JP2010041319A - Cable modem and catv terminal device provided with cable modem - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for eliminating a switching noise when controlling an attenuation means. <P>SOLUTION: The attenuation means capable of increasing/decreasing an attenuation amount is interposed in a signal route between an input end and a tuner, and normally attenuation is executed for transmission to the next stage. The tuner includes an electric field strength-measuring means for measuring and outputting an input signal level, and is further provided with a control means for receiving signal level information measured by the tuner, performing data processing in a prescribed processing order, and outputting a switching control signal for switching so as to increase/decrease the attenuation amount of the attenuator element of the attenuation means on the basis of the result obtained by the data processing. The attenuation means includes the plurality of attenuator elements and the switching means and is configured to selectively utilize the attenuator elements. The control means executes control so that at least one of the plurality of attenuator elements is interposed and switching is performed to permit the attenuation means to send out signals inputted from the input end to the next stage without interruption. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a cable modem for connecting to a CATV network and supplying a data communication signal, and a CATV terminal apparatus including the cable modem.

A conventional cable modem has a tuner and a QAM (Quadrature Amplitude Modulation) demodulator inside, converts the frequency of a CATV signal (downstream signal: downstream) input from the input end by the tuner, and then converts the frequency to the QAM demodulator. Demodulate with
In addition, assuming that the level of the signal input from the input terminal becomes an abnormal value that interferes with the normal operation of the internal tuner and QAM demodulator, in order to adjust it to a normal level, An AGC function is provided.
However, in conventional cable modems, the input signal level (hereinafter also referred to as “practical input level”) within the range in which the tuner can operate normally is input due to various causes such as interference of the input signal. In some cases, the level of the signal to be generated becomes abnormally high, and in a tuner having an AGC function with a narrow AGC range, there is a case where the distortion occurs and cannot be handled normally. In addition, when an excessively high level signal is input in this way, there is a reflection in the tuner, and the signal that the tuner tries to detect is disturbed by the reflection, and the tuner cannot operate normally. Further, when a plurality of tuners (for example, a QAM tuner in a set top box as a CATV terminal device with a built-in cable modem) are adjacent to each other in addition to the cable modem tuner, the other tuners are reflected by the reflection from the tuner. There is also a problem that it interferes with the operation of other tuners.

Therefore, the applicant intervenes attenuation means having an attenuator element capable of adjusting the attenuation amount in the signal path between the input end of the cable modem and the tuner, and the attenuation means converts the input signal into the attenuator element. The tuner is always attenuated and sent to the next stage. The tuner is provided with electric field strength measuring means for measuring the level of the input signal and outputting the signal level information. Further, by performing a predetermined processing procedure based on the reception level information obtained by the electric field strength measuring means, the level of the signal input to the input terminal is small (no excessive level is input). And a control means for performing a switching process so that the attenuation amount of the attenuator element in the attenuation means decreases based on the determination. Tuner proper level signal is input to a cable modem that is configured to operate normally has been proposed.
(For example, see Patent Document 1)

JP 2007-243252 A

However, the cable modem configured in the prior art is used in combination with, for example, a set top box (hereinafter referred to as STB) as a CATV terminal device as described above (including the case where it is built in the STB). Depending on the switching timing of the attenuator element of the attenuating means, noise due to the attenuator element switching may occur due to the impedance variation of the attenuating means, and this may affect other RF connection devices such as the STB image receiving circuit. It has been confirmed that
That is, a system in which an STB and a cable modem are connected to a coaxial cable drawn into a house from a TV terminal or the like via a signal distributing means consisting of a distributor or a branching unit, and a downstream signal from a CATV center station is used. When considering a bi-directional system capable of Internet connection services using upstream signals in addition to broadcasting services, depending on the performance of the distributor or branching unit for connecting the cable modem, the attenuator element of the attenuation means described above The noise caused by the switching of the signal passes through the video tuner of the STB through the distributor or branching device, thereby causing interference. In particular, in the case of a terminal device in which a cable modem is built in the STB, there is a case in which the influence is remarkable due to the fact that the distance of routing is close.

Accordingly, the present invention has been made in view of such problems, and provides an attenuating means suitable for a high-frequency device that requires a wide dynamic range with respect to an incoming signal level and a switching control method thereof. The purpose of this is to provide a cable modem as an example of the above-described high-frequency device, in which the generation of unnecessary noise is reduced.
Another object is to provide a cable modem that does not interfere with the CATV terminal device even when used in combination with a CATV terminal device such as an STB.
Another object of the present invention is to provide a cable modem that can receive a signal input to an input terminal, convert the frequency into a tuner, demodulate it with a QAM demodulator, and output it normally.
Another object is to provide a cable modem in which a tuner accepts an appropriate level signal and can operate normally even when an excessive level signal is input to the input terminal.
Another purpose is to provide a cable modem that can continuously monitor the input level after starting the cable modem and automatically start the cable modem again, even if there is a reception error, so that stable reception can be continued. It is what.
Another object of the present invention is to provide a cable modem that has the above-described characteristics and that can perform the cable modem activation process in as short a time as possible.
Other objects and advantages will be readily apparent from the drawings and the following description associated therewith.

In order to solve the above-mentioned problems, a first aspect of the present invention is a tuner for frequency-converting and outputting a signal input from an input terminal, and a QAM demodulator for receiving and outputting the output signal and performing QAM demodulation. A cable modem comprising:
The signal path between the input terminal and the tuner is provided with an attenuating means having an attenuator element that can adjust the amount of attenuation, and the tuner measures the level of the input signal and outputs the signal level information. Electric field strength measuring means configured to be provided, and further receiving the signal level information measured by the electric field strength measuring means, performing data processing in a predetermined processing procedure based on the signal level information, and performing the data processing Control means for sending a switching control signal so that the attenuation amount of the attenuator element can be adjusted to the attenuation means based on the results obtained in
The attenuating means includes a plurality of attenuator elements and a switching means, and the attenuator elements can be selectively used by switching the switching means to be selectively usable by a switching control signal from the control means. In the switching control toward the attenuating means, at least a plurality of the controlling means are provided so that the attenuating means can send the signal input from the input end to the next stage without interruption. Any one of the attenuator elements is controlled so as to be always switched in the signal path.

According to a second aspect of the present invention, in the cable modem according to the first aspect, the attenuating means is configured to always attenuate the input signal via the attenuator element and send it out to the next stage. The means further outputs a switching control signal for switching so as to reduce the attenuation amount of the attenuator element toward the attenuation means, and a determination step of determining whether or not the QAM demodulator is demodulating the QAM signal. If the QAM demodulator determines that the QAM signal is not demodulated in the determination step, it further accepts the measured signal level information and sums the signal level information. And a comparison step for comparing the sum of the signal level information and the first threshold, and the current incoming level of any one of the signal level information And a comparison step for comparing the second threshold value, and in the comparison of both of the above comparison steps, the sum of the signal level information is less than or equal to the first threshold value, and any one wave of the signal level information has now arrived When the level value is equal to or less than the second threshold value, the third process is performed to perform control to output a switching control signal for switching to reduce the attenuation amount of the attenuator element toward the attenuation unit.

