JP2009021721A - Fm tuner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein distortion arises in a received signal of high modulation to bring the sense of incongruity on acoustic feeling for stereophonic sound, if a variable band of an intermediate frequency band pass filter (IFBPF) of a FM (Frequency Modulation) tuner is narrowed as a countermeasure against neighborhood interference. <P>SOLUTION: A neighborhood interference detection circuit 100 detects neighborhood interference from an output signal S<SB>DET</SB>of a FM detection circuit 78. A bandwidth control circuit 94 narrows a band of an IFBPF 74 at the time of generating of neighborhood interference. On the other hand, a stereophone degree of separation control circuit 96 reduces stereophone separation degree in matrix processing of a matrix circuit 82 at the time of generating of neighborhood interference. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an FM tuner that receives a frequency-modulated (FM) signal.

  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 the FM tuner, the FM tuner is likely to receive interference (adjacent interference) from other signals transmitted at a frequency close to that frequency, which contributes to the quality of the detected audio signal. May have adverse effects. This adjacent interference can be reduced by narrowing the band of a band pass filter (BPF) that extracts a reception target signal (desired wave).

FIG. 4 is a block diagram illustrating the configuration of a conventional FM tuner. An RF (Radio Frequency) signal received by the antenna is frequency-converted to an intermediate signal having a predetermined intermediate frequency (IF) f _IF and input to the IFBPF 2. IFBPF2 _is a band pass filter having a center frequency of _{f IF,} the bandwidth _{W F} is, for example, a variable configured in a range such about 40kHz~ about 220 kHz.

  The FM signal that has passed through IFBPF2 is supplied to the limiter amplifier 4. The limiter amplifier 4 amplifies the amplitude of the FM signal to form a rectangular wave, and removes noise on the FM signal. The FM signal amplified by the limiter amplifier 4 and converted into a rectangular wave is input to the FM detection circuit 6. The FM detection circuit 6 performs FM detection on the output signal of the limiter amplifier 4.

  An audio signal is reproduced based on the FM detection output. Further, the FM detection output is input to the adjacent disturbance detection circuit 8. The adjacent disturbance detection circuit 8 detects an interference wave adjacent to the desired wave of the FM signal.

  The limiter amplifier 4 is also connected to a signal meter (S meter) circuit 10. The limiter amplifier 4 is composed of a circuit in which several stages of buffer amplifiers are connected in series. The S meter circuit 10 uses the output of each buffer amplifier of the limiter amplifier 4 as an input signal, and generates a reception electric field strength signal corresponding to the signal strength of the FM signal based on them.

Bandwidth control circuit 12 is inputted to the reception electric field intensity signal from the output and the S meter circuit 10 of the adjacent-channel interference detection circuit 8, based on these, to control the pass bandwidth W _F of IFBPF2. Bandwidth control circuit 12, when the adjacent interference has occurred is controlled so as to narrow the bandwidth W _F. Thereby, the FM signal from which the adjacent interference wave is removed is input to the FM detection circuit 6, and the deterioration of the voice quality due to the adjacent interference can be suppressed.

Also, the bandwidth control circuit 12, even when the received field intensity is a predetermined weak electric field state is controlled so as to narrow the bandwidth W _F. As a result, the noise component passing through IFBPF2 can be reduced, and the sensitivity can be improved.
JP 2004-312077 A

  In FM stereo broadcasting, a modulation signal for frequency-modulating a carrier wave has a component corresponding to a sum signal “L + R” of left and right audio signals (L signal and R signal) and a component corresponding to a difference signal “LR”. Housed in separate bands. Specifically, the (L + R) signal is stored in the band as it is, but the (L−R) signal is higher than the band of the (L + R) signal by modulating the subcarrier (for example, 38 kHz) with the component. Shifted to region. In this method, monaural sound can be reproduced using only the (L + R) signal, and stereo sound can be reproduced by separating the L and R signals by matrix processing of the (L + R) signal and the (LR) signal. .

