JPS6113665B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a color television receiver;
In particular, the present invention relates to a color television receiver having a video input terminal for inputting a video signal other than the video signal received and detected by the receiver.

Figure 1 is a block wiring diagram showing the parts related to video signals in such a conventional color television receiver. 1 is a tuner, 2 is a video intermediate frequency amplification circuit, and an automatic fine tuning circuit (hereinafter abbreviated as AFT circuit). ) 21 is included in the intermediate frequency amplification circuit 2. 3
4 is a video amplifier circuit, and a synchronization separation circuit 41 is included in the video amplifier circuit 4. 5 is a cathode ray tube circuit, 6 is a detection circuit, 7 is a tuning circuit, 8 is a so-called defect voltage signal line,
9 is the error voltage signal line from the AFT circuit 21, 1
0 is a video signal input terminal.

If an error occurs in the local oscillation frequency of the tuner 1 for some reason while continuously receiving broadcasts from the same transmitting station (not shown), the error will occur in the intermediate frequency input to the intermediate frequency amplifier circuit 2. This error is detected by the AFT circuit 21 and becomes an error voltage, which is applied to the tuner 1 via the tuning circuit 7 to feedback-control the local oscillation frequency of the tuner 1 to maintain correct tuning.

When attempting to receive a channel with a frequency adjacent to the frequency of the channel currently being received, the detection circuit 6
When a deficit voltage is applied to the tuning circuit 7 via the signal line 8 or directly, the error voltage is ignored by this deficit voltage, and the voltage that selects the channel of the above-mentioned adjacent frequency is sent from the tuning circuit 7 to the tuner 1. is input.

Furthermore, even if a certain channel is selected, if the television broadcast waves on that channel are absent or weak, there will be no output from the sync separator circuit 41, and the detection circuit 6 will detect the sync signal output from the sync separator circuit 41. When the presence is detected, a defective voltage is output on the signal line 8, and the tuning circuit 7 inputs a voltage to the tuner 1 to select a channel of an adjacent frequency.

Although automatic channel selection is performed as described above, a video signal other than the video signal amplified and detected by the intermediate frequency amplifier circuit 2 may be input from the terminal 10 and displayed by the cathode ray tube circuit 5. In this case, the switch 3 inputs the video signal from the terminal 10 to the video amplifier circuit 4. In order for the video signal from the terminal 10 to be displayed normally by the cathode ray tube circuit 5, this video signal contains a synchronization signal, but during the transition when the switch 3 is switched, the output of the synchronization separation circuit 41 is lost. The detection circuit 6 detects this state and outputs the signal line 8.
Accordingly, the tuning circuit 7 outputs a signal to the tuner 1 to select an adjacent channel, so that the channel changes, and depending on the timing, the AFT circuit 21 may not be able to pull in the channel. It had the drawback of stopping at a point other than the normal stable point.

The present invention aims to eliminate the above-mentioned drawbacks in conventional color television receivers, and embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block wiring diagram showing an embodiment of the present invention, and the same reference numerals as in FIG. 1 indicate the same or corresponding parts, so a redundant explanation will be omitted. In FIG. 2, 11 is a DC power supply, and 100 is a clamper circuit that clamps the voltages of signal lines 8 and 9, respectively.
The clamper circuit 100 includes, for example, resistors 101,1
03,104,105,106,107,10
8, 109, 110, 111, 112, a capacitor 102, transistors 113, 114, and a diode 115 are connected as shown in the figure.
The voltage at each connection point 12, 13, 14 determines the clamp voltage. Connection point 15 is connected to a +B DC power supply (not shown). 30 is a switch corresponding to switch 3, and 31 is a switch that operates in conjunction with switch 30.

When the switch 30 is in the position to input the output of the video intermediate frequency amplification circuit 2 to the video amplification circuit 4,
Since the movable contact of switch 31 is open and clamper circuit 100 does not perform any clamping action, the operation of the circuit of FIG. 2 is similar to that of the circuit of FIG.

When the switch 30 is in the position to input the video signal from the terminal 10 to the video amplifier circuit 4, the clamper circuit 100 is connected to the power supply 1 via the switch 31.
1 is supplied, and the voltages of the signal lines 8 and 9 are the voltage values when a synchronizing signal is present, and the voltages in the vicinity where automatic fine adjustment is achieved, respectively, regardless of the output of the detection circuit 6 and AFT circuit 21. clamped to the value. Therefore, next switch 30,3
1 is switched and the output of the intermediate frequency amplifier circuit 2 is input to the video amplifier circuit 4, the AFT
It is precisely tuned to the original channel by circuit 21.

That is, when the clamper circuit 100 is operating, the upper limit of the voltage of the signal line 9 is clamped to the voltage at the connection point 13, and when it becomes higher than that, current is caused to flow through the transistor 113 and the voltage decreases to the voltage at the connection point 13. , and the lower limit of the voltage of signal line 9 is at connection point 1
When the voltage becomes lower than that, current flows through the diode 115 and rises to the voltage at the connection point 12. The voltage of the power supply 11 and each resistance value are designed so that the voltage clamped at the upper and lower limits becomes a voltage in the vicinity where automatic fine adjustment is achieved.

Further, the voltage of the signal line 8 is clamped lower than the voltage of the connection point 14, and when it becomes higher than that, a current is caused to flow through the transistor 114, and the voltage is lowered to the voltage of the connection point 14. This low voltage value corresponds to the voltage in the detection circuit 6 that indicates the presence of a synchronization signal, and even if a defective voltage indicating the absence of a synchronization signal is output from the detection circuit 6, the upper limit of the voltage of the signal line 8 is at the connection point 1.
It is clamped to a voltage of 4.

Capacitor 102 constitutes a time constant circuit for maintaining the clamp voltage at the above-mentioned value for a predetermined short time even when switch 31 is separated from power supply 11.

As described above, according to the present invention, even when a video signal other than the video signal received and detected by the television receiver is input, the defect voltage and the error voltage can be kept the same as in the normal tuning state. Immediately after returning to the receiving state, the original channel can be automatically demodulated.

[Brief explanation of the drawing]

Figure 1 is a block wiring diagram showing the parts related to video signals in a conventional color television receiver.
FIG. 2 is a block diagram showing one embodiment of the present invention. In the figure, 1 is a tuner, 2 is a video intermediate frequency amplification circuit, 21 is an AFT circuit, 30 and 34 are switches, 4 is a video amplification circuit, 41 is a synchronous separation circuit,
5 is a cathode ray tube circuit, 6 is a detection circuit, 7 is a tuning circuit, 10 is a video signal input terminal, 11 is a power supply, 1
00 is a clamper circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A synchronous separation circuit that separates synchronous signals, a detection circuit that averages the output of this synchronous separation circuit and outputs it as a defective voltage, and an automatic fine adjustment circuit that detects a frequency error and outputs an error voltage that is a function of this frequency error. , the above-mentioned deficit voltage and the above-mentioned error voltage are input, and when the above-mentioned deficit voltage indicates the presence of the above-mentioned synchronization signal, the above-mentioned error voltage is output, and when the above-mentioned deficit voltage indicates the absence of the above-mentioned synchronization signal, it tunes to the adjacent channel. A tuner whose local oscillation frequency is controlled by the output voltage of the tuner, and a video signal received and detected by the television receiver or a video signal other than this video signal. a switch for inputting the above-mentioned video signal to the video amplifier circuit of the television receiver; 1. A color television receiver comprising: a clamper circuit that clamps the error voltage to a voltage value when a synchronization signal is present, and clamps the error voltage to a voltage value in the vicinity of achieving automatic fine adjustment.