JPH11252524A - Amplifier for catv - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable output without deteriorating distortion by controlling a first variable equalizer and/or a second variable equalizing part based on the level of a pilot signal extracted by a signal extracting part. SOLUTION: A gain adjusting part 6 is provided with a BPF 61, a control part 64, a wave detecting part 63, the first variable equalizer 65, the second variable equalizing part 66, etc. The equalizer 65 is arranged between a standard adjusting part 4 and a preamplifier 5 and adjusts the level of a CATV signal adjusted by the part 4 to a prescribed level to output toward a next stage. The part 64 compares the level of a pilot signal extracted by the BPF 61 and detected by a detecting part 63 with a prescribed reference level and controls the equalizer 65 and/or the equalizing part 66 according to this comparing result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV amplifier connected to a communication line of a CATV system, and more particularly to a CATV amplifier having a feature of adjusting an input level to a preamplifier inside a CATV amplifier.

[0002]

2. Description of the Related Art Generally, in a CATV system,
A CATV signal (a video signal and an audio signal are collectively referred to as a "CATV signal"; the same applies hereinafter) transmitted from the center device is output to terminals such as dwelling units through a communication line such as a coaxial cable. The communication line has C at predetermined intervals.
An ATV amplifier is connected, and the signal to be transmitted is gain-adjusted so that it is transmitted to the terminal without any loss (when simply referred to as “CATV amplifier”, the CATV signal for the downstream signal is used). Amplifier, CA for upstream signal
It includes a TV amplifier and a CATV amplifier for upstream and downstream signals, and can amplify a CATV signal in an arbitrary frequency band. same as below. However, in the following, CAT
It is assumed that the frequency band of the V signal is 70 to 770 MHz).

FIG. 2 shows an example of such a conventional CATV amplifier. In FIG. 2, 1 is an input terminal, 2 is an output terminal, 3 and 10 are HPF (high-pass filter, the same applies hereinafter) or LPF (low-pass filter, the same applies hereinafter),
4 is a standard input adjustment unit, 51 is a pre-amplification unit, 60 is a gain adjustment unit (AGC unit), 7 is a TILT unit, 8 is a final stage amplification unit,
9 is a branch part.

The CATV signal input from the input terminal 1 is narrowed down to a predetermined frequency range by an HPF or LPF (HPF for downstream signal amplification, LPF for upstream signal amplification). And the signal is pseudo-attenuated to the standard input level via the equalizer (or attenuator) 42. The signal is amplified to a predetermined level by the preamplifier 51 and the final-stage amplifier 8, and the TI
The slope is corrected by the LT unit 7. And again HP
The frequency is narrowed down to a predetermined frequency range by the F or LPF 10 (HPF for amplifying the downstream signal and LPF for amplifying the upstream signal), and output from the output terminal 2.

[0005] Here, the gain adjustment unit 60 is provided when the level of the communication line on the input side changes due to temperature characteristics or the like, or when the fixed gain of the preamplifier 51 or the final stage amplifier 8 changes due to temperature change or the like. The output level is kept constant by adjusting the change. For this reason, the CATV signal branched by the branching unit 9 is input to the gain adjusting unit 60, and the CAT
770M which is a high frequency part of the V signal having a large loss change
Only signals around Hz are extracted as pilot signals by a BPF (Band Pass Filter, the same applies hereinafter) 61,
The pilot signal is amplified by a pilot signal amplifier 62 having a fixed gain. The amplified pilot signal is detected by the detection unit 63, the signal is converted into a DC voltage, and then input to the control unit 640.

The control section 640 adjusts the CATV signal from the preamplifier section 51 to the final-stage amplifier section 8, and first determines the level of the pilot signal with respect to a predetermined reference level.
The variable equalizer 660 is controlled according to this determination. FIG. 5 is a characteristic diagram of the variable equalizer 660. As shown in FIG. 5, the conventional variable equalizer 660 has a standard attenuation of -6 dB.
(STD in FIG. 5), the maximum attenuation is -12 dB (MIN in FIG. 5), the minimum attenuation is 0 dB (MAX in FIG. 5), and if the pilot signal level is the same as the reference level, the CATV signal is standardly attenuated. The amount was attenuated by -6 dB.

