JP2672280B2 - Squelch circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a squelch circuit in a television co-listening reception amplifier.

[0002]

2. Description of the Related Art In a television receiver for co-listening, when transmitting a plurality of adjacent channels at the same time, the AGC becomes maximum when the own channel finishes broadcasting, and it interferes with other upper and lower adjacent channels. . In order to eliminate this interference, the output is usually suppressed by a squelch circuit when there is no broadcast.

However, due to the influence of adjacent channels,
The squelch circuit may malfunction. For this reason, at present, the input filter is made steep, and a filter is attached to the front stage of the squelch circuit to suppress adjacent channel waves, thereby preventing malfunction of the squelch circuit.

As described above, since the squelch circuit needs to prevent malfunction due to the influence of adjacent channels of its own channel, conventionally, a method as shown in FIGS. 4 to 6 is used.

In the system shown in FIG. 4, a squelch circuit is arranged after the output filter. That is, a TV reception signal received by a TV antenna (not shown) is distributed by a distributor (not shown), an input filter (BPF: bandpass filter) 1 for channel selection, an amplifier unit 2, an output filter 3 It is input to the squelch circuit 4 via (BPF). And this squelch circuit 4
The output of is sent to the main cable for television common listening through a synthesizer (not shown), is detected by the wave detector 5, and is input to the squelch circuit 4 as a control signal. The detector 5 detects the output signal of the squelch circuit 4 and extracts the received signal, and controls the operation of the squelch circuit 4 depending on the presence or absence of this received signal.

In the system shown in FIG. 5, a filter (BPF) 7 dedicated to each channel is inserted in the first stage of the amplifier unit 6 so as to compensate the attenuation amount of the input filter 1 and suppress adjacent channel waves next to each other. It is a thing. The amplifier unit 6 is provided with a squelch-equipped amplifier 8 at the next stage of the filter 7, a detector 9 detects the output signal of the squelch-equipped amplifier 8 to extract a reception signal, and the squelch-equipped amplifier 8 detects whether or not the reception signal is present. It controls the movement.

In the system shown in FIG. 6, a filter (BPF) 10 dedicated to each channel is provided on the input side of the detector 9 in the amplifier unit 6 instead of the filter 7.
It is designed to suppress adjacent channel waves next to each other.

[0008]

The conventional squelch circuit suppresses the adjacent channel waves of its own channel by using the method shown in FIGS. 4 to 6 and realizes the normal operation of the circuit. There is.

However, in the system shown in FIG. 4, since the squelch circuit 4 is provided separately from the amplifier unit 2,
There is a problem that the AGC control signal of the amplifier unit 2 and the control signal of the squelch circuit 4 cannot be shared, and the overall circuit configuration becomes large.

On the other hand, in the squelch circuit using the system shown in FIGS. 5 and 6, since the squelch amplifier 8 is provided in the amplifier unit 6, the AGC circuit and the squelch circuit 4 are provided.
By sharing the control signal of, the squelch circuit can be simplified. However, it is difficult to reduce the size of the amplifier unit 6 because the filter 7 or the filter 10 dedicated to the channel must be provided in the amplifier unit 6. Further, by providing the filter 7 or the filter 10 dedicated to the channel in the amplifier unit 6, there is a problem that the amplifier unit 6 is dedicated to the channel.

The present invention has been made in view of the above circumstances, and provides an squelch circuit in which an amplifier unit can be made common to each channel, productivity can be improved, and miniaturization can be achieved. To aim.