According to a third aspect of the present invention, in the cable modem according to the second aspect of the present invention, the level value stored in advance and the current input for any one wave of the signal level information are further recorded. A comparison step is performed to compare with the level value that has come, and if the difference between the two exceeds a predetermined value, a switching control signal for switching so as to decrease the attenuation of the attenuator element is output to the attenuation means. Without receiving the signal level information again, the above three comparison steps are performed,
The sum of signal level information is below the first threshold,
The current incoming level value of one wave of signal level information is less than or equal to the second threshold,
Switching control for switching to reduce the attenuation amount of the attenuator element toward the attenuating means when the difference between the current incoming level value and the previously stored target level value is less than a predetermined value The fourth processing for performing control to output a signal is performed.

The invention of claim 4 is the cable modem according to claim 2 or 3, further comprising processing procedure setting means for setting a processing procedure for the received signal reception level information,
In addition to the processing procedure for performing the first processing and performing the third processing when it is determined that the QAM demodulator is not demodulating the QAM signal,
A processing procedure for performing the first processing and performing the first processing even if it is determined that the QAM demodulator is not demodulating the QAM signal;
A determination step of determining whether or not the QAM demodulator demodulates the QAM signal without outputting a switching control signal for switching the attenuation means to decrease the attenuation amount of the attenuator element is performed. And when the QAM demodulator determines that the QAM signal is not demodulated, the second processing is further performed.
Instead of the above three processing procedures, either the third processing or the processing procedure performed from the fourth processing can be selectively set, and the control means can set the processing procedure setting means. Based on the above, it is configured to control to perform any one of the above processing procedures.

According to a fifth aspect of the present invention, in the CATV terminal device including a cable modem, the cable modem is configured to include the cable modem according to any one of the first to fourth aspects.

According to the first aspect of the present invention, in the switching control for the switching circuit provided in the attenuation means, the control means can send the signal input from the input terminal to the tuner without interruption. When at least one attenuator element among the plurality of attenuator elements is controlled so as to be interposed and switched in the signal path, the attenuation amount of the attenuating means is adjusted. The signal path is never opened, and the impedance of the attenuating means does not change greatly, so that no switching noise is generated by the control for switching the attenuator element. In addition, the time during which different attenuator elements are simultaneously interposed between the input terminal and the tuner is set within a predetermined time that does not affect the cable modem activation process, so that the operation of the cable modem is not hindered.

According to the invention of claim 2 and claim 3, in addition to the above effect, the attenuating means always sends an incoming signal through the attenuator element so as not to input an excessive level signal to the tuner. Even if the control means is configured to be attenuated and sent to the next stage, when initialization is completed, the control means first controls the attenuation means to decrease to 0 dB (through), and enters the input terminal. If the signal level is a practical input level, the tuner is controlled so that an appropriate level signal without attenuation is input, and whether the tuner can correctly demodulate immediately for all frequencies in the frequency band of the downstream signal. (1st process) can be performed, which speeds up the cable modem startup process and can be performed in an extremely short time compared to the prior art. To become.
Even when an excessively high level signal is input to the input terminal and the tuner does not operate normally during the process (first process), a predetermined processing procedure (third process) Or the fourth process), the control means always attenuates the input signal by the attenuation means and controls the signal of the appropriate level to be input to the tuner. The signal can be received, and the tuner can be operated normally without causing the conventional problems.

In addition, according to the invention of claim 4 of the present application, it is provided with processing procedure setting means for setting a processing procedure for the input signal and signal reception level information, and the control means is configured to set the processing procedure setting means. On the basis of this, it is configured to control to perform any one of a plurality of processing procedures including “default” which is a standard processing procedure. In addition to the above-mentioned effects in the standard processing procedure that can cope with either the appropriate level or the high level, the state of the input signal level is known in advance, and an appropriate level signal is received. If it is clear that there is a situation where there is a strong signal or a signal with a strong level, the processing procedure in a mode different from the standard processing procedure depending on the situation (only the first processing) By choosing a procedure or procedures by the second processing), the time to carry out some of the search which constitutes the standard procedure can be omitted, it is possible to speed up the startup process of the cable modem.
Further, even if the level of the incoming signal is appropriate or high, the third process or the third process is directly performed without controlling the first process or the second process. If the control mode for performing the fourth process is selected, the signal received by the attenuation means is always attenuated via the attenuator element without performing the first process or the second process. Even if it is configured to send out to the stage, the attenuation amount of the attenuation means is appropriately adjusted regardless of the incoming signal level, and is input to the tuner, so that the tuner can accept an appropriate level signal, There is an effect that the tuner can be operated normally in a shorter time without causing the conventional problems.

According to the invention of claim 5, if the cable modem according to any one of claims 1 to 4 having the above effect is provided in a CATV terminal device, the tuner provided in the cable modem includes: Since a signal of an appropriate level is input without being influenced by the input level, not only can the start-up process be performed normally, but also by control related to switching of the attenuator elements constituting the attenuation means. Since there is no switching noise, the switching noise is not circulated into the video tuner provided in the CATV terminal device, so that it is equipped with a cable modem with extremely stable performance (or built-in). A CATV terminal device can be provided.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. In the figure, reference numeral 1 denotes the presence of a cable modem according to the present invention which is connected to a CATV network and supplies a data communication signal as an example of a high-frequency device.
In the figure, the attenuating means 10, the tuner 5, the QAM demodulator 8 and the like are those used for the downstream signal in the cable modem 1. On the other hand, as is well known in this type of cable modem 1, the related members for upstream signals are substantially present, but are not shown and described because of known matters.

In the cable modem 1, reference numeral 2 denotes an input terminal for inputting a known CATV signal, and 3 denotes an output terminal for outputting a data signal to a terminal device such as a PC.
Next, 5 is a well-known tuner and, as is widely known, tunes to a predetermined frequency (also referred to as one wave) within the frequency band of the CATV signal (downstream signal) input from the input terminal 2; The frequency (one wave) signal is frequency-converted and output.
Reference numeral 6 denotes the presence of a field strength measuring means (RSSI: Received Signal Strength Indicator) built in the tuner 5, and measures the level of an arbitrary predetermined frequency (one wave) in the signal input to the tuner 5. is there. Further, the signal level information measured by the electric field strength measuring means 6 incorporated in the tuner 5 is output to the control means 16 described later.

Reference numeral 8 denotes a known QAM demodulator for receiving the signal 5b output from the tuner 5, QAM demodulating it, and outputting it.

