Abstract: A ceramic resonator, a variable reactance circuit, and a limiter circuit are connected to the output of an amplifier having an output that is fed back to the positive phase-sequence input, and the frequency of oscillation is controlled by varying an equivalent capacitance of the reactance circuit with a control voltage applied to the reactance circuit. The limiter circuit ensures a variable frequency range on the high frequency side, and the symmetry of the capture range when this system is applied to a PLL can be improved.

Abstract: A circuit is provided for detecting the level of noises in received FM signals in an AM/FM receiver which includes at least an FM intermediate-frequency amplifier, an FM detector connected thereto, an AM intermediate-frequency amplifier and an AM detector connected thereto. This FM noise level detecting circuit includes a frequency converter receiving the output of the FM detector for converting noise components contained in the output of the FM detector into a noise signal of the AM intermediate-frequency, which is in turn outputted to the AM intermediate-frequency amplifier, so that the converted noise signal is amplified by the AM intermediate-frequency amplifier and then detected by the AM detector to produce a DC signal. The signal thus obtained is not only representative of the level of the noise contained in the received FM signal, but also representative of the received FM signal strength.

Abstract: A stereo signal demodulator includes a switching circuit for separating the stereo composite signal into left and right signal components. A composite stereo signal is attenuated in a preset quantity and superimposed upon the left and right signal components after they are separated by the switching circuit. The superimposed signals cancel the crosstalk components, not by switching the composite signal, but only by attenuating the stereo composite signal in the preset quantity. Consequently, the attenuator for reducing the stereo composite signal can be provided separately from the switching circuit for the stereo demodulation. The switching circuit can then be driven by the entire power supply voltage without any DC potential loss caused by the attenuator. Moreover, there is no DC potential loss by the attenuator, and transistors of the stereo switching circuit can operate with a power voltage margin. The distortion-free dynamic range of the output can be widened and the separation factor can be enhanced.

Abstract: A semiconductor chip contains a multi-channel signal-processing circuit for processing signals in different frequency bands (e.g., an AM and an FM receiver). An inductor is coupled via an external terminal on a package for the semiconductor chip to a first signal-processing circuit. A circuit detects when a connection is made between the inductor and a power supply terminal contained in the semiconductor chip. When the inductor is connected to the power supply terminals, the first signal-processing circuit is activated, while the second signal-processing circuit is deactivated. When the inductor is disconnected from the power supply terminal, the second signal-processing circuit is activated, while the first signal-processing circuit is deactivated. The circuit for detecting a connection between the inductor and the power supply terminal is either a circuit for detecting a potential change or a circuit for detecting an oscillating signal.

Abstract: A power amplifier includes a bootstrapped driver circuit in which the load element is divided into two parts. A single-ended push-pull circuit provides a feedback to the junction point of those two parts. A resistor element having 0.1 to 10 times the resistance of the load element is connected in parallel with the load element.