JP2002232267A - Fm receiver and its selecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an FM receiver capable of performing a selection operation in a short time even in an area where the separation the transmission frequencies of FM broadcasting stations is narrow and its selecting method. SOLUTION: This FM radio receiver measures the electric field intensity of a received broadcast wave in an automatic selection mode, measures the intermediate frequency of the received broadcast wave for a relatively short time to obtain a first intermediate frequency value, discriminates whether or not broadcasting whose frequency is the same as a set receiving frequency exists on the basis of the electric field intensity of the received broadcast wave and the first intermediate frequency, obtains a second intermediate frequency obtained by measuring the intermediate frequency of the received broadcast wave for a relatively long time only when it is estimated that the broadcasting exists, and judges that a broadcasting of a corresponding frequency exists to finish the selection operation when the second intermediate frequency is within a prescribed tolerance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an FM receiver having an automatic search function for automatically selecting a channel and a method of selecting the same. In particular, the present invention relates to an FM receiver capable of performing an automatic search even in an area where transmission frequency intervals of FM broadcast stations are narrow, and a method of selecting the FM receiver.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a conventional FM receiver. The conventional FM receiver 30 includes a tuning circuit 13 that passes only near a set reception frequency, an RF amplification circuit 15, an output of the RF amplification circuit 15, and a local oscillation circuit 25.
A mixing circuit 17 which mixes the output of the mixing circuit 17 and outputs an intermediate frequency signal having a frequency of the difference between the two frequencies;
IF amplification circuit 19 for amplifying the intermediate frequency signal output from the IF 7, and FM for detecting the output of the IF amplification circuit 19 by FM
It comprises a detector 21, an audio amplifier circuit 23 for amplifying the output of the FM detector 21, and control means 33 b for controlling the entire FM receiver 30. The FM receiver 30 further includes an electric field intensity measuring unit 27 that measures the electric field intensity of the received broadcast wave from the intermediate frequency signal in the IF amplifier circuit 19, and an IF that measures the frequency of the intermediate frequency signal in the IF amplifier circuit 19.
Measuring means 55.

The control means 33b is connected to an operation means 35 and a display means 37. The control unit 33b includes a microprocessor (MPU) and a memory. Control means 3
3b is an electric field strength determining means 5 composed of the MPU or the like.
1 and IF determination means 57. Electric field strength determination means 5
1 determines whether or not the electric field intensity of the received broadcast wave is equal to or higher than a predetermined value based on the output of the electric field intensity measuring means 27. The IF determining means 57 determines, based on the output of the IF measuring means 55, whether or not the tolerance of the intermediate frequency is within a predetermined value.

The local oscillation circuit 25 includes a reference signal oscillation circuit 43
(Phase Loc) using the output of
The PLL comprises a voltage controlled oscillator (VCO) 41, a frequency dividing circuit 42, and a phase comparing circuit 4.
4. It is composed of a low-pass filter (LPF) 45. The output frequency of the local oscillation circuit 25 is changed by changing the frequency division ratio according to a control signal provided from the control means 33b to the frequency division circuit 42. The output of the LPF 45 is also provided to the tuning circuit 13.

In the FM receiver 30, when the user instructs an automatic tuning (auto search) through the operation means 35, the control means 33b activates the mute operation of the audio amplification circuit 23 and changes the frequency of the local oscillation circuit 25. The frequency is raised or lowered at a predetermined frequency width ft (for example, 50 kHz). At the time of performing the auto search, at a certain frequency, the electric field strength determining means 51 determines whether or not the electric field strength of the received broadcast wave is equal to or more than a predetermined value. Change the receiving frequency to the frequency, if the electric field strength of the received broadcast wave is above a predetermined value,
IF determining means 57 determines whether or not the frequency of the intermediate frequency signal is within a predetermined tolerance.

If the value of the intermediate frequency exceeds a predetermined tolerance, it is determined that there is no broadcast of the received frequency, the receiving frequency is changed to the next frequency separated by a predetermined frequency ft, and the intermediate frequency is changed. Is within a predetermined tolerance, it is determined that there is a broadcast having the same transmission frequency as the reception frequency, and the search is terminated.
The mute operation of No. 3 is released, and the broadcast of the reception frequency is continuously received.