[0012]

A squelch circuit according to a first aspect of the present invention comprises an input filter for selecting a television reception signal of a designated channel from television reception signals and a signal of a reception channel selected by the input filter. An amplifier with squelch input, branching means for branching and extracting a part of the signal amplified by the squelch amplifier, a first detector for detecting the signal branched by the branching means, and the first The difference between the video signal and the audio signal of the receiving channel is 4.5M among the signals detected by the detector of
A band pass filter for extracting a beat signal of Hz, and a second detector for detecting a 4.5 MHz beat signal output from the band pass filter and extracting a DC component for use as a squelch control signal of the amplifier with squelch. A squelch circuit comprising:

A squelch circuit according to a second aspect of the present invention is an input filter for selecting a television reception signal of a designated channel from television reception signals and an amplifier with a squelch to which a signal of the reception channel selected by the input filter is input. A branching means for branching and extracting a part of the signal amplified by the squelch amplifier, a first detector for detecting the signal branched by the branching means, and an output signal of the first detector. The above amplifier with squelch is used to
C control means, a bandpass filter for extracting a beat signal of 4.5 MHz which is the difference between the video signal and the audio signal of the receiving channel from the signal detected by the first detector, and this bandpass filter Output 4.
A squelch circuit comprising: a second detector that detects a 5 MHz beat signal, extracts a DC component, and uses it as a squelch control signal for the amplifier with squelch.

A squelch circuit according to a third aspect of the present invention is an input filter for selecting a television reception signal of a designated channel from television reception signals, and an amplifier with squelch to which the signal of the reception channel selected by the input filter is input. A branching means for branching and extracting a part of the signal amplified by the squelch amplifier, a first detector for detecting the signal branched by the branching means, and a detector for detecting the signal by the first detector. A bandpass filter for extracting a beat signal of 4.5 MHz, which is the difference between the video signal and the audio signal of the reception channel, from the received signal, and the 4.5 MHz beat signal output from this bandpass filter is detected to detect a DC component. Is used to perform squelch and AGC control of the squelch-equipped amplifier using the output signal of the second detector. Squelch circuit, characterized by comprising a Nau means.

[0015]

The television reception signal selected by the input filter is amplified by the amplifier with squelch, a part of the signal is branched by the branching means, and the signal is detected by the first wave detector. The signal detected by the first detector has a frequency of 4.5M which is the difference frequency between the video signal and the audio signal of the receiving channel.
Since the beat signal of Hz is included, this 4.5 MHz beat signal is taken out by a 4.5 MHz band pass filter. 4.5MH output from this bandpass filter
The beat signal of z is detected by the second detector to extract the DC component, and is input to the amplifier with squelch as a squelch control signal. In this case, since the second detector outputs a high signal of a certain level or higher while receiving the broadcast signal of the self-channel, the squelch amplifier performs a normal amplification operation.

However, when the broadcast signal of the self channel ends, the beat signal of 4.5 MHz disappears, so that the output signal of the second detector becomes a signal of zero or a very small level, and the output of the amplifier with squelch is output. It is forbidden.

Further, the AGC control for the amplifier with squelch is performed by using the output signal of the first detector or the output signal of the second detector. As described above, by controlling the squelch circuit by using the distortion signal of 4.5 MHz which is the difference component between the video signal and the audio signal, the input filter can be made steep, or the channel dedicated filter can be provided in the preceding stage of the squelch circuit. It is possible to perform a stable squelch operation without providing the. Further, it becomes possible to share the control signal for the squelch circuit and the AGC circuit, and the overall size can be reduced.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing the configuration of a television co-listening receiving amplifier for one channel according to the first embodiment of the present invention.

In FIG. 1, reference numeral 11 is an input filter for channel selection, and a TV reception signal (not shown) received by a TV antenna is distributed by a distributor and input. The reception signal of the predetermined channel selected by the input filter 11 is input to the amplifier unit 12, and the output of the amplifier unit 12 is extracted via the output filter 13. The input filter 11 and the output filter 13 are composed of a BPF (bandpass filter) that selects a specific channel. Then, the signals extracted from the output filter 13 for each channel are combined by a combiner (not shown) and output to the TV common listening main cable.

The amplifier unit 12 includes an amplifier 21 with a squelch to which the signal from the input filter 11 is input, and the output of the amplifier 21 with a squelch is sent to the output filter 13 via a branching means, for example, a branch transformer 22. , A part thereof is branched by the branch transformer 22 and input to the squelch high frequency amplifier 23 and the AGC high frequency amplifier 31.

