JPH0818405A - Automatic tuning device - Google Patents

Abstract

PURPOSE:To prevent the malfunction of an automatic tuning device by improving the S/N of a high frequency amplifier circuit and a mixing circuit. CONSTITUTION:In a PLL receiver provided with an automatic tuning function, this automatic tuning device is provided with a mute circuit 14 for muting intermediate frequency signals, a counter circuit 15 for counting the frequency of the intermediate frequency signals, a station detection circuit 16 for detecting the presence/absence of station signals and a controller 17 for performing all the control of the automatic tuning device and performs the control for stopping the sweep of a tuning frequency when the station signals are detected during automatic tuning, counting the frequency of the intermediate frequency signals by the counter circuit 15, muting the intermediate frequency signals in the mute circuit 14 when the counted value of the counter circuit 15 is a prescribed value, stopping the frequency counting of the intermediate frequency, detecting the station signals again and considering that the station signals are present when both two times of station signal judgement are the station signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic channel selection device used in a PLL receiver.

[0002]

2. Description of the Related Art In recent years, most of the PL
L receiver.

An example of the above-mentioned conventional automatic channel selecting apparatus will be described below with reference to the drawings.

FIG. 3 shows a general PL having an automatic channel selection function.
FIG. 4 is an electrical block diagram of the L receiver, and FIG. 4 is a flow chart showing the tuning procedure of the conventional automatic tuning device in the PLL receiver.

In FIG. 3, the input signal received by the receiving antenna 1 is amplified by the high frequency amplifier circuit 2 and then mixed by the mixing circuit 3.
Are converted to an intermediate frequency by the intermediate frequency amplification circuit 4, amplified by the intermediate frequency amplification circuit 4, detected by the detection circuit 5, and amplified by the low frequency amplification circuit 6 to drive the speaker 7. Reference numeral 8 denotes a voltage control oscillator for adding a signal having a local oscillation frequency for tuning to the mixing circuit 3, and the frequency control oscillator 8 to which the output of the reference signal oscillation circuit 9 is added and the output of the voltage control oscillator 8 are provided. A phase comparator 12 for phase-comparing the respective outputs of the added programmable frequency dividing circuit 11 and its output are added to the voltage controlled oscillator 8 through a low-pass filter 13, and the oscillation frequency thereof is controlled to form a PLL frequency synthesizer. There is. Further, 14 is a mute circuit connected to the intermediate frequency amplifier circuit 4 to mute the intermediate frequency signal, and 15 is a frequency counter for counting the frequency of the intermediate frequency signal. Reference numeral 16 is a station detection circuit which is connected to the detection circuit and determines the presence of a station if the station signal is higher than a prescribed threshold value. Reference numeral 17 is a control circuit,
When changing the oscillation frequency of the LL frequency synthesizer,
The tuning frequency can be changed by changing the division ratio of the programmable frequency dividing circuit 11 by the control circuit 17. The outputs of the frequency counter 15 and the station detection circuit 16 are applied to the control circuit 17, and the control circuit 17 causes the mute circuit 14 and the low frequency amplifier circuit 6 to operate.
Mute is controlled.

Next, the conventional automatic tuning procedure will be described with reference to FIGS. 3 and 4. When the automatic tuning starts, the control circuit 17 changes the frequency division ratio of the programmable frequency dividing circuit 11 to change the PLL frequency by one step, the station detecting circuit 16 detects the station, and if there is a station signal, the frequency counter is displayed. At 15, the frequency of the intermediate frequency signal is counted at the PLL frequency at that time, and when the count value is a predetermined value, it is determined that there is a local signal, and control is performed to turn off the audio mute.

[0007]

However, the conventional channel selecting apparatus as described above has a structure in which the intermediate frequency signal is constantly detected and the intermediate frequency is counted during tuning, and the high frequency amplifier circuit is spatially coupled. In addition, the intermediate frequency signal jumps into the mixing circuit, which deteriorates the S / N ratios of the high frequency amplification circuit and the mixing circuit, causing a malfunction of the automatic channel selection device.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide an automatic channel selecting device having an improved S / N ratio of a high frequency amplifier circuit and a mixing circuit.

[0009]

In order to solve the above-mentioned problems, an automatic channel selection apparatus of the present invention is a PL having an automatic channel selection function.
In the L receiver, a mute circuit for muting the intermediate frequency signal, a counter circuit for counting the frequency of the intermediate frequency signal, a station detection circuit for detecting the presence / absence of a broadcast signal, and a control device for controlling all of the automatic channel selection device are provided. When the station signal is detected during automatic tuning, the tuning frequency sweep is stopped, the counter circuit counts the frequency of the intermediate frequency signal, and when the count value of the counter circuit is a predetermined value, the mute circuit In the control device, the intermediate frequency signal is muted, the frequency counting of the intermediate frequency is stopped, the station signal is detected again, and if the station signal is judged to be the station signal in both of the two times, the station signal is considered to be present.