If the level of the pilot signal is higher than the reference level, the CATV signal is further attenuated from the standard attenuation according to the degree (the maximum attenuation -12d when the level of the pilot signal is +6 dB with respect to the reference level).
B), if lower than the reference level, depending on the degree, CAT
The V signal was attenuated less than the standard attenuation (the minimum attenuation was 0 dB when the pilot signal level was -6 dB relative to the reference level). As a result, the output level of the CATV signal output from the CATV amplifier is maintained at the standard level. In the description of the characteristics of the variable equalizer, when the term “attenuation” is simply used, the attenuation at the highest frequency, ie, 770 MHz, will be described, and the overall characteristics will be referred to as the cable loss Δf characteristics. It is assumed that a standard input loss of about -1.5 dB occurs in the variable equalizer.
Note that dB is decibel. same as below.

[0008]

However, in the conventional CATV amplifier as described above, the variable equalizer 660 is arranged only between the preamplifier 51 and the rear amplifier 8, and the input of the CATV signal is performed. Even if the level is higher than the standard level, the unadjusted CATV signal is input to the preamplifier 51 as it is. Here, since the preamplifier 51 has a fixed gain, CA higher than the standard level is used.
When a TV signal is input, the distortion generated at that time is worse than the distortion generated when a standard-level CATV signal is input. However, even in such a case, since it is necessary to obtain a prescribed distortion value, it is necessary to improve the distortion characteristics of the preamplifier 51, that is, to provide the preamplifier 51 with high output. there were. This has contributed to an increase in the cost of the CATV amplifier as a whole.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the conventional CATV amplifier. Even if the input level of the CATV signal fluctuates without providing a high-output preamplifier, the present invention has been made. It is an object of the present invention to provide a CATV amplifier that can be adjusted to obtain a stable output without deteriorating the signal.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, according to the present invention, a standard input connected to a communication line of a CATV and adjusting the level of an arbitrary CATV signal to a standard level is provided. CATV amplifier comprising: an adjustment unit; a preamplifier for amplifying the CATV signal adjusted by the standard input adjustment unit; and a final-stage amplifying unit for amplifying the CATV signal amplified by the preamplifier. A first variable equalizer disposed between the standard input adjustment unit and the preamplifier, for adjusting the level of the CATV signal adjusted by the standard input adjustment unit to a predetermined level and transmitting the adjusted signal; A second variable equivalent unit that is arranged between the preamplifier and the final-stage amplifying unit, adjusts the level of the CATV signal amplified by the preamplifier to a predetermined level, and transmits the adjusted signal; Amplified by the final stage amplification unit A signal extractor for extracting a pilot signal of a predetermined frequency from an ATV signal, and a controller for controlling a first variable equalizer and / or a second variable equalizer based on the level of the pilot signal extracted by the signal extractor. Is provided.

The present invention described in claim 2 provides the present invention according to claim 1.
In the present invention described in the, the control unit of the gain adjustment unit,
When the level of the pilot signal extracted by the signal extraction unit is higher than a predetermined reference level, the attenuation of the CATV signal in the first variable equivalent unit is set to be equal to or more than a predetermined standard attenuation, and CAT in variable equivalent part
When the attenuation amount of the V signal is a predetermined standard attenuation amount and the level of the pilot signal extracted by the signal extracting unit is lower than a predetermined reference level, the attenuation of the CATV signal in the first variable equivalent unit is reduced. The amount is set to a predetermined standard attenuation amount, and the attenuation amount of the CATV signal in the second variable equivalent unit is set to be equal to or less than the predetermined standard attenuation amount.

The present invention according to claim 3 provides the present invention according to claim 2.
In the present invention, the predetermined standard attenuation amount in the first variable equivalent unit is 0 dB.

[0013]

An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an overall circuit diagram of a CATV amplifier according to the present embodiment, FIG. 3 is a characteristic diagram of a first variable equalizer 65, and FIG.
FIG. In the description of the present embodiment, the same components as those of the conventional CATV amplifier shown in FIG.

As shown in FIG. 1, the CATV amplifier of this embodiment has an input terminal 1, an output terminal 2, an HPF or an LPF.
3, a standard input adjustment unit 4, a preamplification unit 5, a gain adjustment unit 6, a TILT unit 7, a final stage amplification unit 8, and a branch unit 9.

The CATV input from the input terminal 1
The signal is narrowed down to a predetermined frequency range by the HPF or LPF 3, and is pseudo-attenuated to the standard input level via the pseudo line 41 and the equalizer (or attenuator) 42 of the standard input adjustment unit 4. And the preamplifier 5 and / or the final amplifier 8
Is amplified to a predetermined level by the
The slope is corrected by the section 7. Then, the frequency is again narrowed down to a predetermined frequency range by the HPF or LPF 10 and output from the output terminal 2.

