Mitsubishi Denki Kabushiki Kaisha

Mitsubishi Electric Corporation

Kenichi Taura

Masayuki Ishida

Masahiro Tsujishita

Tadatoshi Ohkubo

Masayuki Tsuji

Yoshiharu Ohsuga

Masakazu Morita

Tsuyoshi Nakada

Eizi Asano

Yuji Matsuda

Nobuyoshi Okumura

Eiji Asano

A radio receiver (FM radio receiver) has an amplitude detecting section () for detecting the amplitude level of a received radio wave; a multipath occurrence state detecting section () for monitoring the amplitude level, and for detecting the degree of a multipath occurrence state; a multipath occurrence state deciding section () for deciding the operation limiting level of the amplitude correction according to the degree of the multipath occurrence state; a receiving condition deciding section () for deciding receiving conditions of the radio wave; and a limiting level deciding section () for adjusting the operation limiting level of the amplitude correction output from the multipath occurrence state deciding section () according to a receiving condition decision result output from the receiving condition deciding section (), and suppresses the multipath noise by imposing operation limitations on the amplitude correction of the FM demodulator

Radio receiver

A digital broadcast receiving apparatus has two systems as a receiving system: a first receiving demodulation section including a first tunerand the like; and a second receiving demodulation section including a second tunerand the like. A controllerestablishes either a first receiving mode or second receiving mode. In the first receiving mode, both the receiving systems receive the broadcasting waves of the same station to be viewed according to the signals from a vehicle speed detecting sectionand receiving level detecting sectionsand. In the second receiving mode, one of the two receiving systems receives the broadcasting wave of the station to be viewed, and the other of them receives the broadcasting wave of another station.

Digital broadcast receiving apparatus

The FM broadcast is received and the FM demodulated FM composite signal is stereo demodulated, and when the high band components of the demodulated signal are few, the correction is conducted by using the signals just before and just after the noise generation period, and when the high band components are large, the interpolation is conducted by using a central value calculated from the value of a predetermined period before the noise generation period, and a central value calculated from the value of a predetermined period after the noise generation period.

Noise reduction apparatus and audio output apparatus

A pulse modulated signal (ei) output from a pulse modulator () and a feedback signal (ef) containing distortion caused by a power switch () are integrated in a first integrator () and a second integrator (), respectively, and are input to input terminals of a comparator (or), respectively, so that a correction signal (Vc) is generated.

Class D amplifier

A noise removal unit mounted on a car radio according to the invention removes multipath noise and pulse noise from FM demodulated signals. At this time, the noise removal unit removes all of the multipath noise. Also, in case where the generation density of noise is high, the noise removal unit reduces the detection sensitivity so as not to detect pulse noise, particularly of small level, as noise. Comparing to multipath noise, pulse noise is noise rendering a large correction error than multipath noise. Therefore, in case where the generation density of pulse noise is high, by adapting the unit not to remove pulse noise of small level, it is made possible to reduce distortion of the FM demodulated signals to a minimum. Accordingly, it is made to reduce deterioration of the quality of FM voices to a minimum.

Noise removal apparatus and an FM receiver

A stereo composite signal including a pilot signal is demodulated by processing input samples to obtain internal samples having variable sampling timings, synchronizing these sampling timings with the pilot signal, and digitally processing the internal samples to obtain stereo audio data. The internal samples may be obtained from the input samples by decimation or interpolation. Since the sampling frequency and sampling timing of the input samples do not have to be precisely controlled, no voltage-controlled oscillator is needed, and the demodulator can easily be incorporated into a monolithic integrated circuit.

