JP2009273093A - Fm receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect adjacent interference in an FM receiver quickly and accurately. <P>SOLUTION: A reception electric field strength signal S<SB>M-DC1</SB>corresponding to a broad-band reception signal which may include a signal of a target station and an adjacent interference signal, and a narrow-band reception electric field strength signal S<SB>M-DC2</SB>which includes a signal of the target station and does not include an adjacent interference signal, are generated based on two BPF outputs having respective central frequencies corresponding to the target reception station and having pass bands having different widths. S<SB>M-DC1</SB>and S<SB>M-DC2</SB>are input to a differential amplifier 142, and an output of the differential amplifier 142 is compared with a reference voltage V<SB>ref</SB>in a comparator 144, to determine a relative relationship between a voltage V<SB>W</SB>of S<SB>M-DC1</SB>and a voltage V<SB>N</SB>of S<SB>M-DC2</SB>. When V<SB>N</SB>-V<SB>W</SB><V<SB>ref</SB>, the comparator 144 outputs an L level. In this case, a control circuit 140 determines that adjacent interference occurs, and sets a bandwidth of an IFBPF 70 to a narrow band. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an FM receiver that receives a frequency-modulated (FM) signal, and more particularly to adjacent interference removal at the time of reception of FM broadcasting or the like.

  Since the FM signal changes the frequency of the carrier wave based on an audio signal or the like, its transmission requires a wider frequency band than, for example, an AM signal. Therefore, when receiving an intended transmission signal in an FM receiver, the FM receiver is susceptible to interference (adjacent interference) from other signals transmitted at a frequency close to that frequency, which is the quality of the detected audio signal. May be adversely affected. This adjacent interference can be reduced by narrowing the band of a band pass filter (BPF) that extracts a signal intended for reception. On the other hand, the band limitation may cause distortion of the audio signal of the detection output when the FM signal to be received is highly modulated. In view of this, the BPF bandwidth is switched by detecting the presence or absence of adjacent interference.

  Also, in receiving FM data broadcasts such as RDS (Radio Data System) and VICS (Vehicle Information and Communication System), if adjacent interference is received, the FM detection output signal is distorted, and the bit error rate (BER) is used when decoding the data. ) Deteriorates. In this regard, in data broadcasting, there may be a case where data broadcasting that can be replaced by a broadcasting station other than the currently receiving broadcasting station is performed, and the reception state can be improved by substituting for another station. For example, in RDS, a broadcasting station that performs data broadcasting of the same content is provided. Then, an AF search for automatically selecting a broadcast station having the same reception content and having a good reception state is performed. In this AF search, the presence / absence of adjacent interference is detected and used to determine the reception state.

  FIG. 8 is a block diagram showing a configuration of a conventional FM radio receiver. Many FM radio receivers have an AM radio reception function. The FM radio receiver shown in FIG. 8 also has an AM reception processing unit 4 provided in parallel with the FM reception processing unit 2.

An RF (Radio Frequency) signal received by the antenna 10 is mixed with the first local oscillation signal by the first mixing circuit 12, and the target received signal has a predetermined intermediate frequency (IF) f _IF1 . 1 The frequency is converted to the intermediate signal _SIF1 . The S _IF1 is input to the FM reception processing unit 2 and the AM reception processing unit 4 through the BPF 14, the amplifier 16, and the BPF 18. The BPFs 14 and 18 are set in a wide band so that FM signals can pass through. For example, the bandwidth is set to about 180 kHz. The FM reception processing unit 2 and the AM reception processing unit 4 operate alternatively according to the user's selection, and output the detection output signal _SOUT .

In the FM reception processing unit 2, S _IF1 is mixed with the second local oscillation signal in the second mixing circuit 20 for FM reception, and frequency-converted to a second intermediate signal S _IF2 having a predetermined intermediate frequency f _IF2. . S _IF2 passes through IFBPF 22, which is a BPF having f _IF2 as the center frequency, and is FM detected by FM detection circuit 24, and the extracted detection output signal S _OUT is output to an output circuit including a speaker or the like.

The S _IF1 is input to the signal meter (S meter circuit 26) by the FM reception processing unit 2. The S meter circuit 26 extracts fluctuation components caused by adjacent interference, noise, and the like from the S _IF1 , generates an S meter AC component signal _SM-AC , and smoothes and converts the S _IF1 into a direct current to indicate the received electric field strength. An S meter DC component signal S _M-DC is generated.

On the other hand, in the AM reception processing unit 4, the S _IF1 is mixed with the second local oscillation signal in the AM reception second mixing circuit 30, and the second intermediate signal S _IF- having a predetermined intermediate frequency f _IF-AM is obtained. Frequency converted to _AM . The S _IF-AM is detected by the AM detection circuit 34 after passing through the BPF 32 having the center frequency of f _IF-AM . The BPF 32 is basically required to be able to pass the AM signal from the target receiving station. Since the band of the AM signal is about 10 kHz, for example, the bandwidth of the BPF 32 is also set to a narrow band corresponding to this.

Now, IFBPF22 the FM reception processing section 2 is configured to be able to control the bandwidth _{W F} by the bandwidth control unit 28. FIG. 9 is a block diagram illustrating a configuration of the bandwidth control unit 28. The bandwidth controller 28 includes a control circuit 36, a high pass filter (HPF) 38, a capacitor C _HF , a low pass filter (Low Pass Filter: LPF) 40, and a switch circuit 42.

The switch circuit 42 uses S _OUT and S _M-AC as input signals, and selectively selects one of them as an output signal to the HPF 38 in accordance with S _M-DC . Specifically, the switch circuit 42 outputs _SM-AC as an output signal when the received electric field strength is a weak electric field that is equal to or less than a predetermined threshold, and outputs S _OUT as an output signal when the received electric field strength is equal to or higher than the medium electric field.

The HPF 38 has a cut-off frequency of about 100 kHz, for example, and passes a frequency component exceeding the audio band in the input signal. The high-frequency signal component that has passed through the HPF 38 is smoothed by the capacitor C _HF connected to the output terminal thereof, and the terminal voltage V _HF of the C _HF is input to the control circuit 36 as the output level of the HPF 38.

At the time of adjacent disturbance, high frequency components included in S _OUT and S _M-AC increase. In response to this, the control circuit 36, in the weak high-pass component state of V _HF is less than a predetermined threshold value, the reference bandwidth W _F S _OUT is hardly wide bandwidth occurs audio distortion even at high modulation while setting the w _W, in the strong high-pass component state V _HF exceeds the threshold value is set to W _F narrow effect of adjacent-channel interference removal can be suitably obtained bandwidth w _{N (<w W).} As a result, the influence of adjacent interference can be removed and reduced. Incidentally, conventionally, the control of the W _F, was also carried out taking into consideration the degree of modulation which is detected based on the voice band components of S _OUT passing through the LPF 40.