  Here, the higher the modulation of the FM signal, the wider the bandwidth. Therefore, if the FM modulation degree of the desired wave is high when the band of IFBPF2 is limited in order to suppress adjacent interference, there is a possibility that the sound signal of the detection output is distorted. In particular, as described above, in stereo broadcasting, the (LR) signal, which is a higher band component than the (L + R) signal in the FM signal, is more strongly affected by the band limitation of IFBPF2, and is more powerful than the (L + R) signal. Large distortion is likely to occur. As a result, there is a problem that the reproduced stereo sound tends to cause a sense of incongruity on hearing.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an FM tuner capable of obtaining reproduced sound with reduced auditory discomfort while suppressing adjacent interference.

  An FM tuner according to the present invention performs frequency conversion for shifting a carrier frequency of a reception target FM signal to a predetermined intermediate frequency with respect to a reception signal, an intermediate signal generation circuit that generates an intermediate signal, and a variable pass bandwidth A bandpass filter that can be set and passes through the reception target FM signal converted to the intermediate signal; a detection circuit that detects the reception target FM signal that has passed through the bandpass filter and generates a detection output signal; A stereo demodulation circuit that separates a left signal and a right signal from the detection output signal that is a stereo composite signal, and a stereo separation degree that controls a separation degree between the left signal and the right signal generated by the stereo demodulation circuit A control unit, an adjacent interference detection unit that detects interference of the adjacent signal with respect to the reception target FM signal, and the buffer according to the interference intensity of the adjacent signal. In a strong interference state in which the passband width of the depass filter is controlled and the interference intensity is stronger than a predetermined weak interference state, the predetermined narrow passband width is narrower than that in the weak interference state. The stereo separation degree control unit changes the separation degree according to the interference intensity, and lowers the separation degree in the strong interference state than in the weak interference state.

  According to the present invention, when narrowing the passband width of the bandpass filter at the time of adjacent interference, the sense of incongruity on hearing can be reduced by reducing the left / right separation degree of stereo sound.

  Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings. FIG. 1 is a schematic block diagram of an FM tuner according to the embodiment. The FM tuner 50 is formed on a common circuit board while making its main part into an IC, and is basically configured as an integrated tuner module.

For example, the module is incorporated as a part in an in-vehicle audio device of an automobile. The RF signal S _RF received by the antenna 54 is received in the FM tuner 50 by an FM-RF tuning amplification circuit 56, a first local oscillation unit 58, a first mixing circuit 60, band pass filters (BPF) 62, 66. , Buffer amplifiers 64 and 72, second local oscillator 68, second mixing circuit 70, IFBPF 74, limiter amplifier 76, FM detection circuit 78, noise canceller 80, and matrix circuit (MPX circuit) 82. The output signal S _OUT corresponding to the audio signal of the desired station is generated.

  In addition to the above-described components, the FM tuner 50 includes a crystal oscillation circuit 90, an S meter circuit 92, a bandwidth control circuit 94, a stereo separation degree control circuit 96, a pilot signal extraction circuit 98, an adjacent disturbance detection circuit 100, and a modulation degree detection circuit. 102 and a multipath noise detection circuit 104. The FM tuner 50 is connected to a system bus (not shown), and operates under the control of a control unit (not shown) such as a microcomputer via the system bus.

The RF signal S _RF is input to the FM-RF tuning amplifier circuit 56. FM-RF tuned amplifier circuit 56, of the RF signal _{S RF,} attenuate off-band corresponding to the carrier frequency _{f R} of the received target FM signal components. As a result, the FM-RF tuning amplification circuit 56 passes the RF signal S _{RF in the} band including the frequency f _{R of the} desired reception station, and the output signal of the FM-RF tuning amplification circuit 56 is input to the first mixing circuit 60. Is done.

The first local oscillation unit 58 includes a first oscillation circuit 110 and a frequency divider circuit 112. The first oscillation circuit 110 is constituted by a PLL circuit using the original oscillation signal S ₀ of the crystal oscillation circuit 90 is output as the reference oscillation signal. The PLL circuit outputs an oscillation signal S _OSC1 having a frequency f _OSC1 corresponding to the station desired to receive. The first oscillation circuit 110 is controlled to f _OSC1 by the control unit, and f _OSC1 is set to α · (f _R + f _IF1 ), where α is a frequency dividing ratio of the frequency dividing circuit 112. As described above, the frequency _dividing circuit 112 divides the frequency of S _OSC1 from the first oscillation circuit 110 by α to generate _SLO1 and outputs it to the first mixing circuit 60.

