Abstract: An idle current supplying path is switched during correction operation and during normal operation to detect a magnitude of an idle current flowing through a power amplifying circuit when the correction operation is switched. A bias voltage of the power amplifying circuit is corrected based upon the idle current detecting result. The bias voltage is automatically corrected in such a manner that the magnitude of the idle current flowing through the power amplifying circuit is made coincident with a predetermined current value. As a consequence, the idle current flowing through the respective power amplifying circuit can be continuously maintained to the optimum values respective of to the element deviation.

Abstract: A digital-analog shared circuit in dual mode radio equipment, which shares a local oscillator in a digital mode and analog mode. A first frequency synthesizer generates a first and a second local oscillation frequency in a digital and an analog receiving mode, respectively, in response to a control signal from a switching control. In the digital receiving mode, a quadrature demodulater including a first and a second demodulator in a demodulator section is enabled, and carries out quadrature detection of a received signal fed from an RF stage, thereby supplying the detected signal to a baseband signal processor stage. In the analog receiving mode, a buffer to which the second local oscillation frequency is supplied is enabled to deliver the second local oscillation frequency to the analog IF stage. A second frequency synthesizer generates a third local oscillation frequency in a digital transmitting mode and a fourth local oscillation frequency in an analog transmitting mode.

Abstract: An amplifier amplifies a signal derived from the output of a voltage-controlled oscillator. The frequency control voltage applied to the voltage-controlled oscillator is also applied, after suitable level conversion, to the amplifier as a gain control signal, to correct frequency-dependent power deviation of the amplifier.

Abstract: A data transmission apparatus is capable of data transmissions with and/or without error control. A remote data transmission apparatus with error control recognizes whether or not the carrier sent from the data transmission apparatus is intermittent. Additionally, the data transmission apparatus recognizes, based upon the existence of interruptions of a carrier signal sent from a remote data transmission apparatus, whether or not the remote data transmission apparatus has an error control function.

Abstract: A mobile radiotelephone for speech communication and data communication using signals of a voice frequency in a voice frequency band, having a tone signal generating circuit and connected to a data terminal equipment. Data communication completion is monitored, and the tone signal generating circuit is actuated to generate a tone signal by the speaker of a handset upon the completion of data communication in order to notify the operator of the completion of data communication. The speaker of the handset can be made to sound by controlling the existing tone signal generating circuit for tone dial. Thus, the mobile radiotelephone is able to notify the operator of the completion of data communication without requiring any additional tone signal generating circuit specially for such a purpose.

Abstract: An apparatus for judging the quality of mobile data communication has: (1) a unit for amplifying an incoming electric wave and detecting the strength of the received electric field; (2) a data communication judgement unit for previously setting a limit of data communication, and comparing the reference value with an output from the electric field strength detector unit (3) a visible display unit for visually displaying the received electronicfield signal when the strength of the received electric field is more than the judgment reference value; (4) a digital output terminal for outputting a digital control signal to control a modem; and (5) an audible tone generator for producing a continuous tone or an intermittent tone from a speaker to clearly inform an operator of the quality of the data communication when the strength of the received electric field is less than the judgment reference value.

Abstract: A line switching control system effects switching between a data communication mode and a voice communication mode in mobile communication, particularly mobile telephone service. The line switching control system includes a transmitter/receiver unit for transmitting and receiving signals through an antenna, an input device combined with a telephone, a switching device for effecting switching between the data communication mode and the voice communication mode, and a control unit for controlling switching between the data communication mode and the voice communication mode based on a mode switching command entered through the input device. When a key of the input device at the user's hand is depressed, switching between the data communication mode and the voice communication mode can smoothly be performed.

Abstract: A request repeat system for data communication in which the receiving station transmits a signal indicating the result of reception of data transmitted thereto from the transmitting station. The receiving station transmits a signal indicating the unsatisfactory data reception repeatedly N times at the maximum until the receiving station is able to receive the data normally to request the transmitting station to transmit the data again, when the receiving station does not receive the data in a prescribed time after the receiving station has transmitted the signal indicating the unsatisfactory reception of the data to the transmitting station. Thus, the request repeat system eliminates useless communication charge necessary for restarting data communication after interruption and repetition of operation for requesting the repeated transmission of data, and hence the request repeat system is particularly effectively applicable to mobile data communication.