can be prevented from being transmitted to an external bidirectional CATV system.

That is, the down converter and the up converter used in the CATV system in the building of the present invention are as follows.
In addition to the frequency conversion of the upstream signal or the upstream signal inside the building, it is necessary to pass the downstream signal to the terminal side, so that a passage path for the downstream signal is formed therein.

For this reason, the connection terminal to the terminal terminal, which is the output terminal of the in-building up signal on the up converter side, outputs the in-building up signal after frequency conversion and outputs the down signal input from the terminal terminal. For separating the signal into the up-converter is connected. Similarly,
The connection terminal to the transmission line, which is the input terminal of the in-building up signal on the down converter side, takes in the in-building up signal input from the transmission line into the down converter and sends out the down signal on the transmission line. Are connected.

Since the in-building up signal has a lower frequency than the down signal, each of the signal separation filters provided in each converter usually passes the in-building up signal and blocks the down signal. And a low-pass filter for passing down signals and preventing passage of up signals in the building.

Therefore, if the frequency of the high-frequency signal used for frequency conversion in each converter is set to a higher frequency than the in-building up signal, as in the prior art, the frequency conversion circuit in the up converter will The leaked high-frequency signal for frequency conversion passes through the signal separation filter (high-pass filter) as it is, and leaks out onto the transmission line,
On the down converter side, the synthesized signal of the high frequency signal for frequency conversion leaked from each up converter passes through the signal separation filter (high pass filter) as it is,
This is input to the frequency conversion circuit.

However, in the present invention, as described above, the frequency of the high-frequency signal used for frequency conversion in each converter is set to a lower frequency than the in-building up signal, so that the Even if the high-frequency signal for frequency conversion leaks from the conversion circuit, it can be attenuated by the signal separating filter (high-pass filter), so the signal of the high-frequency signal for frequency conversion leaking out onto the transmission line from the up-converter. The level can be reduced.

The high-frequency signal for frequency conversion leaked from each up-converter is synthesized and input to the down-converter. Even in the down-converter, the synthesized signal is first converted into a signal separating filter (high-pass filter). ) Is further attenuated by this signal separating filter. As a result, the signal level of the composite signal input to the frequency conversion circuit in the downconverter is extremely low as compared with the related art.

Thus, in the in-building CATV system of the present invention, the down converter can accurately restore the in-building up signal input via the transmission line to the original up signal output by the terminal device. And an external bidirectional CAT without lowering the quality of the uplink signal.
It can be sent to the V system.

Here, the CAT in the ridge of the present invention (claim 1)
In the V system, the high-frequency signal for frequency conversion used in each converter is set to a lower frequency than the frequency of the in-building up signal, so that the high-frequency signal is output from the in-building up signal of each converter. Attenuation is performed by the signal separation filter provided in the input path, but when the frequency characteristic of the attenuation on the lower frequency side than the cutoff frequency of the signal separation filter is poor (in other words, the high-pass filter When the cutoff on the low frequency side is poor), it is conceivable that the signal level of the unnecessary synthesized signal input to the frequency conversion circuit in the down converter cannot be sufficiently reduced.

Therefore, in such a case, as described in claim 2, on the transmission path of the in-building up signal from the up converter to the down converter, the up converter converts the up signal to the in-building up signal. A trap circuit for removing the high-frequency signal used for the conversion may be provided.

By doing so, it becomes possible to sufficiently reduce the signal level of the unnecessary composite signal input to the frequency conversion circuit in the down converter, and to perform the operation of restoring the up signal (frequency Conversion) can be performed better.

In this case, the trap circuit only needs to be able to reduce the high-frequency signal component for frequency conversion that cannot be reduced by the signal separating filter in each converter, and may be provided as an auxiliary circuit of the signal separating filter in each converter. Therefore, the frequency of the high-frequency signal for frequency conversion is set to be higher than the frequency of the upstream signal in the same building as before, and the trap circuit is attenuated compared to the case where the high-frequency signal for frequency conversion is removed by the trap circuit alone. It is not necessary to increase the characteristics (the amount of attenuation of the high frequency signal for frequency conversion).

Therefore, according to the present invention, even if the trap circuit is provided as described in claim 2, when the in-building upstream signal passes through the trap circuit, the signal may fall within the band due to the attenuation characteristic of the trap circuit. It does not cause transmission loss on the low frequency side of this.

