JPH0521544U - FM receiver - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain reproduced sound without sound fluctuation even when an overmodulated broadcasting station signal is received. [Structure] Detects the degree of modulation of the received signal, detects an overmodulation state in which this degree of modulation is greater than or equal to a predetermined value, and forces the stereo demodulation circuit to operate in monaural or stop the operation of the multipath noise reduction circuit. By doing so, the fluctuation of the reproduced audio signal in the area where the overmodulated broadcasting station exists is removed.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 This invention relates to FM receivers, and more particularly to FM receivers useful for receiving overmodulated signals.

[0002]

[Prior Art]

 For example, in mobile communication, an FM receiver is often adopted as a communication means. An example of the structure of such an FM receiver is shown in FIG. The IF detection circuit 1 detects the intermediate frequency of the received signal and sends it to the noise extraction circuit 2 and the stereo demodulation circuit 4. The S meter voltage from the IF detection circuit 1 is also supplied to the soft blend control circuit 3. The soft blend control circuit 3 controls the stereo demodulation circuit 4 based on the supplied voltage signal of the S meter to adjust the separation between the L channel and the R channel. The noise extraction circuit 2 has a high-pass filter 21, a noise detection circuit 22, and a single-stable multivibrator 23. The noise component sent from the IF detection circuit 1 passes through the high-pass filter 21 and is supplied to the noise detection circuit 22. It When the signal indicating the noise component detected by the noise detection circuit 22 is input to the monostable multivibrator 23, a pulse having a constant time width is supplied to the multipath noise reduction circuit 5.

The output signal from the monostable multivibrator 23 is supplied to the base of the NPN transistor Tr via the resistor R1 which constitutes the multipath noise reduction circuit. The emitter of the transistor Tr is grounded, the capacitor C1 is connected between the base and ground, and the collector output is input to the stereo demodulation circuit 4 to force the receiver to be monaural. The demodulated signals (L signal and R signal) demodulated by the stereo demodulation circuit are output as reproduced audio signals.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above, in the conventional FM receiver, when multipath noise occurs, the multipath noise reduction circuit is turned “ON” to force the receiver to be monaural. Noise is reduced by rubbing. However, in an area where an overmodulated broadcasting station exists, such as Italy, when the overmodulated broadcasting station signal is received, the high harmonic component of the signal from the IF detection circuit is detected by the noise extraction circuit 2. And is supplied to the multi-pass noise reduction circuit 5. Therefore, the multipath noise reduction circuit 5 is turned “ON” or “OFF”, and the receiver performs complicated monaural operation or stereo operation, and as a result, the sound fluctuation of the reproduced voice is generated. There is a problem that it becomes more intense and hard to hear.

Therefore, an object of the present invention is to provide an FM receiver capable of obtaining reproduced sound without fluctuation even when an overmodulated broadcasting station signal is received.

[0006]

[Means for Solving the Problems]

 In order to solve the above-mentioned problems, an FM receiver according to the present invention stereo-demodulates an intermediate frequency signal from an intermediate frequency detection circuit, extracts a noise component from the intermediate frequency signal, and responds to the noise extraction by using a multipath signal. In an FM receiver that operates a noise reduction circuit, a modulation degree meter that detects the modulation degree of the intermediate frequency signal, and the stereo when the modulation degree obtained by the modulation degree meter exceeds a predetermined value. And an overmodulation detection circuit that sets the demodulation operation to monaural operation. An FM receiver according to another aspect of the present invention stereo demodulates an intermediate frequency signal from an intermediate frequency detection circuit, extracts a noise component from the intermediate frequency signal, and reduces multipath noise in response to the noise extraction. In an FM receiver for operating a circuit, a modulation degree meter for detecting the modulation degree of the intermediate frequency signal, and the multipath noise reduction circuit when the modulation degree obtained by the modulation degree meter exceeds a predetermined value. And a switch means for stopping the operation of.

[0007]

[Action]

 In this invention, the degree of modulation of the received signal is detected, and the overmodulation state in which this degree of modulation is greater than or equal to a predetermined value is detected, forcing the stereo demodulation circuit to monaural operation or stopping the operation of the multipath noise reduction circuit. By doing so, the sound fluctuation of the reproduced audio signal in the area where the overmodulated broadcasting station exists is removed.

[0008]

【Example】

 Next, this invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an FM receiver according to the present invention. In FIG. 1, circuit elements denoted by the same reference numerals as those in FIG. 3 indicate circuit elements having the same function. In this embodiment, the modulation degree meter 6 receives the output signal from the IF detection circuit 1 and measures the modulation degree of the received signal. The overmodulation detection circuit 7 controls the operation of the stereo demodulation circuit 4 so as to output a monaural signal when the measured modulation degree exceeds a predetermined value. Therefore, the influence of the malfunction of the multipath noise reduction circuit 5 can be reduced by the noise signal extracted by the noise extraction circuit 2 from the detection signal obtained by the IF detection circuit 1.

FIG. 2 is a block diagram of another embodiment of the FM receiver according to the present invention. While the embodiment shown in FIG. 1 operates the stereo demodulation circuit in monaural for a predetermined time in response to the extraction of the noise component, this embodiment is a multipath noise reduction circuit when the noise component is extracted. A switch 8 is provided between the monostable multivibrator circuit 23 and the multipath noise reduction circuit 5 in order to stop the operation of the circuit 5. When the modulation degree meter 6 determines that the modulation degree obtained from the detection output from the IF detection circuit 1 is greater than or equal to a predetermined value in the overmodulation detection circuit 7, the switch 8 is turned off to turn off the multipath noise reduction circuit. The operation of 5 is stopped.

[0010]

[Effect of the device]

 As described above, the FM receiver according to the present invention detects the degree of modulation of the received signal, and when the degree of modulation is in the overmodulation state in which the degree of modulation is equal to or higher than the predetermined value, the stereo demodulation circuit operates in monaural or multi-mode. Since the operation of the path noise reduction circuit is stopped, it is possible to remove the fluctuation of the reproduced audio signal in an area where there is an overmodulated broadcasting station such as Italy, so that stable broadcasting can be heard.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing another embodiment of the FM receiver according to the present invention.

FIG. 3 is a configuration diagram of a conventional FM receiver.

[Explanation of symbols]

1 IF detection circuit 2 Noise extraction circuit 3 Soft blend control circuit 4 Stereo demodulation circuit 5 Multipath noise reduction circuit 6 Modulation degree meter 7 Overmodulation detection circuit 8 Switch

Claims (2)

[Scope of utility model registration request] 1. An FM receiver for stereo demodulating an intermediate frequency signal from an intermediate frequency detection circuit, extracting a noise component from the intermediate frequency signal, and operating a multipath noise reduction circuit in response to the noise extraction, A modulation degree meter for detecting the modulation degree of the intermediate frequency signal, and an overmodulation detection circuit for setting the stereo demodulation operation to a monaural operation when the modulation degree obtained by the modulation degree meter exceeds a predetermined value. And an FM receiver comprising: 2. An FM receiver for stereo demodulating an intermediate frequency signal from an intermediate frequency detection circuit, extracting a noise component from the intermediate frequency signal, and operating a multipath noise reduction circuit in response to the noise extraction. A modulation degree meter for detecting the modulation degree of the intermediate frequency signal, and a switch means for stopping the operation of the multipath noise reduction circuit when the modulation degree obtained by the modulation degree meter exceeds a predetermined value. An FM receiver comprising: