JP2005175784A - Fm radio receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an FM radio receiver for executing adjacent interference detection and adjacent interference countermeasures by reducing any malfunction due to multi-path interference and excess modulation. <P>SOLUTION: This FM radio receiver is provided with an intermediate frequency (1)6, an intermediate frequency filter (2)7 whose frequency band width is narrower than the frequency band width of the intermediate frequency filter (1)6 and an FM/IF band switching function constituted of a selector 8 for normally selecting the intermediate filter (1)6, and for switching it to the intermediate frequency filter (2)7 in adjacent interference. The detection of the adjacent interference is executed by independently detecting the change amounts of the FM detection output from an S curve center, the contribution amounts by the upper side of the S curve and the contribution amounts by the lower side of the S curve by a comparator (1)12 and a comparator (2)13, and comparing the comparison results by a comparator (3)26. Thus, even when the contribution amounts by the upper side and the contribution amounts by the lower side are different in the adjacent interference, the multi-path and over-modulation time are made almost the same so that they can be discriminated. The selector 8 is configured to execute band switching based on the comparison result of the comparator (3)26. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an FM radio receiver that prevents interference from adjacent stations.

  Interference by adjacent stations in FM radio, so-called adjacent interference, has become a greater problem than before.

  Adjacent interference is when the interfering station exists in the band of the FM radio band limiting filter (normally 150 kHz to 280 kHz), and both the desired signal and the interfering signal are input to the FM detector, and the electric field of the desired station is strong. In this case, the desired station is received due to the capture effect, but when the jamming station is strong, the jamming station is received. When both magnitudes are almost equal, the FM detector outputs a large noise due to mutual interference. It becomes difficult to hear.

  In particular, in the case of an in-car FM radio, the strength of the desired station and the disturbing station changes from moment to moment, and the conditions become even worse, and it is necessary to implement countermeasures according to the driving of the car.

  Several countermeasures against this adjacent interference have been proposed. As a typical example, there is a method of switching the bandwidth of the intermediate frequency filter from a wide band in a normal reception state to a narrow band that can reduce adjacent interference at the time of adjacent interference.

  This countermeasure means that the adjacent interfering station does not need to be in the band by narrowing the reception band, and the adjacent interference can be reduced, but the FM demodulation band becomes narrower by switching to the narrow band, so that the sound quality deteriorates.

  Although this method is an effective measure against adjacent interference even if the sound quality deteriorates, there is a problem that the sound quality is likely to deteriorate due to other factors such as multipath and overmodulation.

  The reason is that since the frequency of the FM modulated wave changes, it is difficult to distinguish between the frequency change caused by the interference by the adjacent station and the original frequency change of the FM modulated wave, so there is no effective adjacent interference detection means. is the current situation.

  Hereinafter, a conventional FM radio receiver will be described with reference to FIG.

  This FM radio receiver includes an antenna 1, an RF amplifier 2, a mixer 3, a local oscillator 4, an intermediate frequency amplifier (1) 5, an intermediate frequency filter (1) 6, an intermediate frequency filter (2) 7, an intermediate frequency filter (1 ) Selector 8, intermediate frequency amplifier (2) 9, FM detector 10, intermediate frequency signal level detection circuit 16, high-pass filter (HPF) ) 17 and the noise detector 18.

  Here, the intermediate frequency filter (1) uses a broadband filter having a normal reception band, and the intermediate frequency filter (2) is set to have a narrower band than the band of the intermediate frequency filter (1).

  The operation of the conventional FM radio receiver configured as described above will be described.

  In FIG. 9, the broadcast station signal received by the antenna 1 is amplified by the RF amplifier 2, mixed with the local oscillation signal from the local oscillator 4 by the mixer 3, and converted into an intermediate frequency signal. The intermediate frequency signal is amplified by the intermediate frequency amplifier (1) 5, band-limited by the intermediate frequency filter (1) 6 or the intermediate frequency filter (2) 7, and further amplified and amplitude limited by the intermediate frequency amplifier (2) 9. The FM demodulator 10 outputs the FM demodulated signal. Usually, the intermediate frequency filter (1) 6 having a wider bandwidth is selected by the selector in terms of sound quality.

