Pioneer Electronic Corporation

Hitoshi Hirata

Akira Nishioka

Tatsuo Numata

An FM audio system has an FM tuner, a CD player, a stereo modulator for modulating an audio signal from the CD player to produce a composite signal so as to be received by the FM tuner for reproducing the audio signal. A control circuit such as an automatic level controller is provided for controlling a level of the audio signal applied to the stereo modulator to such a level as to prevent tone quality of sound reproduced by the FM tuner from deteriorating.

Audio signal modulating system with pre-emphasis

An FM audio system has an FM tuner, a CD player, a stereo modulator for modulating an audio signal from the CD player to produce a composite signal so as to be received by the FM tuner, for reproducing the audio signal. A notification system has a controller and a muting circuit. The controller produces a control signal in response to the changing of function of the CD player. The muting circuit attenuates the audio signal from CD player in accordance with the control signal. Speech information is generated in response to the changing of the function of the CD player. The speech information is added to an attenuated audio signal and applied to the stereo modulator so as to reproduce the audio signal together with the speech information.

Notification system with voice in an audio system

A muting circuit for an AM stereophonic receiver of the type that having a detector circuit operating upon an AM stereophonic signal, the carrier of which is phase-modulated by the difference signal of first and second stereo channel signals, for detecting the difference signal. The muting circuit includes a muting signal generating circuit for detecting the output level of the detector circuit exceeding a predetermined value and for generating a muting signal at least for periods when the predetermined value is exceeded, and a muting switch circuit for attenuating the output of the detector in response to the muting signal.

Muting circuit for AM stereophonic receiver

A PLL detection circuit for use in an AM-PM type AM stereo receiver in which unwanted AC signal components included in the output of a phase comparator are suppressed by switching the frequency response characteristic of a loop filter in the PLL detection circuit as locking is reached so that only the DC signal component, corresponding to the phase difference of the input signal and a reference signal, is outputted. A changeover circuit, including a switching circuit composed of a pair of parallel-connected transistors, is connected in parallel with an element of the loop filter, the component value of which affects or is at least partially determinative of the frequency response characteristic of the loop filter. The changeover circuit is activated by a control signal indicative of the locking state of the PLL detection circuit.

PLL Detection circuit having dual bandwidth loop filter

An AM detector circuit capable of performing an AGC function having a wide dynamic range and low level of distortion and spurious interference. A first differential amplifier receives an amplitude-modulated signal to be detected as differential inputs. Outputs of the first differential amplifier are connected as constant current source inputs to second and third differential amplifiers. The differential inputs of the second and third differential amplifiers are fed with a signal synchronous with the carrier wave of the amplitude-modulated signal. Outputs of the second and third differential amplifiers are interconnected to provide multiplication outputs representing the product of the amplitude-modulated signal and its carrier wave. The detector AM signal is passed through a low-pass filter and then through a fourth differential amplifier to a current mirror circuit. The current mirror circuit feeds parallel-connected transistors of opposite conductivity types connected across the differential input of the first differential amplifier to provide the AGC function.

Detector circuit having AGC function

A multi-function sound system including an AM stereophonic receiving function in which interference with operating circuits in modes other than the AM stereophonic mode is eliminated. A limiter receives a IF AM stereophonic received signal and removes the amplitude variation components therefrom and couples the resulting signal to a phase detector composed of a phase-locked loop which produces as an output signal a sub-signal. A switch is provided which deactivates both the limiter and the voltage-controlled oscillator in the phase-locked loop circuit when the sound system is set to other than the AM stereophonic receiving mode.

Sound system having suppression of AM stereophonic receiving

A time constant resistor in a phase lock loop filter is short-circuited by a plurality of diodes which are activated in response to a detection output indicating that the filter output is within a desired locking range.

PLL Detection circuit

An AM stereophonic receiver including a stereophonic pilot signal eliminating circuit which substantially completely eliminates a pilot signal in an input stage of a matrix detector. A received AM stereophonic signal, of the type in which the carrier signal is phase-modulated with a sub-signal and amplitude modulated by a main signal, is coupled to a main signal detector and a sub-signal detector. The output of the sub-signal detector is coupled through a band amplifier which produces as an output a signal corresponding to the pilot signal contained in the stereophonic signal. The outputs of the sub-signal detector and main signal detector are coupled to inputs of adder/subtractor circuit in a matrix detector while the output of the band amplifier is also coupled thereto in a phase so as to cancel the pilot signal contained in the output of the sub-signal detector.

Stereo pilot signal eliminating circuit for AM stereophonic receiver

A detector for a modulated AM stereophonic signal of simple configuration in which the sub signal of the stereophonic signal is detected accurately independent of fluctuations in the frequency of the carrier signal. In the detector circuit, the output phase of a VCO in a PLL circuit which is fed with an amplitude limited signal corresponding to the output of an IF amplifier in the receiver is controlled by a variable phase shifter that performs phase shifting according to a control voltage. The phase-controlled output is used as a synchronous detection signal for sub signal detection. The control voltage is produced to correspond to the phase difference between the phase-controlled signal and the carrier signal of the received AM stereophonic signal.

Detector for sub signal of modulated AM stereophonic signal

A muting circuit for an AM stereophonic receiver of the type in which a received signal is phase modulated with a sub signal and amplitude modulated with a main signal and in which noise generated under certain adverse conditions is eliminated. A first detection signal is generated when the level of a received AM stereophonic signal is lower than a predetermined value, a second detection signal is generated upon detection of a non-locked state of a phase-locked loop circuit used to detect the sub signal, a third detection signal is generated when a frequency deviation detection senses is that a free-running frequency of a voltage controlled oscillator in the phase-locked loop circuit and a frequency of the AM stereophonic signal are different in frequency by more than a predetermined value; and a fourth detection signal is generated when a stereo pilot signal is absent. A muting circuit is activated in response to any of first through fourth detection signals. The frequency deviation detector is preferably implemented as a window detector which has an input-output characteristic including hysteresis.

In a current-controlled type division circuit, an auxiliary transistor is employed in conjunction with a division control transistor to allow a divisor signal, which normally flows through the division control circuit, to flow through the auxiliary transistor in the case when a division controlling signal applied to the base of the division control transistor falls below a predetermined level. By the provision of the auxiliary transistor, the divisor signal of a predetermined minimum is adapted to be flown therethrough to prevent the gain of the division circuit from exceeding a predetermined maximum.

Current-controlled type division circuit

A quadrature receiver circuit in which the output frequency of a local oscillator is controlled to follow the free-running frequency of a voltage-controlled oscillator so that accurate four-phase demodulation is maintained independent of oscillator drift. The output control voltage of a phase comparator in a phase-locked loop circuit in the demodulator is coupled through a low-pass filter and a DC amplifier to the frequency control input of a voltage controlled local oscillator.

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Tokyo, Japan

Hitoshi Hirata