Reference numeral 15 denotes a CPU (Central Processing Unit, hereinafter referred to as CPU), which executes various applications for operating a cable modem as is generally known.
16 indicates the presence of the control means, reads the signal level information 17 output from the electric field strength measuring means 6, and based on the signal level information 17, the amount of attenuation is adjusted with respect to the attenuation means 10 described in detail later. The switching control signal 18 is configured to be output, and processing related to steps, determinations, and the like to be described later is controlled.

Reference numeral 10 denotes the attenuating means interposed in the signal path between the input terminal 2 and the tuner 5, and the first attenuator element 11, the second attenuator element 12, and the third attenuator element 13 having different attenuation amounts. And a switching circuit 14 as switching means. The first to third attenuator elements 11, 12, and 13 are configured to be selectively switchable by a switching control signal 18 from the control means 16 for the switching circuit 14. Further, the attenuation levels of the first to third attenuator elements 11, 12, and 13 are selectively switched to each other to adjust the level of the signal input to the input terminal 2 to the practical input level of the tuner 5. Thus, it suffices if a signal is sent to the input point 5a of the tuner 5, for example, 0 dB, 10 dB, and 20 dB, respectively.
Note that the number of attenuator elements may be increased or decreased as necessary. For example, the first attenuator element 11 and the second attenuator element 12 may be configured to be switched and used.
In the present invention, the attenuation means 10 is controlled by the switching control signal 18 from the control means 16 so that the input signal is always attenuated via the attenuator element and sent to the next stage. ing.

As means for switching the first to third attenuator elements 11, 12, and 13, the switching circuit 14 configured using a commonly known PIN diode may be selectively used. The control means 16 includes at least a plurality of attenuators so that the attenuation means 10 can send the signal input from the input terminal 2 to the tuner 5 without interruption in the switching control for the switching circuit 14. Control is performed so that any one of the attenuator elements among the elements 11, 12, and 13 is always interposed in the signal path.

Reference numeral 19 denotes a processing procedure setting means for setting a processing procedure for an input signal or reception level information. The control means 16 performs a plurality of processing procedures (preliminarily set based on the setting of the processing procedure setting means 19 ( In the embodiment of the present invention, in addition to the standard processing procedure which is “default”, three other processing procedures are provided.) Any one of the processing procedures is controlled. In the present invention, four modes are provided as an embodiment of the processing procedure, and parameters and commands are as follows.
In the case of “default” = “SearchMode” (processing procedure parameter) is “0”
In the case of “mode 1” = “Search Mode” (processing procedure parameter) is “1”
In the case of “mode 2” = “Search Mode” (processing procedure parameter) is “2”
In the case of “Mode 3” = “Search Mode” (processing procedure parameter) is “3”.
It is.
Details of each processing procedure will be described later. The example of selecting from the four shown here is only an example. For example, when the cable modem is activated, “default” is set, and the method and type of the processing procedure is not limited to the example. Absent.
In the following description, a standard processing procedure when “default” is selected by the processing procedure setting means 19 from the above four processing procedures will be described unless otherwise specified. This standard processing procedure is a versatile procedure that can be freely adapted to the input level situation.

Reference numeral 20 denotes a flash memory for storing a program and data for operating the cable modem, and reference numeral 21 denotes a RAM used for temporary storage of data when the CPU 15 and the control means 16 are operated.

In the above configuration, the operation of the control means 16 will be described in detail with reference to the flowcharts shown in FIGS. In order to simplify the description, the case where two of the first attenuator element 11 and the second attenuator element 12 are used in the attenuation means 10 will be described.
First, a case where the signal input to the input terminal 2 is at an appropriate level will be described. When the cable modem 1 is activated, the switching control signal 18 is output so as to interpose the second attenuator element 12 (for example, attenuation: 10 dB) of the attenuation means 10 (S10), and the cable modem is initialized (S11). The signal input to the input terminal 2 is attenuated by the attenuation means 10 and sent to the input point 5a. In the embodiment of the present invention, however, the signal is input to the input terminal 2 in accordance with the initialization of the cable modem. For the signal processing procedure, the above-described command is set by the processing procedure setting means 19 (S12). In the following description, the processing procedure when “Search Mode” (processing procedure parameter) that is “default” is set to “0” (standard processing procedure) will be described in detail.
Next, it is determined whether or not the command setting (“SearchMode”) is “3” (S13), and since “SearchMode” is “0” (No in S13), the next process (S14) Migrate to In the next process, “Search Mode” is also determined. Since “Search Mode” is “0” (Yes in S14), the process proceeds to the next process (S15). In this process, the switching control signal 18 is output so that the first attenuator element 11 (for example, attenuation: 0 dB (also referred to as through)) is interposed instead of the second attenuator element 12 of the attenuating means 10 (S15).

Next, an arbitrary frequency (arbitrary wave) in the frequency band of the downlink signal is read (S16), and for each frequency signal, the control means 16 performs a downlink signal as normally performed in the cable modem. It is determined whether or not the signal can be detected (that is, whether or not it is a QAM signal) (S19). If the signal can be detected (Yes in S19), the upstream signal is processed (S20) and the processing is completed. On the other hand, if it cannot be detected as a downlink signal (No in S19), it is determined whether or not a search (whether it is a QAM signal) has been performed once or more for all frequencies in the frequency band of the downlink signal (S21). . If not (No in S21), the process proceeds to S16 to search for the next frequency based on a predetermined channel plan (S22), and the processes after S16 are continued.
On the other hand, if the search is performed at least once for all frequencies (Yes in S21), it is determined whether “SearchMode” is “1” or “2” (S25), and “SearchMode” is “ 0 ”(when S25 is No), the process proceeds to the next process (S101).
Note that the control means 16 outputs a switching control signal 18 for switching so as to decrease the attenuation amount of the attenuator element toward the attenuation means (S15), and the QAM demodulator is not demodulating the QAM signal. A series of processes including the process of performing the determination step of determining whether (S19) is the first process described in the claims.

Here, a case will be described in which “mode 1” or “mode 2” is set (S12) by the processing procedure setting means 19 in place of the “default” setting which is the standard processing procedure as described above. First, when “1” is set in “Mode 1”, that is, “Search Mode” (processing procedure parameter), the command setting determines whether “Search Mode” is “3” (S 13), and “Search Mode”. "Is" 1 "(in the case of No in S13), the process proceeds to the next process (S14). In the next process, it is also determined whether “SearchMode” is “0” or “1”. Since “SearchMode” is “1” (Yes in S14), the process proceeds to the next process (S15). In this process, the switching control signal 18 is output so that the first attenuator element 11 (for example, attenuation: 0 dB (also referred to as “through”)) is interposed instead of the second attenuator element 12 of the attenuation means 10 (S15). Then, it is determined whether the signal can be detected as a downstream signal (that is, whether it is a QAM signal) (S19). The processing so far is the same procedure as the first processing, but the processing after the search is performed once or more for all frequencies (Yes in S21) is different from “default”. That is, in the next process, it is determined whether “SearchMode” is “1” or “2” (S25), and “SearchMode” is “1” (when S25 is Yes). The process proceeds to the next processing (S14) again, and the subsequent processing is performed with the first attenuator element 11 (for example, attenuation: 0 dB) interposed.

