JPH0548983A - Television receiver - Google Patents

Abstract

PURPOSE:To prevent an erroneous operation from occurring in a station selection operation by a station selection circuit and scanning station selection even when an oscillation is caused by the unstable AFT voltage from an AFT circuit at the time of out-of-synchronism. CONSTITUTION:A synchronization detection circuit 4 and an AFT circuit 11 to which an intermediate frequency video signal is supplied, a station selection circuit 16 to which the AFT voltage from the AFT circuit 11 and an electronic tuner 17 controlled by a station selection circuit 16, are provided. A synchronization detection circuit 18 to which the video signal from the synchronization detection circuit 4 is supplied and which detects the presence or absence of a synchronization signal, and a defeat switch 15 connected between one end of the synchronization circuit 12 of the AFT circuit 11 and a reference potential point, are also provided. By controlling the defeat switch 15 so that it can be turned off at normal time and turned on when the synchronization signal, is not detected, the AFT circuit 11 is kept not operated to output the constant voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronous detection circuit and an AFT circuit to which an intermediate frequency video signal is supplied, and a tuning circuit to which an AFT (Automatic Fine Tuning) voltage from the AFT circuit is supplied. The present invention relates to a television receiver having an electronic tuner controlled by the tuning circuit.

[0002]

2. Description of the Related Art Conventionally, a synchronous detection circuit and an AFT circuit to which an intermediate frequency video signal is supplied, and an A from the AFT circuit.
There is a television receiver including a tuning circuit to which an FT voltage is supplied and an electronic tuner controlled by the tuning circuit.

[0003]

In such a television receiver, as shown in FIG. 2 (A), the AFT is performed when the synchronization is lost.
The AFT voltage from the circuit may become unstable and vibrate, in which case a malfunction occurs in the tuning operation by the tuning circuit or the scanning tuning.

In view of the above point, the present invention provides a synchronous detection circuit and an AFT circuit to which an intermediate frequency video signal is supplied, and a tuning circuit to which the AFT voltage from the AFT circuit is supplied.
In a television receiver having an electronic tuner controlled by the tuning circuit, the AFT is performed when out of synchronization.
Even if the AFT voltage from the circuit becomes unstable and oscillates, it is intended to propose a device that does not cause a malfunction in the tuning operation by the tuning circuit or the scanning tuning.

[0005]

According to the first aspect of the present invention, a synchronous detection circuit 4 and an AFT circuit 11 to which an intermediate frequency video signal is supplied, and a channel selection to which an AFT voltage from the AFT circuit 11 is supplied. In a television receiver having a circuit 16 and an electronic tuner 17 controlled by the channel selection circuit 16, a sync detection circuit 18 is supplied with a video signal from the sync detection circuit 4 to detect the presence or absence of the sync signal.
And a defeat switch 15 connected between one end of the tuning circuit 12 of the AFT circuit 11 and the reference potential point.
Normally, the defeet switch 15 is turned off, and when the synchronizing signal is not detected by the synchronizing detection circuit 18, the defeet switch 15 is controlled to be turned on, thereby making the AFT circuit 11 inoperative and constant. Output the voltage.

A second aspect of the present invention relates to a synchronous detection circuit 4 and an AFT circuit 11 to which an intermediate frequency video signal is supplied, and its AF.
Channel selection circuit 16 to which the AFT voltage from the T circuit 11 is supplied
In the television receiver having the electronic tuner 17 controlled by the channel selection circuit 16, a synchronization detection circuit 18 is provided which is supplied with the video signal from the synchronization detection circuit 4 and detects the presence or absence of the synchronization signal. .. Sync detection circuit 18
When the sync signal is not detected by, the tuning circuit 16 is controlled to ignore the AFT voltage.

[0007]

Embodiments of the present invention will be described in detail below with reference to FIG. Reference numeral 1 denotes a video intermediate frequency IC, which shows a circuit configuration of a main part thereof. Reference numeral 16 denotes a tuning microcomputer which controls tuning of the electronic tuning tuner 17 in accordance with tuning by a remote control signal of the television receiver or tuning by a tuning operator.

An intermediate frequency video signal (intermediate frequency amplitude-modulated video signal) from the tuner 17 is input from the input terminal 2 to the IC1.
After being supplied to the intermediate frequency (IF) amplifier 3 and amplified, it is supplied to the synchronous detection circuit 4 and is multiplied by the carrier signal from the PLL 5 to be synchronously detected to obtain a video signal. 8 and is amplified.

The PLL 5 is an APC (automatic phase control circuit) 6
And a VCO (voltage controlled oscillator) 7, the carrier signal from the VCO 7 is supplied to the synchronous detection circuit 4, the intermediate frequency video signal from the IF amplifier 3 and the carrier signal from the VCO 7 are phase-compared by the APC 6, and the comparison is performed. Output is V
It is supplied to CO7 and its oscillation frequency is controlled.