Here, the gain adjusting section 6 for adjusting the level of the CATV signal includes a BPF 61, a pilot signal amplifying section 62, a detecting section 63, a control section 64, and a first variable equivalent section 65.
And a second variable equivalent section 66. Among them, the BPF 61, the pilot signal amplifying section 62, the detecting section 6
Reference numeral 3 is the same as in the gain adjustment section of the conventional CATV amplifier. That is, the BPF 61 includes the final-stage amplifier 6
6 is a signal extractor for extracting a pilot signal of a predetermined frequency from the CATV signal amplified by the pilot signal amplifier 6. A pilot signal amplifier 62 amplifies the pilot signal extracted by the BPF 61 to a signal of a predetermined level, and a detector 63. Detects the pilot signal amplified by the pilot signal amplifier 62.

On the other hand, the control section 64 has different control contents from the control section of the gain control section of the conventional CATV amplifier, and the second variable equivalent section 66 has different characteristics from the variable equivalent section of the conventional gain control section. The first variable equivalent section 65 is not provided in the conventional gain adjustment section. Hereinafter, the characteristics of the first variable equivalent unit 65 and the second variable equivalent unit 66, the control contents of the control unit 64, and the like will be described.

The control unit 64 first compares the level of the pilot signal extracted by the BPF 61 and detected by the detection unit 63 with a predetermined reference level. The first variable equivalent section 65 and / or the second variable equivalent section 66 are controlled according to the comparison result. The details of this control will be described later.

As shown in FIG. 1, the first variable equivalent section 65 is disposed between the standard input adjustment section 4 and the preamplifier 5, and the level of the CATV signal adjusted by the standard input adjustment section 4. Is adjusted to a predetermined level and output to the next stage. As shown in FIG. 3, the characteristics of the first variable equivalent unit 65 are such that the standard attenuation is 0 dB (STD in FIG. 3) and the maximum attenuation is -6 dB (MIN in FIG. 3). If the level of the pilot signal is equal to or lower than the reference level, a standard attenuation amount of 0 dB is controlled by the control unit 64 described later.
Is applied to pass the CATV signal without attenuation except for the standard input loss. On the other hand, if the level is higher than the reference level, an amount of attenuation equal to or higher than the standard attenuation corresponding to the degree of the higher level is applied by the control of the control unit 64 described later,
Pilot signal level is +6 dB relative to reference level
, The maximum attenuation -6 dB is applied and the CAT
The V signal is attenuated by -6 dB and passed.

As shown in FIG. 1, the second variable equivalent section 66 is provided between the preamplifier 5 and the final amplifier 8 (more specifically, between the preamplifier 5 and the TILT section 7). ), And the level of the CATV signal amplified by the preamplifier 5 is adjusted to a predetermined level and transmitted to the next stage. As shown in FIG. 4, the characteristic of the second variable equivalent section 66 is such that the standard attenuation is-
6 dB (STD in the figure), the minimum attenuation is 0 dB
(MAX in the figure). If the level of the pilot signal is equal to or higher than the reference level, the standard attenuation is applied under the control of the control unit 64, which will be described later.
The ATV signal is attenuated by -6 dB and passed. On the other hand, if the pilot signal level is lower than the reference level, an amount of attenuation equal to or less than the standard attenuation amount corresponding to the lower level is applied by the control of the control unit 64, which will be described below. Applies a minimum attenuation of 0 dB, and passes the CATV signal without attenuation except for the standard input loss.

With these configurations, the CATV signal input to the present amplifier is adjusted as follows. First, the CATV signal input from the input terminal 1 is HPF or LPF3.
Then, the signal is sequentially input to the first variable equalizer 65 to the final stage amplifier 8 through the standard input adjustment unit 4. At the beginning of input,
In the first variable equalizer 65 and the second variable equalizer 66, attenuation by the standard attenuation is performed.

When the CATV signal is input to the splitter 9, the pilot signal is extracted and detected as described above, and the control section 64 compares the pilot signal level with a predetermined reference level. Here, when the level of the pilot signal is equal to or lower than the reference level, the first variable equivalent section 65 is controlled so as not to attenuate the CATV signal. That is, the standard attenuation 0 dB is applied as the attenuation of the first variable equivalent section 65. Further, in this case, the attenuation of the second variable equivalent section 66 is reduced according to the degree to which the level of the pilot signal is low, and when the pilot signal is -6 dB with respect to the reference level, the minimum attenuation of 0 dB is applied. According to such control, when the level of the pilot signal is equal to or lower than the reference level, the CATV signal is not attenuated by the first variable equivalent unit 65, but is attenuated only by the second variable equivalent unit 66 as in the related art. You.