  On the other hand, the output of the intermediate frequency amplifier (1) 5 is superposed with a large noise due to the beat component of the signal of the desired station and the signal of the disturbing station at the time of adjacent interference, so the intermediate frequency signal level detection circuit 16 detects the level. By detecting the noise component on the intermediate frequency signal through the HPF 17 by the noise detector 18, the adjacent interference can be detected. When the noise component is large, the selector 8 is controlled to narrow the intermediate frequency filter (2). 7 is selected to take measures against adjacent interference.

  In the conventional FM radio receiver configured as shown in FIG. 9, it is possible to reduce the noise because the band of the intermediate frequency filter can be narrowed at the time of adjacent interference, but the adjacent interference is detected by the noise detector. At this time, noise caused by other factors such as multipath interference, overmodulation, weak input noise, and the like are also detected, so that the intermediate frequency filter may be switched to cause a malfunction other than the adjacent interference.

  Next, malfunction during overmodulation will be described with reference to FIG.

  In FIG. 4, a schematically shows the band characteristics of the intermediate frequency amplifier, b shows the change in the instantaneous frequency of the intermediate frequency signal, and this waveform is output as the FM detector output. Further, c is a signal obtained by detecting the level of the intermediate frequency signal and corresponds to the signal P in FIG.

  Here, when the frequency changes as shown in b in FIG. 4, the level attenuates when the frequency comes out of the band of the intermediate frequency amplifier, so that the intermediate frequency signal level changes as shown in c. The level detection signal of the intermediate frequency signal is detected by 18 noise detectors through the HPF 17 and malfunctions.

  In addition, since direct waves and reflected waves are superimposed during multipath, they may cancel each other and may be enhanced, and the intermediate frequency level output voltage changes. In addition, the signal meter voltage changes due to noise even during weak input. In either case, the noise detector operates similarly. In such a case, the band of the intermediate frequency filter becomes unnecessarily narrow, which causes deterioration in sound quality.

  The present invention solves the above-described conventional problems, and an object thereof is to provide an FM radio receiver capable of detecting interference caused by an adjacent station without malfunction and taking appropriate measures against adjacent interference.

  To achieve this object, the invention according to claim 1 is a mixer that mixes a local oscillation signal with a received high-frequency signal to convert it to an intermediate frequency signal, and a local oscillator that provides the mixer with a local oscillation signal. A first intermediate frequency filter that passes the intermediate frequency signal in a predetermined frequency bandwidth; and a second intermediate frequency filter that passes the intermediate frequency signal in a frequency bandwidth narrower than the frequency band of the first intermediate frequency filter; A selector for selecting output signals of the first intermediate frequency filter and the second intermediate frequency filter, an FM detector for FM detecting the output signal of the selector, and a reference voltage source for providing a reference voltage to the FM detector; A first comparator for comparing the output of the FM detector with a voltage higher than the reference voltage, a second comparator for comparing the output of the FM detector with a voltage lower than the reference voltage, It is characterized in that a control circuit providing a control signal to said selector in response to the output signal of the first and second comparators.

  The invention according to claim 2 is a mixer that mixes a local oscillation signal with the received high-frequency signal to convert it to an intermediate frequency signal; a local oscillator that provides the local oscillation signal to the mixer; A variable bandwidth intermediate frequency filter that passes in the frequency bandwidth, an FM detection circuit that FM-detects an output signal of the intermediate frequency filter, a reference voltage source that provides a reference voltage to the FM detector, and an FM detector A first comparator that compares an output with a voltage higher than the reference voltage, a second comparator that compares an output of the FM detector with a voltage lower than the reference voltage, and a first comparator and a second comparator. And a control circuit for supplying a control signal to the intermediate frequency filter in accordance with an output signal to control the bandwidth.

  The invention according to claim 3 is a mixer that mixes a local oscillation signal with the received high-frequency signal to convert it to an intermediate frequency signal; a local oscillator that provides the local oscillation signal to the mixer; An intermediate frequency filter that passes in the frequency bandwidth of the output, an FM detector circuit that detects an FM output signal of the intermediate frequency filter, a band detection circuit that outputs a band signal from the output of the FM detector, and the FM detector output A mute circuit for attenuating by a band signal of a band detection circuit, a reference voltage source for applying a reference voltage to the FM detector, a first comparator for comparing the output of the FM detector with a voltage higher than the reference voltage, A second comparator for comparing the output of the FM detector with a voltage lower than the reference voltage; and controlling the bandwidth of the band signal according to the output signals of the first and second comparators It is characterized in that a that the control circuit.