  As another mechanism for detecting adjacent interference, there is a mechanism using a signal quality sensor (SQ sensor) or an IF counter.

The SQ sensor extracts high-frequency components of S _OUT and S _M-AC that increase at the time of adjacent interference with HPF, detects and smooths this with a detection circuit, converts it to a DC voltage, and converts the DC voltage to a predetermined value with a comparator. Compared with the threshold value, it is determined that the adjacent disturbance occurs when the threshold value is exceeded.

For example, the IF counter counts the frequency f _IF2 of the intermediate signal _SIF2 . The count value of the IF counter, in no adjacent-channel interference state, becomes an intermediate frequency f _IF2 is theoretically the average frequency of the frequency spectrum of the target receiving station, in a state undergoing adjacent interference, adjacent interference to S _IF2 Since the signal component of the station is included, the frequency spectrum shifts toward the adjacent interfering station, and the count value N obtained corresponding to the average frequency is also a value deviated from f _IF2 . The count value N is monitored by, for example, a control unit of a receiver constituted by a microcomputer or the like, and the occurrence of adjacent interference is detected based on the deviation.
JP 2004-312077 A Japanese Patent Application No. 2007-31832

The configuration for detecting adjacent interference based on the conventional S _OUT and S _M-AC described with reference to FIG. 8 is such that even when there is no adjacent interference and only the desired station is received, S _OUT and S _M- The output level V _HF of the HPF 38 may exceed the threshold value due to high frequency noise components included in the _AC . For this reason, the conventional configuration has a problem that it is not always possible to accurately discriminate between the case where the adjacent interference occurs and the case where it is caused by noise. That is, an event in which V _HF exceeds the threshold includes noise, which is erroneously detected as adjacent interference, and the bandwidth of IFBPF 22 is unnecessarily narrowed, resulting in voice distortion. For example, there is multipath noise as noise. As described above, in the conventional configuration, there is a problem that it is not possible to suitably realize the removal of adjacent interference and suppression of audio distortion.

The SQ sensor detects fluctuation components (AC components) caused by adjacent interference based on S _OUT and S _M-AC as in the configuration of FIG. 8, but AC components are also generated when multipath occurs. To do. That is, the SQ sensor also responds to multipath, and it is difficult to distinguish between adjacent interference and multipath, and it is difficult to accurately detect adjacent interference. The SQ sensor has a time constant associated with the smoothing process. Specifically, since the SQ sensor smoothes and extracts an AC component of 50 kHz or more, a time constant of about 2 mS is required. For this reason, there has been a problem that it is difficult to speed up the AF search so that the reception interruption state of the audio broadcast program at the time of AF search is not perceived by the person as being out of sound. Furthermore, the AC component also varies depending on the modulation degree, and there is a problem that the influence of the adjacent interference detection by the SQ sensor may be lowered due to this influence. Further, when adjacent interference is strongly received, capture due to the adjacent interference signal occurs, and an AC component corresponding to the adjacent interference may not appear in _SOUT or _SM-AC . For this reason, when the adjacent interference is strongly received, the SQ sensor behaves in the same manner as when there is no adjacent interference, and may not be useful as an adjacent interference sensor.

  In the detection of adjacent interference by the IF counter, it is difficult to increase the speed of the AF search because the accuracy of the frequency obtained from the count value N becomes lower as the count time becomes shorter. Further, the frequency of the intermediate signal can be affected by, for example, fluctuations in the oscillation frequency of the oscillator according to temperature changes, fluctuations due to modulation, and the like. If the determination condition is set so as to allow this, there arises a conflicting problem that the detection sensitivity of the adjacent interference is lowered.

  The present invention has been made to solve the above-described problems, and adjacent interference is accurately detected in a short time, and it is suitably realized to eliminate adjacent interference and to suppress sound distortion and sound interruption during AF search. An object is to provide an FM receiver.

  An FM receiver according to the present invention performs, on a received signal, frequency conversion for shifting a carrier frequency of a target FM signal from a target receiving station to a predetermined intermediate frequency, and generates an intermediate signal; Adjacent disturbance inclusion intensity detection for obtaining an adjacent disturbance inclusion intensity according to the received electric field intensity by the target receiving station or its adjacent station based on a signal component included in an adjacent disturbance detection band including the intermediate frequency in the intermediate signal. And a target station strength corresponding to a received electric field strength by the target receiving station based on a signal component included in the target station detection band including the intermediate frequency and narrower than the adjacent interference detection band among the intermediate signals. A target station strength detection unit; and an adjacent interference determination unit that determines the presence or absence of adjacent interference by the adjacent station based on the adjacent interference inclusion strength and the target station strength. That.

According to the present invention, the determination of the adjacent interference is not based on the FM detection output signal S _OUT and the S meter AC component signal S _M-AC but on a plurality of received electric field strength signals obtained corresponding to different bandwidths. Based on. Since the received electric field strength signal is generated by being smoothed and converted to a direct current, it is basically not affected by high frequency noise. Therefore, according to the present invention, it is possible to accurately determine whether adjacent interference has occurred. In addition, it is easy to speed up the determination of the presence or absence of adjacent interference as compared with the method using the SQ sensor or IF counter. Further, based on the determination result, it is possible to suitably select whether the bandpass filter is set to a narrow band for removing adjacent interference or set to a wide band for suppressing voice distortion.

  Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing a schematic configuration of an FM receiver according to the first embodiment of the present invention. The main part of the FM receiver 50 is configured as an integrated circuit (IC), and is used, for example, in an in-vehicle audio device of an automobile. The FM receiver 50 includes an AM reception processing unit 51b provided in parallel with the FM reception processing unit 51a, and enables AM reception while sharing a part of the configuration of the FM receiver 50 with FM reception.

  The FM receiver 50 includes an antenna 52, an RF amplifier 54, a first local oscillation circuit 56, a first mixing circuit 58, BPFs 60 and 64, and an amplifier 62 as parts shared by the FM reception function and the AM reception function. ing. The FM reception processing unit 51a includes a second local oscillation circuit 66, a second mixing circuit 68, an IFBPF 70, an amplifier 72, an FM detection circuit 74, an S meter circuit 76, an AFC (Automatic Frequency Control) circuit 80, and a bandwidth control unit 82. It is comprised including. The AM reception processing unit 51b includes a second local oscillation circuit 84, a second mixing circuit 86, a BPF 88, an amplifier 90, an AM detection circuit 92, and an S meter circuit 94.

