Abstract: A negative feedback amplifier for a transmitter, in which a vector corrector outputs the corrected signals, an adder adds the feedback signals of the in-phase component and the quadrature component to the in-phase component and the quadrature component of the output of the vector corrector, respectively, a modulator performs a quadrature modulation with respect to the in-phase component and the quadrature component of the outputs from the adder, a power amplifier amplifies the output of the modulator, a demodulator performs a quadrature demodulation to a part of the output of the power amplifier and outputs the feedback signals of the in-phase component and the quadrature component, and the vector corrector performs a correcting operation of canceling an error of at least one of the phases and the amplitudes of the in-phase component and the quadrature component occurring in the demodulator.

Abstract: A mobile communication system, and method, having, in an operational area of the base station, a plurality of mobile stations each capable of operating in an arbitrary one of two kinds of communication mode, i.e., a base station dependent mode for conducting communication via a base station and a direct communication mode for conducting direct communication between mobile stations. Information containing an important message to be received by all mobile stations is transmitted from the base station in the base station dependent mode. Upon receiving the information containing the important message, a mobile station placed in the base station dependent mode transmits the information containing the important message in the direct communication mode. As a result, all mobile stations placed in the direct communication mode receive the important message.

Abstract: A communication system having a carrier oscillator for generating a carrier of predetermined frequency, a quadrature modulator for orthogonally modulating the carrier by input baseband I and Q signals and outputting a quadrature modulation wave, and a quadrature demodulator for orthogonally demodulating the quadrature modulation wave using the carrier and outputting demodulation baseband I and Q signals. The phase of the carrier input to the quadrature demodulator is shifted by a predetermined amount in accordance with a phase shift signal. The amplitude of the demodulation baseband I and Q signals output from the quadrature demodulator is corrected on the basis of a control signal, and demodulation baseband I and Q signals thus corrected are output. The amplitude of the input baseband I and Q signals is corrected on the basis of the control signal, and the baseband I and Q signals thus corrected are input to the quadrature modulator.

Abstract: A small-sized buzzer comprises a vibrationally driven vibrator mounted within a case together with drive circuitry for electromagnetically actuating the vibrator. A screw member is threaded into the case at a location spaced from and opposite the free end of the vibrator so as to be repeatedly struck by the vibrator free end during its vibration to produce a buzzer sound. The buzzer sound can be varied by turning the screw member to adjust its spacing from the vibrator.