That is, in the trap circuit, as the amount of attenuation at a specific frequency to be removed is increased, the attenuation characteristic is greatly expanded in a frequency region around the specific frequency, so that the trap circuit alone is used for frequency conversion. If the attenuation characteristic of the trap circuit is increased to attenuate the high-frequency signal, when the high-frequency signal for frequency conversion passes through the trap circuit, a part of the ascending signal in the ridge is attenuated on the side closer to the frequency of the high-frequency signal. As a result, the transmission characteristic of the in-building up signal is deteriorated. However, according to the present invention, even if the trap circuit is provided, such a problem does not occur.

When such a trap circuit is provided in an in-building CATV system, the trap circuit may be installed, for example, on a transmission line from a down converter to each terminal terminal, or in a transmission device provided on the transmission line. Of the transmission paths from the up-converter to the down-converter, such as the passage path of the in-building up signal, the output path of the up signal in the up converter, the input path of the up signal in the down converter, etc. Any route may be used as long as it passes.

Next, a down converter according to a third aspect is for constructing the CATV system in a building according to the first or second aspect, wherein an external connection terminal for connecting to a drop-in line, and a transmission line. And an internal connection terminal for connecting to the line. Then, the down signal input from the drop-in line to the external connection terminal is once taken into the down converter via the first filter for signal separation, and then from the second filter for signal separation via the internal connection terminal, Transmitted on the transmission line.

The in-building up signal input from the transmission line to the internal connection terminal is taken into the down-converter via the second filter, and the first frequency conversion means generates the first high-frequency signal generation means. By being mixed with the high frequency signal for frequency conversion, the frequency is converted into an upstream signal,
Further, the frequency-converted upstream signal is transmitted from the first filter to the service line via the external connection terminal.

In the down converter of the present invention,
The first high-frequency signal generating means is configured to generate a high-frequency signal whose frequency is set lower than that of the in-building up signal as a high-frequency signal for frequency-converting the in-building up signal into an up signal. Therefore, according to the downconverter of the present invention, the high-frequency signals for frequency conversion leaked from the plurality of upconverters on the terminal side are combined on the transmission line, and the combined high-frequency signals are internally connected together with the in-building up signal. Even if the signal is input to the terminal, an unnecessary high-frequency signal (specifically, the high-frequency signal including the phase noise described above) is input to the first frequency conversion unit by the second filter for signal separation.
And the first frequency conversion means can accurately restore the original upstream signal from the in-building upstream signal.

Next, the up-converter according to the fourth aspect of the present invention, together with the down-converter according to the third aspect,
It is for constructing the in-building CATV system according to claim 1 or 2, and comprises a first connection terminal for connecting to a terminal terminal, and a second connection terminal for connecting to a terminal device.

Then, the downstream signal input from the terminal terminal to the first connection terminal is taken into the up-converter via the third filter for signal separation, and thereafter, from the fourth filter for signal separation to the second connection. It is sent to the terminal device via the terminal. Further, the upstream signal input from the terminal device to the second connection terminal is taken into the up-converter via the fourth filter, and the second frequency converting means generates the frequency conversion signal generated by the second high-frequency signal generating means. Is converted into an in-building up signal, and the frequency-converted in-building up signal is transmitted from the third filter to the terminal terminal side via the first connection terminal. .

Then, in the up converter of the present invention,
The second high-frequency signal generating means is configured to generate a high-frequency signal whose frequency is set lower than that of the in-building up signal as a high-frequency signal for frequency-converting the up signal into the in-building up signal. Therefore, according to the up-converter of the present invention, even if the high-frequency signal for frequency conversion leaks from the second frequency conversion means onto the output path of the in-building up signal, the third filter for signal separation uses The high-frequency signal can be reduced, and the signal level of the high-frequency signal for frequency conversion leaking from the up-converter onto the transmission line can be suppressed. Therefore, according to the up-converter of the present invention, it is possible to prevent the down-converter from being unable to restore the original up-signal normally due to the influence of the leaked high-frequency signal.

[0042]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of the entire CATV system in a building according to an embodiment to which the present invention is applied.