Next, when “2” is set in “Mode 2”, that is, “Search Mode” (process procedure parameter) in S12 (S12), it is determined whether or not the command setting “Search Mode” is “3” (S13). Since “SearchMode” is “2” (No in S13), the process proceeds to the next process (S14). In the next process, “SearchMode” is determined to be “0” or “1”, and “SearchMode” is “2” (in the case of No in S14), the second attenuator element 12 of the attenuation means 10 (for example, attenuation) (Mode: 10 dB) is maintained, and “mode 2” is configured to be performed in a procedure different from “default” and “mode 1” in which the attenuation amount of the intervening ATT is different. Are different. Furthermore, the processing after the search is performed once or more for all frequencies (Yes in S21) is also different from “default”. That is, in the next process, it is determined whether “SearchMode” is “1” or “2” (S25). Since “SearchMode” is “2” (when S25 is Yes), in “Mode 2” The process proceeds to the next processing (S14) again, and the subsequent processing is performed with the second attenuator element 12 (for example, attenuation: 10 dB) of the attenuation means 10 interposed.
The QAM demodulation is performed without outputting the switching control signal 18 for switching so as to decrease the attenuation amount of the attenuator element toward the attenuating means (that is, with the second attenuator element 12 interposed). A series of processes including a process of performing a determination step of determining whether or not the device is demodulating the QAM signal (S19) is the second process described in the claims.

In each of “default”, “mode 1” and “mode 2”, a QAM signal is detected by performing a search (whether or not it is a QAM signal) at least once for all frequencies in the frequency band of the downstream signal. If so (Yes in S19), then the upstream signal processing is performed (S20), and the cable modem activation processing is completed. In addition, if a state in which the QAM signal is not detected continues after a lapse of a predetermined time after completion of the cable modem activation process, the cable modem generally performs initialization. Regardless of whether the setting before starting is “mode 1” or “mode 2”, the control means 16 will have a high and low signal level after a predetermined time has elapsed if it is set to “default”. Regardless of this, the attenuator element can be appropriately adjusted to control the signal to be input to the tuner 5 at an appropriate level.

As described above, even after the cable modem 1 is activated, the attenuation means 10 always controls the input signal level to be reduced by the attenuation means 10 so as not to input an excessive level signal to the tuner 5 (S10). If “default” (standard processing procedure in the embodiment of the present invention) is set by the processing procedure setting means 19 (S12), the control means 16 performs the attenuation of the attenuation means 10 by steps S14 to S19 and the like. Since the input signal level is controlled to be increased by setting the amount to 0 dB, if the incoming signal level is a practical input level, the incoming appropriate level signal is input to the tuner 5. . At the same time, the control means 16 immediately controls the search (whether a QAM signal is detected) for all frequencies in the frequency band of the downlink signal, so that the downlink signal processing can be performed quickly. Speed up the startup process. Also, if the state of the input signal level is known in advance and an appropriate level signal is being input, “Mode 1” is selected. If a strong level signal is present, “Mode 2” is selected. If selected, the cable modem startup process can be speeded up.

Here, the switching timing of the first attenuator element 11 and the second attenuator element 12 will be described with reference to FIGS. 6 and 2. This FIG. 6 pays attention to the part that shifts from the initialization state in the standard processing procedure that is “default” to the first process, and shows the switching timing of the first attenuator element 11 and the second attenuator element 12 related to the shift. It is drawing for demonstrating.
Since the attenuating means 10 of the present invention is configured to always attenuate the input signal via the attenuator element and send it to the next stage, the attenuating means 16 is the first attenuator in the initial state. Control is performed by the control means 16 so that the element 11 is OFF (attenuation: 0 dB (also referred to as through)) and the second attenuator element 12 is ON (attenuation 10 dB) (S10 in FIG. 2, FIG. 6). Next, when initialization (S11) and “Search Mode” (processing procedure parameter), which is the “default”, are set to “0” (standard processing procedure), predetermined processing and determination are performed. 2 (Yes in S14 from S12 in FIG. 2), the process proceeds to the next process (S15), and in S15, at the start of the first process, the attenuation means 1 The first attenuator element 11 is turned on in place of the second attenuator element 12 and the first attenuator element 11 is controlled to be interposed in the signal path (S15 in FIG. 2, the first attenuator element in FIG. As shown well in FIG. 6, in the switching of the attenuator element in the present invention, the control means 16 does not disconnect the second attenuator element 12 from the signal circuit before the first attenuator element 11. So that both attenuator elements are interposed between the input terminal 2 and the tuner 5 for a predetermined time indicated by t in the figure, and then the second attenuator element is connected. 12 is controlled to be disconnected from the signal circuit.

That is, in the switching control for the switching circuit provided in the attenuating means 10, the control means 16 at least allows the attenuating means 10 to send the signal input from the input terminal 2 to the tuner 5 without interruption. When any one of the plurality of attenuator elements is controlled so as to be interposed and switched in the signal path, when the attenuation amount of the attenuation means 10 is adjusted, The impedance of the attenuating means 10 does not change greatly, and the signal path is never opened, so that switching noise is not generated when the attenuator element is switched. Also, the time t that both the first attenuator element 11 and the second attenuator element 12 are interposed between the input terminal 2 and the tuner 5 is set within a predetermined time that does not affect the activation process of the cable modem. This does not interfere with the operation of the cable modem.

The description of S101 and subsequent steps in the “default” processing procedure that is the standard processing procedure will be continued. First, the state when the QAM signal is not detected in step S19 and the search for all frequencies in the frequency band of the downstream signal is completed in S21 (in the case of Yes in S21) will be described. In such a case, it is considered that the signal input to the input terminal 2 has an excessive level (for example, 34 dBmV: digital signal 1 wave is +5 dBmV and analog signal 76 wave is +15 dBmV respectively). Then, in the next process, it is determined whether “SearchMode” is “1” or “2” (S25). Since “SearchMode” is “0” (when S25 is No), the next process (S101) is performed. ).