[0007] The frequency interval at which FM broadcasts are arranged differs depending on the country or region.
00KHz, 50KHz or 30kHz in Europe
z, frequency intervals such as 100 kHz are adopted in Japan, and the transmission frequency of each FM broadcasting station is determined. Problems with modulation are likely to occur. Incidentally, in Europe, the frequency band of FM broadcasting in which FM broadcasting is arranged in 50 KHz steps is 87.
5 MHz to 107.9 MHz, and the auto search is performed in this frequency range. In addition to this, there is an FM frequency band in which FM broadcasting is arranged in 30 KHz steps.
0 MHz to 74.0 MHz. In the following description, 87.5 MHz to 107.9 MH unless otherwise specified.
An example in which automatic tuning is performed in 50 kHz steps for FM broadcasting in the frequency band z will be described.

The problem with the overmodulation is, for example, that the frequency step of the FM broadcast is 50 KHz and the modulated wave is
When the signal is a single low-frequency and large-amplitude signal such as a time signal, an overmodulation state occurs for a relatively long time, and the IF determination unit 57 makes a wrong determination. In this case, assuming that the electric field strength determining means 51 has determined that the electric field strength of the received broadcast wave is equal to or more than a predetermined value, the intermediate frequency value obtained by measuring the IF measuring means 55 during, for example, 50 mSEC is:
Due to overmodulation, the IF exceeds a predetermined tolerance (for example, ± 25 KHz), and there is a possibility that the IF determination unit 57 may make an erroneous determination that there is no FM broadcast of the frequency.

[0009]

As a workaround for the above problem, the measurement time in the IF measuring means 55 is set to, for example, 50 m.
There is a method in which the measurement time is set to 200 mSEC, which is longer than SEC, and the measurement is performed for a longer time to determine whether there is a broadcast. However, this method has a problem that the search time is longer. The present invention has been made in view of the above problems, and its object is to provide an FM
An object of the present invention is to provide an FM receiver capable of performing a tuning operation in a short time even in an area where transmission frequency intervals of broadcasting stations are narrow, and a method of selecting the FM receiver.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a first invention is to provide an FM receiver for automatically selecting an FM broadcast in which the electric field strength of a received broadcast wave is reduced. Electric field intensity measuring means for measuring, first IF measuring means for measuring an intermediate frequency of the received broadcast wave for a time t1 and outputting the same as a first intermediate frequency value,
A second IF measuring means for measuring for a time t2 greater than 1 and outputting it as a second intermediate frequency value, based on the electric field strength of the received broadcast wave and the first intermediate frequency value at the time of automatic channel selection. It is estimated whether or not there is a broadcast having the same frequency as the set reception frequency, and the second intermediate frequency value is obtained only when it is estimated that there is a broadcast, and the second intermediate frequency value has a predetermined tolerance. This is an FM receiver that terminates the channel selection operation when it is within.

According to the FM receiver of the present invention, based on the electric field strength of the received broadcast wave and the first intermediate frequency value measured in a relatively short time, the same transmission frequency as the set reception frequency is used. It is estimated whether or not there is a broadcast, and only when it is estimated that there is a broadcast, a second intermediate frequency value measured over a relatively long time is obtained, and the second intermediate frequency value is within a predetermined tolerance. Is determined based on whether or not there is a broadcast in which the set reception frequency and transmission frequency match. Since the second intermediate frequency value has been measured over a relatively long period of time, its value approaches the center value of the intermediate frequency. Therefore, even if the measurement for obtaining the first intermediate frequency value is performed many times during the search, it can be performed in a short time. And in the estimation,
When the broadcast wave of the adjacent frequency in the overmodulation state is erroneously estimated to be the broadcast wave of the frequency, the fact that the second intermediate frequency value approaches the center value of the intermediate frequency is used. Therefore, it is correctly determined that there is no broadcast of the frequency, and the search can be performed at the next frequency separated by one step. In this way, even in an area where the interval between the transmission frequencies of the FM broadcast stations is narrow, automatic tuning is performed in a short time with little erroneous determination.

According to a second aspect, in the FM receiver according to the first aspect, the electric field intensity of the received broadcast wave is equal to or greater than a predetermined value, and the first intermediate frequency value is within a first tolerance. Only when the second intermediate frequency value is obtained, and when the second intermediate frequency value is within a second predetermined tolerance smaller than the first tolerance, the FM receiver ends the tuning operation. is there.

According to the FM receiver of the second invention, even if the first intermediate frequency value is measured in a short time at the moment when the broadcast is in the overmodulation state, the first tolerance is set to be sufficiently large. Thus, the risk of erroneously determining that there is no broadcast having the same frequency as the frequency being received can be reduced.
On the other hand, if the broadcast wave of the adjacent frequency is received by increasing the first tolerance and it is erroneously estimated that there is a broadcast of the set reception frequency, the second tolerance is reduced. As a result, it is correctly determined that there is no broadcast whose set reception frequency and transmission frequency are the same. This utilizes the fact that the second intermediate frequency value obtained by measuring over a relatively long time approaches the center value of the intermediate frequency.

