JPS589607B2 - Tuning device with automatic station searching function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a channel selection device having an automatic channel search function used in a television receiver or the like.

FIG. 1 shows a conventional channel selection device that uses a PLL synthesizer to select television broadcast channels and has an automatic channel search function. received from terminal 9 and terminal 1
a variable frequency divider 2 that divides the local oscillation frequency from the local oscillator 8 by a frequency division signal given to 0; a reference oscillator 4 to which a crystal oscillator is externally attached; and the variable frequency divider 2 and the reference oscillator. This is a PLL/IC having a comparator 3 that compares the phase of the output of the tuner 7, and the output is applied to a low-pass filter 6 via a terminal 11 to be converted into a direct current, and then sent to a local oscillator 8 of a tuner 7 to control its oscillation frequency. supplied to

Reference numeral 12 denotes a control device that provides a frequency division signal to the variable frequency divider 2 of the PLL/IC 1. This control device actually constitutes one device as a microcomputer, but this control device 12 does not operate the operation keys 13. The frequency-divided signal is automatically changed by the operation.

More specifically, the operation keys can be used in one direction (up direction to sweep toward high channels) and in the opposite direction (down direction to sweep toward low channels; however, when sweeping further down from the minimum VHF channel, It has an up key and a down key for driving to the highest UHF channel), and these keys can be operated selectively.

When the frequency division signal of the output terminal 14 is changed by operating the operation key 13, the output of the frequency divider 2 changes, and the output of the phase comparator 3 also changes, causing the local oscillation frequency of the tuner 7 to change. The state of the tuner will be removed from the channel that was in the state.

In this way, when the local oscillation frequency of the tuner changes in the up or down direction and reaches the next channel, the VIP carrier signal is detected in the circuit 19 that detects and smoothes the VIP carrier signal from the output of the vIF circuit 15. This detection output is added as a comparison signal to the IP comparator 24 and compared with the reference voltage E1.

At the same time, a horizontal synchronizing pulse is detected and smoothed by a circuit 20 from the output of the video detection circuit 16, and the output of this horizontal synchronizing pulse detection/smoothing circuit 20 is compared with a reference voltage E2 in a synchronizing signal comparator 25. Ru.

The control device 12 is configured to stop the sweep when the terminal 26 is at the "high" level and the terminal 27 is at the "low" level, but at the broadcast channel, the VIP signal and the synchronization signal are received in accordance with the reception of the broadcast signal. is obtained, and the outputs of the comparators 26 and 27 become "high" and "low", respectively, so the frequency-divided signal obtained at the terminal 14 of the control device 12 stops changing, and the reception state of the channel is set. .

Further operation of the operation key 13 leads to the next adjacent broadcasting channel through a similar operation.

In FIG. 1, 21 is a deflection circuit, 17 is a video circuit, 22 is a picture tube, 18 is an audio circuit, and 23 is a speaker.

By the way, in such a tuning device, in order to ensure that the automatic station searching operation is performed normally even in areas with weak electric fields, a highly sensitive television signal detection circuit (19, 20 in Figure 1) must be used. However, if you do this, cross-modulation will occur on the adjacent empty channel of the channel with the strong electric field, and it will be inconvenient that the search operation will stop on that channel even though it is determined that there is a TV signal and it is not a TV radio reception channel. There is a possibility that this may occur.

The present invention proposes a channel selection device having an automatic station search function designed to avoid such inconveniences.

In FIG. 2, in which the present invention is implemented, the same parts as in FIG. 1 are given the same symbols.

In FIG. 2, the output of the VIP carrier detection and smoothing circuit 19 is given to the H terminal as the comparison input of the first comparator 24a, and the output of the synchronization signal detection circuit 20 is given to the H terminal as the comparison input of the second comparator 24b. terminal and the third comparator 25
In the fourth comparator 25b, the output of the IFAGC voltage forming circuit 28 is supplied as a comparison input to the H terminal, and the output of the synchronizing signal detection and smoothing circuit 20 is supplied to the L terminal of the fourth comparator 25b.

The terminals of the first comparator 24a, the second comparator 24b, and the third comparator 25a are connected to R and R in FIG. 3, respectively.
A constant voltage at a level corresponding to L and R A is constantly applied as a reference voltage, while the H of the fourth comparator 25b
Similarly, a constant level reference voltage corresponding to RH in FIG. 3 is applied to the terminal.

The outputs of the first to fourth comparators have a "high level" when the voltage at the H terminal is higher than the voltage at the L terminal, and a "low" level when the voltage at the H terminal is lower than the voltage at the L terminal.

Further, the output terminals of the first and second comparators 24a and 24b are commonly connected to the terminal 26 of the control device 12, and the output terminals of the third and fourth comparators 25a and 25b are commonly connected to the terminal 27 of the control device 12. It is connected to the.

When the output of either the first or second comparator 24a, 24b becomes a "low" level, their common output point becomes a "low" level.

The same applies to the common output point of the third and fourth comparators 25a and 25b.

As shown in FIG. 3, the IFAGC voltage is a low voltage in a weak electric field, and becomes a high voltage in a medium electric field or higher.

Further, this AGC voltage becomes high voltage in an empty channel due to the influence of an adjacent broadcast channel.

Next, the operation will be explained.

