JPH1169333A - Reception amplifier for catv - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CATV reception amplifier which can be used even in a place where the fluctuation of a reception level is large by automatically switching an attenuator with simple circuit constitution. SOLUTION: The CATV reception amplifier is provided with an amplifier circuit 2 with AGC, which amplifies a signal from a switch-type input attenuator 1 that can switch attenuation quantity, detects a part of the amplified signal, sets it to be a feedback voltage V1 , compares the feedback voltage V1 with a reference voltage V0 , outputs an AGC voltage V2 and varies the amplification gain of the signal with AGC voltage V2 on the signal input side. In such a case, a switch 3 changes over the attenuation quantity of the input attenuator 1 and attenuation quantity is changed over by the switch 3 in response to the level of feedback voltage V1 or AGC voltage V2 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV receiving amplifier installed at a receiving point or a head end of a CATV system.

[0002]

2. Description of the Related Art As shown in FIG. 2, a signal received by a receiving antenna A is amplified for each channel at a receiving point and a head end of a CATV system. The ratio is adjusted, and the output of each channel is adjusted to a specified tilt characteristic.
, A receiving amplifier C for sending the signal to the receiver. As the receiving point amplifier C, there is a wide band type which amplifies a plurality of channels collectively, in contrast to a channel only type which amplifies a signal for each channel.

A receiving amplifier C shown in FIG. 2 is a conventional example of a channel-only type having only a signal amplifying function. An input attenuator D is provided on a signal input side, and an amplifying circuit E with an AGC is provided at a subsequent stage. ing. Further, a band-pass filter F for passing a signal of a desired channel is provided at a stage before the attenuator D and a stage after the amplifying circuit B, respectively. The input attenuator D can manually set the attenuation amount to 0 dB or 10 dB, and can attenuate the input signal by 0 dB or 10 dB and input the signal to the amplifier circuit E. The amplification circuit E
Then, the output of the input attenuator D is amplified, a part of the amplified signal is internally branched and detected, and a feedback voltage is generated. The feedback voltage is compared with a reference voltage to generate an AGC voltage. By controlling a PIN attenuator (not shown) provided inside the amplifier circuit with a voltage, the gain is decreased when the level of the input signal is high, and the gain is increased when the level of the input signal is low, so that the input signal having a level variation can be reduced. Output with the level stabilized.

[0004]

In the CATV receiving amplifier, even if the input level of the received signal fluctuates, the AGC function of the amplifying circuit E allows the signal level to fluctuate within ± 10d.
If it is about B, the output level is kept constant, so if the level of the received signal is checked at the start of operation of the system and the attenuator D is set to an appropriate amount of attenuation, then the setting will be changed You don't have to do much. However, when the reception level fluctuates greatly due to the fading phenomenon of the atmosphere or the like, it is necessary to adjust the signal level by switching the amount of attenuation of the attenuator D while measuring the signal level with a measuring instrument such as a spectrum analyzer. However, the attenuator D has a problem that the switching of the amount of attenuation cannot be performed quickly because the amount of attenuation is manually changed, and that the signal level cannot be switched at an appropriate timing unless the signal level is separately monitored and monitored by an operator. was there. Therefore, a headend could not be installed in an area where the reception level fluctuates greatly due to the fading phenomenon.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a CATV receiving amplifier which enables automatic switching of an attenuator with a simple circuit configuration and can be used even in an area where the reception level varies greatly. .

As shown in FIG. 1, the CATV receiving amplifier of the present invention amplifies a signal from a switchable input attenuator 1 capable of switching an amount of attenuation to a signal input side, and a part of the amplified signal. Is detected as a feedback voltage V1, the feedback voltage V1 is compared with a reference voltage V0, an AGC voltage V2 is output, and an amplification circuit 2 with an AGC is provided which varies the amplification gain of the signal with the AGC voltage V2. In the CATV receiving amplifier, the amount of attenuation of the input attenuator 1 can be switched by the switch 3, and the amount of attenuation can be switched by the switch 3 according to the level of the feedback voltage V1 or the AGC voltage V2. It is characterized by the following.

[0007]

Embodiment 1 FIG. 1 shows an embodiment of a CATV receiving amplifier according to the present invention, which comprises a switching type attenuator 1 in which the amount of attenuation can be switched by a switch 3 on the signal input side. An amplifying circuit 2 with AGC is provided after the switchable attenuator 1, and a band-pass filter 11 is provided before and after the amplifying circuit 2.