The RF signal S _RF received by the antenna 52 is amplified by the RF amplifier 54 and then input to the first mixing circuit 58. The first mixing circuit 58 mixes the input RF signal S _RF with the first local oscillation signal S _LO1 input from the first local oscillation circuit 56 to generate a first intermediate signal S _IF1 . Frequency _{f LO1} of the S _{LO1 is} adjusted so that the signal of interest received station included in _{S RF} is converted to a first intermediate frequency _{f IF1} predetermined by the frequency conversion to _{S IF1} by the first mixing circuit 58 . Note that the frequency band of SRF _differs between FM reception and AM reception. In response to this, the first local oscillation circuit 56 switches, for example, the frequency division ratio of its internal frequency _{dividing circuit,} and generates S _LO1 having different frequencies for FM reception and AM reception. The first intermediate frequency _{f IF1} is set to, for example, 10.7 MHz.

The S _IF1 is input to the FM reception processing unit 51a and the AM reception processing unit 51b via the BPF 60, the amplifier 62, and the BPF 64, respectively. BPF60,64 is shared by the FM receiver and the AM reception, the pass band centered at _{f IF1,} is set to a width corresponding to the FM signal is a broadband than AM signal. It is preferable to set the bandwidths of the BPFs wide so that distortion in the BPFs 60 and 64 when the modulation degree of the signal of the target receiving station is high is reduced. For example, the −3 dB bandwidth of the BPFs 60 and 64 can be set to 180 kHz.

The first intermediate signal _SIF1 is input to the second mixing circuit 68 and the S meter circuit 76 in the FM reception processing unit 51a. The second mixing circuit 68 mixes the S _IF1 input from the BPF 64 with the second local oscillation signal S _LO2 input from the second local oscillation circuit 66, and the second intermediate signal S _{IF2 having} the second intermediate frequency f _IF2 . Is generated. The frequency f _{LO2 of} S _LO2 is set to (f _IF1 −f _IF2 ), and the target reception signal of the frequency f _IF1 included in S _IF1 is converted into the frequency f _IF2 in the second mixing circuit 68. The second intermediate frequency f _IF2 is set to 450 kHz, for example.

The S _IF2 is input to the FM detection circuit 74 via the IFBPF 70 and the amplifier 72.

IFBPF70 is basically a center frequency _{f IF2,} and a band-pass filter the pass bandwidth _{W F} can be variably set. Bandwidth _{W F} passing IFBPF70 is controlled by the bandwidth control unit 82. For example, W _F is the reference bandwidth w _W received FM signal is hardly wide bandwidth occurs audio distortion even at high modulation, narrow bandwidth effect of adjacent-channel interference removal can be suitably obtained w _{N (<w W} ). For example, _{w W} is set to about 200kHz, _{w N} can be set to about 50 kHz.

The FM detection circuit 74 is composed of, for example, a quadrature detection circuit. The FM detection circuit 74 performs FM detection on the S _IF2 input from the amplifier 72, extracts a detection output signal S _OUT in the voice band, and outputs it to an output circuit composed of a speaker or the like.

The S meter circuit 76 generates a received electric field strength signal S _M-DC1 based on S _IF1 input from the BPF 64.

  The AFC circuit 80 detects a frequency where a large signal is present in the vicinity of the currently received frequency, and generates a voltage signal Vs corresponding to the frequency shift. This voltage signal Vs is generally used for automatic tracking of the target receiving station or the like, but can also be used to determine whether or not the detected large signal is an adjacent interference wave.

  The bandwidth controller 82 will be described in detail later.

The first intermediate signal _SIF1 is also input to the second mixing circuit 86 of the AM reception processing unit 51b. The second mixing circuit 86 mixes the S _IF1 input from the BPF 64 with the second local oscillation signal S _LO-AM input from the second local oscillation circuit 84 to generate a second intermediate frequency f _IF-AM second. An intermediate signal S _IF-AM is generated. Frequency _{f LO-AM} of S _{LO-AM is} set to _{(f IF1 -f IF-AM)} , Purpose received signal in the frequency _{f IF1} included in the _{S IF1} is frequency _{f IF-AM} in the second mixing circuit 86 Converted. The second intermediate frequency f _IF-AM is set to, for example, 450 kHz common to f _IF2, and in this case, f _LO-AM and f _LO2 have the same value, so the second local oscillation circuit 84 and the FM reception process The second local oscillation circuit 66 of the unit 51a can be configured by a single circuit. Also, the second mixing circuit 86 and the second mixing circuit 68 of the FM reception processing unit 51a can be shared. That is, the FM second mixing circuit and the AM second mixing circuit can be shared.

The S _IF-AM is input to the AM detection circuit 92 via the BPF 88 and the amplifier 90.

The pass band of the BPF 88 is set to a width corresponding to the bandwidth of the AM signal with f _IF-AM as the center. That is, the pass band width of the BPF 88 is set to be narrower than that of the BPF 64. For example, the pass band width of the BPF 88 is set to about 7 kHz.

AM detection circuit 92, the _{S IF-AM} input from the amplifier 90 and AM detection, and extracts the detection output signal _{S OUT} of the audio band, and outputs to an output circuit comprising a speaker or the like.

The S meter circuit 94 generates a reception electric field strength signal S _M-DC2 based on S _IF-AM limited to a narrow band by the BPF 88.

  The amplifier 90 and the AM detection circuit 92 are operated when receiving AM, but are stopped when receiving FM. On the other hand, the S meter circuit 94 is also operated during FM reception, and its output is used to control the IFBPF 70. At the time of FM reception, the bandwidth control unit 82 controls the bandwidth of the IFBPF 70 according to the received radio wave state, and an output that is preferably bandwidth limited by the IFBPF 70 is input to the FM detection circuit 74 via the amplifier 72. .

Next, the S meter circuits 76 and 94 will be described. FIG. 2 is a circuit diagram showing a schematic configuration of the S meter circuit 76. Here, S not only meter DC component signal _{S M-DC1,} S meter AC component signal _{S M-AC} described in the prior art also shows a possible product configurations, the _{S M-AC} in this embodiment There is not necessarily a portion related to the generation of. S meter circuit 76, for example, six stages of limiter amplifiers 100-1 to 100-6 connected in series, an adder 102 which is input to their outputs in parallel, based on the output current _{I OUT} of the adder 102 S _M-DC1 and _{S M-AC} current mirror circuit 104 draws current used for generating the smoothing circuit respectively generates a _{S M-DC1} and _{S M-AC} on the basis of the output current of the current mirror circuit 104 106 It is comprised including.