The first mixing circuit 60 mixes the input RF signal S _RF with the first local oscillation signal S _LO1 input from the first local oscillation unit 58 to generate a first intermediate signal S _IF1 . Frequency of S _{LO1 f LO1,} as the signal of the desired station frequency _{f R} included in the _{S RF} is converted to a first intermediate frequency _{f IF1} predetermined by the frequency conversion to _{S IF1} by the first mixing circuit 60 Adjusted. The first intermediate frequency _{f IF1} is set to, for example, 10.7 MHz.

S _IF1 is input to the second mixing circuit 70 via the BPF 62, the buffer amplifier 64, and the BPF 66. For example, the BPFs 62 and 66 can be configured using ceramic filters.

The second local oscillating unit 68 generates S _LO2 having a frequency f _LO2 of 10.25 MHz corresponding to the case where f _IF1 = 10.7 MHz and f _IF2 = 450 kHz. In order to generate this S _LO2 , the second local oscillation unit 68 of the present embodiment has a _{frequency dividing} circuit 114. The frequency dividing circuit 114 divides the oscillation signal S _{0 of,} for example, 20.5 MHz output from the crystal oscillation circuit 90 by ₂ to generate the S _LO2 and supplies it to the second mixing circuit 70.

The second mixing circuit 70 mixes the first intermediate signal S _IF1 input from the BPF 66 with the second local oscillation signal S _LO2 input from the second local oscillation unit 68 to generate the second intermediate frequency f _IF2 . 2 Intermediate signal S _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 70. The second intermediate frequency f _IF2 is set to 450 kHz, for example.

S _IF2 is input to the IFBPF 74 via the buffer amplifier 72. IFBPF74 _is centered frequency _{f IF2,} and a band-pass filter the pass bandwidth _{W F} can be variably set. Bandwidth _{W F} passing IFBPF74 is controlled by the bandwidth control circuit 94 as will be described later.

The S _IF2 output from the IFBPF 74 is input to the FM detection circuit 78 via the limiter amplifier 76. The FM detection circuit 78 is composed of, for example, a quadrature detection circuit. The FM detection circuit 78 performs FM detection on the S _IF2 input from the limiter amplifier 76, and outputs a detection output signal _SDET .

The noise canceller 80 removes pulse noise from the detection output signal _SDET . For example, in an in-vehicle FM tuner, pulsed noise with a short time width and a large amplitude can be superimposed on a received signal due to the operation of a vehicle engine, an electric mirror, a wiper, or the like. The noise canceller 80 suppresses sound quality deterioration due to such pulse noise. S _DET removed pulse noise is input to a matrix circuit 82.

A pilot signal extraction circuit 98 is provided at the output of the noise canceller 80. S _DET is a stereo composite signal composed of (L + R) signal, (LR) signal and pilot signal S _PL , and pilot signal extraction circuit 98 extracts pilot signal S _PL from this S _DET . The extracted pilot signal _SPL is input to the matrix circuit 82.

Further, the pilot signal extraction circuit ₉₈ according to the presence or absence of the pilot signal _{S PL} during _{S DET,} generates a stereo indicator signal _{S SI.} When the pilot signal _SPL is detected during _SDET , the signal _SSI is a state indicating that the received signal is a stereo broadcast, for example, a predetermined voltage V _H (corresponding to a logical value “1”). On the other hand, when the pilot signal _SPL is not detected, the signal _SSI is, for example, a predetermined voltage V _L corresponding to the logical value “0” as a state representing monaural broadcasting. (L level, V _L <V _H ). The _SSI is input to the stereo separation degree control circuit 96.

Matrix circuit 82, during stereo broadcast, using a pilot signal _{S PL} input from the pilot signal extraction circuit _98, to cancel the pilot signal _{S PL} from the _{S DET,} (L + R) signal, the (L-R) signal, respectively Can be extracted. Then, the L signal and the R signal can be separated and output from the (L + R) signal and the (LR) signal by a matrix method.

  The stereo separation degree control circuit 96 controls the separation degree of the stereo signal by adjusting the relative strength of the difference signal (LR) with respect to the sum signal (L + R) in the matrix processing in the matrix circuit 82. This control of stereo separation will be described later.

S meter circuit 92, for example, on the basis of the _{S IF1} inputted from the BPF _66, and generates a fluctuation component signal _{S M-AC} included in the _{S IF1,} the variation component low pass filter (Low Pass Filter: LPF ) To generate a reception electric field strength signal S _M-DC .