In the first process, since the first attenuator element 11 (for example, attenuation: 0 dB) of the attenuating means 10 is used (S15), here, instead of the first attenuator element 11 again, a second attenuator element ( For example, the switching control signal 18 is output so as to intervene (attenuation amount: 10 dB) (S101). The signal input to the input terminal 2 is attenuated by the attenuation means 10 and sent out toward the input point 5a. Therefore, “weak signal” (a parameter indicating whether or not the signal is weak) is set to “1” (weak signal) (S102).
Next, all frequencies within the frequency band of the downlink signal (for example, a maximum of 117 waves in Japan) based on the channel plan in a predetermined area, which is input to the tuner 5, are scanned (S103, S104). The electric field strength measuring means 6 measures the level (L1) for each of all frequencies and outputs the signal level information 17 thereof. The control means 16 reads the signal level information 17 (S105) and stores it in the RAM 21 (S106).
Next, it is determined whether or not all the stored signal level information 17 is greater than a predetermined value P1 (for example, −7.8 dBmV) (S107). Here, it is determined that the value is larger than the predetermined value P1 (Yes in S107), the parameter “weak signal” is set to “0” (not a weak signal) (S108), and the process proceeds to the next process (S109). .
Next, after determining whether or not the downlink frequency is in a channel plan (for example, Japan) in a predetermined area (S109), input level unit conversion (S110), and input level integration (S111) , The process proceeds to the next process (S112). If it is not the predetermined area (when S109 is No), the processing of input level unit conversion (S110) and input level integration (S111) is skipped, and the process proceeds to the next processing (S112). The determination of the channel plan (channel arrangement) in S109 depends on the downlink frequency channel plan, because the channel plan for the downlink frequency varies from country to country (90 to 770 MHz in Japan, 88 to 860 MHz in North America). It is a process for making it possible to cover. The channel plan determination may be provided as in the embodiment or may not be provided depending on the specification.
Next, it is determined whether or not the reading of the signal level information 17 relating to all the frequencies has been completed (S112). If it has not been completed (No in S112), the process returns to S104, and the processes after S104 are repeated.

Next, when it is determined as “complete” in S112 (Yes in S112), the sum of the signal level information 17 regarding all frequencies is calculated and unit conversion is performed (S113).
Next, the sum of the signal level information 17 and the first threshold value T1 (for example, 31.0 dBmV) are compared (S114). Here, it is determined that the sum of the signal level information 17 is larger than the first threshold T1 (in the case of Yes in S114), and “Multi-channel” (a parameter indicating whether the sum of the signal levels is high or low) is an initial value “1”. (Environment with high input level) is set (S115), the process proceeds to S201, and the process proceeds to the next process.
The process of receiving the signal level information measured in the electric field strength measuring means 6, calculating the sum of the signal level information, and comparing the sum of the signal level information with the first threshold value T1 is described in the three comparisons in the claims. This is the first comparison step among the steps.

Next, an arbitrary frequency (arbitrary wave) in the frequency band of the downstream signal is read (S201), and the switching control signal 18 is output so that the second attenuator element 12 is continuously interposed with respect to the attenuation means 10. (S202). Next, the level L2 measured by the electric field strength measuring means 6 for the read arbitrary wave is read (S203). The level value L2 (also referred to as the current incoming level value) is compared with the level value L1 of the same frequency previously stored in S106, and the difference is calculated (S204). It is determined whether the difference is larger than a predetermined value G (for example, 4 dB) (S205). Here, it is determined that the difference does not exceed the predetermined value G (No in S205), and the process proceeds to the next process (S206).
Next, it is determined whether or not the level value L2 read in S203 is larger than a predetermined value P2 (for example, −2.8 dBmV) and “weak signal” is “1” (weak signal) (S206). It is determined that “weak signal” is “0” (not a weak signal) (in the case of No in S206), and the process proceeds to the next process (S207).
The process of comparing the level value L1 previously targeted and stored with the current incoming level value L2 for any one of the received level signals is the three comparisons according to claim. This is the second comparison step among the steps.

Next, the level value L2 of an arbitrary wave that has currently entered (the level value read in S203) is compared with the second threshold value T2 (for example, −1.8 dBmV). Then, it is determined whether or not the second threshold value T2 or less and the sum of the signal level information 17 is equal to or less than the first threshold value T1 (“Multi-channel” is “0”, that is, the level is low) (S207). Since “Multi-channel” is “1”, it is determined that both are not equal to or less than the first threshold value T1 and the second threshold value T2 in both comparisons (in the case of No in S207), the control means 16 sends the attenuation means 10 The process proceeds to S209 without outputting the switching control signal 18 for switching to the first attenuator element 11 (for example, attenuation: 0 dB (also referred to as “through”)) so as to reduce the attenuation of the attenuator element. The signal input to the input terminal 2 is sent out toward the input point 5a at a level that is still attenuated by the attenuation means 10.
In addition, the process which compares the level value L2 of the arbitrary one incoming wave and the 2nd threshold value T2 is the 3rd comparison step of the 3 comparison steps described in a claim.

Next, the control means 16 determines whether or not it is a signal that can be detected as a downlink signal (whether it is a QAM signal) as is normally done in a cable modem (S209), and if it can be detected (Yes in S209). In the case, the upstream signal is processed (S210). On the other hand, if it cannot be detected as a downlink signal (No in S209), it is determined whether or not a search (measurement of L2 level) has been performed once or more for all frequencies in the frequency band of the downlink signal (S211). . If not (No in S211), the process proceeds to S201 so as to search for the next frequency based on a predetermined channel plan (S212), and the processes after S201 are continued.
On the other hand, when the search is performed at least once for all frequencies (Yes in S211), the process proceeds to S101, and the processes after S101 are performed again.

As described above, if the processing procedure is set to the standard “default” and the level of the incoming signal is appropriate, it is only necessary to perform the first processing. In addition to the upstream signal processing, the cable modem startup processing can be speeded up.
Even if the signal level is abnormally high and no QAM signal is detected in the first processing after the cable modem 1 is started, the attenuator element of the attenuation means 10 is set and input in S101. Since the level of the signal from the end 2 is attenuated and sent to the tuner 5, an excessive level signal is not input to the tuner 5, and the tuner can be operated normally without causing the conventional problems. In other words, it is possible to provide a cable modem that is highly versatile and convenient regardless of the level of incoming signals.

Next, while describing “mode 3”, which is the remaining mode among the four processing procedures according to the embodiment of the present invention, the processing procedures after S101 will be further described. Unlike the “default”, “mode 1”, and “mode 2”, the “mode 3” according to the embodiment of the present invention does not go through the first process or the second process, but directly after S101. (That is, a third process or a fourth process, which will be described later). Compared with the case where “default” is set, when the “mode 3” is set, the first process is not performed if the incoming signal level is high. The advantage is that the cable modem startup processing time is short. Furthermore, the original function provided for “default” is that an appropriate level signal is input to the tuner 5 so that the tuner 5 can operate normally regardless of whether the level of the incoming signal is appropriate or high. It has the same versatility as “Default”.

