JPH01268307A - Channel selecting device - Google Patents

Abstract

PURPOSE:To stably execute the reception against a variation of a receiving frequency by varying a frequency division ratio of a frequency divider by synchronizing with a vertical synchronizing signal. CONSTITUTION:For instance, in case a receiving channel is shifted to the lower side against a normal frequency, a controller 3 judges whether an output voltage of an AFC circuit 5 exceeds a threshold for some prescribed period or not, and if said voltage exceeds, the controller detects a signal from a vertical synchronization generator 13, and raises a frequency division ratio of a variable frequency divider 7 by '1' synchronously in an edge or output period of its signal. Such a procedure is repeated, and when an AFC output voltage becomes between the first and the second threshold voltages, the variation of the frequency division ratio of the variable frequency divider 7 is stopped. In such a way, since the timing for varying the frequency division ratio is executed in a vertical blanking interval, a disturbance on a screen can be reduced.

Description

[Detailed Description of the Invention] [Field of Application of Shokutojo] The present invention is applied to the yI! The present invention relates to a four-station device, and particularly to a channel selection device using a pLL frequency synthesizer method.

[Traditional Keijutsu]

Conventional devices use a single VcA when attempting to finely tune the receiving frequency, as was the case in Japanese Patent Publication No. 56-45524.
It has been common practice to vary the frequency division ratio of the °C variable frequency divider in response to the output voltage of the FC circuit.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, the timing for varying the frequency division ratio of the variable frequency divider is determined by FUt 141. If this is not done and the receiving frequency is corrected under normal receiving conditions of 1g, it will respond immediately, causing horizontal interference to appear on the screen, or changing the frequency division ratio up or down in a short period of time. There was always a problem when so-called hunting agglomeration occurred. In the case of satellite broadcasting damage, using a method in which the converter unit outside the station vibrates to the intermediate frequency once cannot ignore the drift of the frequency i due to changes in the prefectural border, and the number of corrections for the reception frequency RHL increases. Furthermore, since Bonshō's f-key system was an FM system, there were problems such as interference being easily visible on the screen when the receiving frequency was changed. It is an object of the present invention to eliminate the drawbacks of the prior art and to enable stable reception against changes in reception frequency.
! 4@Providing direct service. 1 [Measures for solving the problem] In order to achieve the above object, the present invention continuously monitors the output of a vertical synchronization generation circuit and an AFC circuit that generate each vertical synchronization issue of a received signal or a vertical synchronization pulse. , means for determining whether the output level exceeds a certain threshold voltage in a certain period of time, and means for making the frequency division ratio of the frequency divider equal to one in synchronization with the vertical synchronization signal. .

[Effect]

When the receiving frequency changes, the AFC circuit outputs a voltage corresponding to the changed number of cycles tL. If the voltage exceeds a certain threshold 1 hold voltage for a certain period of time, a vertical synchronization pulse or a vertical synchronization pulse VC is used to synchronize and change the division ratio of the frequency divider by 1. . At this time, since this is done at the timing of changing the frequency division ratio or within the vertical retrace period, disturbances on the screen can be reduced.

〔Example〕

Hereinafter, the present invention will be specifically explained using an example illustrated in FIG. In Figure 1, 1 is the keyboard for tuning,
2 is a fake 2-digit channel display device, 6 is a con)o-
4 is the tuner, 5 is the AFC circuit, 6 is the circuit 40
A fixed frequency divider that divides the local oscillation output, 7 is a fixed frequency divider 6
The frequency of the local excavation output divided from &C is further divided, and the frequency division ratio can be changed by the output from the controller 5.A variable frequency divider, 8 is a fixed frequency divider 6j, and a vibration frequency divider 7 is used for frequency division. 9 is a low-pass filter that extracts the LT wave component from the error voltage of the phase comparator 8; 1o is a fixed frequency divider that divides the output of the photostimulator 11, and 12 is an AFC having first and second threshold voltages for determining the output of the AFC circuit.
15 is a vertical synchronization generation circuit which generates a vertical synchronization signal or a vertical synchronization pulse of the signal that has been input, and 14 is a video signal input terminal A. Now, when a certain channel code is inputted from the channel selection keyboard 1, data corresponding to that channel is inputted from the controller 3 to the variable frequency divider 7. As a result, the frequency division ratio corresponding to the channel assigned to the a channel is set in the variable frequency divider 7.

