JPH01149686A - Television receiver - Google Patents

Abstract

PURPOSE:To switch the AFC function of a TV receiver automatically in accordance with a telecasting system being received by providing a detecting means which detects whether or not a synchronizing signal is synchronous to the synchronizing signal of TV signals and outputting keyed pulses to an AFC circuit when the output of the detecting means indicates a synchronizing state. CONSTITUTION:When, for example, signals of a NTSC system are received, the reproduced synchronizing signal of the synchronous reproducing circuit 16b of a MUSE decoder is asynchronous to input signals. The asynchronism is detected by means of an asynchronism detecting circuit 31. When an asynchronous state is detected, the circuit 31 disconnects the synchronous reproducing circuit 16b from a keyed AFC circuit 22 and a pulse detecting circuit 30 so that no keyed pulse can be inputted to the circuits 22 and 30. When no keyed pulse is inputted, the pulse detecting circuit 30 changes over switches S11 and S12 to a mean-value AFC circuit 21 side. In other words, the AFC function of the circuit 21 is switched to an operating state suitable for signals of the NTSC system.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a television receiver capable of receiving television broadcasts of different formats, and which performs automatic frequency control according to the television format being received. (AFC) The operating state is automatically switched.

(Prior art) In satellite television broadcasting, when broadcasting signals of different systems, such as the NTSC system and the MUSE system, the receiver needs a reception system compatible with the two systems as shown in Figure 4. It is.

The satellite broadcast wave transmitted in the SHF band is converted into a first intermediate frequency signal in the GHz band by a first frequency converter, and then supplied to the input terminal 10 . The first intermediate frequency signal at the input terminal 10 is converted into a second intermediate frequency signal in the second frequency converter 12 .

The second intermediate frequency signal is supplied to the FM demodulator 13 and converted to baseband.

When receiving an NTSC signal, the FM demodulated signal is
The signal is decoded in the NTSC signal processing circuit 14 and outputted to the output terminal 15 as an NTSC composite signal.

On the other hand, when a MUSE signal is received, the FM demodulation output of the FM demodulator 13 is transmitted to the FM demodulation output of the FM demodulator 13,
The signal is introduced into the SE decoder 16, where it undergoes video and audio reproduction processing, and is output to the output terminal 17 as a high-definition video signal. The MUSE decoder 16
E signal processing unit 16a and a system clock necessary for signal processing.

It has a synchronization reproducing circuit 16b that obtains a synchronization signal and keyed AFC control output.

The block surrounded by 18 in the figure is an AFC circuit section. This control voltage from the AFC circuit unit 18 is added to the tuning voltage from the tuning device 20 in an adder 19 and is supplied to a control terminal of a local oscillator inside the second frequency converter 12. This stabilizes the output of the FM demodulator 13. When an NTSC signal is being received, AFC
Inside the circuit section 18, the average value AFC circuit 21 is activated, and the average level of the FM demodulated output is used as the AFC control voltage. On the other hand, when a MUSE signal is being received, the keyed AFC circuit 22 is activated. The selection of the AFC circuits 21 and 22 is performed by interlocking switches S1. This is performed by S2. Switch S1. S2
is manually switched by the user.

The reason why the keyed AFC circuit 22 is used when receiving the MUSE method is because in the MUSE method signal, AFC information can be obtained only during the clamp level period of the signal, so the AFC operation state is set only during this period, and the other This is because it is necessary to maintain the previous AFC control voltage during the period. For this purpose, keyed pulses from the synchronous regeneration circuit 16b are supplied to the keyed AFC circuit 22, and the keyed pulses are configured to take in AFC information and generate an AFC control voltage.

(Problems to be Solved by the Invention) According to the conventional receiving system, the AFC function is changed by manually switching the switches Sl and S2 according to the broadcasting system. However, even if the receiving channel is the same, a problem arises when the broadcasting system is switched midway through the operation. For example, if you are in the NTSC reception state and the reception condition temporarily deteriorates, the screen will be distorted, but similar screen disturbances may occur if the broadcasting method switches to the MUSE method midway through, and the AFC function is set to NTSC. This may also occur if the system is left unattended. For this reason, it is difficult for viewers to determine whether the cause is a deterioration in reception conditions or a change in broadcasting system.