In this “mode 3”, the description of the operation when the incoming radio wave is abnormally high is the same as the processing procedure after S101 in “default” already described in detail, and is omitted here. A case will be described in which an appropriate level (practical input level of the tuner 5, for example, 24 dBmV) is input.
First, the switching control signal 18 is output so as to interpose the second attenuator element 12 (for example, attenuation: 10 dB) of the attenuation means 10 (S10), and the cable modem is initialized (S11). The signal input to the input terminal 2 is attenuated by the attenuating means 10 and sent to the input point 5a. Here, the signal processing procedure is set in accordance with the initialization of the cable modem. The means 19 sets “Search Mode” (a parameter of the processing procedure) which is “Mode 3” to “3” (S12). It is determined whether or not “SearchMode” is “3” (S13), and since “SearchMode” is “3” (Yes in S13), the process proceeds to the next process (S101). Since the attenuator 10 outputs the switching control signal 18 so that the second attenuator element 12 (for example, attenuation: 10 dB) is interposed (S101), the signal input to the input terminal 2 is attenuated by the attenuator 10. , Sent to the input point 5a. Then, “weak signal” (a parameter indicating whether or not the signal is weak) is set to “1” (weak signal) (S102). Next, the process proceeds to 103, and the processes of S103 to S106 are continued.
Next, it is determined whether or not all the stored signal level information 17 is greater than a predetermined value P1 (for example, −7.8 dBmV) (S107). Here, it is determined that the value is equal to or less than the predetermined value P1 (No in S107), and the parameter “weak signal” remains “1” and the process proceeds to the next process (S109).
Next, after determining whether the downstream signal is in Japan or the like (S109), input level unit conversion (S110), and input level integration (S111), the process proceeds to the next process.
Next, it is determined whether or not the reading of the signal level information 17 relating to all the frequencies has been completed (S112). If it has not been completed (No in S112), the process returns to S104, and the processes after S104 are repeated.

Next, when it is determined as “complete” in S112 (Yes in S112), the sum of the signal level information 17 regarding all frequencies is calculated and unit conversion is performed (S113).
Next, the sum of the signal level information 17 and the first threshold value T1 (for example, 31.0 dBmV) are compared (S114). Since the signal input to the input terminal 2 is attenuated by the attenuation means 10 and sent to the input point 5a, the sum of the signal level information 17 is determined to be equal to or less than the first threshold T1 (in the case of No in S114). , “Multi-channel” (parameter indicating whether the sum of the signal levels is high or low) is shifted to the next processing with the initial value “0” (level is low) (No in S114). Further, the process proceeds to S201, and the processes from S201 to S204 are continued.

Next, whether or not the difference between the current incoming level value L2 obtained in S204 and the level value L1 of the same frequency previously stored in S106 is greater than a predetermined value G (for example, 4 dB). Is determined (S205). It is determined that the difference does not exceed the predetermined value G (No in S205), and the process proceeds to the next process (S206).
Next, it is determined whether or not the level value L2 read in S203 is larger than a predetermined value P2 (for example, −2.8 dBmV) and “weak signal” is “1” (weak signal) (S206). The signal input to the input terminal 2 is determined to have no level fluctuation (in the case of No in S206), and the process proceeds to the next process (S207).

Next, the level value L2 of an arbitrary wave that has currently entered (the level value read in S203) is compared with the second threshold value T2 (for example, −1.8 dBmV). Then, it is determined whether it is equal to or lower than the second threshold T2 and the sum of the signal level information 17 is equal to or lower than the first threshold T1 (“Multi-channel” is “0”) (S207). In both comparisons, it is determined that the first threshold value T1 and the second threshold value T2 or less (Yes in S207), and the control unit 16 reduces the attenuation amount of the attenuator element toward the attenuation unit 10. A switching control signal 18 for switching to 11 (for example, attenuation: 0 dB (also referred to as through)) is output and switched (S208). The signal input to the input terminal 2 is sent to the input point 5a at the same level without being attenuated by the attenuation means 10.
Note that the results obtained in the first and third comparison steps (the sum of the signal level information is less than or equal to the first threshold value and the current incoming level value of any one of the signal level information is the first level value). The process of outputting the switching control signal 18 for switching so as to reduce the attenuation amount of the attenuator element toward the attenuating means based on the case of 2 threshold value or less) is a third process according to the claims.
Further, the results obtained in the first to third comparison steps (the sum of the signal level information is less than or equal to the first threshold value, the current incoming level value and the previously stored level value) The amount of attenuation of the attenuator element is reduced toward the attenuating means on the basis of the difference between the signal level information and the current level value of any one wave of the signal level information that is less than or equal to the second threshold value). The process of outputting a switching control signal for switching so as to be performed is a fourth process described in the claims.

As described above, if the processing procedure is set to “mode 3”, the attenuation means 10 is always used so that an excessive level signal is not input to the tuner 5 regardless of the level of the incoming signal being appropriate. Even if the level of the input signal is reduced by the above (S101), the control means 16 causes the level of the signal input to the input terminal 2 to be small (an excessive level is input by the steps S114 and S207). Therefore, in step S208, an instruction is given to switch the attenuation amount of the attenuator element in the attenuation means 10 to decrease, so that a signal of an appropriate level is input to the tuner 5. Can operate normally.

Next, regarding the operation of the control means 16 when the level of the signal input to the input terminal 2 is a low level when the cable modem is activated but then becomes an excessive level (when the input level varies). It is. Since this processing procedure is the same regardless of whether it is “default” or “mode 3”, the processing of S101 to S106, S109 to S113, and S201 to S204 is input to the input terminal 2 described above. Because the processing is the same as when the signal level is excessive, some redundant explanations have been saved.
First, the second attenuator element 12 (for example, attenuation: 10 dB) of the attenuation means 10 is set to be interposed (S101). The signal input to the input terminal 2 is attenuated by the attenuation means 10 and sent out toward the input point 5a. “Weak signal” (a parameter indicating whether or not the signal is weak) is set to “1” (weak signal) (S102). Next, the process proceeds to step S103, and the processes of S103 to S106 are subsequently performed.

Next, it is determined whether or not all the stored signal level information 17 is greater than a predetermined value P1 (for example, −7.8 dBmV) (S107). Here, it is determined that the value is equal to or less than the predetermined value P1 (in the case of No in S107), the parameter “weak signal” remains “1” and the process proceeds to the next process. Next, the process proceeds to step S109, and the processes of S109 to S113 are subsequently performed.
Next, the sum of the signal level information 17 and the first threshold value T1 (for example, the first threshold value T1: 31.0 dBmV) are compared (S114). Here, it is determined that the sum of the signal level information 17 is equal to or less than the first threshold T1 (No in S114), and “Multi-channel” (a parameter indicating whether the sum of the signal levels is high or low) is an initial value “0” (the level is low). The process proceeds to the next process (S201) while keeping (low) (S114). Subsequently, the processing of S201 to S204 is performed.

