JPH05328238A - Television reception circuit - Google Patents

Abstract

PURPOSE:To provide the television reception circuit stopping an automatic channel selection operation of a television tuner only when a signal channel having an electric field strength in a normal strength by the television tuner is received. CONSTITUTION:The television reception circuit including a television tuner 1 capable of automatic channel selection, an intermediate frequency circuit 2, a detection circuit 3 and an audio signal amplifier circuit 6 is provided with a synchronizing signal detection circuit 7 detecting a synchronizing signal from a composite video signal obtained by the intermediate frequency circuit 2 and generating a synchronizing signal detection signal at the detection of the synchronizing signal and a noise signal amplifier circuit 8 extracting a noise signal from the audio signal obtained by the detection circuit 3, converting the noise signal into a DC and generating an inverted noise DC voltage through inversion and the automatic channel selection of the television tuner 1 is stopped through the coincidence between the synchronizing signal detection signal and the inverted noise DC voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiving circuit for automatically selecting a channel, and more particularly, in the case of normal reception when a composite video signal is present and a noise signal component is not present in an audio signal. The present invention relates to a television receiving circuit that stops an automatic tuning operation.

[0002]

2. Description of the Related Art Conventionally, in a television receiver provided with a television tuner capable of automatically selecting a channel, particularly in a vehicle-mounted television receiver, a sync signal is detected from a composite video signal obtained by an intermediate frequency circuit. An automatic channel selection means is used which stops the automatic channel channel selection operation in the television tuner by using a synchronization signal detection signal obtained during this detection. According to the automatic channel selection means, when the sync signal cannot be detected from the composite video signal obtained by the intermediate frequency circuit, the automatic channel channel selection operation in the television tuner is continued to generate the composite video signal. If a synchronization signal can be detected from the, the automatic tuning operation of the signal channel in the television tuner is stopped, and the signal channel automatically selected at this time is continuously received in the television tuner. It is a thing.

In addition to this, an on-vehicle television receiver is used when a car moves to a position far away from a transmitting station of a received television signal due to traveling of the car, or when the car enters a tunnel. As described above, when the electric field strength of the television radio wave being received suddenly changes, the audio signal amplifying circuit of the television receiver is appropriately muted, and a mute means for preventing a discontinuous tone from being emitted is provided. ing.

By the way, FIG. 3 is a block diagram showing a conventional television receiving circuit provided with the above-described muting means.

In FIG. 3, 21 is a television tuner, 22 is an intermediate frequency circuit, 23 is a detection circuit, 24 is a noise canceller circuit, 25 is a multiplex circuit, 2
6 is an audio signal amplifier circuit, 27 is an AGC signal amplifier circuit, 2
Reference numeral 8 is an operational amplifier, 29 is a reference voltage source, and 30 is a receiving antenna.

Then, the receiving antenna 30 is connected to the input end of the television tuner 21, and the input end of the intermediate frequency circuit 22 is connected to the output end thereof. The output end of the intermediate frequency circuit 22 is connected to the input end of the detection circuit 23, and the detection circuit 2
The input end of the noise canceller circuit 24 is connected to the output end of the noise canceller circuit 3. The output end of the noise canceller circuit 24 is connected to the input end of the multiplex circuit 25, and the output end of the multiplex circuit 25 is connected to the input end of the audio signal amplifier circuit 26. Further, the AGC signal amplifier circuit 27 includes an operational amplifier 28 and a 29 reference voltage source connected to its non-inverting input terminal, the inverting input terminal of the operational amplifier 28 is connected to the intermediate frequency circuit 22, and the output terminal of the operational amplifier 28 is It is connected to the audio signal amplifier circuit 26.

The television receiving circuit having the above structure is
The following operations are performed.