A third aspect of the present invention relates to an F which automatically selects an FM broadcast.
In the channel selection method of the M receiver, at the time of automatic channel selection, the electric field strength of the received broadcast wave is measured, the intermediate frequency of the received broadcast wave is measured for a time t1, and a first intermediate frequency value is obtained. Based on the electric field strength of the broadcast wave and the first intermediate frequency value, it is estimated whether or not there is a broadcast of the same frequency as the set reception frequency. A second intermediate frequency value obtained by measuring the intermediate frequency of the wave for a time t2 greater than t1 is obtained, and when the second intermediate frequency value is within a predetermined tolerance, the channel selection operation is terminated. This is a method for selecting a FM receiver.

According to a fourth aspect, in the method of selecting a FM receiver according to the third aspect, the electric field strength of the received broadcast wave is equal to or higher than a predetermined value, and the first intermediate frequency value is equal to the first intermediate frequency value. The second intermediate frequency value is obtained only when the value is within the tolerance, and the tuning operation is terminated when the second intermediate frequency value is within a second predetermined tolerance smaller than the first tolerance. FM
This is a method of selecting a receiver.

[0016]

Embodiments of the present invention will be described below. In the FM receiver and the tuning method of the present invention, at the time of automatic tuning, the frequency to be received is set, and the value of the intermediate frequency of the broadcast wave received at the frequency is first measured in a short time. Estimating whether there is a broadcast of the same transmission frequency as the set reception frequency based on the electric field strength of the broadcast wave and the intermediate frequency measured over a relatively long time only when it is estimated that there is a broadcast When the measured value is within a predetermined tolerance, it is determined that there is a broadcast having the same reception frequency and transmission frequency, and the channel selection operation ends. If it is estimated that there is no broadcast in the estimation, the reception frequency is increased or decreased by a predetermined number of steps and set. As described above, the intermediate frequency is measured over a relatively long time only when it is determined that the broadcast of the frequency is present, so that the search operation can be performed in a short time, and the erroneous determination regarding the presence or absence of the broadcast is reduced. Can be.

FIG. 1 is a block diagram showing an embodiment of the FM receiver according to the present invention. In the FM receiver 10 of the present invention shown in FIG. 1 and the FM receiver 30 of the conventional example shown in FIG. 3, the blocks having the same functions and the same functions are denoted by the same reference numerals, and the description thereof will be omitted. The main difference between the two is that the FM receiver 1 shown in FIG.
0, the first IF measuring means 2 is used instead of the IF measuring means 55.
9 and the second IF measuring means 31 are provided, and the control means 33 includes a first IF determining means 52 and a second IF determining means 53 instead of the IF determining means 57. The reference signal oscillation circuit 43 of the local oscillation circuit 25 is, for example, 50K.
It is a reference signal oscillation circuit that oscillates at 50 Hz, and the auto search is performed in steps of 50 KHz. The setting of the receiving frequency at the time of the automatic search is performed by setting the frequency division ratio of the frequency dividing circuit 42 under the control of the control means 33.

When automatically selecting an FM broadcast, first, the frequency dividing ratio corresponding to the frequency received by the control means 33 is determined by a frequency dividing circuit 42.
The local oscillation circuit 25 outputs to the mixing circuit 17 a frequency higher than the received frequency by an intermediate frequency (for example, 10.7 MHz). The output of the LPF 45 is tuned to the tuning circuit 13
, The tuning circuit 13 outputs the frequency band (for example, 65 MHz-107.9 MHz) of the FM broadcast.
Only frequencies near the reception frequency are passed. The electric field strength measuring means 27 measures the electric field strength of the received broadcast wave, and the electric field strength determining means 51 determines whether or not the measured electric field strength is equal to or more than a predetermined value. The first IF measuring means 29 measures the intermediate frequency of the received broadcast wave for a relatively short time t1 (for example, 5 mSEC) and outputs the first intermediate frequency value to the first IF determining means 52. First IF determining means 5
2 indicates that the first intermediate frequency value has a first tolerance (eg, ± 3
(0 KHz).