S _IF1 is input to the limiter amplifier 100-1 at the first stage, is sequentially amplified by each limiter amplifier 100, and is added as an output signal S _Ak of each limiter amplifier 100-k (k is an integer satisfying 1 ≦ k ≦ 6). 102 is input. The adder 102 obtains a voltage difference δV _Ak (≡S _Ak −Va) between each S _Ak and the reference voltage Va, generates a current δI _Ak corresponding to the voltage difference for δV _{Ak where} δV _Ak > 0, their combined current output as _{I OUT.}

I _OUT is folded back to the output side path having T _r2 and the output side path having T _r3 via the transistor T _r1 in the input side path of the current mirror circuit 104, respectively. The smoothing circuit 106 connected to the output side path having T _r2 includes a resistor R ₁ and a capacitor C ₁ connected in parallel with each other between the collector of T _r2 and the ground potential GND. The smoothing circuit 106 smoothes I _OUT output from T _r2 with a time constant determined according to the resistance value R ₁ and the capacitance value C ₁ to generate S _M-DC1 . For example, by providing R ₁ and C ₁ to provide LPF characteristics, an AC component signal superimposed on the output of the adder 102 (modulation signal, multipath, fluctuation caused by adjacent interference) as _SM-DC1 Component) is smoothed to obtain a signal which can be regarded as substantially a direct current.

On the other hand, the smoothing circuit 108 connected to the output side path having T _r3 is similar to the smoothing circuit 106 in that the resistor R ₂ and the capacitor connected in parallel with each other between the collector of T _r3 and the ground potential GND. consisting of C _2. The smoothing circuit 108 smoothes I _OUT output from T _r3 with a time constant determined according to the resistance value R ₂ and the capacitance value C ₂ , and generates S _M-AC . For example, by setting the time constant of R _2, C _2, the time constant of the smoothing circuit 108 is a value enough to follow the amplitude variation of the S _IF1. As a result, an AC signal corresponding to the amplitude fluctuation generated in SIF1 due to adjacent interference or noise is obtained as _{SM -AC, and} as described above, this is conventionally used for detecting adjacent interference. In contrast, in the present _invention, the presence or absence of adjacent interference is determined by using the _{S M-DC2} generated by _{S M-AC} rather than _{S M-DC1} and S meter circuit 94. In addition, you may use combining the method using the conventional _SM-AC and this method.

The S meter circuit 94 has the same basic configuration as the S meter circuit 76 described above. FIG. 3 is a schematic graph showing changes according to the received electric field strength of the output signal S _M-DC1 of the S meter circuit 76 and the output signal S _M-DC2 of the S meter circuit 94. In the figure, the horizontal axis represents the received electric field intensity E at the antenna 52, and the vertical axis represents the voltages V _W and V _N of the signals S _M-DC1 and S _M-DC2 . As will be described later, in the present invention, it is possible to determine the presence or absence of adjacent interference in the slope sections 122 of the characteristic curves 120a and 120b of the S _M-DC1 and S _M-DC2 respectively. The fact that 120b has basically the same slope in the section 122 is utilized. This condition can be realized, for example, by making the basic configuration of the S meter circuits 76 and 94 common. That is, by making the basic configuration of the S meter circuits 76 and 94 common, as shown in FIG. 3, the change of the characteristic curve 120a of S _{M-DC1 and} the characteristic curve 120b of S _M-DC2 with respect to the received electric field strength E Can be made common.

FIG. 4 is a schematic diagram showing the positional relationship on the frequency axis of the filter characteristics 130w of the BPFs 60 and 64, the filter characteristic 130n of the BPF 88, the band 132 of the reception signal of the target receiving station, and the band 134 of the adjacent interfering signal. In FIG. 4, the horizontal axis is the frequency f, and the filter characteristics 130w and 130n are shown by matching the center frequencies f _IF1 and f _IF-AM of the respective passbands. The target receiving station (band 132) preferably passes through both the wide band BPFs 60 and 64 and the narrow band BPF 88. On the other hand, the signal (band 134) of the adjacent station can pass through the wide band BPFs 60 and 64, but basically does not pass through the narrow band BPF 88.

That is, the filter characteristic 130w of BPF60,64 is set to have a band that can detect neighbor (adjacent interference detection zone), the received field strength is S meter circuit 76 generates, based on the _{S IF1} having passed through the BPF60,64 S _M-DC1 represents the strength (adjacent disturbance inclusion strength) including not only the target receiving station but also adjacent stations. On the other hand, the filter characteristic 130n of the BPF 88 is set to have a band (target station detection band) in which only the target receiving station can be detected, and the received electric field generated by the S meter circuit 94 based on the S _IF-AM that has passed through the BPF 88. The strength S _M-DC2 basically represents the strength based on only the target receiving station (target station strength).

Here, FIG. 3 shows a state in which the characteristic curves 120a and 120b are shifted from each other up and down. The vertical deviation between the characteristic curves 120a and 120b is caused by the difference in the bandwidth of the input signal to each of the S meter circuits 76 and 94 as described above, even if the S meter circuits 76 and 94 have the same configuration. obtain. Further, the vertical deviation between the characteristic curves 120a and 120b, that is, the offset voltage between S _M-DC1 and S _M-DC2 is, for example, in the output side path having T _r2 of the current mirror circuit 104 in FIG. The flowing current can be set and adjusted by providing a predetermined difference between the S meter circuit 76 and the S meter circuit 94 using a current bias circuit or the like. For example, the FM receiver 50 can have a DAC (Digital-to-Analog Converter) and a register function, and can control the offset voltage of the characteristic curves 120a and 120b by controlling the register from the outside. By adjusting the offset voltages of the characteristic curves 120a and 120b, the difference in offset voltage between the characteristic curves 120a and 120b can be set to a desired value. In addition, the offset voltage of the output voltage S _M-DC2 of the S meter circuit 94 can be set to a different value when AM is received and when FM is received.

The offset voltage ΔV _SM between the characteristic curves 120a and 120b is
ΔV _SM ≡V _N (e) −V _W (e)
It is defined as Here, V _N (e) and V _W (e) are values of S _M-DC1 and S _{M-DC2 when} the received electric field strength E = e, respectively.

As described above, when the characteristic curves 120a and 120b are parallel with respect to the total received electric field strength, ΔV _SM is constant without depending on e. In reality, it may be difficult to make the characteristic curves 120a and 120b parallel to all received electric field strengths. In that case, it is set to be substantially parallel in the inclined section 122, and ΔV _SM can be represented by an average value or the like in the section 122.

In the present embodiment, ΔV _SM is set to a predetermined reference value, and the intensity relationship between V _N (e) and V _W (e) maintained at the difference ΔV _SM in the section 122 is actually used as a reference mutual relationship. The relationship between V _N and V _W obtained from the S meter circuits 76 and 94 is compared with the reference mutual relationship to determine whether or not adjacent interference has occurred. Specifically, the measured value _{V N} (e.g., point _{P N} corresponds to the FIG. 3) value constituting a reference correlation against _{V W-REF} (e.g., corresponding to a point _{P W-REF} in FIG. 3) than , The magnitude of the measured value V _W (for example, corresponding to the point P _W in FIG. 3), and the difference between V _N and V _W (V _N −V _W ) is expressed as ΔV _SM (≡V _N −V _{W− Judged} against _REF ). A state where V _W is higher than V _W-REF by a predetermined threshold or more is determined to be that adjacent interference has occurred.