SUMMARY OF THE INVENTION An object of the present invention is to provide a television receiver that can automatically switch the AFC function of the receiver depending on the broadcasting system being received.

[Structure of the Invention] (Means for Solving the Problems) In the present invention, when a television signal of the first broadcasting system is being received, the average value of the output of the FM demodulator is used as the output of the tuning device. is added to the selected channel signal, and added to the selected FM signal.
a first AFC means for stabilizing the demodulated output; and a pulse (clamp level) related to the synchronization signal of the second broadcasting system television signal when the television signal is being received.
The output of the FM demodulator is averaged only during a period, and is returned to the output section of the channel selection device and added to the channel selection signal, thereby switching the operating state with a second AFC means for stabilizing the FM demodulation output. In this case, the AFC circuit is switched by detecting whether or not the pulse is input, and the synchronization signal of the synchronization reproducing circuit of the signal processing circuit that processes the signal of the second broadcasting system is used to switch the AFC circuit. By providing a detection means for detecting whether or not the synchronization signal is synchronized with the synchronization signal of the television signal, and outputting a keyed pulse to the AFC circuit when the output of the detection means indicates the synchronization state, the second The first AFC is activated by activating the AFC means and not outputting a keyed pulse when indicating an asynchronous state.
The structure is such that the means is brought into operation.

(Operation) According to the above means, when the second broadcasting method is received, the detection means outputs a keyed pulse to the AFC circuit, and the second AF suitable for the second method is automatically activated.
It is possible to switch to the AFC function using the C circuit.

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

FIG. 1 shows an embodiment of the present invention, and the difference from the circuit shown in FIG. 4 is the switch Sll of the AFC circuit section 18.
, S12 is an electronic switch, which is controlled by the output of the pulse detection circuit 30, and the MUSE decoder 1
6, there is provided an asynchronous detection circuit 31 that monitors the synchronous state of the synchronous reproducing circuit 16b, and a switch 813 that is controlled by the output of the asynchronous detection circuit 31 to make the keyed pulse conductive or non-conductive. switch S13
The keyed pulse that has passed through is supplied to the keyed AFC circuit 22 and also to the pulse detection circuit 30. Since the other parts are the same as the circuit configuration in FIG. 4, the same reference numerals as in FIG. 4 are given.

Assuming that an NTSC signal is being received now, M
The reproduction synchronization signal of the synchronization reproduction circuit 16b of the USE decoder 18 is asynchronous with respect to the human input signal. This is detected by the asynchronous detection circuit 31. Asynchronous detection circuit 3
1, when such a state is detected, switch S1 is activated.
3 to control the synchronous regeneration circuit 16b and the keyed AFC circuit 2.
2 and the pulse detection circuit 30 to prevent keyed pulses from being input to the keyed AFC circuit 22 and the pulse detection circuit 30. The pulse detection circuit 30 switches the switch 5llSS12 to the average value A'FC circuit 21 side when a keyed pulse is not input. That is, the AFC function is switched to an operating state suitable for NTSC signals.

Conversely, when a MUSE signal is being received,
The synchronization signal of the synchronous reproduction circuit 16b performing synchronous reproduction in the USE decoder 16 is synchronized with the input signal. This synchronous state is determined by the asynchronous state detection circuit 3.
1 is detected.

When the reproduction synchronization signal and the input signal are synchronized, the asynchronous state detection circuit 31 connects the switch S13 to the synchronous reproduction circuit 16b, and the keyed pulse is detected by the pulse detection circuit 30.
and the keyed AFC circuit 22.

When a keyed pulse is input to the pulse detection circuit 30, the detection output controls the switches Sll and SL2 to switch to the keyed AFC circuit 22 side. Therefore, the AFC function of the system is switched to an operation suitable for the MUSE method.

