JPH06260954A - Television signal receiver - Google Patents

Abstract

PURPOSE:To provide a TV signal receiver which can eliminate the buzz disturbance due to the video signals. CONSTITUTION:A TV signal receiver contains a tuner 1 which inputs the received signals of a TV broadcast for selection of the frequency and outputs the received signals after amplifying and converting them into the intermediate frequency signals. Then an AGC 13 inputs the audio intermediate frequency signals transmitted through a BPF 11 to an audio receiver system as the gain control voltage to be applied to the tuner 1 and then generates the AGC voltage. In such a constitution, the AGC voltage generated based on only the receiving level of an audio signal component can be supplied with no intervention of the video signals. Thus it is possible to eliminate the modulation caused to the high frequency signals by the video signals and also to prevent the buzz interference.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a television signal receiver.

[0002]

2. Description of the Related Art A conventional television signal receiver has a tuner 71 as shown in the block diagram of FIG.
And BPF (bandpass filter: hereinafter referred to as BPF) 7
2, 74 and 81, a video amplification circuit 73, a video demodulation circuit 75, a phase comparison circuit 76, an LPF (low pass filter: hereinafter referred to as LPF) 77, a VCO (voltage controlled oscillator: hereinafter referred to as VCO). 78), an AGC (automatic gain control circuit: hereinafter referred to as AGC) 79, a MIX (frequency conversion circuit: hereinafter referred to as MIX) 80, a limiter amplifier 82, and a voice demodulation circuit 83. The received signal in the UHF band or the VHF band received is
The signal is input from the input terminal 97 to the tuner 71, frequency-selected and amplified, and the frequency is converted to an intermediate frequency. One is input as an image intermediate frequency signal to the image amplification circuit 73 via the BPF 72, and the other is an audio intermediate. The frequency signal is input to the MIX 80 via the BPF 74. The video intermediate frequency signal is amplified by the video amplification circuit 73, and then the video demodulation circuit 75 and the phase comparison circuit 7
6 is input. In the phase comparison circuit 76, the phase difference between the video intermediate frequency signal and the oscillation signal of the VCO is detected by multiplication, and the phase difference signal is input to the VCO 78 as a frequency control signal for the VCO 78 via the LPF 77. To be done. As a result, the video amplifier circuit 7
3 forms a phase synchronization system corresponding to the video intermediate frequency signal, the phase of the VCO 78 is synchronized with the phase of the video intermediate frequency signal, and its oscillation frequency is equal to the frequency of the video intermediate frequency signal. Becomes

In the video demodulation circuit 75, the video intermediate frequency signal input from the video amplification circuit 73 is VCO7.
8 is synchronously detected by the oscillation signal input from
The video signal output is output via the video output terminal 98. In the current terrestrial television broadcasting, the video signal is broadcast as an amplitude-modulated wave with respect to the carrier. Therefore, the AGC 79 is required to demodulate the video signal without distortion in a wide electric field strength range. , This A
The gain control signal generated and output by the GC 79 controls the gains of the tuner 71 and the video amplification circuit 73.

On the other hand, the audio intermediate frequency signal input to the MIX 80 via the BPF 74 is converted into an audio intermediate frequency signal by multiplication with the oscillation frequency of the VCO 78 in the MIX 80, and input to the limiter amplifier 82 via the BPF 81. It Then, it is amplified in the limiter amplifier 82 and demodulated in the sound in the sound demodulation circuit 83, and the sound signal output is output through the sound output terminal 99.

[0005]

In the above-mentioned conventional television signal receiver, the gain control function for the tuner has the same function as that of the gain control for the video amplifier circuit. Since the gain control signal generated by referring to the level is used,
The video signal, especially the vertical sync signal with a low frequency, is superimposed on the gain control signal for the tuner.
The audio high frequency signal is in a state of being modulated by the vertical synchronizing signal, and noise called buzz is generated at the audio output terminal, which deteriorates the sound quality of the receiver.

[0006]

A television signal receiver of the present invention receives a television broadcast reception signal to select a frequency,
In a television signal receiver including a tuner that amplifies the received signal and converts it into an intermediate frequency signal for output, as a gain control voltage for the tuner, refer only to the reception level of an audio signal component included in the received signal. AGC configured to supply the generated AGC voltage
At least a circuit is provided.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. As shown in FIG. 1, in this embodiment, a tuner 1, BPFs 2, 3 and 11 and a video amplifier circuit 4 are provided.
, Video demodulation circuit 5, phase comparison circuit 6, and LPF 7
, VCO8, AGC9 and 13, and MIX10
And a limiter amplifier 12 and a voice demodulation circuit 14. The received signal in the UHF band or the VHF band received is input to the tuner 1 through the input terminal 91, frequency-selected and amplified, and the frequency is converted into an intermediate frequency, one of which is a BPF as a video intermediate frequency signal.
2 is input to the video amplifier circuit 4 and the other is input to the MIX 10 as an audio intermediate frequency signal via the BPF 3. The video intermediate frequency signal is amplified by the video amplifier circuit 4, and then the video demodulation circuit 5 and the phase comparison circuit 6
Entered in. In the phase comparison circuit 6, the phase difference between the video intermediate frequency signal and the oscillation signal of the VCO 8 is detected by multiplication, and the phase difference signal is detected by the VCO 8 as a frequency control signal for the VCO 8 via the LPF 7.
8 is input. As a result, a phase synchronization system corresponding to the video intermediate frequency signal output from the video amplification circuit 4 is formed, the phase of the VCO 8 is synchronized with the phase of the video intermediate frequency signal, and the oscillation frequency thereof is the video intermediate frequency signal. The frequency is equal to the frequency of the signal.