FIG. 2 is a circuit diagram showing a schematic configuration of the S meter circuit 92. The S meter circuit 92 includes, for example, six stages of limiter amplifiers 120-1 to 120-6 connected in series, an adder 122 whose outputs are input in parallel, and an output current I _OUT of the adder 122 as _{SM A} current mirror circuit 124 to be taken out to the output circuits of the _DC and S _M-AC, and a smoothing circuit 126 that generates S _M-DC based on the output current of the current mirror circuit 124, respectively.

S _IF1 is input to the first-stage limiter amplifier 120-1 and is sequentially amplified by each limiter amplifier 120, and is added as an output signal S _Ak of each limiter amplifier 120-k (k is an integer satisfying 1 ≦ k ≦ 6). 122 is input. The adder 122 calculates 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.}

The current mirror circuit 124 has an input-side path through which _IOUT flows and two output-side paths provided in parallel, and folds the input-side _IOUT into each output-side path. On the other hand, a smoothing circuit 126 including a resistor R ₁ and a capacitor C ₁ is provided on the output side path. The smoothing circuit 126 has a large time constant and generates _SM-DC , which is a signal that is sufficiently smoothed and can be substantially regarded as a direct current. A signal corresponding to I _OUT extracted to the other output side path is output as S _M-AC while including various fluctuation components.

The S _M-AC is input to the multipath noise detection circuit 104, for example. The multipass noise detection circuit 104 includes a high pass filter (HPF) 130 and a detection circuit 132. The cut-off frequency f _C of the HPF 130 is set so that the main component of multipath noise included in the SM _-AC passes through the HPF 130. In FM radio broadcasting, for example, f _C can be about 50 kHz. The detection circuit 132 rectifies and detects the high frequency component that has passed through the HPF 130 and converts it into a DC voltage. Thus, the multipath noise detection circuit 104 generates a DC signal S _MP with a voltage level corresponding to the intensity of the multipath noise in the received signal, the S _MP is input to the stereo separation level control circuit 96.

The adjacent interference detection circuit 100 detects adjacent interference based on the output signal _SDET of the FM detection circuit 78. Adjacent interference can occur when other stations are present at frequencies close to the desired receiving station. When the difference in the RF frequency of the broadcast station and the desired station providing adjacent interference and Delta] f, the frequency S _DET when adjacent-channel interference occurs is superimposed on the signal component of the audio band corresponding to the desired station, in accordance with Delta] f Having a high frequency component. The adjacent disturbance detection circuit 100 includes an HPF 134 and a detection circuit 136, and outputs a DC signal S _AI having a voltage level corresponding to the strength of a high-frequency component that can be generated by adjacent interference. For example, since the FM broadcast channel step in Japan is 100 kHz, the cutoff frequency f _C of the HPF 134 can be set to about 100 kHz, for example. The S _AI is used in the bandwidth control circuit 94 and the stereo separation degree control circuit 96.

The modulation degree detection circuit 102 detects the modulation degree of the received signal based on _SDET . Modulation degree detection circuit 102, LPF138, and a detection circuit 140, removes the high-frequency component caused by adjacent interference or the like, and outputs a DC signal S _MD having a voltage level that corresponds to the modulation degree. The _SMD is used in the bandwidth control circuit 94.

Bandwidth control circuit 94, based on the _{S MD to S M-DC} for S meter circuit 92 generates, generates the adjacent interference detecting circuit 100 _{S AI,} and the modulation degree detection circuit 102 generates the bandwidth W of IFBPF74 _F is controlled. For example, the bandwidth control circuit 94 based on the S _AI, determines whether the state intensity of adjacent interference exceeds a predetermined threshold value, the threshold or less, the spread W _F so as not to cause audio distortion Set to reference bandwidth. On the other hand, if the S _AI is greater than the threshold value, the bandwidth control circuit 94, as adjacent interference has occurred, narrowed from the reference bandwidth W _F, thereby, the removal of the adjacent interference wave in IFBPF74 Can be planned.