  According to the present invention, adjacent interference and other interference can be distinguished by independently detecting and comparing the upper part and the lower part of the FM detection output on the time axis. By switching the intermediate frequency filter according to the operation, it is possible to configure an excellent FM radio receiver capable of effective countermeasures against adjacent interference.

  Also, adjacent interference and other interference can be distinguished by independently detecting and comparing the upper and lower portions on the time axis of the FM detection output, and the effective adjacent interference detection operation makes it possible to distinguish between intermediate frequencies. An excellent FM radio receiver capable of changing the filter band and effectively taking adjacent interference countermeasures can be configured.

  Also, adjacent interference and other interference can be distinguished by independently detecting and comparing the upper and lower portions of the FM detection output on the time axis, and band mute is performed by effective adjacent interference detection operation. It is possible to configure an excellent FM radio receiver that can operate and can effectively prevent adjacent interference.

  Hereinafter, FM radio receivers according to embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram showing the configuration of an FM radio receiver according to Embodiment 1 of the present invention. The same parts as those in the prior art shown in FIG.

  As shown in FIG. 1, the FM radio receiver of Embodiment 1 includes an antenna 1, an RF amplifier 2, a mixer 3, a local oscillator 4, an intermediate frequency amplifier (1) 5, an intermediate frequency filter (1) 6, an intermediate frequency. Selector 8, intermediate frequency amplifier (2) 9, FM detector 10, and reference voltage source 11 for selecting the output of filter (2) 7, intermediate frequency filter (1) 6 or intermediate frequency filter (2) and transmitting it to the subsequent stage , The comparator (1) 12, the comparator (2) 13, and the adjacent disturbance detection unit 14. Here, the intermediate frequency filter (1) uses a broadband filter having a normal reception band, and the intermediate frequency filter (2) is set to have a narrower band than the band of the intermediate frequency filter (1).

  The operation of the FM radio receiver of the present invention configured as described above will be described.

  The broadcast station signal received by the antenna 1 is amplified by the RF amplifier 2, mixed by the mixer 3 with the local oscillation signal from the local oscillator 4, and converted into an intermediate frequency signal. The intermediate frequency signal is amplified by the intermediate frequency amplifier (1) 5, band-limited by the intermediate frequency filter (1) 6 or the intermediate frequency filter (2) 7, and further amplified and amplitude limited by the intermediate frequency amplifier (2) 9. Thereafter, the signal is FM demodulated by the FM detector 10 and output from the output terminal 15. Usually, the intermediate frequency filter (1) 6 having a wider bandwidth is selected by the selector in terms of sound quality.

  Here, the FM detector output (Vo) draws an S-shaped curve (S curve) with respect to the frequency axis as shown in FIG. 8 with the reference voltage (Vr) output from the reference voltage source 11 as the center. The voltage V + higher than Vo and Vr is compared in the comparator (1) 12, and when Vo is higher than V +, the determination signal Va is output from the comparator (1) 12. Further, the voltage V− lower than Vo and Vr is compared by the comparator (2) 13, and when Vo is lower than V−, the determination signal Vb is output from the comparator (2) 13.

  This state is shown in FIG. 6 and FIG.

  FIG. 6 is an explanatory diagram showing Vo (a and d in FIG. 6), Va (b in FIG. 6), and Vb (c in FIG. 6) at the time of overmodulation or multipath interference, where d is a normal FM Indicates the output of the detector. 6 is output from the comparator (1) 12 when Va is higher than V + in the example of overmodulation or multipath interference, and when it is lower than V−, the comparator (2) 13 is output. To Vb in FIG. 6 is output.

  FIG. 7 shows an example at the time of adjacent interference, and the content is the same as that of FIG. 6. However, at the time of adjacent interference, the FM detector output Vo is targeted with respect to the time axis as shown in FIG. Not biased to either. For this reason, in the example shown in FIG. 7, the output Va is output from the comparator (1) 12, but the output Vb from the comparator (2) 13 is zero.

  Va and Vb are held or integrated for a sufficiently long time compared to the change of Vo in the adjacent disturbance detection unit 14, and become Vao and Vbo, respectively, and are compared by the comparator (3) 26.

  At the time of adjacent disturbance, since Vao and Vbo are not equal as shown in FIG. 7, a band switching signal is output from the comparator (3) 26 to the selector 8 to select the narrow-band intermediate frequency filter (2) 7.

  Further, in the case of noise other than adjacent interference such as overmodulation or multipath, Vao and Vbo are almost equal as shown in FIG. 6, and in this case, the output of the comparator (3) 26 disappears and the wideband intermediate frequency filter (1) Operate so that 6 is selected.

  The above V + and V− are set so that V + is higher and V− is lower than the reference voltage Vr, but the difference between Vr and V + and Vr and V− is the detection gain (Vo / Δf) of the FM detector used. And the frequency deviation to be detected are set so as not to operate when the frequency deviation is small. Furthermore, when the intermediate frequency filter is set to the narrow band side, the FM detector output is limited as shown in e in FIG. 7, but the frequency shift detected by V + and V− is limited to the bandwidth of the narrow band filter. If it is set smaller than this, the detection operation similar to the above can be performed even in a narrow band state.

  Here, Δf represents a frequency shift from the intermediate frequency. The frequency shift to be detected is set to V + and V− so that the frequency shift to be detected is several tens of kHz in order to prevent interference with a neighboring station of 100 kHz in a normal FM radio receiver.

  As shown in FIG. 5, since the frequency of the normal FM modulated wave changes, the FM detection output Vo changes along the S curve at the time of overmodulation or multipath, or at the time of noisy input. In the S curve, the object moves substantially around the origin O, and the time variation of the detection output is approximately zero on average.

  On the other hand, since signals having different frequencies are simultaneously input to the FM detector at the time of adjacent interference, the time change of the detection output is not zero and is biased to either one on average.

  In the FM radio receiver of the present invention, adjacent characteristics and other disturbances are distinguished by independently detecting and comparing the upper part and the lower part of the FM detection output on the time axis using this characteristic. Therefore, it is possible to effectively switch the intermediate frequency filter, and to realize an FM radio receiver capable of taking measures against adjacent interference with few malfunctions.

(Embodiment 2)
Hereinafter, the FM radio receiver in Embodiment 2 of this invention is demonstrated using figures.

  FIG. 2 is a block diagram showing a configuration of an FM radio receiver according to Embodiment 2 of the present invention. The same parts as those in FIG.

  As shown in FIG. 2, the FM radio receiver according to the second embodiment includes an antenna 1, an RF amplifier 2, a mixer 3, a local oscillator 4, an intermediate frequency amplifier (1) 5, and an intermediate frequency filter 19 having a variable pass bandwidth. The intermediate frequency amplifier (2) 9, the FM detector 10, the reference voltage source 11, the comparator (1) 12, the comparator (2) 13, the adjacent disturbance detection unit 14 and the adjacent disturbance detection unit receive the outputs of the intermediate frequency. And a control signal source 20 for controlling the bandwidth of the filter.

  The operation of the FM radio receiver of the second embodiment configured as described above will be described.

  The broadcast station signal received by the antenna 1 is amplified by the RF amplifier 2, mixed by the mixer 3 with the local oscillation signal from the local oscillator 4, and converted into an intermediate frequency signal. The intermediate frequency signal is amplified by the intermediate frequency amplifier (1) 5, band-limited by the intermediate frequency filter 19, further amplified and amplitude limited by the intermediate frequency amplifier (2) 9, and then FM demodulated by the FM detector 10. Output from the output terminal 15. Usually, the intermediate frequency filter has a wide bandwidth from the viewpoint of sound quality.

  Here, the FM detector output (Vo) draws an S-shaped curve (S curve) with respect to the frequency axis as shown in FIG. 8 with the reference voltage (Vr) output from the reference voltage source 11 as the center. The voltage V + higher than Vo and Vr is compared by the comparator (1) 12, and when Vo is higher than V +, the determination signal Va is output from the comparator (1) 12.

  Further, the voltage V− lower than Vo and Vr is compared by the comparator (2) 13, and when Vo is lower than V−, the determination signal Vb is output from the comparator (2) 13.

  This state is shown in FIG. 6 and FIG.

  FIG. 6 shows Vo (a and d in FIG. 6), Va (b in FIG. 6), and Vb (c in FIG. 6) at the time of overmodulation or multipath interference. In FIG. The output of the FM detector. 6 is output from the comparator (1) 12 when the part a in FIG. 6 is higher than V + due to overmodulation or multipath interference, and from the comparator (2) 13 when it is lower than V−. 6's Vb is output.

  FIG. 7 shows an example at the time of adjacent disturbance, and the contents are the same as those in FIG. 6. However, at the time of adjacent disturbance, the FM detector output Vo is not targeted with respect to the time axis as shown in FIG. Depends on Therefore, in the example of FIG. 7, the output Va is output from the comparator (1) 12, but the output Vb from the comparator (2) 13 is zero.

  Va and Vb are held or integrated for a sufficiently long time compared to the change of Vo in the adjacent interference detection unit 14 and become Vao and Vbo, respectively, and are compared by the comparator (3) 26.

  At the time of adjacent interference, since Vao and Vbo are not equal as shown in FIG. 7, a band switching signal is output from the comparator (3) 26 to the control signal source 20, and the band is set to a narrow band.

  Further, in the case of noise other than adjacent interference such as overmodulation or multipath, Vao and Vbo are almost equal as shown in FIG. 6, and in this case, the output of the comparator (3) 26 is lost and the band of the variable intermediate frequency filter is widened. Works to set.

  The above V + and V− are set so that V + is higher than the reference voltage Vr and V− is lower, but the difference between Vr and V + and the difference between Vr and V− is the detection gain (Vo / Δf) of the FM detector used. If the frequency deviation is set by the relationship with the detected frequency deviation, the operation is not performed.

  Further, when the intermediate frequency filter is set on the narrow band side, the FM detector output is limited as shown in e of FIG. However, if the frequency shift detected by V + and V− is set smaller than the bandwidth of the intermediate frequency filter in which the frequency shift is set, the detection operation similar to the above can be performed even in a narrow band state.

  Here, Δf represents a frequency shift from the intermediate frequency. The frequency shift to be detected is set to V + and V− so that the frequency shift to be detected is several tens of kHz in order to prevent interference with a neighboring station of 100 kHz in a normal FM radio receiver.

  As shown in FIG. 5, since the frequency of the normal FM modulated wave changes, the FM detection output Vo changes along the S curve at the time of overmodulation or multipath, or at the time of noisy input. In the S curve, the object moves substantially around the origin O, and the time variation of the detection output is approximately zero on average.

  On the other hand, since signals having different frequencies are simultaneously input to the FM detector at the time of adjacent interference, the time change of the detection output is not zero and is biased to either one on average.

  In the FM radio receiver according to the second embodiment, adjacent interference and other interference are detected by independently detecting and comparing the upper part and the lower part on the time axis of the FM detection output using this characteristic. Since it can be distinguished, the bandwidth of the intermediate frequency filter can be changed effectively, and an FM radio receiver capable of taking measures against adjacent interference with few malfunctions can be realized.

(Embodiment 3)
Hereinafter, an FM radio receiver according to Embodiment 3 of the present invention will be described with reference to the drawings.

  As shown in FIG. 3, it is a block diagram which shows the structure of the FM radio receiver in Embodiment 3, and the same code | symbol is used for the same part as FIG.

  In FIG. 3, this FM radio receiver includes an antenna 1, an RF amplifier 2, a mixer 3, a local oscillator 4, an intermediate frequency amplifier (1) 5, an intermediate frequency filter 6, an intermediate frequency amplifier (2) 9, and an FM detector 10. , Reference voltage source 11, comparator (1) 12, comparator (2) 13, adjacent disturbance detector 14, band signal detection circuit 22 for generating a band signal from the output of the FM detector, and FM detection by the output of the band signal detection circuit And a mute circuit 21 for attenuating the device output.

  The operation of the FM radio receiver of the third embodiment configured as described above will be described.

  In FIG. 3, the broadcast station signal received by the antenna 1 is amplified by the RF amplifier 2, mixed by the mixer 3 with the local oscillation signal from the local oscillator 4, and converted into an intermediate frequency signal. The intermediate frequency signal is amplified by the intermediate frequency amplifier (1) 5, band-limited by the intermediate frequency filter 6 (1), further amplified and amplitude limited by the intermediate frequency amplifier (2) 9, and then FM demodulated by the FM detector 10. Then, the signal is output from the output terminal 23 through the mute circuit 21.

  Next, as the FM detector output, the band signal detection circuit 22 outputs a band signal as shown in FIG. 8b. The mute circuit is driven by this band signal, and when the signal is out of band, the FM detector output is output. It operates as a band mute circuit as shown in FIG.

  8a and 8b show the band detection output, FIG. 8a shows the normal reception, FIG. 8b shows the output when there is adjacent interference, FIG. 8c and FIG. 8d show the AF output. FIG. 8c shows the case of normal reception, and FIG. 8d shows the case of adjacent interference. The horizontal axis is the intermediate frequency.

  Here, the FM detector output (Vo) draws an S-shaped curve (S curve) with respect to the frequency axis as shown in FIG. 8 with the reference voltage (Vr) output from the reference voltage source 11 as the center. The voltage V + higher than Vo and Vr is compared by the comparator (1) 12, and when Vo is higher than V +, the determination signal Va is output from the comparator (1) 12.

  The comparator (2) 13 compares the voltage Vo and the voltage V− lower than Vr. When the voltage Vo is lower than V−, the comparator (2) 13 outputs the determination signal Vb.

  This state is shown in FIG. 6 and FIG.

  FIG. 6 shows Vo (a and d in FIG. 6), Va (b in FIG. 6), and Vb (c in FIG. 6) at the time of overmodulation or multipath interference. In FIG. The output of the FM detector. 6 is output from the comparator (1) 12 when the part a in FIG. 6 is higher than V + due to overmodulation or multipath interference, and from the comparator (2) 13 when it is lower than V−. 6's Vb is output.

  FIG. 7 shows an example at the time of adjacent disturbance, and the contents are the same as those in FIG. 6. However, at the time of adjacent disturbance, the FM detector output Vo is not targeted with respect to the time axis as shown in FIG. It is biased. Therefore, in the example of FIG. 7, the output Va is output from the comparator (1) 12, but the output Vb from the comparator (2) 13 is zero.

  Va and Vb are held or integrated for a sufficiently long time compared to the change of Vo in the adjacent interference detection unit 14 and become Vao and Vbo, respectively, and are compared by the comparator (3) 26.

  At the time of adjacent interference, since Vao and Vbo are not equal as shown in FIG. 7, the band detection signal of FIG. 8B is output from the comparator (3) 26 to the band signal detection circuit 22, and the mute circuit 21 outputs an out-of-band signal. On the other hand, the AF output is attenuated as shown in FIG.

  In the case of noise other than adjacent interference such as overmodulation or multipath, Vao and Vbo are substantially equal as shown in FIG. 6, and in this case, the band detection signal is as shown in FIG. As shown, the normal reception state is established.

  The above V + and V− are set so that V + is higher than the reference voltage Vr and V− is lower, but the difference between Vr and V + and the difference between Vr and V− is the detection gain (Vo / Δf) of the FM detector used. If the frequency deviation is set by the relationship with the detected frequency deviation, the operation is not performed. In this case, unlike the first and second embodiments, the FM detector output Vo does not change even during the band mute operation, so the disturbance detection operation does not change.

  Here, Δf indicates a frequency shift from the intermediate frequency. The frequency shift to be detected is set to V + and V− so that the frequency shift to be detected is several tens of kHz in order to prevent interference with a neighboring station of 100 kHz in a normal FM radio receiver.

  As shown in FIG. 5, since the frequency of an FM modulated wave usually changes, the FM detection output Vo changes along the S curve at the time of overmodulation or multipath, or at the time of noisy input. Even in this case, the object moves on the S curve around the origin O, and the temporal change of the detection output becomes almost zero on average.

  On the other hand, since signals having different frequencies are simultaneously input to the FM detector at the time of adjacent interference, the amount of time change of the detection output is not zero but depends on either.

