JP3138206B2 - Radio receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver capable of increasing the speed of an AF search in RDS broadcasting.

[0002]

2. Description of the Related Art Conventionally, a system for multiplexing an RDS (Radio Data System) data signal in addition to an audio signal in FM broadcasting and transmitting various information such as a program of a receiving broadcasting station has been used in Europe. And many European broadcasters are broadcasting the same program on a network. Therefore, for example, a radio receiver capable of receiving RDS broadcasts performs the same program when listening to a radio broadcast station while traveling by car and the electric field intensity of the broadcast station being listened to decreases. A function of searching for another broadcast station and automatically selecting that broadcast station when the broadcast station has an electric field strength equal to or higher than a predetermined value (hereinafter, referred to as AF search) is provided. The AF search is performed in a conventional radio receiver as shown in FIG. 2 according to a specific procedure shown in FIG.

When the AF search starts, first, during normal reception of the first broadcast station of the radio receiver in FIG. 2, an AF (alternative frequency list) signal and a received electric field strength are temporarily stored in the control circuit 1 (S1). ). Thereafter, the local oscillation frequency of the local oscillation circuit 2 is changed by the control signal of the control circuit 1,
The received RF signal is also changed (S2). The received RF signal is
The frequency is converted into an IF signal by the frequency conversion circuit 3. The IF signal is amplified by an IF amplifier 4 and then FM detected by an FM detector 5. Also, the output signal of the IF amplifier circuit 4 is subjected to peak detection by the electric field intensity detection circuit 6 to detect the received electric field intensity. The muting signal generation circuit 7 generates a muting signal corresponding to the received electric field intensity only when the electric field is weak, in accordance with the output signal of the electric field intensity detection circuit 6. The output signal of the electric field strength detection circuit 6 is compared with a reference value Vref by a comparison circuit 8. The muting signal and the output signal of the comparison circuit 8 are applied to the station detection circuit 9 to detect the presence or absence of a broadcasting station (S3).
Note that the muting signal is originally used for the muting circuit 10 to mute the output signal of the FM detection circuit 10 and to prevent the S / N of the output signal of the FM detection circuit 5 from deteriorating when the electric field is weak. ing.

When the frequency of the RF signal is changed and the second broadcast station is present, a station detection signal is generated from the station detection circuit 9. In response to the station detection signal, the control circuit 1 detects whether the electric field strength of the second broadcasting station is higher than the first electric field strength. That is, the output signal of the electric field intensity detection circuit 6 is applied to the control circuit 1, and the electric field intensity of the second broadcast station is compared with the electric field intensity of the first broadcast station temporarily stored in the control circuit 1 (S4).

When the electric field strength of the second broadcasting station is larger than the electric field strength of the first broadcasting station, the control circuit 1 detects whether or not the AF signals of the first and second broadcasting stations match. The RDS modulation signal in the output signal of the FM detection circuit 5 is decoded into an RDS signal by the decoder 11 and then applied to the control circuit 1. The control circuit 1 compares the AF signal in the RDS signal of the second broadcast station with the temporarily stored AF signal of the first broadcast station (S5).

If the AF signals match, the radio receiver receives the second broadcast station as it is (S6). When the station detection signal is not generated from the station detection circuit 9, when the electric field strength of the second broadcasting station is smaller than the electric field strength of the first broadcasting station, or when the AF signals do not match, the output signal of the control circuit 1 Accordingly, the local oscillation signal is changed again, and the radio receiver receives the first broadcast station.

[0007]

The muting generating circuit 7 has a large time constant and generates a muting signal which does not follow a change in the electric field intensity. Therefore, the muting circuit 10 follows the change in the electric field strength.
Does not change, and it is possible to prevent a sense of incongruity due to muting. If the muting signal is used for station detection, erroneous detection of a broadcast station due to a change in electric field strength can be prevented. If such a station detection is performed during a general search, a reliable broadcast station can be detected. However, in the conventional AF search for detecting a broadcast station by moving from the first broadcast station to another station during normal reception, the rising time of the muting signal is long due to a large time constant, so that the station detection period is long. Therefore, when returning to the first broadcast station, there is a problem that the listening of the first broadcast station is interrupted. Actually, the value of the capacitor of the muting signal generation circuit 7 is set to 1 μF. It takes about 20 ms until the muting signal rises and the result of the station detection can be determined. I was

[0008]

SUMMARY OF THE INVENTION The present invention relates to an FM radio receiver comprising: a reception electric field strength detection circuit for detecting a reception electric field strength; and an FM detection circuit for FM detecting an IF signal. A station detection circuit for generating an output signal when a received electric field strength equal to or higher than a predetermined level is detected in accordance with an output signal of the circuit; and detecting that a receiving broadcast station is present within a predetermined band in accordance with an output signal of the FM detection circuit. Then, a band station detection circuit that generates an output signal, a first station detection signal generation circuit that generates a first station detection signal according to the presence of both output signals of the station detection circuit and the band station detection circuit, It is characterized by having.

In addition, the radio receiver has a search function and generates a muting signal for increasing a muting amount as the electric field intensity at the time of a weak electric field decreases, and the FM detection circuit. A muting circuit that mutes the output signal of the second station, and a second station detection signal generating circuit that generates a second station detection signal in response to both the output signal of the station detection circuit and the muting signal. The second during the search period
A selection circuit for selecting a station detection signal.

[0010]

FIG. 1 is a diagram showing an embodiment of the present invention. Reference numeral 12 denotes a window comparator for comparing an output signal of an FM detection circuit 5 with a reference value and performing band station detection. A first station detection signal generation circuit for generating a first station detection signal in response to the presence of both the output signal of the comparison circuit 8 and the output signal of the window comparator 12, and 14 controls the radio receiver to indicate the AF search mode state A selection circuit for selecting a first station detection signal from the first and second station detection signals in accordance with an output signal of the circuit 1; In FIG. 1, FIG.
The same reference numerals are given to the same circuits as in the conventional example, and the description is omitted. However, in FIG. 1, the station detection signal generation circuit 9 in FIG. 2 is a second station detection signal generation circuit. FIG.
In the above, the normal reception operation of the radio receiver and the entire operation of the AF search are the same as those in the related art, and the description of the operation is omitted.

Next, the station detecting operation of the radio receiver shown in FIG. 1 during the AF search will be described. First, at the time of the AF search, the selection circuit 14 selects the first signal according to the output signal of the control circuit 1.
The first station detection signal of the station detection signal generation circuit 13 is selected. In a state where the radio receiver is temporarily receiving a station of another frequency from the currently receiving broadcast station, the received RF signal corresponding to the other broadcast station is frequency-converted into an IF signal by the frequency conversion circuit 2. . The IF signal is amplified by the IF amplification circuit 4 and then detected by the FM detection circuit 5. An electric field strength detection circuit 6 detects the received electric field strength of another broadcasting station according to the output signal of the IF amplifier circuit 4. The output signal of the electric field strength detection circuit 6 is compared with a reference level REF by a comparison circuit 8. When the output signal of the electric field strength detection circuit 6 is larger than the reference level,
For example, an output signal of “H” level indicating that the broadcast station is detected is generated from the comparison circuit 8.

The output signal of the FM detection circuit 5 is applied to a window comparator 12 to detect whether the output signal is within a range between a reference level A and a reference level B higher than the reference level. If a broadcasting station is present, the output signal of the FM detection circuit 5 is within the above range, so that an output signal of, for example, “H” level is generated from the window comparator 12. by the way,
The relationship between the frequency of the IF signal and the output signal level of the FM detection circuit 5 is such that the output signal V0 is obtained when the center frequency is f0, as shown in FIG. Such characteristics appear when a broadcasting station is present, and the reference values A and B of the window comparator 12 are set as shown in FIG.
The output signal of window comparator 12 is at "H" level.

Comparison circuit 8 and window comparator 12
Is applied to the first station detection signal generation circuit 13,
When both output signals are at “H” level, the first
A station detection signal is generated. The control circuit 1 determines that a broadcasting station exists according to the first station detection signal, and proceeds to the next operation. The output signal level of the electric field strength detection circuit 6 is
If the reference level is lower than the reference level, the comparison circuit 8 generates an "L" level output signal indicating that there is no broadcast station.
When the broadcasting station is detuned, the characteristics shown in FIG. 4 do not occur, and the output signal of the FM detection circuit 5 is out of the range of the reference values A and B of the window comparator 12, so that the The output signal becomes “L” level indicating that the broadcasting station is detuned. When the reference values A and B of the window comparator 12 are set for the characteristics of the FM detection circuit 5 as shown in FIG. 4A, the input / output relationship of the window comparator 12 becomes as shown in FIG. When one or both of the output signals of the comparison circuit 8 and the window comparator 12 are at the “L” level, the “L” level signal is not generated from the first station detection signal generation circuit 13 and the control circuit 1
Determines that there is no station.

The electric field strength detection circuit 6 detects a peak of the output signal of the IF amplifier circuit 4 to detect the received electric field strength. When smoothing, a capacitor having a time constant sufficient to smooth the frequency of the IF signal may be used.
The time from the start of the AF search to the rise of the electric field strength detection circuit 6 is short. Further, the rise of the output signal of the window comparator 12 is fast because the output signal of the FM detection circuit 5 is used. Although the output signal of the FM detection circuit 5 is generated after being smoothed, the rise time is about 0.5 ms because the time constant for smoothing is set to 0.047 μF. Therefore, it is possible to shorten the station detection operation of the AF search.

In an operation other than the AF search, for example, in a normal search for a broadcast station having a predetermined electric field strength or more, the selection circuit 14 selects an output signal of the second station detection signal generation circuit 9 according to an output signal of the control circuit 1. . The second station detection signal generation circuit 9 generates the second station detection signal in accordance with the output signals of the muting signal generation circuit 7 and the comparison circuit 8 as in the conventional example of FIG. Therefore, erroneous detection of a broadcast station due to a rapid change in the electric field strength can be prevented.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG.
When the frequency is 0.7 MHz, the IF signal frequency can be sufficiently smoothed even if the capacitor used for detecting the peak of the electric field strength detection circuit 6 is 0.47 μF. When such a capacitor is used, the rise of the output signal of the electric field strength detection circuit is about 0.5 ms. Therefore, A
The F search can be performed in 1 ms or less, and it is possible to prevent a sense of incongruity in hearing.

[0017]

As described above, according to the present invention, band station detection is performed in accordance with the output signal of the station detection circuit for performing station detection in accordance with the output signal of the electric field strength detection circuit and the output signal of the FM detection circuit. A according to the output signal of the band station detection circuit that performs
Since the station detection at the time of the F search is performed, the time for the station detection can be reduced. Therefore, the time for the AF search can be reduced, and the sense of incongruity due to the AF search can be prevented.

In a search other than the AF search, a station is detected using a muting signal for muting a weak electric field, so that erroneous detection of a broadcast station due to a rapid change in electric field strength can be prevented. Therefore, both shortening of the AF search time and reliable station detection during other searches can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a flowchart illustrating a procedure of an AF search.

FIG. 4 is a characteristic diagram for describing the present invention.

[Explanation of symbols]

 12 Window comparator 13 First station detection circuit 14 Selection circuit

Claims (1)

(57) [Claims] A frequency conversion of a received RF signal into an IF signal.
And a peak detector for the IF signal.
A reception field strength detection circuit for detecting a received field strength Ri, and an FM detection circuit for the FM detection of the IF signal, the FM detection
Muting the output signal of the wave circuit
And an output signal of the reception electric field strength detection circuit.
Detection with a time constant larger than the time constant of the signal strength detection circuit
When the electric field strength at weak electric field decreases based on the detection result,
Accordingly, the muting amount of the muting circuit is increased.
Muting to generate a muting signal
A normal search function and R
AF search function based on AF data of DS broadcast signal
An FM radio receiver, comprising: a station detection circuit that generates an output signal when a reception electric field strength equal to or higher than a predetermined level is detected in accordance with an output signal of the reception electric field strength detection circuit; and a reception unit that receives an output signal of the FM detection circuit. A band station detecting circuit for generating an output signal when detecting that the broadcasting station is within a predetermined band; a first station detecting signal according to the presence of both output signals of the station detecting circuit and the band station detecting circuit. A first station detection signal generating circuit that generates the signal, an output signal of the station detection circuit, and the muting signal.
A second station that generates a second station detection signal in accordance with the presence of both
Select the detection signal generation circuit and the first station detection signal during the AF search period , and perform a normal search.
A selection circuit for selecting the second station detection signal during a period, wherein each search is performed when the first and second station detection signals are generated.
A radio receiver stopped by an output signal of a road .