In the video demodulation circuit 5, the video intermediate frequency signal input from the video amplification circuit 4 is synchronously detected by the oscillation signal input from the VCO 8, and the video signal output is output via the video output terminal 92. Is output. Then, as in the case of the above-mentioned conventional example, in order to suppress the distortion generated corresponding to the received signal level, the gain control signal generated and output in the AGC 9 is supplied to the video signal amplifier circuit 4. It is supplied to the video amplifier circuit 4.

On the other hand, the audio intermediate frequency signal input to the MIX 10 via the BPF 3 is V in the MIX 10.
It is converted into an audio intermediate frequency signal by multiplication with the oscillation signal of CO8, and is input to the limiter amplifier 12 and AGC 13 via the BPF 11. The audio intermediate frequency signal amplified by the limiter amplifier 12 is the audio demodulation circuit 1
4 is demodulated, and the audio signal output is output via the audio output terminal 93. In addition, in this embodiment,
Unlike the case of the conventional example described above, the gain control for the tuner 1 is performed by the gain control signal generated by referring to the input level of the audio intermediate frequency signal output from the BPF 11. This is the feature of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the AGC 13 shown in FIG. 1 and includes resistors 21-23, 26, 27, and
36, 37, 39, 40, 45, 46, 51, 52, 5
5, 61-64 and NPN transistors 24, 25, 3
0-35, 53, 54, 59, 60, PNP transistors 41, 42, 47-50, and voltage sources 28, 56, 5
8, 65, constant current sources 29, 38, 43, 57, and a capacitor 44.

In FIG. 2, the audio intermediate frequency signal input from the input terminal 94 includes the first NPN transistors 24 and 25, the resistors 26 and 27, the current source 29 and the like.
Differential amplifier circuit and NPN transistors 34 and 3
5, to the second differential amplifier circuit including resistors 36 and 37, current source 38 and the like. The output current of the second differential amplifier circuit is switched by the output voltage of the first differential amplifier circuit, and the audio intermediate frequency signal is input to NPN transistors 30, 31, 32 and 33. It is detected synchronously. The synchronous detection current output from the collectors of the NPN transistors 31 and 33 via this synchronous detection action is inverted by the current mirror circuit formed by the PNP transistors 41 and 42 and the resistors 39 and 40, and further the constant current source. The difference is made with the current of 43, and the voltage is converted by the resistor 55 and output. The detected output voltage output from the resistor 55 is smoothed by the capacitor 44 connected to the terminal 95 and input to the differential amplifier circuit formed by the NPN transistors 53 and 54. The voltage sources 56 and 58 are bias voltage supply sources for the NPN transistors 53 and 54, and the resistor 55 forms a bias resistor. In this state, when the base potential of the NPN transistor 53 is lower than the base potential of the NPN transistor 54, the potential of the output terminal 96 rises to almost the power source potential, and the base potential of the NPN transistor 53 is higher than that of the NPN transistor 54. When it is higher than the base potential, the potential of the output terminal 96 drops to approximately the ground potential. By utilizing such a change in the detected output voltage, the voltage of the voltage sources 55 and 58 functioning as a bias power source for the NPN transistors 53 and 54 is set to an appropriate voltage level to output from the output terminal 96. The detected detection output voltage can be supplied to the tuner 1 as a gain control voltage.

As described above, by using the gain control voltage generated by referring to the level of the audio intermediate frequency signal as the gain control voltage for the tuner 1, the received high frequency signal generated in the tuner 1 is modulated by the video signal. The effect is completely eliminated.

[0014]

As described above, according to the present invention, the gain control by the AGC for the tuner is performed by using the gain control voltage generated by referring to the reception level of the audio intermediate frequency signal. There is an effect that it is possible to significantly improve the quality of audio output by eliminating the modulation interference caused by the signal into the high frequency reception signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing one embodiment of AGC for the tuner of this embodiment.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

1, 71 Tuner 2, 3, 11, 72, 74, 81 BPF 4, 73 Video amplification circuit 5, 75 Video demodulation circuit 6, 76 Phase comparison circuit 7, 77 LPF 8, 78 VCO 9, 13, 79 AGC 10, 80 MIX 12, 82 Limiter amplifier 14, 83 Audio demodulation circuit 21-23, 26, 27, 36, 37, 39, 40, 4
5, 46, 51, 52, 55, 61-64 Resistance 24, 25, 30-35, 53, 54, 59, 60
NPN transistor 28, 56, 58, 65 Voltage source 29, 38, 43, 57 Constant current source 41, 42, 47-50 PNP transistor 44 Capacitor

Claims (1)

[Claims] 1. A television signal receiver including a tuner for inputting a reception signal of a television broadcast, selecting a frequency, amplifying the reception signal, converting the reception signal to an intermediate frequency signal and outputting the intermediate frequency signal, as a gain control voltage for the tuner. A television signal receiver comprising at least an AGC circuit configured to supply an AGC voltage generated by referring to only a reception level of an audio signal component included in the reception signal.