The video signal from the video amplifier 8 is supplied to an intermediate frequency (IF) AGC circuit 9 and a lock detection circuit 10. The AGC signal from the IF AGC circuit 9 is the IF amplifier 3
And its gain is controlled. Further, the detection output from the lock detection circuit 10 is supplied to the APC 6.

Reference numeral 11 is an AFT circuit, to which the IF amplifier 3
The intermediate frequency video signal is supplied from which the AFT voltage is obtained. Reference numeral 12 is an external tuning circuit of the AFT circuit 11, which is composed of a parallel circuit of a capacitor 13 and a coil 14.

Therefore, in this embodiment, the synchronous detection circuit 4
Sync signal detection circuit (sync signal detection circuit) that detects the presence or absence of a sync signal (horizontal sync signal) when the video signal is supplied from (the sync signal detection circuit detects the presence or absence of a sync signal) 18 and a defeat switch 15 connected between one end of the tuning circuit 12 of the AFT circuit 11 and the ground. The presence / absence of the horizontal sync signal by the sync detection circuit 18 is supplied to the tuning microcomputer 16 as the detection signal 1 and to the defeat switch 15 as the detection signal 2.

Next, the operation of the television receiver of this embodiment will be described. When the horizontal detection signal is detected by the synchronization detection circuit 18, the defeet switch 15 is off, and the AFT circuit 11 outputs the AFT signal according to the frequency of the intermediate frequency video signal as shown in FIG. The voltage V changes up and down (the lower limit is close to 0V and the upper limit is close to 5V) around 2.5V, for example.

When the horizontal sync signal is not detected by the sync detection circuit 18, the defeat switch 15 is turned on, so that the AFT circuit 11 stops the AFT operation and is related to the change in the frequency of the intermediate frequency video signal. Instead, it outputs a constant voltage of 2.5V. Therefore, as shown in FIG. 2B, unlike the conventional example, there is no possibility that the AFT voltage from the AFT circuit 11 becomes unstable and oscillates when the synchronism is lost. Therefore, the tuning circuit 16 selects a channel. There is no risk of malfunction in operation or scanning channel selection.

Incidentally, without providing the defeat switch 15,
When the synchronization signal is not detected by the synchronization detection circuit 18, the synchronization detection circuit 18 controls the tuning circuit 16 to
The AFT voltage from the AFT circuit may be ignored.

Further, in addition to the pure synchronous detection type television receiving device of the above-described embodiment, the present invention can be applied to a pseudo synchronous detection type television receiving device provided with a tuning circuit instead of the PLL. ..

[0017]

According to the present invention described above, a synchronous detection circuit and an AFT circuit to which an intermediate frequency video signal is supplied, and a tuning circuit to which the AFT voltage from the AFT circuit is supplied,
In a television receiver having an electronic tuner controlled by the tuning circuit, the AFT is performed when out of synchronization.
Even if the AFT voltage from the circuit becomes unstable and vibrates, it is possible to obtain a device that does not cause a malfunction in the tuning operation by the tuning circuit or the scanning tuning.

[Brief description of drawings]

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

FIG. 2 is a curve diagram showing changes in AFT voltage in a conventional example and an example.

[Explanation of symbols]

 1 Video Intermediate Frequency IC 4 Synchronous Detection Circuit 5 PLL Circuit 6 APC Circuit 7 VCO 11 AFT Circuit 12 Tuning Circuit 15 Defeat Switch 16 Tuning Microcomputer 17 Electronic Tuning Tuner 18 Synchronization Detection Circuit

Claims (2)

[Claims] 1. A synchronous detection circuit and an AFT circuit to which an intermediate frequency video signal is supplied, a tuning circuit to which an AFT voltage from the AFT circuit is supplied, and an electronic tuner controlled by the tuning circuit. In a television receiver having the video signal from the synchronous detection circuit, the synchronous detection circuit for detecting the presence or absence of the synchronous signal is connected between one end of the tuning circuit of the AFT circuit and a reference potential point. A defeet switch is provided, the defeet switch is normally turned off, and when the synchronizing signal is not detected by the synchronizing detection circuit, the defeet switch is controlled to be turned on. A television receiver characterized in that a circuit is made inoperative to output a constant voltage. 2. A synchronous detection circuit and an AFT circuit to which an intermediate frequency video signal is supplied, a tuning circuit to which the AFT voltage from the AFT circuit is supplied, and an electronic tuner controlled by the tuning circuit. In the television receiver having the video signal from the synchronous detection circuit, a synchronization detection circuit for detecting the presence or absence of the synchronization signal is provided, and when the synchronization detection circuit does not detect the synchronization signal, the selection is performed. A television receiver characterized in that a local circuit is controlled to ignore the AFT voltage.