Further, the bandwidth control circuit 94, for example, has a received electric field strength in a predetermined weak electric field state based on S _M-DC and _SMD and has a predetermined weak electric field state even when the adjacent disturbance strength is equal to or lower than a predetermined threshold. of when detecting the state is a low degree of modulation is set to be narrower bandwidth W _F. As a result, high-frequency component noise that increases in a weak electric field state is removed by IFBPF 74, and the sensitivity is improved. Incidentally, susceptible to audio distortion when in the case of high modulation degree narrowed W _F. Therefore, the bandwidth control circuit 94, in the case of a high modulation degree even when the weak electric field, as long as the adjacent-channel interference has not occurred, and sets the W _F to the reference bandwidth. On the other hand, in a state where even adjacent interference a high degree of modulation occurs, narrowing the preferentially W _F adjacent interference removing than audio distortion prevention. Incidentally, the present FM tuner 50 reduces the influence of sound distortion that may occur at this time in terms of audibility by controlling the degree of separation R _SEP described later.

The stereo separation control circuit 96 receives S _M-DC from the S meter circuit 92, S _MP from the multipath noise detection circuit 104, S _AI from the adjacent interference detection circuit 100, and S _SI from the pilot signal extraction circuit 98. The stereo separation degree R _SEP is controlled based on. FIG. 3 is a graph schematically showing an example of a control characteristic curve in the stereo separation degree control circuit 96, where the horizontal axis represents the received electric field strength V _R (unit: dBμV), and the vertical axis represents the separation degree R _SEP (unit: dB). The characteristic curve 150 corresponds to a normal state without multipath noise and adjacent interference. In this state, when the received electric field intensity V _R is preset predetermined in more field (or threshold V _th) is, R _SEP is set to the maximum value, eg, L signal, R signal completely Separated stereo sound is played. On the other hand, in a range _{where V R} is below _{V th,} the stereo separation level control circuit 96, to the change in _{V R,} changing the _{R SEP} a preset inclination, reduces the degree of separation _{R SEP} as a weak electric field . Thereby, the noise feeling in stereo sound can be reduced. For example, V _th can be set to about 60 dBμV, and the maximum value of R _SEP can be set to about 40 dB.

Next, when there is a multipath signal, the stereo separability control circuit 96 is compared with the normal time when no multipath occurs in order to reduce the influence of the multipath noise of the (LR) signal caused by the multipath signal. The degree of separation R _SEP is reduced. Here, the greater the multipath noise intensity is, the lower the separation degree R _SEP can be. For example, the stereo separation degree control circuit 96 sets the control characteristic to the characteristic curve 150 as the multipath noise becomes stronger. To the characteristic curve 152 and then to the characteristic curve 154. This control can be performed stepwise or continuously. For example, the SM _-DC input to the stereo separation control circuit 96 is input to the attenuator, and the attenuation rate is controlled according to _SMP , thereby realizing a continuous change according to multipath noise. Can do. _Further, within a range _{that S MP} exceeds a certain threshold, the separation degree _{R SEP} may be so varied in accordance with the _{S MP.}

Further, in the FM tuner 50 of the present embodiment, the stereo separation degree control circuit 96 controls the separation degree R _SEP according to the presence or absence and the strength of adjacent interference. This reduces the sense of incongruity by reducing the degree of separation R _SEP even if distortion occurs in the signal of the desired station when narrowing the passband of IFBPF74 during adjacent interference and removing adjacent interference can do.

For example, when the attenuation factor of the aforementioned attenuator is to be variable configuration by S _AI, according to the intensity of the adjacent-channel interference becomes stronger, the control characteristics of the stereo separation level control circuit 96 as the characteristic curve 150, 152 It can be gradually lowered. Further, for example, in a state where S _AI exceeds a predetermined threshold, the stereo separation degree control circuit 96 may control the matrix circuit 82 so that monaural sound is generated.

In addition, the control of the separation degree R _SEP according to the above S _AI may be selectively performed in a state where it is detected that the broadcast is a stereo broadcast based on the stereo indicator signal S _SI .

In the above-described configuration, the adjacent disturbance is detected from the output signal _SDET of the FM detection circuit 78. However, in the present invention, any method for detecting the adjacent disturbance is free. For example, the adjacent interference can be detected based on a specific high frequency component included in the S _M-AC of the S meter circuit 92.