As shown in FIG. 1, the CATV in the building according to the present embodiment
The system draws a drop line 6 branched from a transmission line (CATV transmission line) 2 of an external two-way CATV system via a branching device 4 into a building such as an apartment or an apartment via a protector 8, A transmission line L composed of a coaxial cable wired in the building, and a bidirectional amplifier 12, a branch unit 14, and a distributor 16 provided on the transmission line L.
And the like, the down signal (frequency: 70 MHz to 770 MH) of the bidirectional CATV system input from the service line 6
z) is transmitted to a plurality of terminal terminals 18 such as a series unit installed at each subscriber's house in the building,
From the various terminal devices on the subscriber side, an up converter 2 described later
0 to the terminal 18 via the terminal 0
This is transmitted to the service line 6.

In the in-building CATV system according to the present embodiment, the subscriber can enjoy the Internet via the center device of the external two-way CATV system, or can reserve the center device for viewing or paying for a pay program. When transmitting data for shopping or the like, an information terminal device (such as a personal computer) 24 for data communication is connected to the terminal 18 on the subscriber side via an up-converter 20 and a cable modem 22. .

As a result, the transmission data for data communication output from the information terminal device 24 is transmitted by the cable modem 22 to a predetermined frequency band (10 MHz to 55 MHz in this embodiment) which can be transmitted by an external bidirectional CATV system. ), And is converted by the up-converter 20 into a predetermined frequency band (821 in this embodiment).
(MHz to 866 MHz), which is frequency-converted into an in-building upstream signal and input to the terminal 18.

For this reason, the connection between the transmission line L of the in-building CATV system and the drop-in line 6 from the external bidirectional CATV system is connected to the in-building which has been transmitted via the transmission line L from each terminal 18. The upstream signal is sent to an external bidirectional CATV
A down converter 10 is provided for frequency conversion into an original upstream signal that can be transmitted by the system.

In FIG. 1, reference numeral 26 is connected to the terminal 18 to which the upconverter 20 is not connected.
External bidirectional CATV transmitted via transmission line L
It represents a television receiver that receives a downlink signal from the system and demodulates and reproduces a television broadcast of a desired channel.

Next, the configuration of the down converter 10 and the up converter 20 used in the CATV system in the building of the present embodiment will be described with reference to FIG. [Downconverter] As shown in FIG. 2A, the downconverter 10 includes an external connection terminal T1 for connecting a service line 6 from an external bidirectional CATV system, and a transmission line L in the building 10. And an internal connection terminal T2 for connection.

The downstream signal input to the external connection terminal T1 is taken into the down converter 10 via a high-pass filter (hereinafter, referred to as HPF) 31, and is received by a mixing circuit 32, a low-pass filter (hereinafter, LPF). 33) and the internal connection terminal T2, and transmitted on the transmission line L on the terminal side.

Here, the HPF 31 is for passing the downstream signal and preventing the passing of the frequency-converted upstream signal, and the cutoff frequency is set to, for example, 70 MHz. The LPF 33 is for passing the downstream signal and preventing the passage of the in-building upstream signal input to the internal connection terminal T2 via the transmission line L, and the cutoff frequency is set to, for example, 770 MHz. I have. Therefore, in the down converter 10 of the present embodiment, H
The PF 31 and the LPF 33 form a passage for the first downstream signal.

The mixing circuit 32 provided on the path for passing the downstream signal between the HPF 31 and the LPF 33 mixes the downstream signal passing through this path with a reference signal to be described later to convert the reference signal to the downstream signal. And the transmission line L on the terminal side
It is intended to be transmitted upward, and is constituted by a so-called directional coupler.

Next, the in-building up signal from the terminal input to the internal connection terminal T 2 is taken into the down converter 10 via the HPF 34. The HPF 34 is
This is to prevent the downstream signal output from the LPF 33 from wrapping around and selectively capture only the in-building upstream signal, and the cutoff frequency is set to, for example, 821 MHz. In this embodiment, the HPF 34 and
The LPF 33 functions as a second filter for signal separation according to the present invention (claim 3).

Next, the in-building upstream signal taken into the down converter 10 via the HPF 34 is supplied with an attenuator (so-called attenuator, hereinafter referred to as ATT) 35 for adjusting the signal level and a band-pass filter (hereinafter referred to as ATT). , BPF
) Is input to the amplifier circuit 37. The BPF 36 is for selectively passing the in-building up signal, and the signal pass band is set to the transmission frequency of the in-building up signal (821 MHz to 866 MHz).