When the predetermined value of the counter is registered in the control device, the mute circuit mutes the intermediate frequency signal to stop the frequency counting of the intermediate frequency, and the station signal is judged to determine the station signal. When there is, the sweep of the tuning frequency is stopped, the mute circuit is turned off, the frequency count of the intermediate frequency is started, and the count value of the counter circuit is registered in the control circuit. Furthermore, the PLL is automatically used to detect each predetermined station signal.
It is an automatic channel selection device characterized in that automatic channel selection is performed by performing frequency sweep and repeating station signal determination as described above.

[0011]

According to the present invention, the S / N of the high frequency amplifier circuit and the mixing circuit is improved by the above configuration.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the automatic channel selecting apparatus of the present invention will be described in detail below with reference to FIGS.

FIG. 1 is a flow chart showing the tuning procedure of the automatic tuning apparatus in the first embodiment of the present invention.

FIG. 2 is a flow chart showing a tuning procedure of the automatic tuning apparatus according to the second embodiment of the present invention.

A first embodiment of the present invention will be described below with reference to the drawings. 1 and 3, when the automatic channel selection is started, the control circuit 17 changes the frequency division ratio of the programmable frequency dividing circuit 11 to change the PLL frequency by one step, and the station detecting circuit 16 detects the station. If there is a station signal, stop the tuning frequency sweep,
The frequency counter 15 counts the frequency of the intermediate frequency signal at the PLL frequency at that time, and when the count value is a predetermined value, the mute circuit 14 mutes the intermediate frequency signal to stop the frequency counting by the frequency counter 15. The station signal is detected again by the station detection circuit 16,
When the two station signal determinations are both station signals, it is considered that there is a station signal, and control is performed to turn off the audio mute.

The second embodiment will be described below with reference to FIG. When the predetermined value of the frequency counter 15 is registered in the control circuit 17, the PLL frequency is changed by one step by the control device 17 as in the case of the first embodiment, the intermediate frequency signal is muted by the mute circuit 14, and the intermediate value by the frequency counter 15 is set. The frequency counting of the frequency is stopped, the judging operation of the station signal is performed, and when there is the station signal, the mute circuit 14 is turned off, the frequency of the intermediate frequency is started, and the frequency counter 1 is added to the control circuit 17.
The count value corresponding to the channel selection frequency of 5 is registered.

Further, for the detection of each predetermined station signal, the PLL frequency is automatically swept, and the automatic tuning can be performed by repeating the above-described processing until the sweep range is within the specified range.

As described above, according to this embodiment, the S / N ratios of the high frequency amplifier circuit and the mixing circuit are improved, and the malfunction of the automatic channel selection device can be prevented.

[0019]

As described above, according to the present invention, the S / N ratios of the high frequency amplifier circuit and the mixing circuit are improved, and the malfunction of the automatic channel selection device can be prevented.

[Brief description of drawings]

FIG. 1 is a flowchart showing a tuning procedure of an automatic tuning device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a tuning procedure of the automatic tuning device in the second embodiment of the present invention.

FIG. 3 is an electrical block diagram showing an example of a general automatic channel selection device.

FIG. 4 is a flowchart showing a tuning procedure of the automatic tuning device in the conventional embodiment.

[Explanation of symbols]

 1 Receiving Antenna 2 High Frequency Amplifier Circuit 3 Mixing Circuit 4 Intermediate Frequency Amplifier Circuit 5 Detection Circuit 6 Low Frequency Amplifier Circuit 7 Speaker 8 Voltage Controlled Oscillator 9 Reference Signal Oscillation Circuit 10 Frequency Dividing Circuit 11 Programmable Frequency Dividing Circuit 12 Phase Comparator 13 Low Pass Filter 14 Mute circuit 15 Frequency counter 16 Station detection circuit 17 Control circuit

Claims (2)

[Claims] 1. A PLL receiver having an automatic tuning function, including a mute circuit for muting an intermediate frequency signal, a counter circuit for counting the frequency of the intermediate frequency signal, and a station detection circuit for detecting the presence or absence of a station signal. , Including a control device for performing all the control of the automatic tuning device, when the station signal is detected during automatic tuning, the sweep of the tuning frequency is stopped, and the frequency of the intermediate frequency signal is counted by the counter circuit, When the count value of the counter circuit is a predetermined value, the mute circuit mutes the intermediate frequency signal to stop the frequency count of the intermediate frequency, detects the station signal again, and performs the station signal determination of the two times. If it is a signal, it is an automatic channel selection device that controls the station signal. 2. The mute circuit mutes the intermediate frequency signal to stop counting the frequency of the intermediate frequency to determine the station signal. When there is a station signal, the sweeping of the selected frequency is stopped, and the mute circuit. The automatic channel selection device according to claim 1, wherein the counter value is turned off, the frequency count of the intermediate frequency is started, and the count value of the counter circuit is registered in the control circuit.