As mentioned above, according to this system, AFC operation automatically switches to an appropriate state according to the receiving method,
No user interaction required. For this reason, for example, when receiving one channel, the broadcasting method is NTSC.
From MUSE method.

Or when switching to the opposite method, the AFC is automatically switched to the optimum AFC, which is extremely convenient.

FIG. 2 shows another embodiment of the AFC circuit section 18. In this circuit, an output from the FM demodulator 13 is supplied to an input terminal 41, and a keyed pulse is supplied to an input terminal 47. The input terminal 41 is connected to a human powered amplifier 42, and the output end of the input amplifier 42 is connected to an output terminal 46 via a switch 43, a resistor 44, and an output amplifier 45. Further, a capacitor 51 is connected between the input terminal of the output amplifier 45 and ground, and a series circuit of a switch 449 and a capacitor 50 is also connected. A keyed pulse introduced into input terminal 47 controls switch 43 and is supplied to monostable multivibrator 48 .

A timing chart of the above circuit is shown in FIG. First, the switch 43 is turned on every time a keyed pulse is input. Further, as long as the keyed pulse is correctly input, the monostable multivibrator 48 outputs a high level and maintains the switch 49 in the off state.

Therefore, when receiving the MUSE method, the human power information when the switch 43 is turned on for one line is the capacitor 51.
Therefore, the time constant is determined by the resistor 44 and capacitor 51. On the other hand, when the keyed pulse is not manually operated, both switches 43 and 49 are maintained in the on state. Therefore,
The time constant of the circuit is determined by the resistor 44 and capacitor 50.51.

The time constant at this time is 2 to obtain average value AFC operation.
~3 field values.

[Effects of the Invention] As explained above, according to the present invention, the AFC function of the receiver can be automatically switched depending on the broadcasting system being received.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a circuit diagram showing another example of the AFC circuit section in FIG. 1, and FIG. 3 is for explaining the operation of the circuit in FIG. 2. FIG. 4 is a block diagram showing a conventional multi-system reception television receiver. 12... Frequency converter, 13... FM demodulator, 14
...NTSC signal processing circuit, 16...MUSE decoder, 16a...MUSE signal processing circuit, 16b...
- Synchronous regeneration circuit, 18... AFC circuit section, 19...
Adder, 20... Tuning device, 21... Average value AFC
Circuit, 22... Keyed AFC circuit, S11°Si2.
313...Switch, 30...Pulse detection circuit, 3
1...Asynchronous detection circuit. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Scope of Claims] In a television receiver that receives two or more television broadcast signals composed of different synchronization systems, the oscillation frequency is controlled according to the channel selection signal from the channel selection device, and the oscillation frequency is controlled according to the channel selection signal from the channel selection device. a frequency converter for frequency converting an arbitrary channel signal to derive an intermediate frequency signal; an FM demodulator to which the intermediate frequency signal derived from the frequency converter is supplied and performs FM demodulation; When a television signal is being received, the FM
a first AFC means that returns an average value of the output of the demodulator to the output section of the channel selection device and adds it to the channel selection signal to stabilize the FM demodulation output; and a television of a second broadcasting system. When a synchronization signal is being received, the FM
a second AFC means that averages the output of the demodulator and returns it to the output section of the channel selection device and adds it to the channel selection signal to stabilize the FM demodulation output; AF that detects whether the pulse is input and switches the second AFC means to the operating state when the pulse is input, and switches the first AFC means to the operating state when the pulse is not input.
C switching means; a plurality of signal processing circuits to which the output of the FM demodulator is supplied and performs signal processing corresponding to signals of respective broadcasting systems; and for switching the operation of the first and second AFC means. , detection means for reproducing a synchronization signal using the signal of the signal processing circuit that processes the signal of the second broadcasting system, and detecting whether or not the synchronization signal of the television signal is in synchronization with the synchronization signal; and pulse output control means for outputting the pulse to the AFC switching means when the output of the detection means indicates a synchronous state, and inhibiting output of the pulse when the output of the detection means indicates an asynchronous state. television receiver.