The in-building up signal input to the amplifier circuit 37 is amplified to a predetermined level by the amplifier circuit 37,
It is input to a mixer 38 as first frequency conversion means.
The mixer 38 outputs a high-frequency signal from a frequency-variable type local oscillation circuit 40 whose oscillation frequency is controlled to be constant (in this embodiment, 811 MHz having a lower frequency than the in-building up signal) by the PLL circuit 39, and By mixing the inbound signal with the inbound signal, the inbound signal in the building is
0 is frequency-converted to the original upstream signal before frequency conversion.

Here, the PLL circuit 39 divides the high-frequency signal for frequency conversion and the reference signal output from the local oscillation circuit 40 and fetches them, and sets the phase difference between the divided signals to zero. By controlling the oscillation frequency of the local oscillation circuit 40 as described above, the high-frequency signal for frequency conversion in the down converter 10 is controlled to a constant frequency (811 MHz) corresponding to the reference signal. In the present embodiment, a reference signal used by the PLL circuit 39 to control the oscillation frequency of the local oscillation circuit 40 is generated by a reference oscillation circuit 41 in the down converter 10. Therefore, in the present embodiment, the PLL circuit 39, the local oscillation circuit 40, and the reference oscillation circuit 41 function as the first high-frequency signal generation means of the present invention, and the high-frequency signal for frequency conversion whose frequency is lower than the in-building up signal. Will generate a signal.

The oscillation frequency of the reference oscillation circuit 41 is
The frequency lower than the downstream signal is set to be lower than the frequency of the downstream signal, and the reference signal output from the reference oscillation circuit 41 and having a lower frequency than the downstream signal is input to the PLL circuit 39 as described above. Narrow band B that selectively passes
The signal is input to the mixing circuit 32 via the PF 42.
As a result, the reference signal is mixed with the downstream signal by the mixing circuit 32 as described above, and then transmitted onto the transmission line L via the LPF 33 and the internal connection terminal T2.

The reason why the reference signal is transmitted from the internal connection terminal T2 onto the transmission line L is that the reference signal is transmitted to each of the upconverters 20 on the terminal side, and the downconverted signal is also transmitted to each of the upconverters 20. This is because a high-frequency signal for frequency conversion can be generated using the same reference signal as that of converter 10. That is, in the present embodiment, by transmitting a reference signal from the down converter 10 to each of the up converters 20 on the terminal side, each of the up converters 20 is transmitted.
Makes the frequency of the high frequency signal used for frequency conversion coincide with the high frequency signal used by the down converter 10 for frequency conversion.

Next, the upstream signal whose frequency has been converted by the mixer 38 has a signal pass band whose transmission frequency (10 MHz to 55 MHz) for selectively transmitting the upstream signal.
The signal is input to the amplification circuit 44 for amplifying the upstream signal via the BPF 43 set in z). Then, the upstream signal is amplified to a predetermined level by the amplifier circuit 44, and then transmitted to the service line 6 via the signal level adjusting ATT 45, the LPF 46, and the external connection terminal T1. Note that L
The PF 46 is for blocking the passage of the downstream signal input to the external connection terminal T1 and passing only the upstream signal after the frequency conversion, and the cutoff frequency thereof is set to, for example, 55 MHz. And in this embodiment,
The LPF 46 and the HPF 31 function as a first filter for signal separation of the present invention (claim 3). [Up-Converter] As shown in FIG. 2B, the up-converter 20 is connected to the terminal 18 via a coaxial cable or the like.
And a second connection terminal T4 for connecting to a communication terminal device such as the cable modem 22 that outputs an upstream signal.

Then, from the terminal terminal 18 to the first connection terminal T
3 is taken into the up-converter 20 via the LPF 51,
The data is transmitted to the communication terminal via the F53 and the second connection terminal T4. Here, the LPF 51 is for blocking the passage of the in-building up signal after the frequency conversion and passing only the down signal inputted to the first connection terminal T3.
The cutoff frequency is set to, for example, 770 MHz. The HPF 53 is for blocking the passage of the upstream signal input from the communication terminal device to the second connection terminal T4 and passing only the downstream signal, and the cutoff frequency is set to, for example, 70 MHz. . Therefore, in the up-converter 20 of the present embodiment, the LPF 51 and the HPF 53 form a path through which a downstream signal passes.

