Abstract: An FM demodulating circuit using a tracking filter is disclosed, in which the operation of the tracking filter following the frequency of the signal inputted therein is made more precise by using the tracking filter and an oscillator driven by a same control signal.

Abstract: A pulsating noise removal device includes first and second variable attenuators for varying signal levels of an audio signal component and a noise signal component both involved in an entered signal to use an output of the first variable attenuator to control the first and second variable attenuators and to use an output of the second attenuator to control a gate circuit for switching the entered signal, so that an inversion phenomenon is reliably prevented against a change either in the audio signal level or in the audio signal frequency.

Abstract: A pulsating noise removal device detects a pulsating noise, controls a gate circuit for selectively permitting an audio signal to pass through in response to the detection, and removes pulsating noises from the audio signal. The device particularly includes filter circuits for extracting pulsating noises and signal components from the audio signal, respectively, and includes automatic gain control circuits responsive to respective output signals of the filter circuits to respectively control the gain of an amplifier circuit for detecting pulsating noises.

Abstract: A gate circuit is configured to output a received signal via a buffer amplifier, enter the output in a storage capacitor via a first switching circuit normally taking its off-position, compare the signal levels at both ends of the switching circuit and feed back the comparison result to an input terminal via a second switching circuit normally taking its on-position, and configured so that when noise components in the received signal are detected, a control signal is produced to change the first switching circuit to its on-position and the second switching circuit to its off-position.

Abstract: A high-cut and high-blend control voltage generating circuit for activating a noise reduction circuit of an FM stereo receiver is configured to be simply responsive to multipath noises and never to plug noises. A changing and discharging circuit in the control voltage circuit may have a relatively long charging time constant, and the voltage control circuit may be configured to be simply responsive to multipath noises above a predetermined level. Thus the circuit is much less liable to operate erroneously.

Abstract: A noise eliminating signal compensation circuit in an audio device such as a car radio is configured to produce a compensation signal having the same frequency and level as those of an entered signal for signal compensation during noise removal, so as never to degrade its signal compensation capacity during noise removal when the switching time for noise removal is relatively long with respect to the wavelength of the entered signal.

Abstract: In a demodulator comprising an indicator (31) for indicating either stereo reception or monaural reception, an indicator circuit (30) is used to cancel a pilot signal included in a stereophonic signal and to produce a drive signal for driving the indicator. The indicator circuit comprises a negative feedback loop formed by an adder circuit (41), a phase detector (43), and a cancellation circuit (45). The cancellation circuit supplies the indicator and the adder circuit with the drive signal and a cancelling signal synchronized with and approximate to the pilot signal, respectively. The adder circuit substracts the cancelling signal from the pilot signal to deliver an intermediate signal to a multiplex decoder and to the cancellation circuit through the phase detector. The cancellation circuit comprises a wave generator for generating a pair of currents proportional to an amplitude of the pilot signal and a level adjusting circuit for converting one of the currents into the cancelling signal.

Abstract: In a circuit arrangement comprising a differential transistor circuit which has a threshold level and is operable in response to an input signal level and a reference signal level for producing an output signal, a resistor circuit is provided for changing the reference level. The resistor circuit comprises a resistor (30) for supplying the differential transistor circuit with the reference level and a modifying circuit coupled to the resistor for modifying the reference level by changing a current flowing through the resistor. Consequently, the threshold level can be voluntarily adjusted.

Abstract: A control circuit is configured to detect by an active filter white noise levels in detection outputs from an intermediate frequency amplifier in an FM stereo demodulation circuit so as to control the separation of outputs from the stereo demodulation circuit into left and right stereo channels, responsively to the white noise level, and is characterized in provision of a current detection circuit which is actuated by the output from the active filter and responsive to a current flowing into a resistor connected between the feedback terminal of the active filter and a reference potential point to control a blend control circuit so as to change the point whereat the separation ratio begins to vary.

Abstract: A gate circuit comprised of a first gate transistor normally off; a second gate transistor normally on and connected in a signal path; said first gate transistor being adapted to be turned on when a pulse is applied thereto and said second gate transistor being adapted to be turned off upon the conducting of said first gate transistor, and a limiter for holding the potential at the input of the second gate transistor lower than the potential at the output thereof.

Abstract: In order to reduce a discontinuity resulting from noise cancellation in an output signal of a noise canceller, particularly in lower-frequency components, a compensator (10) for use in, for example, a radio receiver, comprises two amplifiers (21, 22) for amplifying an input signal in which one or more noise pulses may be superposed. One of the amplifier output signals is given a delay relative to the other. Supplied with a noise detection signal, gates (26, 27) interrupts the amplifier output signals to cancel the noise pulse that substantially simultaneously appears in the both signals. A combination of capacitors (31-33) superposes one of the noise-cancelled signal on the other during presence of the noise pulse to provide an output signal in which the discontinuity is compensated for.