The electric field strength of the received broadcast wave is equal to or higher than a predetermined value, and the first intermediate frequency value has a first tolerance (for example, ±
If the frequency is within 30 kHz, the control unit 33 estimates that there is a broadcast having the same transmission frequency as the set reception frequency. If the electric field strength of the received broadcast wave is smaller than a predetermined value,
When the first intermediate frequency value exceeds the first tolerance, the control unit 33 estimates that there is no broadcast having the same transmission frequency as the set reception frequency. Then, when it is estimated that there is a broadcast of the set reception frequency, the second IF measuring means 31 outputs a relatively long time t2 (for example, 100 mSE).
The value of the intermediate frequency is measured over C) and output to the second IF determination means 53 as a second intermediate frequency value.

The second IF determining means 53 determines whether the second intermediate frequency value is within the second tolerance (for example, ± 30 KHz). When it is determined that the second intermediate frequency value is within the second tolerance, the control means 33
Determines that there is an FM broadcast whose set reception frequency and transmission frequency are the same, cancels the mute operation of the audio amplifier circuit 23 set at the start of automatic channel selection, ends the auto search, and sets the FM detector 21 The audio signal subjected to the FM detection is output from the audio amplifier circuit 23.

FIG. 2 is a flowchart showing a channel selection procedure according to the FM receiver of the present invention. When it is confirmed that the user has pressed the tuning key (step S11), step S1 is performed.
In step 3, the mute operation is activated so that the audio signal is not output from the audio amplification circuit 23, and the process proceeds to step S1.
Go to 5. In step S15, the tuning frequency of the tuning circuit 13 is set to the frequency to be searched next, and in step S17
Proceed to. In step S17, the electric field intensity of the received broadcast wave is measured, and the process proceeds to step S19. In step S19, it is checked whether or not the electric field strength is equal to or higher than the reference value. If the electric field intensity is equal to or higher than the reference value, the process proceeds to step S21. If the electric field intensity does not reach the reference value, the process proceeds to step S15. 50 kHz).

In step S21, the first IF measuring means 29
, The IF frequency is measured for a time t1 (for example, 5 mSEC), output to the first IF determination means 52 as a first IF frequency value, and the process proceeds to step S23. In step S23, the tolerance of the first IF frequency value is equal to the first reference value (for example, ± 30
KHz)? , And it is estimated whether or not there is an FM broadcast having the same transmission frequency as the frequency set as the reception frequency. If it is estimated that there is a broadcast, the process proceeds to step S25 with Yes, and if it is estimated that there is no broadcast, the process proceeds to step S15 with No, and the reception frequency is lowered by one step (for example, 50 KHz). In step S25, the second IF
The measuring means 31 sets the IF frequency to a time t2 longer than t1.
(For example, 100 mSEC), and is given to the second IF determination means 53 as a second IF frequency value.
Proceed to 7.

In step S27, is the tolerance of the second IF frequency value within the second reference value (for example, ± 30 KHz)? ,
In the case of Yes, the process proceeds to step S29, and in the case of No, the process proceeds to step S15 to lower the reception frequency by one step (for example, 50 KHz). In step S29,
It is determined that there is an FM broadcast having the same transmission frequency as the frequency set as the reception frequency, the audio mute set at the start of the auto search is released, and the channel selection processing ends.

In the above embodiment, the electric field intensity is measured by the electric field intensity measuring means 27, and then the IF is measured by the first IF measuring means 29.
It is described that the frequency measurement is performed, and then the IF frequency measurement is performed by the second IF measurement unit 31. However, the order of starting these measurements is not particularly limited, and the above three measurements may be started simultaneously. However, the first IF determination means 52 determines that the first I
When it is determined that the F frequency value is not within the first tolerance,
At that time, the measurement by the second IF measurement means 31 is stopped, and the process stands by until the measurement for the next search frequency is performed.

In the above-described embodiment, the first tolerance used for the determination by the first IF determination means 52 is equal to the second tolerance used for the determination by the second IF determination means 53. Can be set to a value larger than the period of the lowest audible frequency, and the second tolerance can be set to a smaller value. Assuming that the automatic search is performed in 50 KHz steps, for example, the first tolerance can be set to a relatively large value of ± 40 KHz, and the second tolerance can be set to a relatively small value of ± 20 KHz. By the way, the modulation degree of ± 20 kHz is 100
% Corresponds to the frequency transition amount.

In this case, since the first tolerance is sufficiently large, even if the first intermediate frequency value is measured in a short time at the moment when the broadcast is in the overmodulation state, the broadcast having the same frequency as the reception frequency will not be obtained. It is possible to reduce the risk of erroneously determining that there is not. And, suppose that while receiving broadcast waves of adjacent frequencies, there is a broadcast of the set reception frequency,
Even if erroneous estimation is made, it is correctly determined that there is no broadcast of the set reception frequency by reducing the second tolerance. This is because the second IF determination unit 53 uses the second intermediate frequency value measured over a relatively long time t2 (for example, 100 mSEC) in the determination. Since the second intermediate frequency value measured over a relatively long time approaches the center value of the intermediate frequency (for example, 10.7 MHz), even if the second tolerance is set to a small value, the second intermediate frequency value actually exists. The danger of erroneously determining that a broadcast is not present is reduced.