As described above, the reception signals from the target reception station and adjacent stations pass through the BPFs 60 and 64 and are input to the FM reception processing unit 51a. In IFBPF70 provided FM reception processing section 51a, in a state in which the pass bandwidth _{W F} is set to the reference bandwidth _{w w,} a portion of the signals of the adjacent stations may protrude to the attenuation band side filter characteristic of IFBPF70 . Therefore, even if the target receiving station and the adjacent station have the same signal intensity at the input of the antenna 52 and the S meter circuit 76, the input level to the FM detection circuit 74 is lower in the adjacent station than in the target receiving station. Can be. In this case, the received field strength of the neighboring stations, the attenuation of the absolute value E _A and the capture ratio E _C and added strength or more in IFBPF70, occurs adjacent interference when stronger than the target receiving station. On the other hand, even stronger than the target reception station received signal strength of the neighboring stations, the excess amount is equal to or less than the strength obtained by subtracting the capture ratio E _C from the absolute value E _A of attenuation at IFBPF70, no adjacent interference . FIG. 5 is a schematic graph showing characteristic curves of S _M-DC1 and S _M-DC2 for explaining determination of adjacent interference in this case, and is expressed in the same manner as FIG. In FIG. 5, for example, ΔV _SM is set to an increase amount of S _M-DC1 (that is, V _W ) when the received electric field strength increases (E _A + E _C ). According to this setting, the difference (V _N −V _W ) between the measured value V _N (for example, corresponding to the point P _N in FIG. 5) and the measured value V _W (for example, corresponding to the point P _W in FIG. 5) is obtained. When 0, that is, V _N = V _W , the signal strength of the adjacent station at the output of IFBPF 70 becomes stronger than the target receiving station by the capture ratio. Therefore, it is possible to determine the presence or absence of adjacent interference based on the magnitude relationship between V _N and V _W, and the determination can be performed by a hardware comparator, for example, and the configuration of the determination circuit can be simplified. It becomes.

  FIG. 6 is a block diagram showing a schematic configuration of the bandwidth controller 82 and its peripheral circuits. The bandwidth controller 82 includes a control circuit 140, a differential amplifier 142, a comparator 144, an LPF 146, and a switch circuit 148.

Output signals S _M-DC1 and S _M-DC2 of the S meter circuits 76 and 94 are input to the differential amplifier 142 in the bandwidth controller 82. The differential amplifier 142 outputs a voltage V _N−W obtained by multiplying the difference (V _N −V _W ) between the voltage values V _W and V _N of the S _M−DC1 and S _M−DC2 by a predetermined gain. The comparator 144 compares V _N−W input from the differential amplifier 142 with the reference voltage V _ref . The comparator 144 outputs a logic level corresponding to the comparison result as the output signal V _COMP to the control circuit 140 as a determination result of the presence / absence of adjacent interference. Control circuit 140, if there determination is adjacent interference by the comparator 144 sets the passband width _{W F} of IFBPF70 the narrow bandwidth _{w N,} if no adjacent interference, _{W F} a reference bandwidth _{w W} Set to.

For example, the [Delta] V _SM, received field strength is set to increase in _{V W} when the increased _{E A.} According to this setting, the polarity of the output voltage of the differential amplifier 142 represents the magnitude of the signal strength between the target receiving station and the adjacent station at the output of the IFBPF 70. By setting V _{ref according} to the capture ratio E _C , it is possible to obtain the determination result of the presence / absence of adjacent interference from the comparator 144 as a logic level output. For example, the output V _{COMP of the} comparator 144 becomes H (High) level when V _N−W ≧ V _ref , and becomes L (Low) level when V _N−W <V _ref . At this time, the H level corresponds to the determination that there is no adjacent interference, and the L level corresponds to the determination that there is adjacent interference. _{Incidentally,} by setting a higher _{V ref,} the bandwidth _{W F} of IFBPF70 it tends to be set to the narrow bandwidth _{w N,} it is possible to prioritize the adjacent interference removing than the suppression of audio distortion that can occur IFBPF70, reverse In addition, by setting V _ref low, priority can be given to suppression of audio distortion over adjacent interference removal.

The above configuration utilizes the fact that the characteristic curves 120a and 120b of the S meter circuits 76 and 94 basically have the same inclination in the inclination section 122 as shown in FIGS. It was. However, the determination of adjacent interference by comparing S _M-DC1 and S _M-DC2 of the present invention is possible even when the slopes of the characteristic curves of S _M-DC1 and S _{M-DC2 in} the slope section 122 are not the same. Applicable.

In this case, the offset voltage ΔV _SM between the characteristic curves of S _M-DC1 and S _M-DC2 is a function of the received electric field strength E. That is, the offset voltage ΔV _SM at the received electric field strength E = e is
ΔV _SM (e) ≡V _N (e) −V _W (e)
It is expressed. E = e ₀ is set as a reference point for the received electric field strength,
ΔV _SM0 ≡ΔV _SM (e ₀ )
If ΔV _SM (e) at an arbitrary received electric field strength is defined as α (e) representing a ratio to ΔV _SM0 ,
ΔV _SM (e) ≡α (e) ΔV _SM0
It can be expressed as. α (e) is obtained corresponding to the characteristic curves of S _M-DC1 and S _M-DC2 . By using this ratio α (e), adjacent interference can be determined by comparing V _W and V _N as a relative comparison based on the state at E = e ₀ . Incidentally, when ΔV _SM is a function of the received electric field strength E, this relative comparison is possible when αV _SM is a function of the received electric field strength E by considering α (e). This can also be understood from the fact that ΔV _SM described with reference to FIGS. 3 and 5 can be converted when it becomes constant regardless of E in the inclined section 122.

Also, the presence / absence determination of adjacent interference when the slopes of the characteristic curves of S _M-DC1 and S _{M-DC2 in} the slope section 122 are not the same can be determined by other methods. For example, based on the characteristic curves of S _M-DC1 and S _M-DC2 , the output of S _M-DC1 at the received electric field strength E corresponding to the voltage value V _N of S _M-DC2 output from the S meter circuit 94 An estimated value V _W-REF is obtained. On the other hand, the measured value V _W of S _M-DC1 is obtained from the S meter circuit 76. These differences (V _W −V _W−REF ) may be compared with a predetermined threshold, and if the difference is equal to or greater than the threshold, it may be determined that there is adjacent interference, and if it is less than the threshold, there is no adjacent interference.