Then fixed frequency divider 6. Variable frequency divider 71 phase comparator 8.
Feedback by the phase-locked loop consisting of the low-pass filter 9 sets the local oscillation frequency of the tuner 40 to a frequency corresponding to the #J violet channel.

A case will be described in which the frequency of the reception channel is shifted by one from the normal frequency set in this manner.

In general, the output voltage characteristic of the -AFC circuit with respect to frequency is an inverted S1 shape, as shown in FIG. Here, if the reception channel is lower than the normal frequency, the output voltage of A F CIgIR1I5 will be lower than the first threshold voltage VTR&, and the request to increase the reception frequency will be sent to the controller 3. Given. Here, ripples are generally said to be present in the AFC output, and there is a possibility that these ripples may give a false impression. For this reason, it is necessary to determine whether a certain period threshold has been exceeded, and if it has been exceeded,
Next, a signal from the serial synchronization generator 13 is detected, and the frequency division ratio of the variable frequency divider 70 is increased by 1 in synchronization with the edge or output period of the signal.

By repeating these steps, the AFC output voltage becomes the threshold 1 hold voltage of the first and nest 2 VTM+ *Vri2
When the frequency is between 1 and 2, the variable frequency divider 70 stops changing the division ratio. With Vc in this manner, the same operation will occur even if the receiving channel deviates from the normal frequency to Shimame Senj. In addition, during the first channel selection operation, it should be asynchronous with the vertical synchronization signal to quickly correct frequency deviations, and then synchronize with the vertical synchronization signal in response to frequency deviations due to subsequent drift, etc. You can also do it. Figure 5 shows the vertical synchronization signal (
This shows the timing relationship between α1 and reception frequency change (bl).

〔Effect of the invention〕

According to the present invention, even if the receiving frequency is changed to correct the deviation of the receiving frequency in a normal receiving state, the timing of the change is performed within the vertical retrace period, so that interference on the screen can be reduced. , correction (gla can also be reduced).

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram showing the relationship of threshold 1 hold voltage to ANC output voltage change, and Fig. 3 is a diagram showing a time chart of the main part. .

Claims (1)

[Claims] 1. In a tuning device using a PLL frequency synthesizer method that divides the local oscillation frequency of the tuner, compares the frequency and phase with a reference oscillator, and controls the tuning voltage of the tuner, the controller , a variable frequency divider whose frequency division ratio is controlled by the controller, an AFC circuit connected to the tuner, and an AF having first and second threshold voltages for determining the S-shaped output of the AFC circuit.
C discrimination circuit, and a vertical synchronization generation circuit that generates a vertical synchronization signal or a vertical synchronization pulse of the received signal,
When the output voltage of the AFC circuit is higher than the first threshold voltage, the variable frequency divider is finely adjusted to adjust the frequency division ratio in synchronization with the edge or output period of the signal from the vertical synchronization generating circuit. and when the voltage falls below a first threshold voltage, the change in the division ratio of the variable frequency divider is stopped, while the output voltage of the AFC circuit is lower than the second threshold voltage. In this case, the frequency division ratio is similarly controlled to be lowered in synchronization with the vertical synchronization signal, and when the voltage exceeds the second threshold voltage, the change in the frequency division ratio of the variable frequency divider is stopped. A channel selection device featuring: 2. In the channel selection device according to claim 1, the output voltage of the AFC circuit is continuously higher than the first threshold voltage for a certain period of time or continuously lower than the second threshold voltage for a certain period of time. A channel selection device characterized in that the frequency division ratio of the variable frequency divider is changed in the case of the present invention.