  The stereo separation degree control circuit 96 generates a control signal for the matrix circuit 82 by analog processing from various sensor signals input as analog signals, and for example, the matrix circuit 82 by logic processing and software processing. It is also possible to adopt a configuration for generating a control signal for. In the logic processing, for example, various sensor signals are converted into digital values by the ADC, the register contents are set based on the result obtained by the logic circuit, and the matrix circuit 82 is controlled based on the register contents. To do. In the software processing, the sensor signal digitized by the FM tuner 50 is transmitted to the control unit via the system bus, and the matrix circuit 82 is set based on the result obtained by the control unit executing the program. Set the contents of the register to be controlled.

  In the above configuration, the bandwidth control circuit 94 and the stereo separation control circuit 96 perform the bandwidth control and the separation control separately based on various sensor signals. However, other configurations may be used. it can. For example, when the bandwidth control circuit 94 determines that the adjacent interference or weak electric field is present and performs control for narrowing the bandwidth of the IFBPF 74, the stereo separation degree control circuit 96 is configured to perform control for reducing the separation degree. it can.

1 is a schematic block configuration diagram of an FM tuner according to an embodiment of the present invention. It is a circuit diagram which shows the structure of the outline of S meter circuit. It is the graph which showed typically an example of the characteristic curve of control in a stereo separation degree control circuit. It is a block diagram explaining the structure of the conventional FM tuner.

Explanation of symbols

  50 FM tuner, 54 antenna, 56 FM-RF tuning amplifier circuit, 58 first local oscillation unit, 60 first mixing circuit, 62, 66 BPF, 64, 72 buffer amplifier, 68 second local oscillation unit, 70 second mixing Circuit, 74 IFBPF, 76 limiter amplifier, 78 FM detection circuit, 80 noise canceller, 82 matrix circuit, 90 crystal oscillation circuit, 92 S meter circuit, 94 bandwidth control circuit, 96 stereo separation control circuit, 98 pilot signal extraction circuit, 100 adjacent interference detection circuit, 102 modulation degree detection circuit, 104 multipath noise detection circuit, 110 first oscillation circuit, 112, 114 frequency dividing circuit, 120 limiter amplifier, 122 adder, 124 current mirror circuit, 126 smoothing circuit, 130,134 HPF, 132,136, 140 detector circuit, 138 LPF.

Claims (4)

An intermediate signal generation circuit that performs frequency conversion on the received signal to shift the carrier frequency of the reception target FM signal to a predetermined intermediate frequency, and generates an intermediate signal;
A band-pass filter that can variably set a pass bandwidth and passes the reception target FM signal converted into the intermediate signal;
A detection circuit that detects the reception target FM signal that has passed through the bandpass filter and generates a detection output signal;
A stereo demodulation circuit for separating a left signal and a right signal from the detection output signal which is a stereo composite signal;
A stereo separation degree control unit for controlling the separation degree between the left signal and the right signal generated by the stereo demodulation circuit;
An adjacent interference detector that detects interference of an adjacent signal with respect to the reception target FM signal;
The width of the passband of the bandpass filter is controlled according to the interference strength of the adjacent signal, and in the strong interference state where the interference strength is stronger than a predetermined weak interference state, the passbandwidth is changed to the weak interference. A bandwidth controller that provides a narrower predetermined narrow passband in the state;
Have
The stereo separation degree control unit changes the separation degree according to the interference intensity, and lowers the separation degree in the strong interference state than the weak interference state;
FM tuner characterized by. The FM tuner according to claim 1,
A signal type determining unit for determining whether the detection output signal is the stereo composite signal or the monaural signal;
The stereo separation degree control unit selectively controls the separation degree according to the interference intensity when the detection output signal is the stereo composite signal;
FM tuner characterized by. The FM tuner according to claim 1 or 2,
A reception field strength detector for detecting a reception field strength of the reception target FM signal;
The bandwidth control unit controls the width of the passband width according to the received electric field strength, and when the received electric field strength is weak compared to a predetermined strong electric field state, the passband width is set to the strong electric field. With a narrower predetermined narrow passband in the electric field state,
The stereo separation degree control unit changes the separation degree according to the received electric field strength, and lowers the separation degree in the weak electric field state than the strong electric field state,
FM tuner characterized by. In the FM tuner as described in any one of Claims 1-3,
2. The FM tuner according to claim 1, wherein the stereo separation degree control unit causes the output of the stereo demodulation circuit corresponding to the strong interference state to be a monaural signal.

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