  In the FM radio receiver according to the third embodiment, by utilizing this characteristic, the upper part and the lower part on the time axis of the FM detection output are independently detected and compared to thereby detect adjacent interference and other interference. Since the band mute function can be effectively operated because they can be distinguished from each other, it is possible to realize an FM radio receiver capable of taking measures against adjacent interference with few malfunctions.

  The present invention realizes an FM radio receiver capable of taking appropriate countermeasures against adjacent interference, and can be used particularly in the field of in-vehicle FM radio receivers.

The block diagram of the FM radio receiver in the 1st Embodiment of this invention The block diagram of the FM radio receiver in the 2nd Embodiment of this invention The block diagram of the FM radio receiver in the 3rd Embodiment of this invention Illustration of the operation of the noise detection circuit during overmodulation Illustration of FM detector output (S curve) Explanatory diagram of noise detection operation of the present invention during over modulation or multipath Explanatory diagram of noise detection operation of this embodiment at the time of adjacent interference Illustration of band detection signal and band muting Block diagram of a conventional FM radio receiver

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna 2 RF amplifier 3 Mixer 4 Local oscillator 5 Intermediate frequency amplifier (1)
6 Intermediate frequency filter (1)
7 Intermediate frequency filter (2)
8 Selector 9 Intermediate Frequency Amplifier (2)
10 FM detector 11 Reference voltage source 12 Comparator (1)
13 Comparator (2)
14 Adjacent disturbance detection unit 15 Output terminal 16 Intermediate frequency level detection circuit 17 High pass filter (HPF)
DESCRIPTION OF SYMBOLS 18 Noise detector 19 Bandwidth variable intermediate frequency filter 20 Control signal source 21 Mute circuit 22 Band signal detection circuit 23 Output terminal 24, 25 Integrator 26 Comparator (3)

Claims (3)

A mixer for mixing the local oscillation signal with the received high-frequency signal and converting it to an intermediate frequency signal;
A local oscillator for providing a local oscillation signal to the mixer;
A first intermediate frequency filter that passes the intermediate frequency signal in a predetermined frequency bandwidth;
A second intermediate frequency filter that passes the intermediate frequency signal in a frequency bandwidth narrower than a frequency band of the first intermediate frequency filter;
A selector for selecting output signals of the first intermediate frequency filter and the second intermediate frequency filter;
An FM detector for FM detection of the output signal of the selector;
A reference voltage source for providing a reference voltage to the FM detector;
A first comparator for comparing the output of the FM detector with a voltage higher than the reference voltage;
A second comparator for comparing the output of the FM detector with a voltage lower than the reference voltage;
An FM radio receiver comprising: a control circuit that provides a control signal to the selector in accordance with output signals of the first and second comparators. A mixer for mixing the local oscillation signal with the received high-frequency signal and converting it to an intermediate frequency signal;
A local oscillator for providing a local oscillation signal to the mixer;
A variable bandwidth intermediate frequency filter that passes the intermediate frequency signal at a predetermined frequency bandwidth; and
An FM detection circuit for FM detection of the output signal of the intermediate frequency filter;
A reference voltage source for providing a reference voltage to the FM detector;
A first comparator for comparing the output of the FM detector with a voltage higher than the reference voltage;
A second comparator for comparing the output of the FM detector with a voltage lower than the reference voltage;
An FM radio receiver comprising: a control circuit that applies a control signal to the intermediate frequency filter in accordance with output signals of the first and second comparators to control a bandwidth. A mixer for mixing the local oscillation signal with the received high-frequency signal and converting it to an intermediate frequency signal;
A local oscillator for providing a local oscillation signal to the mixer;
An intermediate frequency filter that passes the intermediate frequency signal in a predetermined frequency bandwidth; and
An FM detection circuit for FM detection of the output signal of the intermediate frequency filter;
A band detection circuit that outputs a band signal from the FM detector output; and a mute circuit that attenuates the FM detector output using a band signal of the band detection circuit;
A reference voltage source for providing a reference voltage to the FM detector;
A first comparator for comparing the output of the FM detector with a voltage higher than the reference voltage;
A second comparator for comparing the output of the FM detector with a voltage lower than the reference voltage;
An FM radio receiver comprising: a control circuit that controls a bandwidth of the band signal in accordance with output signals of the first and second comparators.

Images