On the other hand, when the level of the pilot signal is equal to or higher than the reference level, the first variable equivalent section 65 is controlled so as to attenuate the CATV signal. That is, as the attenuation of the first variable equivalent section 65, the attenuation of the first variable equivalent section 65 is increased according to the level of the pilot signal. When the pilot signal is +6 dB with respect to the reference level, the maximum is obtained. An attenuation of -6 dB is applied. In this case, the second
The standard attenuation amount of -6 dB is applied as the attenuation amount of the variable equivalent unit 66. According to such control, when the level of the pilot signal is equal to or higher than the reference level, the CATV signal is attenuated by the first variable equivalent unit 65 before being sent to the preamplifier 5. Therefore, it is possible to prevent distortion in the preamplifier 5 from deteriorating.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea. is there. For example, the frequency range to be amplified by the present amplifier may be any range, and in the above embodiment, C
Although the input level of the ATV signal is set to ± 6 dB, the present invention is not limited to this, and a CATV signal of an arbitrary range of levels may be input. The standard attenuation of the first variable equalizer is 0
It may be other than dB.

[0025]

As described above, the present invention according to claims 1 to 3 is arranged between a standard input adjustment unit and a pre-amplification unit, and is used for converting a CATV signal adjusted by the standard input adjustment unit. A first variable equalizer that adjusts the level to a predetermined level and transmits the same, and a CATV signal that is arranged between the preamplifier and the final-stage amplifier and that is amplified by the preamplifier to a predetermined level. A second variable equalizer that adjusts and sends the signal; and a controller that controls the first variable equalizer and / or the second variable equalizer based on the level of the pilot signal extracted by the signal extractor. For example, even when the pilot signal level is equal to or higher than the reference level, the level of the CATV signal sent to the preamplifier can be adjusted in advance, and a stable output can be obtained without deteriorating the distortion in the preamplifier. be able to. Therefore, a high output preamplifier is not required, and the manufacturing cost of the entire amplifier can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall circuit diagram of a CATV amplifier according to an embodiment of the present invention.

FIG. 2 is an overall circuit diagram of a conventional CATV amplifier.

FIG. 3 is a characteristic diagram of the first variable equalizer 65 of FIG.

FIG. 4 is a characteristic diagram of a second variable equalizer 66 of FIG. 1;

FIG. 5 is a characteristic diagram of the variable equalizer 660 of FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 input terminal 2 output terminal 3, 10 HPF or LPF 4 standard input adjustment unit 5, 51 preamplification unit 6, 60 gain adjustment unit 7 TILT unit 8 final stage amplification unit 9 branch unit 41 pseudo line 42 equalizer or attenuator 64 , 640 control unit 65 first variable equalizer 66 second variable equalizer 660 variable equalizer

Claims (3)

[Claims] 1. A standard input adjustment unit connected to a communication line of a CATV, for adjusting the level of an arbitrary CATV signal to a standard level, and a preamplifier for amplifying the CATV signal adjusted by the standard input adjustment unit. And a final-stage amplifier for amplifying the CATV signal amplified by the preamplifier, the CATV amplifier being provided between the standard input adjustment unit and the preamplifier, A first variable equalizer that adjusts the level of the CATV signal adjusted by the standard input adjustment unit to a predetermined level and sends the adjusted signal, and is disposed between the preamplifier and the final-stage amplifier, A second variable equivalent section for adjusting the level of the CATV signal amplified by the preamplifier to a predetermined level and transmitting the adjusted signal, and extracting a pilot signal of a predetermined frequency from the CATV signal amplified by the final-stage amplifier Signal extraction And a control unit that controls the first variable equalizer and / or the second variable equivalent unit based on the level of the pilot signal extracted by the signal extraction unit. CATV amplifier. 2. The control section of the gain adjusting section, wherein when the level of the pilot signal extracted by the signal extracting section is higher than a predetermined reference level, the amount of attenuation of the CATV signal in the first variable equivalent section. Is equal to or more than a predetermined standard attenuation, and the CAT in the second variable equivalent section is
When the attenuation amount of the V signal is a predetermined standard attenuation amount and the level of the pilot signal extracted by the signal extracting unit is lower than a predetermined reference level, the attenuation of the CATV signal in the first variable equivalent unit is reduced. 2. The CATV amplifier according to claim 1, wherein the amount is a predetermined standard attenuation amount, and an attenuation amount of the CATV signal in the second variable equivalent section is equal to or less than a predetermined standard attenuation amount. 3. The CATV amplifier according to claim 2, wherein the predetermined standard attenuation in said first variable equivalent section is 0 dB.