[0008] The television tuner 21 selects a desired signal channel in the television radio waves received by the receiving antenna 30, and then converts a radio frequency (RF) signal corresponding to the desired signal channel into an intermediate frequency signal. The converted signal is supplied to the intermediate frequency circuit 22. The intermediate frequency circuit 22 band-amplifies the intermediate frequency signal and supplies it to the subsequent detection circuit 23. The detection circuit 23 detects the intermediate frequency signal and reproduces the composite video signal and the audio signal. The noise canceller circuit 24 removes a noise signal component from the reproduced audio signal and supplies it to the multiplex circuit 25. The multiplex circuit 25 demodulates the audio signal from which the noise signal component has been removed into an audio stereo signal, and supplies the audio stereo signal to the audio signal amplification circuit 26. The audio signal amplifier circuit 26 amplifies the demodulated audio stereo signal and supplies it to a speaker or the like (not shown). Further, the automatic gain control (AGC) signal amplification circuit 27 performs a voltage comparison between the composite video signal obtained by the intermediate frequency circuit 22 and the reference voltage (Vo) obtained by the reference voltage source 29, and the comparison signal is The mute execution signal is supplied to the control terminal CT of the audio signal amplifier circuit 26. In this case, corresponding to the size of the mute execution signal,
The operation of the audio signal amplification circuit 26 is switched to the audio stereo signal amplification state or the mute state.

Now, when the level of the video signal supplied to the AGC signal amplifying circuit 27 is relatively high, that is, when the electric field strength of the television signal of the receiving signal channel is relatively strong, the output of the AGC signal amplifying circuit 27. Since the comparison signal (mute execution signal) obtained at 1 becomes small, the audio signal amplification circuit 26 is switched to the audio stereo signal amplification state, and the audio signal amplification circuit 26 amplifies the input audio stereo signal, It is sent to a speaker.

On the other hand, when the level of the video signal supplied to the AGC signal amplifier circuit 27 is low, or when the level of the video signal is close to zero, that is, the electric field strength of the television signal of the reception signal channel is high. When it is considerably weak, the comparison signal (mute execution signal) obtained at the output of the AGC signal amplifying circuit 27 becomes a level close to the reference voltage (Vo) obtained by the reference voltage source 29, so that the audio signal amplifying circuit 26 becomes an audio stereo. Switched to the signal mute state, the audio signal amplifier circuit 26 blocks the input audio stereo signal without amplifying it, and enters the signal mute state.

[0011]

However, the automatic tuning means of the conventional vehicle-mounted television receiver, based on the detection or non-detection of the synchronization signal in the composite video signal,
Since it is to stop or continue automatic tuning of the television tuner, it is adjacent to a signal channel where the electric field strength of the television radio wave is considerably weak or its electric field strength is close to zero (hereinafter referred to as weak small non-selected channel). Then, the signal channel (hereinafter,
In the case where there is a strong adjacent channel), a part of the signal of the strong adjacent channel is captured by the television tuner when the weak non-tuned channel is automatically selected. Then, when the signal of the strong adjacent channel is taken in by the television tuner, the synchronizing signal in the signal is detected in the intermediate frequency circuit, so that the television tuner is at the time of automatic tuning of the weak non-tuned channel. Even if there is, it will erroneously stop the tuning operation. As described above, the automatic channel selection means has a problem that the television tuner causes a malfunction when the strong adjacent channel exists.

Further, the muting means of the conventional vehicle-mounted television receiver sets whether or not to mute the audio stereo signal in the audio signal amplifier circuit based on the composite video signal obtained by the intermediate frequency circuit. However, since the variable range of the composite video signal is quite limited, it is difficult to set whether or not to execute the mute.

Here, if an audio signal is used instead of the composite video signal, the audio signal is a received radio wave such that the video screen becomes invisible on the display unit such as a display from the level when the electric field strength of the received radio wave is the maximum. In theory, a practical mute characteristic can be obtained because the level smoothly changes to the level when the field strength is weak, but in the actual television receiving circuit, the limiter circuit inserted in the intermediate frequency circuit is used. Since the level change of the audio signal is limited, even when the audio signal is used, it is still difficult to set execution or non-execution of the mute as in the case of using the composite video signal. is there.

The present invention eliminates the above-mentioned problems, and the first object of the present invention is to eliminate the above-mentioned problems only when a signal channel having a normal electric field strength is received in a television tuner. An object of the present invention is to provide a television receiving circuit that stops the automatic tuning operation of the television tuner.