All-digital FM stereo demodulator and demodulation method

A multipath noise reducer extracts a high-frequency signal from a demodulated signal obtained from a frequency-modulated signal, and generates a noise reduction coefficient from the extracted high-frequency signal. The demodulated signal is also separated into high-frequency and low-frequency components, the high-frequency component is multiplied by the noise reduction coefficient, and the resulting product is added to the low-frequency component. An output signal is thereby obtained in which the spike noise that characterizes multipath reception of a frequency-modulated signal is reduced with relatively little distortion of other parts of the signal, including the parts between noise spikes. The distortion can be further reduced by replacing the demodulated signal with an interpolated signal during noise spikes before the low-frequency component is separated.

Multipath noise reduction method, multipath noise reducer, and FM receiver

An impulse noise reducer detects impulse noise in an audio signal by detecting and smoothing the high-frequency amplitude of the audio signal, attenuating the non-smoothed amplitude according to the smoothed amplitude, and comparing the attenuated amplitude with a threshold. Impulse noise is discriminated from high-frequency audio components because the latter tend to occur in longer-lasting bursts and are therefore attenuated more strongly. The impulse noise reducer is simplified because it does not have to perform intermediate-frequency signal processing, and its sensitivity is not affected by adjacent-channel signals because these signals are substantially absent from the audio signal. The impulse noise reducer can be implemented by digital signal processing, and is suitable for use in a medium-wave AM audio broadcast receiver.

Impulse noise reducer detecting impulse noise from an audio signal

A noise reducer generates a gate signal by detecting noise in a demodulated signal, and changes the lengths the gate pulses indicating the presence of noise according to the electric-field strength of a radio signal from which the demodulated signal has been obtained. The demodulated signal is modified during intervals indicated by the gate pulses, to reduce the noise. The amount of change of the gate-pulse lengths is preferably increased as the electric-field strength decreases. Noise can then be removed satisfactorily under even weak electric-field conditions.

Receiver noise reduction with expanding gated pulses

A multipath noise reducer detects and removes the individual noise spikes occurring in an interval of multipath noise, thereby reducing the multipath noise with minimal distortion of the audio output signal. The multipath noise spikes are detected by comparing a rectified signal with a threshold signal derived from the rectified signal. When the multipath noise reducer is used in an FM stereo radio receiver, stereo separation may also be controlled according to the detection of multipath noise.

Multipath noise reducer, audio output circuit, and FM receiver

An audio signal noise reduction system comprises a noise detecting circuit for detecting a noise from an audio signal and outputting a detection signal indicating a start time and an end time of a noise period of the noise, an LPF for extracting a low frequency component of the audio signal, an HPF for extracting intermediate and high frequency components of the audio signal, a polynomial interpolation circuit for polynomial-interpolating the noise period of the low frequency component being extracted, a mute circuit for muting an output level of the noise period of the intermediate and high frequency components being extracted, and a signal synthesizing circuit for synthesizing the low frequency component whose noise period is polynomial-interpolated and the intermediate and high frequency components the level of whose noise period is suppressed to thus output the audio signal.

Audio signal noise reduction system

A digital FM demodulator converts a digital FM input signal to a demodulated signal, detects the amplitude of the digital FM input signal, generates a corresponding amplitude signal, and adjusts the amplitude of the demodulated signal according to the amplitude signal, thereby compensating for variations in the amplitude of the digital FM input signal and removing amplitude distortion from the demodulated signal. This reduces the performance requirements of, for example, a low-pass analog filter preceding the digital FM demodulator in an FM radio broadcast receiver, permitting the analog filter to be implemented in a semiconductor integrated circuit.

Digital FM demodulator performing amplitude compensation

A multipath noise reducer detects and removes the individual noise spikes occurring in an interval of multipath noise, thereby reducing the multipath noise with relatively little distortion of the output signal. The threshold signal used to detect multipath noise is varied depending on reception conditions. The gate pulses indicating the presence of multipath noise spikes are preferably expanded by variable amounts, depending on both reception conditions and the signal level. Multipath noise spikes are preferably replaced by a smoothed signal. These provisions further reduce perceived distortion of the audio output signal.

Growing community of inventors

Tokyo, Japan

Kenichi Taura