A branch circuit 52 provided on a path for passing a downstream signal between the LPF 51 and the HPF 53 is for branching a part of the downstream signal passing through this path, and is called a directional coupling. It is composed of a container. Then, the downstream signal branched by the branch circuit 52 is input to a narrow band BPF 60 for extracting a reference signal transmitted from the down converter 10.

Next, the upstream signal input from the communication terminal device to the second connection terminal T 4 is taken into the up converter 20 via the LPF 54. In addition, LPF54
Is for preventing the downstream signal output from the HPF 53 from wrapping around and selectively capturing only the upstream signal, and the cutoff frequency is set to, for example, 55 MHz. In the present embodiment, the LPF 54 and the HPF
F53 functions as a fourth filter for signal separation of the present invention (claim 4).

Next, the upstream signal taken into the up-converter 20 via the LPF 54 is input to the mixer 57 as the second frequency conversion means via the ATT 56 for adjusting the signal level. Then, the mixer 57 includes a PLL
By mixing the high frequency signal from the frequency variable type local oscillation circuit 59 whose oscillation frequency is controlled to be constant (in this embodiment, 811 MHz lower in frequency than the in-building up signal) by the circuit 58 and the up signal, The frequency of the upstream signal is converted into the upstream signal.

Here, the PLL circuit 58 outputs the reference signal extracted by the BPF 60 (in other words, the down converter 1
0) and a local oscillation circuit 59
And the high-frequency signal for frequency conversion output from
The high frequency signal for frequency conversion in the up-converter 20 is down-converted by controlling the oscillation frequency of the local oscillation circuit 59 so that the phase difference between the divided signals becomes zero. This is for controlling to the same constant frequency (811 MHz) as the high frequency signal for frequency conversion on the converter 10 side. Therefore, in this embodiment, the branch circuit 52, the BPF 60, the PLL circuit 58, and the local oscillation circuit 59 function as the second high-frequency signal generating means of the present invention, and are used for frequency conversion whose frequency is lower than the in-building up signal. A high frequency signal will be generated.

Next, the in-building up signal frequency-converted by the mixer 57 has a signal pass band of the transmission frequency of the in-building up signal (821M) in order to selectively pass the in-building up signal.
(Hz to 866 MHz) is input to an amplification circuit 62 for amplifying the in-building upstream signal through a BPF 61 set to a frequency in a range from about 1 Hz.
Then, the in-building up signal is amplified to a predetermined level by the amplifier circuit 62, and then the signal level adjustment ATT6 is used.
3, via the HPF 64 and the first connection terminal T3, to the terminal terminal 18 (and thus the transmission line L). still,
The HPF 64 is for blocking the passage of the downstream signal input to the first connection terminal T3, and for passing only the upstream signal after the frequency conversion, the cutoff frequency of which is:
For example, it is set to 821 MHz. In this embodiment, the HPF 64 and the LPF 51 function as a third filter for signal separation according to the present invention (claim 4).

As described above, the CA in the building of this embodiment
In the TV system, a high-frequency signal used to frequency-convert an upstream signal into an in-building up signal by the up-converter 20 and a high-frequency signal used to frequency-convert an in-building up signal into an up-signal by the down converter 10. In order to match the frequency with the signal, a reference signal for frequency control is transmitted from the down converter 10 onto the transmission line L,
In each of the up converters 20 on the terminal side, similarly to the down converter 10 controlling the oscillation frequency of the local oscillation circuit 40, the oscillation frequency of the local oscillation circuit 59 is controlled based on this reference signal. .

In the up-converter 20 and the down-converter 10, the PLL circuits 39, 58 for controlling the oscillation frequencies of the local oscillation circuits 40, 59 are supplied from the local oscillation circuits 40, 59 as high-frequency signals for frequency conversion. A high-frequency signal (811 MHz) having a lower frequency than the inbound signal (821 MHz to 866 MHz) is generated.

For this reason, in the up-converter 20, the BPF 61 that selectively passes only the in-building up signal out of the output from the mixer 57 cannot sufficiently reduce the high-frequency signal for frequency conversion. Even if the signal leaks at a relatively high level, the high-frequency signal can be reduced by the in-building upstream signal passing HPF 64 that functions as a third filter for signal separation.