Incidentally, the bandwidth control unit 82 may further be configured to utilize the output signal Vs of the output signal _{S OUT} and AFC circuit 80 of the FM detection circuit 74 to control the _{W F.}

First, a configuration utilizing an output signal _{S OUT} of the FM detection circuit 74 to control the _{W F.} S _{OUT in a} weak electric field state tends to include a high-frequency noise component that is not related to adjacent interference, and as a result, there is a possibility that voice quality (S / N ratio) may be reduced. Therefore, even if it is a weak high-frequency component state and the need for the narrow band w _N is low from the standpoint of adjacent interference, if the degree of modulation is low and the weak electric field state, the IFBPF 70 has a narrow pass band. As w _N , it is possible to reduce the high-frequency noise appearing in S _OUT and improve the voice quality. In this case, since a low degree of modulation, audio distortion also set to narrowband w _N is less likely to occur. It should be noted that the switch 148 can have a hysteresis so that it does not switch frequently with respect to changes in the modulation signal. The amount of hysteresis is related to the time constant of the output of the LPF 146, but it is assumed that the temporal variation of the electric field strength is taken into consideration.

Specifically, the FM detection output signal S _OUT is input to the LPF 146, and the control circuit 140 determines that the modulation level is low when the output level V _{LF of the} LPF 146 is equal to or lower than a predetermined threshold value d _LF . Further, the input from the LPF 146 to the control circuit 140 becomes possible when the switch circuit 148 is turned on in a weak electric field state based on S _M-DC1 , so that the control circuit 140 has the input from the LPF 146, It can be determined that the electric field is weak. Control circuit 140, based on the output _{V LF} of LPF146, detects the case of low modulation and a weak electric field state, sets the _{W F} to _{w N.}

Next, a configuration using the output signal Vs of the AFC circuit 80 will be described. For example, when the reception field strength of the target receiving station is small while the reception field strength of the adjacent interfering station is large, Vs is used when only the target receiving station is receiving or when the adjacent interfering wave is the target reception. Compared with the case where the intensity is smaller than the signal, it can be abnormally large. From this point, it may be possible to determine whether the frequency shift is a normal frequency shift or a frequency shift due to adjacent interference based on Vs. Control circuit 140, for example, set to the narrow bandwidth w _N if it detects an adjacent interference based on at least one of V _COMP and Vs, when suggesting adjacent interference both V _COMP and Vs only It can be configured to set the narrow bandwidth w _N.

In the above-described configuration, the case where ΔV _SM is set to an increase amount of S _M-DC1 (that is, V _W ) when the received electric field intensity increases (E _A + E _C ) has been described. However, even if ΔV _SM is set to another value, by adjusting V _ref , the comparator 144 can obtain an output V _COMP corresponding to the presence or absence of adjacent interference similar to the above-described configuration.

Incidentally, control such as frequency tuning operation and switching operation between FM reception and AM reception in the FM receiver 50 is performed by, for example, a microcomputer connected via a system bus. Conventionally, during FM reception, in order not appear AM detection output signal S _OUT, stops the operation of the AM signal processing unit. On the other hand, in the FM receiver 50 of the present embodiment, at the time of FM reception, the second mixing circuit 86 and the S meter circuit 94 of the AM signal processing unit 51b are operated to generate S _M-DC2 , for example, The AM detection circuit 92 is controlled to stop and not output _SOUT .

In the present embodiment, the narrow band BPF 88 that the AM signal processing unit 51b has conventionally used is used to extract a signal in order to generate the narrow band received field strength signal S _M-DC2 . However, another narrow band BPF may be used. For example, when the AM signal processing unit 51b is not provided, the BPF 88 and the S meter circuit 94 are provided regardless of the AM reception to generate the S _M-DC2 . At this time, the frequency of the intermediate signal used for generating S _M-DC2 may be the same as the frequency f _IF1 of the intermediate signal S _IF1 used for generating S _M-DC1 , or different as in the above embodiment. It is good also as a frequency.

In the above-described embodiment, the example in which the comparison between S _M-DC1 and S _M-DC2 is performed by analog processing using the comparator 144 is shown, but the configuration for comparison is not limited to this. For example, a system including the above-described microcomputer can be used. In that case, for example, S _M-DC1 and S _M-DC2 are converted into digital values by an ADC built in an ADC (Analog-to-Digital Converter) of the microcomputer or an IC (tuner IC) in which the FM receiver 50 is formed. Detection is performed, and processing similar to the above-described analog processing is performed by calculation using the digital value. This digital processing can improve the detection accuracy of adjacent interference than the analog processing described above. For example, using analog or hardware methods for low-cost tuners, and using digital methods including ADCs and microcomputers for middle-class and higher tuners, the trade-off between cost and accuracy can be set well. Can be made.

In the above embodiment, two types of received field strength signals S _M-DC1 and S _M-DC2 are generated using two types of wide and narrow signals S _IF1 and S _IF-AM, and the presence or absence of adjacent interference is determined by comparing them. To do. Here, by extracting three or more types of signals having different bandwidths from the received signal and comparing the received electric field strength signals, not only the presence / absence of adjacent interference, but also the frequency far from the target receiving station. It can also be configured to detect whether there is an adjacent jamming station.

[Second Embodiment]
The FM receiver according to the second embodiment of the present invention has a modulation degree M _IF1 based on an intermediate signal S _IF1 used for generating S _M-DC1 in addition to the configuration of the FM receiver 50 shown in FIG. And a threshold control circuit for controlling the threshold voltage V _ref of the comparator 144 in accordance with the modulation degree M _IF1 .

In the first embodiment, ΔV _SM is constant, but the vertical difference between S _M-DC1 and S _M-DC2 may change according to the modulation degree of the received signal. Specifically, since the pass band width of the BPF 88 used for extracting the FM signal of the target receiving station is narrower than that of the BPFs 60 and 64, it can be set so that only a part of the band of the FM signal passes. For this reason, the higher the degree of modulation of the signal of the target station, the more components that cannot pass through the BPF 88, so that SM _-DC2 becomes lower and VN _-W can be lowered. On the other hand, the lower the modulation degree, the higher the _{SM-DC2 and the} higher _{VN -W} . Therefore, in the present embodiment, as described above, the modulation degree M _IF of the signal S _IF1 before being input to the BPF 88 is obtained, and the threshold voltage V _ref of the comparator 144 is controlled according to the modulation degree M _IF1 . The processing in the comparator 144 can also be realized digitally by using an ADC, a microcomputer, and a DAC. In this case, the threshold voltage V _ref can be set by microcomputer software.

The modulation degree detection circuit can be configured by an analog signal processing circuit using an LPF or the like, or can be configured by a digital signal processing circuit such as a DSP (Digital Signal Processor). The threshold control circuit receives the output of the modulation degree detection circuit and increases V _ref in response to an increase in V _N-W when M _IF decreases. With this configuration, in the detection of the above-described adjacent interference based on S _M-DC1 and S _M-DC2 , it is possible to eliminate the influence of the difference in modulation degree of the target receiving station and improve detection accuracy.

[Third Embodiment]
FIG. 7 is a block diagram showing a schematic configuration of an FM receiver 200 according to the third embodiment of the present invention. In the present embodiment, the same components as those of the FM receiver 50 of the first embodiment are denoted by the same reference numerals, and the following description is simplified. FIG. 7 shows a microcomputer 202 and a system bus 204 that control the operation of the FM receiver 200. The microcomputer 202 rewrites the stored value of a register (not shown) provided corresponding to the control target of the FM receiver 200 such as the first local oscillation circuit 56 via the system bus 204, for example. Can be controlled. Switching control of the wide and narrow the pass bandwidth W _F of IFBPF70 can also be carried out by rewriting the contents stored in these registers. The IFBPF 70 may be either an analog filter or a digital filter. By changing the bandwidth W _F, it is possible to vary the bandwidth of the signal received electric field strength is detected by the S meter circuit 94. The output of the S meter circuit 76 by comparing the output of the S meter circuit 94 in the case of setting narrow W _F, similar to the embodiment described above, can be detected adjacent interference. Moreover, compared with the output of the S meter circuit 94 in the case of sequentially acquired by switching the wide and narrow bandwidth W _F of IFBPF70, and sets a narrow output and W _F of S meter circuit 94 in the case of setting a wide W _F By doing so, adjacent interference can be detected. In this case, the output of the S meter circuit 94 in the case of setting large the W _F is used in place of the output of the S meter circuit 76.

  For example, the above-described register is provided in the control circuit 140 of FIG. 6, and the control circuit 140 includes a circuit that generates a control voltage signal having a predetermined voltage corresponding to the stored value of the register and outputs the control voltage signal to the IFBPF 70. For example, the setting of the register is performed by an output signal of a sensor circuit such as the comparator 144, and the microcomputer 202 of FIG. 7 can be performed via the system bus 204.

In the FM receiver 200 of FIG. 7, the S meter circuit 94 that generates the S _M-DC2 is configured to receive the S _IF2 that has passed through the IFBPF 70. _{That, S M-DC2} is generated based on the _{S IF2} that has been amplified by the amplifier 72 is output from IFBPF70. Note that S _M-DC1 is generated by the S meter circuit 76 based on _SIF1 in the same manner as the FM receiver 50 described above.

The FM receiver 200 shown in FIG. 7 uses the IFBPF 70 in order to extract a narrowband signal for generating the received electric field strength signal S _M-DC2 . When performing the process for determining the presence or absence of adjacent interference, by operating the value of the register by the microcomputer 202 is provided in the control circuit 140 of FIG. 6, to set the passband width W _F of IFBPF70 narrowband w _N. Based on the _SM-DC2 output from the S meter circuit 94 in that state and the SM _-DC1 from the S meter circuit 76 obtained at the same time, the differential amplifier 142 and the comparator 144 in FIG. A signal V _COMP indicating the determination result of the presence or absence of adjacent interference is generated and input to the control circuit 140. Control circuit _140, based on _{V COMP,} rewrites the value of the register, and sets the IFBPF70 passband width _{W F} corresponding to the adjacent interference judgment result.

In this configuration, in a state where IFBPF70 is set to the reference bandwidth _{w W,} Doing adjacent interference judgment operation, temporarily IFBPF70 is switched to the narrow bandwidth _{w N.} Doing this determining operation at the time of receiving the high modulation FM signal may be heard as noises caused distortion in S _OUT. Therefore, the microcomputer 202 performs a mute operation in conjunction with the determination operation. Incidentally, since the determination operation can be completed in a short time of about 1 mS, for example, the influence on the audibility of mute is slight.

  The FM receiver 200 includes an RDS decoder (not shown), and can be configured to receive RDS data. The RDS decoder demodulates the RDS data transmitted by modulating the 57 kHz subcarrier.

  When the reception state deteriorates, the RDS can perform an AF search for searching for an alternative candidate station and can automatically switch to the alternative station. In that control, when the reception condition deteriorates, the audio output is muted, the reception frequency is set to the frequency of the alternative candidate station obtained from the RDS data, and the presence / absence of the alternative candidate station with the reference electric field strength or higher is determined. To do. If it is determined that there is an alternative candidate station, a program identification (PI) code determination is performed. If the PI code is the same in a good reception state, the alternative candidate station is determined as an alternative station, The reception state is maintained, AF search is stopped, and switching to an alternative station is performed. On the other hand, if a good alternative station is not found, the original receiving station is restored. In this case, the received signal to the RDS decoder is not muted.

For example, the microcomputer 202 performs the adjacent interference determination based on the comparison of the above-described S _M-DC1 and S _M-DC2 when the channel is changed from the currently receiving channel to another channel in the AF search. This determination result can be used to determine whether or not the reception state is good when selecting an alternative station. The input of the received signal to the RDS decoder is configured to be mutable by a switch or the like controlled according to the adjacent interference determination result. If it is determined that adjacent interference has occurred, the input to the RDS decoder is muted, and the RDS decoder erroneously detects the transition destination channel as an alternative candidate station based on the received signal in which adjacent interference has occurred. To prevent that.

Further, when it is determined that adjacent-channel interference is present, it sets the bandwidth W _F to the reference bandwidth narrower value w _N, suppresses loss of RDS data by the adjacent-channel interference is easily demodulate the RDS data structure It can also be. In this configuration, when there is no adjacent interference is that the bandwidth W _F is set to the reference bandwidth w _W, to improve the sensitivity to signal for transmitting RDS data so that PI code detection is rapidly performed Can do.

  Here, as already described, the AF search is required to be performed in a short time such as 3 to 7 mS so that the reception interruption state of the audio broadcast program at the time of the AF search is not detected by the person as a sound interruption. However, in the AF search, it is necessary to move to another channel and perform processing such as PLL lock, station detection, adjacent interference detection, multipath interference detection, and PI code detection. It is not easy to accurately perform AF search within the above-mentioned short time. In particular, in European RDS, since AF search is performed with one tuner, it is essential to increase the speed of AF search in order to suppress sound interruption.

In this regard, the above _- described adjacent interference determination by the S _M-DC1 and S _M-DC2 of the present invention can detect adjacent interference with high accuracy in a short time, and facilitates high speed AF search. Also, station detection in AF search can be performed using the _SM-DC1 . That is, since adjacent interference detection and station detection can be performed with a common sensor output, the time required for the microcomputer or the like to acquire the sensor output is shortened, which also contributes to speeding up of the AF search.

Further, it is possible to improve accuracy by performing AF search using the IF counter and SQ sensor described in the prior art together. At that _time, the station detection by _{S M-DC1,} and adjacent-channel interference determination by the _{S M-DC1, S M-} DC2 are in parallel, also performed prior to other stations detecting means can be performed at high speed, this Only when the station is detected by the preceding means, the other station detecting means using the IF count or the SQ sensor is executed to shorten the processing time and the processing load while improving the accuracy of the AF search. be able to.