Next, in S205, it is determined whether or not the difference calculated in the process of S204 is larger than a predetermined value G (for example, 4 dB). For any one wave in the signal level information 17, the gap between the level value L1 stored in S106 and the current incoming level value L2 (the value of S203) is larger than the predetermined value G (Yes in S205). If so, the process proceeds to S101, and the processes after S101 are repeated again.

On the other hand, if the difference is equal to or smaller than the predetermined value G in S204 and S205, the process proceeds to the next process (S206).
It is determined whether or not the level value read in S203 is larger than a predetermined value P2 (for example, -2.8 dBmV) and “weak signal” is “1”. If both of the conditions are satisfied (Yes in S206: if it is determined that the signal level is weak at the time of S107 and if it is determined that the signal level of the incoming S203 is high), the process proceeds to S101. The process proceeds to step S101 and subsequent steps.

As described above, if the level of the signal input to the tuner 5 fluctuates during the calculation of the sum of the signal level information 17, for example, between 10 seconds and 20 seconds (for example, the user connects the cable modem). Even when the cable modem 1 is started up without connecting the RF connector and then connected, or when the cable modem 1 changes due to poor contact of the RF connector), the change is detected in S205 and directed to the attenuation means 10. Thus, without outputting the switching control signal 18 that decreases the attenuation amount of the attenuator element, the process proceeds to S101 and three comparison steps (S114, S205, S207) are performed. Can be prevented from being input to the tuner 5, and the tuner can be operated normally.
Furthermore, since the presence / absence of fluctuation is also determined in S206, the tuner can be operated normally by detecting the presence / absence of fluctuation with higher accuracy.
If the QAM signal is not detected after a lapse of a predetermined time after the completion of the cable modem startup process, the cable modem will be initialized. Even if the setting before restart is “mode 3”, if it is set to “default”, the attenuator element can be adjusted appropriately to suit the tuner 5 regardless of the signal level fluctuation state. A signal with a proper level is input.

Next, FIG. 5 which shows an example different from FIG. 1 in terms of switching means for a plurality of attenuator elements will be described.
Reference numerals 25, 26 and 27 denote the same damping means, first attenuator element and second attenuator element as described above. Reference numeral 28 denotes an input point from the input end 2, 29 denotes an output point to the tuner 5, 30 denotes a contact point, and a first attenuator element 26 is connected via a known coaxial relay 31 by a control signal 18 from the control means 16. The second attenuator element 27 can be selectively used at two points.
In FIG. 5, the contacts 30, 30 are provided on both sides of the attenuator element, but one of them may be short-circuited and only one contact 30 may be switched.
Further, a switching circuit constituted by a well-known FET (field effect transistor) may be used to selectively switch at two points of the first attenuator element 26 and the second attenuator element 27. Also in this embodiment, in the switching control for the switching circuit 14 by the control means 16, at least the attenuation means 10 can send the signal inputted from the input end to the next stage without interruption. It is preferable to perform switching control so that any one of the plurality of attenuator elements 26 and 27 is always present in the signal path.

Next, the CATV terminal device 50 including the cable modem 1 according to the present invention will be described in detail with reference to FIG. FIG. 7 is a schematic block diagram showing an example of the CATV terminal device 50.
The CATV terminal device 50 includes a signal distribution unit 26, a broadcast signal receiver 100, a bidirectional communication device 101, and a connection line 102 that transmits a digital signal. In the example of FIG. 7, a broadcast signal receiver 100, a bidirectional communication device 101, and a connection line 102 that transmits a digital signal are housed in one housing 51.
A CATV transmission line (not shown in the figure) drawn into the subscriber's home is connected to both the broadcast signal receiver 100 and the bidirectional communication device 101 via the input terminal 25 and the signal distribution means 26. The The signal distribution means 26 may be composed of a distribution circuit or a branch circuit.

The broadcast signal receiver 100 receives signals output from a reception processing unit (tuner) 32 and a reception processing unit 32 for selecting a desired channel from broadcast signals transmitted from a center station (not shown). 2 receives the control of the signal processing unit 37 and the reception processing unit 32 for conversion into signals handled by a television receiver not shown in FIG. 1 and the operation program of the broadcast signal receiver 100, and transmits MIB information and receives broadcast signals. It comprises a control unit 33 that performs control for performing the Internet on the device 100, and a memory 34 that stores an operation program of the broadcast signal receiver 100 and other data. In the signal input to the broadcast signal receiver 100, a desired channel is selected by the reception processing unit 32, converted into a signal handled by the television receiver by the signal processing unit 37, and output from the television connection terminal 28. .

The other output of the signal distribution means 26 is connected to the bidirectional communication device 101. The bidirectional communication device 101 includes the cable modem 1 according to the present invention and the switching hub 4. The switching hub 4 has a plurality of digital signal input / output terminals and is connected to the broadcast signal receiver 100 and an apparatus (for example, a personal computer) for performing Internet communication. Both the broadcast signal receiver 100 and the bidirectional communication device 101 are connected to the CATV transmission line, and these two devices are connected to each other via a connection line 102 for transmitting digital signals. However, even from the broadcast signal receiver 100, bidirectional communication with the inside and outside of the CATV network 10 is possible.

When the cable modem shown in the prior art is used when the CATV terminal device 50 configured in this way is considered, this cable modem is temporarily used when the attenuator element of the attenuation means 10 is switched as described above. In any case, since the signal path becomes open and the impedance changes greatly to generate noise related to the switching of the attenuator element, the signal distribution means for connecting the broadcast signal receiver 100 and the bidirectional communication device 101 is connected. Depending on the performance of the distributor / branch 26, the switching noise wraps around the video tuner on the STB side via the signal distributing means 26, thereby causing interference. Particularly, in the case of the CATV terminal device 50 in which the cable modem 1 is built in the same casing 51 as in the embodiment of FIG. 7, there is a problem that the influence is remarkable due to the fact that the routing distance is close. It was.