Therefore, according to the in-building CATV system of this embodiment, the frequency of the high-frequency signal for frequency conversion is changed to the in-building up signal (821 MHz to 866 MHz) as in the prior art.
As compared with the case where the frequency is set to be higher (in this case, 876 MHz), the transmission from the upconverter 20 to the transmission line L in the building via the first connection terminal T3, the coaxial cable, and the terminal terminal 18 is performed. The signal level of the transmitted high frequency signal for frequency conversion can be reduced. Therefore, even if the high-frequency signals for frequency conversion leaked from the plurality of up-converters 20 on the terminal side are synthesized on the transmission line L and the synthesized signal is input to the down-converter 10, the input level of the synthesized signal is reduced to the conventional level. Can be made sufficiently small.

When an unnecessary synthesized signal is input to the downconverter 10, the LPF 33 and the HPF34 constituting the second filter for signal separation are connected to the internal connection terminal T2 of the downconverter 10. Therefore, the unnecessary synthesized signal input to the down converter 10 is transmitted to the mixer 38 through the HP
It is further attenuated by F34.

For this reason, even if the synthesized signal is transmitted to the mixer 38 together with the in-building up signal, the signal level of the combined signal becomes sufficiently small, and when the mixer 38 converts the frequency of the in-building up signal, The phase noise generated when the high frequency signal for frequency conversion leaked from the up-converter 20 onto the transmission line L is synthesized on the transmission line,
This can be prevented from being added to the frequency-converted upstream signal and transmitted to an external bidirectional CATV system.

Therefore, according to the CATV system in the building of the present embodiment, the down converter 10 accurately restores the original upstream signal from the upstream signal in the building without lowering the quality of the upstream signal. It is possible to transmit to an external bidirectional CATV system.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.
Various embodiments can be adopted. For example, in the above embodiment, by setting the frequency of the high-frequency signal for frequency conversion to a lower frequency than the in-building up signal, the high-frequency signal leaking from the up-converter 20 onto the transmission line, and
The combined signal of the high-frequency signal input to the mixer 38 of the down converter 10 is converted into an HPF which forms an input path or an output path of an in-building up signal in each of the converters 20, 10.
Although it has been described that the high-frequency signal for frequency conversion cannot be sufficiently attenuated by the HPFs 34 and 64, the transmission line L and the bidirectional amplifier provided on the transmission line L are described. 12, an output path of an in-building up signal in the up-converter 20 (for example, a stage before or after the BPF 61), or an input path of an in-building up signal in the down converter 10 (for example, a BPF 36. A trap circuit for removing a high-frequency signal of a specific frequency is provided in
This trap circuit may be used to further attenuate unnecessary high-frequency signals leaking from the up-converter 20 and input to the down-converter 10.

Incidentally, as this trap circuit, for example,
As shown in FIG. 3 (a), a so-called parallel resonance circuit composed of a coil L1 and a capacitor C1 is connected to a passage of an in-building up signal through a capacitor C3 which is a capacitive reactance. A C-coupled trap circuit may be used.

That is, as the trap circuit, an L-coupled trap circuit configured to connect a parallel resonance circuit to a signal passage through a coil that is an inductive reactance, a parallel resonance circuit, a transformer, or the like is used. 2. Description of the Related Art An M-coupled trap circuit configured to be connected to a signal passing path via a signal line is known.

Then, as in the present embodiment, the BPF 36,
When a high frequency signal of a predetermined frequency is removed in cooperation with the HPF 61 and the HPFs 34 and 64, if a C-coupled trap circuit is used, the frequency characteristic is reduced by impedance matching with another filter as shown in FIG. As shown in the figure, the drop of the attenuation on the higher frequency side becomes sharper with respect to the frequency of the signal to be removed (resonance frequency at which the attenuation becomes maximum in the figure). In a circuit, the opposite characteristic is obtained.

Therefore, when the frequency of the unnecessary signal to be removed is lower than that of the in-building up signal to be passed as in this embodiment, the so-called C-coupling as shown in FIG. By using the trap circuit, it is possible to reduce in-band transmission loss that occurs when an in-building up signal passes through the trap circuit.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a configuration of an in-building CATV system according to an embodiment.

FIG. 2 is a block diagram illustrating a configuration of a down converter and an up converter according to the embodiment.

FIG. 3 is an explanatory diagram showing a configuration of a trap circuit suitable for being provided in the in-building CATV system of the embodiment and a frequency characteristic thereof.