It is a block diagram which shows the structure of the outline of the FM receiver which is the 1st Embodiment of this invention. It is a circuit diagram which shows the structure of the outline of S meter circuit. It is a typical graph which shows the change according to the received electric field strength of the output signals S _M-DC1 and S _M-DC2 of the S meter circuit. Schematic diagram showing the filter characteristics of the wideband BPF corresponding to S _M-DC1 and the narrowband BPF corresponding to S _M-DC2 and the positional relationship on the frequency axis with respect to the bands of the target receiving station and adjacent interfering signals. It is. It is a typical graph which shows the characteristic curve of S _M-DC1 and S _M-DC2 for demonstrating the judgment of adjacent disturbance. It is a block diagram which shows the schematic structure of a bandwidth control part and its peripheral circuit. It is a block diagram which shows the structure of the outline of the FM receiver which is the 3rd Embodiment of this invention. It is a block diagram which shows the structure of the conventional FM radio receiver. It is a block diagram which shows the structure of the bandwidth control part of the conventional FM radio receiver.

Explanation of symbols

  50,200 FM receiver, 51a FM reception processing unit, 51b AM reception processing unit, 52 antenna, 54 RF amplifier, 56 first local oscillation circuit, 58 first mixing circuit, 60, 64, 88 BPF, 62, 72, 90 amplifier, 66, 84 second local oscillation circuit, 68, 86 second mixing circuit, 70 IFBPF, 74 FM detection circuit, 76, 94 S meter circuit, 80 AFC circuit, 82 bandwidth control unit, 92 AM detection circuit, 100 limiter amplifier, 102 adder, 104 current mirror circuit, 106, 108 smoothing circuit, 140 control circuit, 142 differential amplifier, 144 comparator, 146 LPF, 148 switch circuit, 202 microcomputer, 204 system bus.

Claims (9)

An intermediate signal generating circuit that performs frequency conversion on the received signal to shift the carrier frequency of the target FM signal from the target receiving station to a predetermined intermediate frequency, and generates an intermediate signal;
Adjacent disturbance inclusion intensity detection for obtaining an adjacent disturbance inclusion intensity according to the received electric field intensity by the target receiving station or its adjacent station based on a signal component included in an adjacent disturbance detection band including the intermediate frequency in the intermediate signal. And
Based on the signal component included in the target station detection band that includes the intermediate frequency and is narrower than the adjacent interference detection band among the intermediate signals, the target station strength that determines the target station strength according to the received electric field strength by the target receiver station A detection unit;
Based on the adjacent interference inclusion strength and the target station strength, an adjacent interference determination unit that determines the presence or absence of adjacent interference by the adjacent station,
An FM receiver comprising: The FM receiver according to claim 1,
A variable band-pass filter capable of variably setting a pass bandwidth and passing the target FM signal converted into the intermediate signal;
A detector for FM-detecting the output signal of the variable band-pass filter to generate a detection output corresponding to the target receiving station;
A bandwidth control unit that controls the pass bandwidth according to the determination result of the presence or absence of the adjacent interference by the adjacent interference determination unit, and suppresses the adjacent interference in the detection output;
An FM receiver comprising: The FM receiver according to claim 1 or 2,
The adjacent disturbance inclusion intensity detecting unit is
A first bandpass filter for extracting a signal component corresponding to the adjacent disturbance detection band from a signal under measurement corresponding to the intermediate signal;
A first signal meter circuit for smoothing a signal under measurement based on an output signal of the first bandpass filter to generate a first electric field strength signal corresponding to the adjacent disturbance inclusion strength;
Have
The target station intensity detector
A second bandpass filter for extracting a signal component corresponding to the target station detection band from the signal under measurement corresponding to the intermediate signal;
A second signal meter circuit for smoothing a signal under measurement based on an output signal of the second bandpass filter to generate a second electric field strength signal corresponding to the target station strength;
An FM receiver comprising: The FM receiver according to claim 3.
An AM reception band-pass filter having a bandwidth corresponding to a target AM signal in the received signal; and an AM reception signal meter circuit that generates an electric field strength signal based on an output signal of the AM reception band-pass filter. An AM receiver capable of detecting the target AM signal based on the intermediate signal;
Using the AM reception bandpass filter as the second bandpass filter,
Using the AM reception signal meter circuit as the second signal meter circuit;
FM receiver characterized by. The FM receiver according to claim 2.
The adjacent disturbance inclusion intensity detecting unit is
A first bandpass filter for extracting a signal component corresponding to the adjacent disturbance detection band from a signal under measurement corresponding to the intermediate signal;
A first signal meter circuit for smoothing a signal under measurement based on an output signal of the first bandpass filter to generate a first electric field strength signal corresponding to the adjacent disturbance inclusion strength;
Have
The FM receiver further includes a second signal meter circuit that smoothes a signal under measurement based on an output signal of the variable band-pass filter to generate an electric field strength signal, and the target station strength detection unit includes: Using the band-pass filter and the second signal meter circuit,
The bandwidth control unit sets the passband of the variable bandpass filter to the target station detection band when determining the presence or absence of the adjacent interference,
The second signal meter circuit generates a second electric field strength signal corresponding to the target station intensity based on an output signal of the variable band bandpass filter set in the target station detection band;
FM receiver characterized by. The FM receiver according to claim 3, wherein:
The change characteristics of the electric field strength signal with respect to the received electric field strength of the first and second signal meter circuits are the first electric field strength signal and the second electric field in a state where only the target receiving station is received. Having an equilibrium section where the intensity signal is kept in a reference correlation with an intensity difference according to a predetermined reference value;
The adjacent disturbance determination unit has a state in which the first electric field strength signal is higher than a signal strength that has the reference correlation with the second electric field strength signal by a predetermined threshold or more in the equilibrium section. Determining that the adjacent disturbance has occurred;
FM receiver characterized by. The FM receiver according to claim 6,
The first electric field strength signal in the reference correlation is set lower than the second electric field strength signal by the threshold value, in absolute value or relative value,
The adjacent disturbance determination unit
Comparing means for comparing the first electric field strength signal and the second electric field strength signal;
Determining the presence or absence of the adjacent disturbance based on a magnitude relationship between the first and second electric field strength signals;
FM receiver characterized by. The FM receiver according to claim 6 or 7,
A modulation degree detection means for obtaining a modulation degree of an FM signal included in the adjacent disturbance detection band;
Threshold control means for controlling the threshold according to the degree of modulation;
An FM receiver comprising: The FM receiver according to claim 3, wherein:
The adjacent interference determination unit is estimated from the actual level of the second electric field strength signal when the actual level of the first electric field strength signal is in a state where only the target receiving station is received. Determining that the adjacent disturbance has occurred in a state higher than a level of the first electric field strength signal by a predetermined threshold or more,
FM receiver characterized by.

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