A second object of the present invention is to provide a television receiving circuit which can easily set execution or non-execution of mute in an audio signal amplifier circuit.

[0016]

In order to achieve the first object, the present invention includes at least a television tuner capable of automatic channel selection, an intermediate frequency circuit, a detection circuit, and an audio signal amplification circuit. In a television receiving circuit including, a sync signal detection circuit for detecting a sync signal from the composite video signal obtained by the intermediate frequency circuit, and generating a sync signal detection signal when the sync signal is detected; A noise signal is extracted from the extracted voice signal, the extracted noise signal is converted into a direct current and then inverted, and a noise signal amplifier circuit that generates an inverted noise direct current voltage is provided, and the synchronization signal detection signal and the inversion are provided. A first means is provided for stopping the automatic channel selection operation of the television tuner when it coincides with the noise DC voltage.

Further, in order to achieve the second object,
According to the present invention, the audio signal amplifier circuit includes a mute means, and second means for operating the mute means when the inverted noise direct current voltage from the noise signal amplifier circuit is equal to or lower than a predetermined level.

[0018]

According to the first means, the sync signal detection circuit detects the sync signal from the composite video signal obtained by the intermediate frequency circuit, and the noise signal amplification circuit is obtained by the detection circuit. The noise signal component is extracted from the voice signal. Then, when the sync signal is detected by the sync signal detection circuit and the noise signal component is not extracted by the noise signal amplification circuit, that is, the signal channel having a normal electric field strength is received by the television tuner. Only when this occurs, a tuning stop signal for stopping the automatic tuning operation of the television tuner is generated. Therefore, the automatic tuning operation of the television tuner can be stopped only when the signal channel having the normal electric field strength is received, and the malfunction of the television tuner during the automatic tuning can be prevented. be able to.

According to the second means, when the inverted noise direct current voltage obtained by the noise signal amplifier circuit is used and the inverted noise direct current voltage is lowered to a predetermined level or lower, for example, a television. The mute means of the audio signal amplifying circuit is operated when the electric field strength of the radio wave of the signal channel being received by the tuner sharply decreases. Since the inverted noise DC voltage is significantly changed in response to the variation in the electric field strength of the radio wave of the signal channel being received, the operation of the mute means of the audio signal amplification circuit is started. It becomes possible to appropriately select the inversion noise direct current voltage level. Therefore, the setting of execution or non-execution of mute in the audio signal amplifier circuit is very flexible, and the setting of execution or non-execution of mute can be easily performed.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a television receiving circuit according to the present invention.

In FIG. 1, 1 is a television tuner, 2 is an intermediate frequency circuit, 3 is a detection circuit, 4 is a noise canceller circuit, 5 is a multiplex circuit, 6 is an audio signal amplifier circuit, 7 is a noise signal amplifier circuit, Reference numeral 8 is a synchronization signal detection circuit, 9 is a determination circuit (NAND gate circuit), and 10 is a receiving antenna.

Then, the television tuner 1 at least R amplifies the received radio frequency (RF) signal.
An F signal amplification section and a tuner section for selecting an RF signal of a desired signal channel and converting the selected RF signal into an intermediate frequency signal. The tuner section has a function of automatically selecting a signal channel. is there. A receiving antenna 10 is connected to the input end of the television tuner 1, and an input end of the intermediate frequency circuit 2 is connected to the output end thereof.
The output end of the intermediate frequency circuit 2 is connected to the input end of the detection circuit 3, and the output end of the detection circuit 3 is connected to the input end of the noise canceller circuit 4. The output end of the noise canceller circuit 4 is connected to the input end of the multiplex circuit 5, and the output end of the multiplex circuit 5 is connected to the input end of the audio signal amplification circuit 6. Here, the audio signal amplification circuit 6 has a mute means, and the mute means performs the mute operation only when the mute execution signal is supplied to the control terminal CT. The input end of the noise signal amplification circuit 7 is connected to the output end of the detection circuit 3, and the output end of the noise signal amplification circuit 7 is connected to the control end of the audio signal amplification circuit 6 and one input of the NAND gate circuit 9. It The input end of the sync signal detection circuit 8 is connected to the intermediate frequency circuit 2, and the output end thereof is connected to the other input of the NAND gate circuit 9. The output end of the NAND gate circuit 9 is connected to the control end of the television tuner 1.