[Explanation of symbols]

6 ... drop-in line, 10 ... down converter, 12 ... bidirectional amplifier, 18 ... terminal terminal, 20 ... up converter, 22
... Cable modem, 24 ... Information terminal device, T1 ... External connection terminal, T2 ... Internal connection terminal, T3 ... First connection terminal, T
4: second connection terminal, 31, 34, 53, 64 ... HPF
(High-pass filter), 32 ... mixing circuit, 33, 46,
51, 54... LPF (low-pass filter), 35, 4
5,56,63 ... ATT (attenuator), 36,43,4
2, 60, 61 ... BPF (bandpass filter), 3
7, 44, 62: amplifier circuit, 38, 57: mixer, 3
9, 58 ... PLL circuit, 40, 59 ... local oscillation circuit, 4
1: Reference oscillation circuit, 52: Branch circuit

Claims (4)

[Claims] 1. A drop line from an external two-way CATV system is drawn into a building, and a down signal input from the drop line is transmitted to a plurality of terminal terminals in the building via a transmission line in the building. Along with the transmission, an in-building up signal having a higher frequency than the down signal, which is input from the terminal device on the subscriber side to each terminal via an up converter, is transmitted to the drop-in line via the transmission line. Further, by a down converter provided between the transmission line and the drop-in line, the in-building up signal is frequency-converted into an original up signal having a lower frequency than the down signal,
The up-converter and the down-converter are configured to transmit the signal on the service line, and the up-converter and the down-converter each use a high-frequency signal of the same frequency to perform frequency conversion on the up signal or the up signal in the building.
In the TV system, a ridge CATV system, wherein a frequency of a high-frequency signal used for frequency conversion by the up-converter and the down-converter is set to a lower frequency than that of the ridge up signal. 2. A high-frequency signal used by the up-converter to convert the frequency of the upstream signal into the upstream signal in the building on a transmission path of the upstream signal from the up converter to the down converter. 2. The in-building CATV system according to claim 1, further comprising a trap circuit for performing the operation. 3. The in-building CAT according to claim 1 or 2.
In the V system, a down converter provided between the service line and the transmission line, wherein an external connection terminal for connecting to the service line, an internal connection terminal for connecting to the transmission line, and In order to capture the downstream signal input to the external connection terminal, and to transmit the frequency-converted in-building up signal from the external connection terminal onto the drop-in line, a signal separation provided on the external connection terminal side A first filter, and captures an in-building up signal input to the internal connection terminal from the transmission line, and transfers the downstream signal captured via the first filter from the internal connection terminal onto the transmission line. A second filter for signal separation provided on the internal connection terminal side for transmission, and a high frequency for converting the frequency of the in-building upstream signal to the upstream signal. First high-frequency signal generating means for generating a high-frequency signal whose frequency is set lower than that of the in-building up signal, the in-building up signal taken in through the second filter, and the first high frequency By mixing the high-frequency signal generated by the signal generating means, the in-building up signal is frequency-converted into the up signal, and the frequency-converted up signal is transmitted to the service line through the first filter. A down converter, comprising: first frequency conversion means. 4. The in-building CAT according to claim 1 or 2.
In the V system, an up-converter provided between the terminal terminal and a subscriber terminal device, a first connection terminal for connecting to the terminal terminal, and a second connection terminal for connecting to the terminal device. A connection terminal, the first connection for capturing a downstream signal input from the terminal terminal to the first connection terminal, and transmitting an upstream signal after frequency conversion from the first connection terminal to the terminal terminal; A third filter for signal separation provided on the terminal side, and captures an upstream signal input to the second connection terminal from the terminal device, and converts the downstream signal captured via the third filter to A fourth filter for signal separation provided on the second connection terminal side for transmitting the signal from the second connection terminal to the terminal device; A second high-frequency signal generating means for generating a high-frequency signal whose frequency is set lower than that of the in-building up-signal as the high-frequency signal of the above-mentioned, the up-signal taken through the fourth filter, and the second high-frequency By mixing the high-frequency signal generated by the signal generating means, the upstream signal is frequency-converted into the ridge upstream signal, and the ridge upstream signal after the frequency conversion is passed through the third filter to the terminal terminal side. An up-converter, comprising: a second frequency conversion means for transmitting to the up-converter.