On the other hand, the cable modem 1 according to the present invention is configured such that the control means 16 performs switching control so as to adjust the attenuation means 10 based on the reception level information from the electric field strength measurement means 6. , Since a signal of an appropriate level is input to the tuner 5 without being affected by the input level, it has not only the feature that the startup process can be normally performed even if an abnormally high level signal is input, In addition, in the switching control for the attenuation means 10, the control means 16 can send the signal input from the input end to the next stage without interruption to the attenuation means 10. In order to be able to do so, at least one of the attenuator elements is cut off so as to be always present in the signal path. Even if the attenuation amount of the attenuating means 10 is adjusted by the control structure, the signal path is never opened, and the impedance of the attenuating means 10 may change greatly. Therefore, there is no switching noise due to the control related to the switching of the attenuator element, and the switching noise wraps around the video tuner of the two-way communication device 101 via the signal distribution means 26 and interferes with the video tuner. It has excellent advantages, such as the problem that the conventional technology does not occur, and it is possible to operate extremely stably by incorporating the cable modem 1 according to the present invention instead of the cable modem of the conventional technology. A CATV terminal device 50 that is compatible with bidirectional communication can be realized.
In the CATV terminal device 50 according to the embodiment of the present invention, the example in which the bidirectional communication device 101 is built in the same casing 51 is shown. However, the bidirectional communication device 101 is different from the casing 51. Needless to say, the same effect can be obtained even if the system is configured by the CATV terminal device 50 and the external signal distribution means 26 provided outside the housing 51 so as to be housed in the housing. .

As an application example of the attenuation means and its switching control method in the above embodiment, a cable modem as a high-frequency device and an example of a CATV terminal device provided with a cable modem have been described. Further, as in the example shown below, It goes without saying that the attenuating means and its switching control method in the above embodiment may be used as long as the high frequency device requires a wide dynamic range for incoming signals and radio waves.
For example, input level control of an RF circuit such as frequency conversion means in a high-frequency device in which dynamic level fluctuation is assumed, such as vehicle-to-vehicle communication that performs communication between a running car and a car.
Also, an RF circuit such as a frequency conversion means in a high-frequency device such as an ETC (Electronic Toll Collection System) that performs communication between an antenna installed on the road or an antenna installed in a gantry and an in-vehicle device mounted on a vehicle. Input level control.

1 is a schematic block diagram for explaining a cable modem. The flowchart for demonstrating operation | movement of a control means is shown. The flowchart for demonstrating operation | movement of a control means is shown. The flowchart for demonstrating operation | movement of a control means is shown. The schematic block diagram for demonstrating the example different from the attenuation | damping means of FIG. 1 is shown. It is a figure for demonstrating the switching timing of an attenuator element. The schematic block diagram for demonstrating a CATV terminal device is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cable modem, 2 ... Input end, 3 ... Output end, 4 ... Switching hub, 5 ... Tuner, 5a ... Input point, 5b ... Output signal, 6 ... Electric field strength measuring means (RSSI), 8 ... QAM demodulator, DESCRIPTION OF SYMBOLS 10 ... Attenuating means, 11 ... 1st attenuator element, 12 ... 2nd attenuator element, 13 ... 3rd attenuator element, 14 ... Switching circuit, 15 ... CPU, 16 ... Control means, 17 ... Signal level information, 18 ... Switching control Signal 19, processing procedure setting means 20, flash memory, 21 RAM, 25 input terminal 26 signal distribution means 28 television connection terminal 29 personal computer connection terminal 32 reception processing section 33 ... Control unit, 34 ... Memory, 37 ... Signal processing unit, 50 ... CATV terminal device, 51 ... Case, 100 ... Broadcast signal receiver, 101 ... Bidirectional communication device, 102 Connecting lines.

Claims (5)

A tuner that converts the frequency of the signal input from the input terminal and outputs it;
In a cable modem comprising a QAM demodulator that receives the output signal, demodulates and outputs the QAM,
Attenuating means having an attenuator element capable of adjusting the amount of attenuation is interposed in the signal path between the input end and the tuner,
The tuner is provided with electric field strength measuring means for measuring the level of the input signal and outputting the signal level information.
Furthermore, the signal level information measured by the electric field strength measuring means is received, data processing is performed in a predetermined processing procedure based on the signal level information, and the attenuation means is based on the result obtained by the data processing. And a control means for sending a switching control signal so that the attenuation of the attenuator element can be adjusted.
The attenuating means includes a plurality of attenuator elements and a switching means, and the attenuator elements can be selectively used by switching the switching means to be selectively usable by a switching control signal from the control means. Is configured,
In the switching control toward the attenuating means, the control means is capable of transmitting at least one of the attenuator elements so that the attenuating means can send the signal input from the input end to the next stage without interruption. A cable modem characterized in that any one attenuator element is controlled so as to be always interposed in the signal path.
The attenuation means is configured to always attenuate the input signal via the attenuator element and send it to the next stage.
The control means further outputs a switching control signal for switching so as to reduce the attenuation amount of the attenuator element toward the attenuation means, and determines whether or not the QAM demodulator is demodulating the QAM signal. While performing the 1st process which performs a judgment step,
If it is determined in the determining step that the QAM demodulator is not demodulating the QAM signal, the measured signal level information is further received, the sum of the signal level information is calculated, and the sum of the signal level information is calculated. A comparison step for comparing the first threshold with
A comparison step of comparing the current incoming level value of any one wave of the signal level information with a second threshold value;
If the sum of the signal level information is less than or equal to the first threshold and the current incoming level value of any one of the signal level information is less than or equal to the second threshold in the comparison of both the comparison steps, the attenuation means is used. The cable modem according to claim 1, wherein a third process for performing control to output a switching control signal for switching so as to reduce the attenuation amount of the attenuator element is performed.
In the control means, for any one wave in the signal level information, a comparison step is performed for comparing the level value previously stored as a target with the currently received level value. If the difference exceeds a predetermined value, the signal level information is accepted again without outputting a switching control signal for switching to reduce the attenuation of the attenuator element toward the attenuation means, and the three comparisons are performed. Perform the comparison step
The sum of signal level information is below the first threshold,
The current incoming level value of one wave of signal level information is less than or equal to the second threshold,
Switching control for switching to reduce the attenuation amount of the attenuator element toward the attenuating means when the difference between the current incoming level value and the previously stored target level value is less than a predetermined value 3. The cable modem according to claim 2, wherein a fourth process for controlling to output a signal is performed.
Furthermore, a processing procedure setting means for setting a processing procedure for the received signal reception level information is provided,
In addition to the processing procedure for performing the first processing and performing the third processing when it is determined that the QAM demodulator is not demodulating the QAM signal,
A processing procedure for performing the first processing and performing the first processing even if it is determined that the QAM demodulator is not demodulating the QAM signal;
A determination step of determining whether or not the QAM demodulator demodulates the QAM signal without outputting a switching control signal for switching the attenuation means to decrease the attenuation amount of the attenuator element is performed. And when the QAM demodulator determines that the QAM signal is not demodulated, the second processing is further performed.
Instead of the above three processing procedures, any one of the processing procedures performed directly from the third processing or the fourth processing can be selectively set.
4. The control unit according to claim 2, wherein the control unit controls to perform any one of the processing procedures based on a setting for the processing procedure setting unit. Cable modem as described in
In a CATV terminal device provided with a cable modem,
A CATV terminal apparatus comprising the cable modem according to any one of claims 1 to 4.

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