JPS5916469B2 - Automatic tuning device for television receivers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Conventionally, as shown in FIG. 1, an automatic tuning device for a television receiver includes a frequency discriminator that outputs a voltage according to the deviation of the tuner local oscillation frequency, and a frequency discriminator that applies the output of the frequency discriminator. It is composed of elements that control the local oscillation frequency of the tuner by controlling the local oscillation frequency of the tuner.

That is, in Fig. 1, 1 consists of a high frequency amplification section, a local oscillation section, a mixer section, and an element for controlling the local oscillation frequency, which is usually called a tuner section, 2 a video intermediate frequency amplification section, and 3 a frequency discrimination section. It takes out a part of the output of the intermediate frequency amplifier section 2, and when the local oscillation frequency of the tuner section 1 changes from a predetermined zero value, it outputs a voltage according to the deviation.

Therefore, numeral 3 is called an automatic local oscillation frequency control section, hereinafter abbreviated as AFS section. 4 is an AFS output terminal, 5 is a DC power supply section that generates a reference fixed voltage Vo, 6 is a terminal of the DC power supply section 5, 1 is a terminal of a local oscillation frequency control element of tuner 15 section 1, and 8 is a terminal 7 connected to terminal 4 and terminal 6.

Now, when switch arm 8 is switched as shown by the solid arrow and terminals 7 and 4 are connected, a closed loop circuit of 1 → 2 → 3 → 4 → T is created, and the local oscillator of tuner 1 has a predetermined wave number. (This is called automatic tuning.) Next, when switching as shown by the dotted arrow on the switch arm 8, the automatic control described above is canceled and a fixed voltage Vo is applied to the frequency control element. The local oscillation frequency remains constant unless the receiving channel 25 is switched.

FIG. 2 is a diagram showing the characteristics of the device shown in FIG. 1, where the horizontal axis represents the deviation of the local oscillation frequency, the vertical axis represents the output of the AFS 3 or the output voltage of the DC power supply section 5, and the straight line 11 represents the deviation of the local oscillation frequency control element. Curve 12 shows the AFS characteristic when there is no adjacent signal in the signal received by the channel 30-na 1, and curve 13 shows the AFS characteristic when there is an adjacent signal below the received signal. Now, when the voltage of the DC power supply section 5 in FIG. 1 is set to 7.0 V, for example, and the switch arm 8 is switched 35 as indicated by the dotted arrow, the local oscillation frequency will be as shown at point B on the straight line 11 in FIG. FL (approximately 1.5MH) from the regular frequency
2) is off. At this time, when switching to automatic tuning, if there is no lower adjacent signal, the AFS characteristic is curve 12, so the local oscillation frequency is F lower than the normal frequency as at point C on straight line 11. It becomes misaligned. Even if you switch the reception channel or open or close the power switch while the automatic tuning is in progress, the above F will still occur. maintain the shifted state. However, when there is a lower adjacent signal to the received signal, the AFS characteristic is curve 13.
Therefore, as mentioned above, F at point B
When switching to automatic tuning from a state where the frequency is deviated by L, the frequency is controlled to be deviated by F from the normal frequency because it moves only to point A without going to point C, resulting in an AFS malfunction. The present invention aims to improve the above-mentioned drawbacks and provide a watch tuning device that does not cause malfunctions, and provides a frequency discriminator capable of outputting a voltage according to the deviation of the tuner local oscillation frequency of a television receiver.
and an element for controlling the local oscillation frequency of a tuner by applying the output of the frequency discriminator, the direct current voltage having a voltage outside the output voltage range of the frequency discriminator. and a switching switch associated with the output terminal of the voltage source and the output terminal of the frequency discriminator, the switching switch controlling the local oscillation frequency when operating the receiver operating device of the television receiver. The device is characterized in that the element controlling the voltage is connected for a short time to the output terminal of the fixed voltage source. Incidentally, the above-mentioned "when operating the reception operator" means when switching the reception channel, when switching from manual tuning to automatic tuning, and when turning on and off the power switch.

FIG. 3 shows a block diagram of an embodiment of the present invention.

In FIG. 3, the symbols 1 to 7 indicate the same components as in FIG. 1, and 30 is a DC voltage source whose voltage is different from the voltage of the power source 5 and is selected outside the output voltage range of the frequency discriminator. . 31 and 32 are switching switches associated with the output terminal of the voltage source 30 and the output terminal of the frequency discriminator, and when operating the reception operation of the television receiver, the element for controlling the local oscillation frequency is switched to the fixed position. Configured for short-term connection to the output terminal of a voltage source.

When various operations are performed, such as when operating the reception controller of a television receiver, that is, switching the reception channel, when switching the switch arm of the automatic tuning device to the solid line, and when turning the power switch on and off. , 1→2→3→3 of the automatic tuning device in Figure 3
The closed loop of 2→4→7 is temporarily disconnected by opening the switch 32, and at the same time, the switch 31 is closed, and the voltage of the voltage source 30 is applied to the local oscillation frequency control element. As will be described later, after a predetermined period of time has elapsed after the operation of the local oscillation frequency Fbl element has ended (actually, after a very short period of time, one instant),
When the switches 31 and 32 are opened and closed as shown in FIG. 3, an automatic tuning device that does not malfunction can be obtained. 4th figure similar to figure 2
To explain further with the figures, 11 is the characteristic of the local oscillation frequency control element, and 13 is the AFS when there is a lower adjacent signal.
When the switch arm 8 shown in FIG. 3 is connected to the terminal 6 of the DC power supply section 5, the local oscillation frequency is at point B on the straight line 11.

When the receiver is operated such as when setting the automatic tuning state, a voltage outside the output voltage range of the frequency discriminator (12V in Fig. 3) is applied to the terminal 7 of the frequency control element, so the local oscillation frequency is controlled to be deviated from the normal frequency by FH as shown at point D on the straight line 11. Then, by operating the switches 31 and 32, during automatic tuning, that is, when the closed loop is established, the AFS is placed at the intersection point C between the characteristic curve 13 and the straight line 11, and is shifted by the local oscillation frequency FO. .

Therefore, in this case, the line 11 does not move from point B to point A, but rather jumps from point B to point D and then moves to point C, so that automatic tuning does not malfunction. In this manner, according to the present invention, an automatic tuning device without AFS malfunction can be obtained by simply adding a switching switch and a power source.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional automatic tuning device, Fig. 2 is an explanatory diagram of the operation of Fig. 1, Fig. 3 is a plotter diagram showing an embodiment of the present invention, and Fig. 4 is an explanation of the operation of Fig. 3. It is a diagram. 1... Tuner unit including a local oscillation frequency control element, 3... AFS unit including a frequency discriminator, 30
......DC voltage source, 31, 32......Switch switch.

Claims (1)

[Claims] 1. A local oscillator having a variable capacitance element, a frequency discriminator that generates a discrimination voltage according to the frequency deviation between the received signal frequency and the local oscillation frequency, and a frequency discriminator that supplies the output voltage of the frequency discriminator to the variable capacitance element to determine the local oscillation frequency. and a voltage changing means for forcibly shifting the output voltage of the frequency discriminator to a voltage higher than the maximum value of the above-mentioned discrimination voltage for a short time when the power switch is turned on. An automatic tuning device for a television receiver, characterized in that it prevents malfunctions from occurring when a power switch is turned on.