FIG. 2 is a circuit configuration diagram showing an example of a concrete circuit configuration of the noise signal amplifier circuit 7 used in the embodiment of FIG.

In FIG. 2, 11 is a first operational amplifier,
12 is a second operational amplifier, 13 is a reference power supply, 14 is an input noise signal selection filter, 15 is a voltage doubler rectifier circuit, 16 is a negative feedback circuit of the first operational amplifier 11, 17 is a negative feedback circuit of the second operational amplifier 12. Is.

The first operational amplifier 11 has a negative feedback circuit 16 composed of two resistors, and the second operational amplifier 12 has a negative feedback circuit 17 composed of two resistors and one capacitor. ing. Input noise signal selection filter 1
Reference numeral 4 is composed of one series resistor and one capacitor and one shunt resonance circuit, and is connected between the output end of the detection circuit 3 and the non-inverting input of the first operational amplifier 11. The voltage doubler rectifier circuit 15 includes two diodes and a resistor, and is connected between the output of the first operational amplifier 11 and the inverting input of the second operational amplifier 12. Reference power supply 13
Are connected between the non-inverting input of the second operational amplifier 12 and ground.

Here, the operation of this embodiment will be described with reference to FIG.

The television tuner 1 sequentially tunes RF signals of a plurality of signal channels received by the receiving antenna 10 in a tuner section having an automatic channel selection function. When a tuning stop signal is supplied, the R of the signal channel selected at that time
After that, the F signal is maintained and selected. Then, the selected RF signal is converted into an intermediate frequency signal in the tuner section and supplied to the next intermediate frequency circuit 2. Next, the intermediate frequency circuit 2 band-amplifies this intermediate frequency signal and supplies it to the subsequent detection circuit 3, and also branches and extracts only the composite video signal and supplies it to the synchronization signal detection circuit 8. Subsequently, the detection circuit 3 detects the applied intermediate frequency signal and reproduces the composite video signal and the audio signal. At this time,
The reproduced audio signal is supplied to the noise canceller circuit 4 and also to the noise signal amplifier circuit 7.
Next, the noise canceller circuit 4 removes the noise signal component from the reproduced audio signal and supplies only the audio signal to the multiplex circuit 5. Then, the multiplex circuit 5 demodulates the applied audio signal into an audio stereo signal and supplies the demodulated audio stereo signal to the audio signal amplifier circuit 6. Next, the audio signal amplifier circuit 6 operates so as to amplify the demodulated audio stereo signal and supply the audio stereo signal to a speaker (not shown) or the like. When a signal is supplied, the demodulated audio stereo signal is muted by the operation of the mute means and is not supplied to the speaker or the like.

When the noise signal amplifier circuit 7 receives the reproduced voice signal from the output terminal of the detector circuit 3,
First, the input noise signal selection filter 14 extracts only the noise signal component contained in the reproduced audio signal, and then the first operational amplifier 11 amplifies the extracted noise signal, and further Voltage rectifier circuit 15
At, the amplified noise signal is subjected to voltage doubler rectification and converted into a noise DC voltage proportional to the noise signal level. Next, in the second operational amplifier 12, the noise DC voltage is compared with the reference voltage Vo from the reference power supply 13, and an inverted noise DC voltage is generated at the output. The inversion noise direct current voltage obtained here is supplied to the control terminal CT of the audio signal amplifier circuit 6 as the mute execution signal and also to one input of the NAND gate circuit 9.

When the sync signal detection circuit 8 receives the branched and extracted composite video signal, the sync signal detection circuit 8 detects the sync signal therein and generates a sync signal detection signal when the sync signal is detected. .. In this case, the sync signal detection signal is supplied to the other input of the NAND gate circuit 9.