The AGC-equipped amplification circuit 2 includes first and second
And a gain adjusting circuit (PIN attenuator) 15 between the first and second amplifying units 12 and 13. The splitter 1 is provided downstream of the second amplifying unit 13.
6 is provided. An AGC feedback circuit including a detector 18 and an arithmetic circuit (comparator) 19 is provided between the splitter 16 and the gain adjustment circuit 15.
The input signal branched at 6 is amplified by the amplifier 17 and the detector 1
8, a feedback voltage V1 corresponding to the signal level of the input signal is generated, and the feedback voltage V1 is compared with a reference voltage in an arithmetic circuit 19 to obtain an AGC voltage V2.
The C voltage V2 is applied to the gain adjustment circuit 15, and the amplification circuit 2
Stabilizes the output level of the input signal that is amplified by. In this case, the feedback voltage V1 increases as the signal level at the branching device 16 increases, and decreases as the signal level decreases.
2 is such that it decreases when the signal level increases, and increases when the signal level decreases.

The switchable attenuator 1 has an attenuation of 0 dB.
And a fixed attenuator 21 having an attenuation of 10 dB
And these can be switched by the switch 3. The switch 3 allows the arithmetic circuit (comparator) 22 to process the feedback voltage V1 generated by the AGC function of the amplifier circuit 2 so that the arithmetic circuit 22 can switch the feedback voltage V1.
That is, by utilizing the signal level detection function of the AGC in the amplifier circuit 2, the amount of attenuation corresponding to the level of the input signal can be automatically selected. Specifically, when the level of the input signal exceeds the specified value, the fixed attenuator 21 having the attenuation of 10 dB is selected, and when the level does not exceed the specified value, the attenuation is 0 d.
The B through circuit 20 is selected. Note that the switching of the switch 3 may be performed by using the AGC voltage V2 generated by the AGC function, processing the AGC voltage V2 by another arithmetic circuit, and performing switching by the same arithmetic circuit.

The above is an example of a channel-only receiving amplifier having a signal amplifying function. The receiving amplifier includes a channel converting function, a video / audio carrier wave level ratio adjusting function, and an output of each channel. Some receiving amplifiers have a function of adjusting the tilt characteristics to a specified value. In these receiving amplifiers, the attenuation of the switching attenuator 1 can be switched using the feedback voltage V1 or the AGC voltage V2 of the AGC-equipped amplifier circuit 2.

In the CATV receiving amplifier according to the present invention, a plurality of fixed attenuators are provided in the input attenuator 1, and the plurality of attenuators and the through circuit can be selected by a switch. By providing many fixed attenuators with different attenuation,
Distortion or NP like PIN attenuator used in AGC section
It is also possible to omit non-linear elements that cause deterioration, and to configure an amplifier with less distortion. Or AG
It is also possible to reduce the occurrence of distortion and the like by narrowing the width of the gain adjustment function in the C section. Further, a fixed attenuator 24 may be provided at a stage further preceding the input attenuator 1.

[0012]

According to the CATV receiving amplifier of the present invention, the following effects can be obtained. 1. Since the amount of attenuation of the input attenuator 1 is switched using the AGC function, the circuit configuration is not complicated and the cost is low compared with the conventional one. 2. A good retransmission signal can be output even if the receiver is installed in a location where the fluctuation of the reception level is large. 3. By limiting the gain adjustment range by AGC,
Generation of distortion due to a non-linear element such as a PIN attenuator can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of a CATV receiving amplifier of the present invention.

FIG. 2 is a schematic diagram showing an example of a conventional CATV receiving amplifier.

[Explanation of symbols]

 1 input attenuator 2 amplifying circuit 3 switch

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 5/52 H04N 5/52

Claims (1)

[Claims] 1. A signal from a switchable input attenuator (1) capable of switching an amount of attenuation to a signal input side is amplified, and a part of the amplified signal is detected to obtain a feedback voltage V1. A CATV provided with an AGC-equipped amplifier circuit (2) for comparing the voltage V1 with a reference voltage V0 to output an AGC voltage V2 and varying the amplification gain of the signal with the AGC voltage V2.
In the receiving amplifier for use, the amount of attenuation of the input attenuator (1) can be switched by a switch (3), and the amount of attenuation can be switched by the switch (3) according to the level of the feedback voltage V1 or the AGC voltage V2. A receiving amplifier for CATV, characterized in that the receiving amplifier can be used.