The signal amplified by the high frequency amplifier 23 is detected by a 4.5 MHz beat generating detector 24 using, for example, a diode and input to a 4.5 MHz band pass filter (BPF) 25. The output signal of the bandpass filter 25 is the squelch detector 26.
The signal is detected as a DC component and is amplified as a DC component by the DC amplifier 27 and input to the squelch amplifier 21 as a squelch control signal. This squelch amplifier 2
No. 1 performs a normal amplification operation if the squelch control signal output from the DC amplifier 27 is equal to or higher than the set level, and stops the signal output if the squelch control signal is smaller than the set level.

The signal amplified by the AGC high-frequency amplifier 31 is detected by the AGC control signal detector 32, amplified by the DC amplifier 33, and input to the squelch amplifier 21 as an AGC control signal.

Next, the operation of the above embodiment will be described. The signal input from the input filter 11 to the amplifier unit 12 is amplified by the squelch amplifier 21 and then output to the output filter 13 via the branch transformer 22.
A part thereof is branched by the branch transformer 22 and input to the squelch high frequency amplifier 23 and the AGC high frequency amplifier 31 and amplified. The signal amplified by the AGC high-frequency amplifier 31 is detected by the AGC control signal detector 32, amplified by the DC amplifier 33, and input to the squelch amplifier 21 as an AGC control signal.

On the other hand, the squelch high-frequency amplifier 23 has a high amplification factor and amplifies the signal branched by the branch transformer 22 to a sufficiently high level, that is, to the saturation region of the detector 24. By thus amplifying the signal branched by the branch transformer 22 to the saturation region of the detector 24 and detecting it, a distortion signal of a frequency difference component between the video signal and the audio signal of the TV reception signal, that is, 4.5 MHz.
The beat signal of is efficiently generated. This 4.5MHz
The beat signal is a 4.5MHz bandpass filter 2
The unnecessary component is removed at 5, and the direct current component is extracted at the detector 26. The detection output of the detector 26 is DC-amplified by the DC amplifier 27 and input to the squelch amplifier 21 as a squelch control signal. In this case, when the broadcast signal of the self channel is being received, the DC amplifier 27 outputs a high signal of a certain level or higher, so that the squelch amplifier 21 performs a normal amplification operation.

However, when the broadcast signal of the self-channel is completed, the beat signal of 4.5 MHz disappears, so that the output signal of the DC amplifier 27 becomes zero or a very small level signal, and the output of the squelch amplifier 21 is prohibited. It

As described above, by controlling the squelch circuit by using the distortion signal of 4.5 MHz which is the difference component between the video signal and the audio signal, the input filter 11 can be made steep, or the squelch circuit can be provided in the preceding stage. A stable squelch operation can be performed without providing a channel-dedicated filter (BPF). Therefore, the amplifier unit 1
Even if a squelch circuit is provided in the channel 2, the amplifier unit 12 can be shared for each channel and the productivity can be improved.

As the 4.5 MHz beat generating detector 24 in the above embodiment, various methods such as a method using a mixer can be used in addition to diode detection.

(Second Embodiment) FIG. 2 is a block diagram showing the configuration of the second embodiment of the present invention. In this second embodiment,
In the first embodiment shown in FIG. 1, the signal branched by the branch transformer 22 for AGC control is amplified by the AGC high-frequency amplifier 31, and then the AGC control signal detector 32.
Detected by, and the detected output is amplified by the DC amplifier 33 and A
It outputs to the amplifier 21 with a squelch as a signal for GC.
In this case, the amplification degree of the amplifier 31 is lowered and the AGC control signal detector 32 is operated in the non-saturation region, that is, the linear region. Even when the AGC control signal detector 32 is operated in the non-saturation region, a 4.5 MHz beat signal is generated in the state where the TV signal is being received. After being extracted by the bandpass filter 25, amplified by the high frequency amplifier 34, it is detected by the squelch detector 26 and input to the squelch amplifier 21 as a squelch control signal.
The rest of the configuration is the same as that of the first embodiment, so a detailed description is omitted.