Now, when the automatic search reaches a broadcast channel with a weak electric field, the AG
Since C voltage<RA, the output of the third comparator 25a becomes "low" level, and the level of their common output point becomes "low" regardless of the input of the fourth comparator 25b.

In this state, the first comparator 24a and the second comparator 24b
When the level of the common output point becomes “high”, the control device 12
It is determined that there is a TV signal (that is, the state is tuned), and the automatic station search stops at that channel.

In order for the outputs of both the first comparator 24a and the second comparator 24b to be at the "high" level, it is necessary that the IF signal>R and the synchronization signal>RL, which is indicated by β in FIG. This condition is satisfied on the right side of the sensitivity setting position.

Therefore, automatic station searching can be performed reliably even in a weak electric field.

Next, when the automatic station search reaches a broadcast channel with a strong electric field, the AGC voltage will be larger than the RA, so the synchronization signal>
When the signal is RH, the output level of the fourth comparator 25b becomes "low", and the common output point of the third and fourth comparators 25a, 25b becomes "low" level.

On the other hand, since the IF signal is larger than R and the synchronizing signal is still larger than RL, the common output point of the first and second comparators 24a and 24b becomes a "high" level.

In this way, a normal stopping operation is performed even in the strong electric field broadcasting channel.

Next, it will be explained that malfunctions do not occur in an empty channel due to the influence of an adjacent channel having a strong electric field, which is also an object of the present invention.

If the adjacent broadcasting channel has a strong electric field, but the aftereffects are also reaching the empty channel, the IF signal and synchronization signal of the adjacent broadcasting channel at the position of the empty channel can be considered to be a weak electric field, but in that case, in Fig. 3 , if it is weak enough to correspond to the part to the left of the sensitivity setting position β, it is natural that it will not stop at the empty channel because the IP signal is R and the synchronization signal is < RL, but it is weaker than the sensitivity setting position β. In the case on the right, the influence of the IF signal and synchronization signal is at most less than X, but only the AGC voltage
For example, as shown by point A in the figure, the value is larger than <RA.

Therefore, the output of the third comparator 25a becomes "high" level, and the fourth comparator 25b also becomes "high" level, so the level of the common output point of the third and fourth comparators 2ga and 25b is "high". Yes, this means that the control device 12 has the terminal 26 “
Since the latter condition of stopping when the terminal 27 is "high" and the terminal 27 is "low" is not satisfied, it will not stop at the empty channel.

FIG. 4 shows only the essential parts of another embodiment of the present invention, in which a switch SW is provided, and the switch SW can be switched to the left side as shown in the figure, or as shown in FIG. You can select whether to switch to the right side and do as shown in Figure 6.

In the case of switching as shown in FIG. 5, the effect described above is achieved in substantially the same manner as in the embodiment of FIG. 2.

In the case of the embodiment shown in FIG. 4 as shown in FIG. 5, the search sensitivity is achieved up to the point β shown in FIG. 3, but when the switch SW is switched as shown in FIG. Until,
No search operation is performed for the electric field to the left of the α point.

In short, in FIG. 4, it can be done as shown in FIG. 5 in weak electric field areas, and as shown in FIG. 6 in strong electric field areas.

In addition, in FIG. 4, a fifth comparator 24c is provided, but this operates when the switch SW is switched to the right side, and when it is switched to the left side, the power supply voltage VB
However, since it is set higher than ■A, the output is always “
Since it is at the "high" level, it is omitted in FIG.

In the case of FIG. 6, the explanation will be omitted since it is not directly related to the gist of the present invention.

As explained above, according to the present invention, even if the sensitivity is increased so that automatic station searching is performed sufficiently in a weak electric field, the station searching operation stops in the empty channel due to the influence of the adjacent strong electric field channel. There is no inconvenience of doing
It is extremely effective as a channel selection device with an automatic channel search function.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of a conventional station selection device having an automatic station search function. FIG. 2 is a block circuit diagram of a channel selection device having an automatic station searching function embodying the present invention, and FIG. 3 is an explanatory diagram thereof. FIG. 4 is a main part circuit diagram of another embodiment of the present invention, and FIG.
The figure and FIG. 6 are explanatory diagrams thereof. 1...PLL/IC, 2...Variable frequency divider, 4...Reference oscillator, 7...Tuner, 8...Local Oscillator, 12...Control equipment, 24a...First comparator, 24b...
...Second comparator, 25a...Third comparator, 25
b...Fourth comparator.

Claims (1)

[Claims] 1. A PLL synthesizer that compares the phase of the output of a variable frequency divider that divides the local oscillation output of the tuner according to a frequency division ratio and the output of a reference oscillator, and controls the local oscillation frequency of the tuner based on the comparison output; A channel selection device comprising a control device that changes a frequency division signal given to a frequency divider in response to a station searching operation and stops the change in response to a television signal indicating the state of reception of television radio waves, the device transmitting a stop signal to the control device. A comparator for the television signal is connected to give a signal and has increased sensitivity so that the termination occurs even in a weak electric field, and the AGC voltage becomes large in an empty channel when influenced by an adjacent strong electric field channel. What is claimed is: 1. A channel selection device having an automatic station searching function, comprising means for preventing the output of the comparator from acting in the direction of stopping by taking advantage of this fact.