As described in detail above, according to the FM receiver of the present invention and the channel selection method thereof, first, the electric field strength of the received broadcast wave and the first intermediate frequency value measured in a relatively short time are used. Then, it is estimated whether or not there is a broadcast of the set reception frequency. Only when it is estimated that there is a broadcast, the second intermediate frequency value is obtained over a relatively long period of time, and based on whether or not the second intermediate frequency value is within a predetermined tolerance, the set reception is set. It is determined whether there is a broadcast whose frequency matches the transmission frequency. Since the second intermediate frequency value is measured over a relatively long period of time, its value approaches the center value of the intermediate frequency (for example, 10.7 MHz).

Therefore, the measurement by the first IF measuring means 29, which requires a large number of measurements during the search, is performed in a short time. Even if the broadcast of the set reception frequency does not actually exist due to the influence of the broadcast wave of the adjacent frequency in the overmodulation state, even if the second intermediate frequency value is erroneously estimated to be present, the second intermediate frequency value is set to the intermediate frequency. Utilizing the fact that it is close to the center value, it can be correctly determined that there is no broadcast, and the search can proceed to the next frequency separated by one step. In this way, even in an area where the interval between the transmission frequencies of the FM broadcast stations is narrow, automatic tuning is performed in a short time with little erroneous determination.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an FM receiver according to the present invention.

FIG. 2 is a flowchart showing a channel selection procedure according to the FM receiver of the present invention.

FIG. 3 is a block diagram showing an embodiment of a conventional FM receiver.

[Explanation of symbols]

 Reference Signs List 13 tuning circuit 15 RF amplifier circuit 17 mixing circuit 19 IF amplifier circuit 21 FM detector 23 audio amplifier circuit 25 local oscillation circuit 27 electric field strength measuring means 29 first IF measuring means 31 second IF measuring means 33 control means 35 operating means 41 voltage control Oscillator (VCO) 42 Divider 43 Reference signal oscillator 44 Phase comparator 45 Low-pass filter (LPF) 51 Electric field strength determining means 52 First IF determining means 53 Second IF determining means

Claims (4)

[Claims] 1. An FM receiver for automatically selecting an FM broadcast, comprising: an electric field intensity measuring means for measuring an electric field intensity of a received broadcast wave; and an intermediate frequency of the received broadcast wave for a first time by measuring an intermediate frequency of the received broadcast wave for a time t1. First IF measuring means for outputting as an intermediate frequency value, and second IF measuring means for measuring the intermediate frequency for a time t2 greater than t1 and outputting the same as a second intermediate frequency value. Based on the electric field strength of the broadcast wave and the first intermediate frequency value, it is estimated whether or not there is a broadcast having the same frequency as the set reception frequency. An FM receiver for obtaining an intermediate frequency value and terminating a tuning operation when the second intermediate frequency value is within a predetermined tolerance. 2. The FM receiver according to claim 1, wherein the electric field intensity of the received broadcast wave is equal to or greater than a predetermined value and the first intermediate frequency value is within a first tolerance. An FM receiver for obtaining a second intermediate frequency value, and terminating a tuning operation when the second intermediate frequency value is within a second predetermined tolerance smaller than the first tolerance. 3. An FM receiver channel selecting method for automatically selecting an FM broadcast, wherein at the time of automatic channel selection, an electric field intensity of a received broadcast wave is measured, and an intermediate frequency of the received broadcast wave is measured for a time t1. Then, based on the electric field strength of the received broadcast wave and the first intermediate frequency value, it is estimated whether or not there is a broadcast having the same frequency as the set reception frequency. Only when it is estimated that there is a second intermediate frequency value obtained by measuring the intermediate frequency of the received broadcast wave for a time t2 greater than t1, the second intermediate frequency value is within a predetermined tolerance. A channel selection method for the FM receiver, wherein the channel selection operation is terminated when. 4. The FM receiver tuning method according to claim 3, wherein the electric field strength of the received broadcast wave is equal to or more than a predetermined value, and said first intermediate frequency value is within a first tolerance. Receiving the second intermediate frequency value only in the case where the second intermediate frequency value is within a second predetermined tolerance smaller than the first tolerance. How to select a machine.