With the above structure, the control signals of the AGC circuit and the squelch circuit can be shared. (Third Embodiment) FIG. 3 is a block diagram showing the configuration of the third embodiment of the present invention.

This third embodiment is the same as the second embodiment shown in FIG. 2 except that the detection output of the detector 26 is amplified by the DC amplifier 27 to be used as a squelch control signal and used as an AGC signal. Is. The rest of the configuration is the same as that of the second embodiment, so detailed description will be omitted.

With the above configuration, the DC amplifier 33 in FIG. 2 can be omitted, and the control signals of the squelch circuit and the AGC circuit can be shared as in the second embodiment.

[0032]

As described above in detail, according to the present invention, since the squelch circuit is controlled by using the beat signal of 4.5 MHz which is the difference component between the video signal and the audio signal, the front stage of the amplifier unit is controlled. It is possible to perform stable squelch operation without making the input filter provided in the input device steep or without providing a channel-dedicated filter in the preceding stage of the squelch circuit. Therefore, even if the squelch circuit is provided in the amplifier unit, the amplifier unit can be shared for each channel, and the productivity can be improved. Further, it becomes possible to share the control signal for the squelch circuit and the AGC circuit, and the overall size can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a squelch circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a squelch circuit according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a squelch circuit according to a third embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration example of a conventional squelch circuit.

FIG. 5 is a block diagram showing another configuration example of a conventional squelch circuit.

FIG. 6 is a block diagram showing still another configuration example of a conventional squelch circuit.

[Explanation of symbols]

 11 Input Filter 12 Amplifier Unit 13 Output Filter 21 Amplifier with Squelch 22 Branch Transformer 23 High Frequency Amplifier 24 4.5 MHz Beat Generation Detector 25 25 MHz Band Pass Filter (BPF) 26 Squelch Detector 27 DC Amplifier 31 High Frequency Amplifier 32 AGC control signal detector 33 DC amplifier 34 High frequency amplifier

Claims (3)

(57) [Claims] 1. An input filter for selecting a television reception signal of a designated channel from television reception signals, a squelch amplifier to which a signal of a reception channel selected by the input filter is input, and an amplification by the squelch amplifier. Branching means for branching and extracting a part of the generated signal,
A first detector for detecting the signal branched by the branching means, and a difference of 4.5 between the video signal and the audio signal of the receiving channel among the signals detected by the first detector.
A bandpass filter that extracts the beat signal of MHz,
A squelch circuit comprising a second detector for detecting a 4.5 MHz beat signal output from the bandpass filter, extracting a DC component, and using the detected squelch control signal as a squelch control signal. 2. An input filter for selecting a television reception signal of a designated channel from among television reception signals, an amplifier with a squelch into which a signal of a reception channel selected by this input filter is input, and an amplifier with this squelch amplifier. Branching means for branching and extracting a part of the generated signal,
A first detector for detecting the signal branched by the branching means, a means for AGC controlling the amplifier with squelch using an output signal of the first detector, and a detector for detecting the signal by the first detector. A bandpass filter for extracting a beat signal of 4.5 MHz, which is the difference between the video signal and the audio signal of the reception channel, from the received signal, and the 4.5 MHz beat signal output from this bandpass filter is detected to detect a DC component. And a second wave detector for taking out as a squelch control signal for the amplifier with squelch, and a squelch circuit. 3. An input filter for selecting a television reception signal of a designated channel from television reception signals, an amplifier with a squelch into which a signal of a reception channel selected by this input filter is input, and an amplifier with this squelch amplifier. Branching means for branching and extracting a part of the generated signal,
A first detector for detecting the signal branched by the branching means, and a difference of 4.5 between the video signal and the audio signal of the reception channel among the signals detected by the first detector.
A bandpass filter that extracts the beat signal of MHz,
A second detector for detecting a 4.5 MHz beat signal output from the band pass filter to extract a DC component, and squelch and AGC control of the squelch amplifier using the output signal of the second detector. A squelch circuit comprising: