FM receiver noise suppression circuit

Claim 2

In an FM receiver which includes an FM discriminator connected to an intermediate-frequency amplifier having a limiter, and a stereo demodulator circuit connected to said discriminator for reproducing stereophonic audio signals, the combination comprising a gate circuit connected to an output stage of said stereo demodulator circuit, a noise signal detector circuit connected to said discriminator for detecting a noise signal of a frequency higher than that of a composite stereo signal, means for producing a control signal by said noise signal derived from said noise signal detector circuit to control said gate circuit to cut it off with said control signal when said noise signal is detected, a switching signal producing means for producing the switching signal to be supplied to said demodulator circuit, the switching signal producing means including a resonance circuit resonant with a pilot signal, the resonance of the resonance circuit being changed with said control signal, said control signal producing means comprising a monostable multivibrator operable with said noise signal and a waveform shaping circuit causing the output of the multivibrator to form a rectangular wave of a width corresponding to the duration of the noise signal.

Claim 3

In an FM receiver of the type set forth in claim 1 and having the combination therein defined wherein said waveform shaping circuit consists of an integrator circuit and a Schmitt circuit.

Claim 4

In an FM receiver which includes an FM discriminator connected to an intermediate-frequency amplifier having a limiter, and a stereo demodulator circuit connected to said discriminator for reproducing stereophonic audio signals, the combination comprising a gate circuit connected to an output stage of said stereo demodulator circuit, a noise signal detector circuit connected to said discriminator for detecting a noise signal of a frequency higher than that of a composite stereo signal, means for producing a control signal by said noise signal derived from said noise signal detector circuit to control said gate circuit to cut it off with said control signal when said noise signal is detected, a switching signal producing means for producing the switching signal to be supplied to said demodulator circuit, the switching signal producing means including a resonance circuit being changed with said control signal, a second noise detector circuit connected to said intermediate-frequency signal, and selecting means for selectively supplying said control signal producing circuit with the noise signal contained in said intermediate-frequency signal and the noise signal contained in the output signal of the discriminator.

Claim 5

In an FM receiver which includes an FM discriminator connected to an intermediate-frequency amplifier having a limiter, and a stereo demodulator circuit connected to said discriminator for reproducing stereophonic audio signals, the combination comprising a gate circuit connected to an output stage of said stereo demodulator circuit, a noise signal detector circuit connected to said discriminator for detecting a noise signal of a frequency higher than that of a composite stereo signal, means for producing a control signal by said noise signal derived from said noise signal detector circuit to control said gate circuit to cut it off with said control signal when said noise signal is detected, a switching signal producing means for producing the switching signal to be supplied to said demodulator circuit, the switching signal producing means including a resonance circuit being changed with said control signal, a second noise detector circuit connected to said intermediate-frequency signal, and selecting means for selectively supplying said control signal producing circuit with the noise signal contained in said intermediate-frequency signal and the noise signal contained in the output signal of the discriminator.

Claim 6

In an FM receiver of the type set forth in claim 3 and having the combination therein defined wherein said selectively means is a switching circuit operable in accordance with the level of a signal being received.

Claim 7

In an FM receiver of the type set forth in claim 4 and having the combination therein defined wherein said switching circuit consists of a first switching transistor for supplying the control signal producing circuit with a signal containing a noise and derived from the intermediate-frequency amplifier and a second switching transistor for supplying the control signal producing circuit with a signal containing a noise and derived from the discriminator, the first and second switching transistors being differentially operated in accordance with the level of the received signal.

Claim 8

In an FM receiver of the type set forth in claim 3 and having the combination therein defined wherein said noise detector circuit is a diode detector.

Claim 9

In an FM receiver which includes an FM discriminator connected to an intermediate-frequency amplifier and a stereo demodulator circuit connected to said discriminator for reproducing sterophonic audio signals, the combination comprising: a gate circuit connected to an output stage of said stereo demodulator circuit, a first noise signal detector circuit connected to said intermediate-frequency amplifier for detecting a first noise signal mixed with an intermediate-frequency signal in a relatively weak electric field, a second noise signal detector circuit connected to said discriminator for detecting a second noise signal mixed with the audio signals in a relatively strong electric field, selecting means connected to said first and second noise signal detector circuits for selecting one of said first and second noise signals, means connected to said selecting means for producing a control signal in response an output signal derived from said selecting means, means for using said control signal to cut off said gate circuit, and means connected to an output stage of said gate circuit for storing audio signals at the last-occuring value before said gate circuit is cut off and for supplying the stored signal to an output terminal of said FM receiver while said gate circuit is cut off.

Claim 10

In an FM receiver which includes an FM discriminator connected to an intermediate-frequency amplifier and a stereo demodulator circuit connected to said discriminator for reproducing sterophonic audio signals, the combination comprising: a gate circuit connected to an output stage of said stereo demodulator circuit, a first noise signal detector circuit connected to said intermediate-frequency amplifier for detecting a first noise signal mixed with an intermediate-frequency signal in a relatively weak electric field, a second noise signal detector circuit connected to said discriminator for detecting a second noise signal mixed with the audio signals in a relatively strong electric field, selecting means connected to said first and second noise signal detector circuits for selecting one of said first and second noise signals, means connected to said selecting means for producing a control signal in response an output signal derived from said selecting means, means for using said control signal to cut off said gate circuit, and means connected to an output stage of said gate circuit for storing audio signals at the last-occuring value before said gate circuit is cut off and for supplying the stored signal to an output terminal of said FM receiver while said gate circuit is cut off.