Now, when the television tuner 1 is performing an automatic channel selection operation, when the level of the RF signal of the signal channel currently undergoing automatic channel selection is relatively high, that is, the received signal channel. When the electric field strength of the television radio wave corresponding to is relatively strong, the level of the noise extraction signal extracted by the input noise signal selection filter 14 of the noise signal amplification circuit 7 is small, so the noise signal amplification circuit 7 Output of the reference voltage V
Since the inverted noise direct current voltage substantially equal to o is obtained and the synchronizing signal detecting circuit 8 detects the synchronizing signal, a synchronizing signal detecting signal is generated at the output of the synchronizing signal detecting circuit 8. At this time, the NAND gate circuit 9 receives an inversion noise direct current voltage substantially equal to the reference voltage Vo at one input,
The sync signal detection signal is supplied to the other input, respectively, and the matching condition as the NAND gate is satisfied, so that the inverted matching signal is generated at the output of the NAND gate circuit 9. Next, this inverted coincidence signal is supplied as a tuning stop signal to the television tuner 1 to stop its automatic tuning operation. Therefore, in the television tuner 1, the RF of the signal channel for which automatic tuning is currently being performed is performed.
The signal will continue to be selected.

On the other hand, the inversion noise DC conversion voltage, which is substantially equal to the reference voltage Vo, is also supplied to the control terminal CT of the audio signal amplifier circuit 6, but the inversion noise DC conversion voltage (reference voltage V
Since o) is a positive voltage having a predetermined magnitude, the mute means of the audio signal amplifier circuit 6 does not operate, and the audio stereo signal input to the audio signal amplifier circuit 6 is amplified and then the speaker or the like. , And is normally vocalized there.

Next, in the television tuner 1, 1
When the RF signal of one signal channel is continuously selected and the electric field strength of the radio wave of the one signal channel is suddenly weakened, extraction is performed by the input noise signal selection filter 14 of the noise signal amplification circuit 7. Since the noise extraction signal generated suddenly increases, the output voltage of the noise signal amplifying circuit 7 changes to an inversion noise DC conversion voltage or a negative polarity inversion noise DC conversion voltage that is considerably smaller than the reference voltage Vo. Further, since the sync signal detection circuit 8 does not detect the sync signal, the sync signal detection signal generated at the output of the sync signal detection circuit 8 disappears. Therefore, the NAND gate circuit 9 cannot meet the matching condition at the two inputs, and
The inverted coincidence signal generated in the output of the gate circuit 9 disappears, and along with the disappearance of the inverted coincidence signal, the tuning stop signal supplied to the television tuner 1 also disappears, and the television tuner 1 automatically selects. The station operation will be restarted.

Further, the control terminal CT of the audio signal amplifier circuit 6
Is supplied with an inversion noise DC conversion voltage that is considerably smaller than the reference voltage Vo or a negative polarity inversion noise DC conversion voltage as a mute execution signal.
The muting means is put into a mute state, the audio stereo signal inputted to the audio signal amplifying circuit 6 is not amplified, the supply to the speaker is stopped, and the television receiving circuit becomes silent.

Then, after the television tuner 1 restarts the automatic channel selection operation, the television tuner 1 is restarted.
In, when the electric field strength of the radio wave of the received signal channel is strong and an RF signal having a relatively large level is automatically selected, the automatic tuning operation in the television tuner 1 is performed by the same operation as the above operation. Stopped,
In the television tuner 1, the RF signal of the signal channel is continuously selected.

In the above description, when the television tuner 1 continuously selects the RF signal of one signal channel, the electric field strength of the radio wave of the one signal channel sharply decreases. The behavior of the case is not limited to such a case, for example ,.
If the audio signal of the signal channel being received is at an almost normal level but the level of the composite video signal decreases ,. When the voice level of the voice signal of the signal channel being received is not so lowered, but the noise signal is considerably included ,. In the case where the sync signal in the composite video signal is extremely disturbed due to some cause and becomes out of sync, etc., as in the case described above, the NA
Since the ND gate circuit 9 does not satisfy the matching condition at the two inputs, the tuning stop signal supplied to the television tuner 1 disappears, and the automatic tuning operation is restarted in the television tuner 1. Become. In any of the above cases, if the automatic tuning operation in the television tuner 1 is restarted, the control terminal CT of the audio signal amplifying circuit 6 has an inverted noise direct current voltage much smaller than the reference voltage Vo or a negative voltage. Since the reverse noise direct current DC voltage is supplied as the mute execution signal, the mute means of the audio signal amplifier circuit 6 is in the mute state.

As described above, according to the present embodiment, in the television tuner 1 capable of automatic channel selection, only when the signal channel having the normal electric field strength is received, the television tuner 1 is automatically operated. Since the tuning operation is stopped, the automatic tuning of the television tuner 1 can be accurately executed regardless of the electric field strength of the radio wave of the adjacent signal channel. It is possible to prevent malfunction during automatic channel selection operation.

Further, according to the present embodiment, the noise signal extracted by the noise signal amplification circuit 7 which greatly changes in response to the variation of the electric field strength of the radio wave of the signal channel being received is Since the mute means of the audio signal amplifier circuit 6 is operated by using the inverted noise direct current voltage which is inverted after the direct current is converted, the level of the inverted noise direct current voltage for starting the operation of the mute means is changed. It becomes possible to select appropriately, and the setting of execution or non-execution of the mute in the audio signal amplifier circuit 6 becomes very flexible, and the execution or non-execution of the mute can be easily set. It is a thing.

[0039]

As described above, according to the present invention,
In a television tuner capable of automatic tuning, the automatic tuning operation of the television tuner is stopped only when a signal channel having a normal electric field strength is received. There is an effect that the automatic tuning of the television tuner can be accurately executed regardless of the strength of the electric field strength of the radio wave, and the malfunction in the automatic tuning operation of the television tuner can be prevented.

Further, according to the present invention, the inversion noise direct current voltage obtained by the noise signal amplifier circuit, which greatly changes corresponding to the variation of the electric field strength of the radio wave of the signal channel being received, is used. Since the mute means of the audio signal amplifier circuit is operated, it is possible to appropriately select the level of the inversion noise direct current voltage for starting the operation of the mute means. The non-execution setting becomes very flexible, and there is an effect that the execution or non-execution setting of the mute can be easily performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a television receiving circuit according to the present invention.

FIG. 2 is a circuit configuration diagram showing a specific example of a noise signal amplifier circuit used in the embodiment of FIG.

FIG. 3 is a block diagram showing an example of a conventional television receiving circuit having a mute means.

[Explanation of symbols]

 1 Television Tuner 2 Intermediate Frequency Circuit 3 Detection Circuit 4 Noise Canceller Circuit 5 Multiplex Circuit 6 Audio Signal Amplification Circuit 7 Noise Signal Amplification Circuit 8 Synchronous Signal Detection Circuit 9 Judgment Circuit (NAND Gate Circuit) 10 Reception Antenna 11 First Operational Amplifier 12 Second operational amplifier 13 Reference power supply 14 Input noise signal selection filter 15 Double voltage rectifier circuit 16 Negative feedback circuit of first operational amplifier 11 17 Negative feedback circuit of second operational amplifier 12

Claims (2)

[Claims] 1. A television receiver circuit comprising at least a television tuner capable of automatic channel selection, an intermediate frequency circuit, a detection circuit, and an audio signal amplifier circuit, and a composite video image obtained by the intermediate frequency circuit. A sync signal detection circuit that detects a sync signal from a signal and generates a sync signal detection signal when the sync signal is detected, and a noise signal is extracted from the voice signal obtained by the detection circuit, and the extracted noise signal is converted to a direct current. And a noise signal amplifying circuit for generating an inversion noise DC voltage, and stopping the automatic tuning operation of the television tuner when the sync signal detection signal and the inversion noise DC voltage match. A television receiving circuit characterized by: 2. The audio frequency amplifier circuit includes a mute means, and the mute means is operated when the inverted noise direct current voltage from the noise signal amplifier circuit is below a predetermined level. 1. The television receiving circuit according to 1.