Abstract: A noise eliminating circuit capable of detecting a frequency component largely contained in a pulsive noise from an input signal and cutting off a signal path upon detection of such a frequency component for eliminating the pulsive noise, which circuit is characterized by means for keeping the signal path cut off for the duration when the input signal exceeds a preset level.

Abstract: In an automatic gain control circuit specifically adapted to control the gain of an amplifier for operating a noise cancelling circuit, a detector is provided for detecting a detector input signal, such as detected noise pulses. The detector includes a differential amplifier comprising a transistor pair connected to a constant current source. According to the detector input signal level, the constant current is switched between the transistor pair. The normally off transistor of the pair is connected to a third transistor, through which a substantially invariant current flows to relatively slowly charge a capacitor in a time constant circuit when the input signal level exceeds a reference level given by the difference between a pair of bias voltages for the transistor pair. The voltage accumulated across the capacitor serves as an automatic gain control signal, which rapidly disappears when the input signal level decreases below the reference level.

Abstract: For use in combination with a gain controllable amplifier for amplifying an input signal to produce an amplified signal with the gain controlled by a gain control signal, an automatic gain control circuit comprises a first section for shifting the level of the amplified signal by a first reference level and a second section for carrying out envelope detection of the amplified signal to produce an envelope detected signal of which the level is shifted by a second reference level different from the first reference level. A comparator compares the level-shifted signal with the envelope-detected signal to produce a pulse signal when the level of the latter signal traverses that of the former. The pulse signal is supplied to a smoothing circuit to produce a smoothed signal serving as the gain control signal.

Abstract: A noise eliminating circuit comprising means for generating a signal having a phase difference with respect to an input signal, means for simultaneously cutting off the input signal and the phase difference signal at the time when a noise is entering the circuit, means for retaining the levels of the respective signals that have developed immediately before said signals are cut off, and means for outputting a retained signal of one level by adding the same to a retained signal of the other level at a given time constant, thereby to make up for the signal interruption, preventing deterioration in tone quality caused by such signal interruption.

Abstract: A noise eliminating circuit for detecting and eliminating a noise pulse component included in an amplitude modulated wave, characterized by a circuit arrangement wherein an output of a detector circuit which is adapted to receive an input signal from an IF stage is coupled to an input of a band-pass filter through a noise amplifier; an output of said band-pass filter is coupled to an input of a pulse generator circuit; an output of said pulse generator circuit is connected to a gate circuit for stopping an audio AGC control operation and a gate circuit for eliminating a noise; an output of said noise amplifier is connected to an AGC control circuit through said gate circuit for stopping the audio AGC operation in order to apply an audio AGC control signal to said noise amplifier; and an output of said band-pass filter is connected to said AGC control circuit in order to apply a noise AGC to said noise amplifier; whereby said pulse generator circuit generates a pulse in response to the detection of the noise s

Abstract: A system for eliminating a noise from a stereo signal is disclosed comprising first and second signal paths to which an input stereo signal is applied simultaneously, storage means provided in the first signal path for storing an audio signal component, a pilot tone signal component and a sub-signal component of the stereo signal, the output of the storage means being grounded through a switch that is on when no noise exists, said switch being turned off when a noise exists in the stereo signal and extracting only the noise component by cancelling each signal component by its counterpart stored in the storage means, said noise component being phase inverted to be applied to the output of the second signal path.

Abstract: In an audio reproducing system including mixer means, intermediate frequency transformer means, first gate means and audio reproducing means following said first gate means, a noise detecting circuit comprising detector means for detecting a high frequency component of the output signal of said mixer means; amplifier means for amplifying a signal having said high frequency component from said detector means; pulse generator means for producing a pulse in response to a noise component in the output of said amplifier means; automatic gain control means for controlling the gain of said amplifier means, second gate means provided between said automatic gain control means and said amplifier means; and means for applying said pulse to said first and second gate means to operate them to thereby prevent application of said noise component to said audio reproducing means.

Abstract: A noise eliminating circuit for an AM receiver wherein noise pulse component included in an amplitude modulated wave are eliminated by making the RF or IF stage of the receiver an open circuit during such noise, while at the same time, compensating for the carrier components of the incoming signal that have lacked during such switching. The circuit comprises:(i) a noise detector for detecting the noise components and responsive thereto for generating a trigger output signal;(ii) a switch responsive to the trigger signal of the noise detector for making said RF or IF stage an open circuit;(iii) a signal generating circuit connected through the switch to the RF or IF stage; and(iv) a phase detector for controlling the oscillator frequency generated by the signal generating circuit so that it is coincident with that of the carrier of the incoming signal at the time just before the switch opens.

Abstract: A noise clearing system is described which comprises a means for applying a signal representing the existing period of an impulsive noise which is contained in an incoming signal, a means for detecting the impulsive noise, a means for reversing the phase of the detected noise, a means for summing the phase-reversed noise and the incoming signal to clear the noise, and a means for actuating the noise detecting means and the noise phase-reversing means in response to the noise period representing signal during the existing period of the noise.