Claim 11

In an FM receiver as described in claim 7 the combination wherein said control signal producing means includes an integrator circuit and a Schmidt circuit to form a rectangular wave of width corresponding to the duration of the noise signal.

Claim 12

In aN FM receiver as described in claim 8 the combination wherein said control signal producing means further includes a monostable multivibrator operable by said noise signal.

Claim 13

In an FM receiver as described in claim 9 the combination which further includes a delay means connected between said discriminator and said demodulator circuit for causing said control signal to coincide in time with that of the signal passing through said demodulator circuit.

Claim 14

In an FM receiver which includes an FM discriminator connected to an intermediate-frequency amplifier and a stereo demodulator circuit connected to said discriminator for reproducing stereophonic audio signals the combination comprising: a gate circuit connected to an ouput stage of said stereo demodulator circuit a control signal producing means which includes, a noise signal detector circuit connected to said intermediate-frequency amplifier for detecting a noise signal mixed with an intermediate-frequency signal means for producing a control signal in response to detection of noise in said noise signal detector circuit, said control signal producing means including a monostable multivibrator operable by said noise signal and a waveform shaping circuit consisting of an integrator circuit and a Schmitt circuit for causing the output of the multivibrator to form a rectangular wave of a width corresponding to the duration of the noise signal means for using said control signal to cut off said gate circuit, and means connected to an output stage of said gate circuit for storing audio signals at the last-occurring value before said gate circuit is cut off and for coupling the stored signal to an output terminal of said FM receiver while said gate circuit is cut off.

Claim 15

In an FM receiver which includes an FM discriminator connected to an intermediate-frequency amplifier and a stereo demodulator circuit connected to said discriminator for reproducing stereophonic audio signals the combination comprising: a gate circuit connected to an ouput stage of said stereo demodulator circuit a control signal producing means which includes, a noise signal detector circuit connected to said intermediate-frequency amplifier for detecting a noise signal mixed with an intermediate-frequency signal means for producing a control signal in response to detection of noise in said noise signal detector circuit, said control signal producing means including a monostable multivibrator operable by said noise signal and a waveform shaping circuit consisting of an integrator circuit and a Schmitt circuit for causing the output of the multivibrator to form a rectangular wave of a width corresponding to the duration of the noise signal means for using said control signal to cut off said gate circuit, and means connected to an output stage of said gate circuit for storing audio signals at the last-occurring value before said gate circuit is cut off and for coupling the stored signal to an output terminal of said FM receiver while said gate circuit is cut off.

Claim 16

In an FM receiver as described in claim 11 having the combination which further includes a delay means connected between said discriminator and said demodulator circuit for causing said control signal to coincide in time with that of the signal passing through said demodulator circuit.

Claim 17

In an FM receiver which includes an FM discriminator connected to an intermediate-frequency amplifier and a stereo demodulator circuit connected to said discriminator for reproducing stereophonic audio signals the combination comprising: a gate circuit connected to an output stage of said demodulator circuit, a noise signal detector circuit connected to said discriminator for detecting a noise signal, means for producing a control signal in response to detection of noise in said noise signal detector circuit, said control signal producing means comprising a monostable multivibrator operable by said noise signal and a waveform shaping circuit consisting of an integrator circuit and a Schmidt circuit for causing the output of the multivibrator to form a rectangular wave of a width corresponding to the duration of the noise signal, means for using said control signal to cut off said gate circuit, and means connected to an output stage of said gate circuit for storing audio signals at the last occurring value before said gate circuit is cut off and for supplying the stored signal to an output terminal of said FM receiver while said gate circuit is cut off.

Claim 18

In an FM receiver which includes an FM discriminator connected to an intermediate-frequency amplifier and a stereo demodulator circuit connected to said discriminator for reproducing stereophonic audio signals the combination comprising: a gate circuit connected to an output stage of said demodulator circuit, a noise signal detector circuit connected to said discriminator for detecting a noise signal, means for producing a control signal in response to detection of noise in said noise signal detector circuit, said control signal producing means comprising a monostable multivibrator operable by said noise signal and a waveform shaping circuit consisting of an integrator circuit and a Schmidt circuit for causing the output of the multivibrator to form a rectangular wave of a width corresponding to the duration of the noise signal, means for using said control signal to cut off said gate circuit, and means connected to an output stage of said gate circuit for storing audio signals at the last occurring value before said gate circuit is cut off and for supplying the stored signal to an output terminal of said FM receiver while said gate circuit is cut off.

Claim 19

In an FM receiver as described in claim 13 the combination which further includes a delay means connected between said discriminator and said demodulator circuit for causing said control signal to coincide in time with that of signal passing through said demodulator circuit.