Abstract: A cellular phone in which a data storage means can be installed while meeting the requirements for a compact and lightweight design, imposed on the cellular phone, different types of batteries are selectively used on the basis that a battery used in the cellular phone is removable. That is, when a data storage means is to be additionally provided in the cellular phone, a battery having such a specially designed structure that can be installed together with a data storage memory in the cellular phone, is used with the cellular phone. When the cellular phone should preferentially be compact and lightweight, a standard battery conforming to the compact design requirement is used with the cellular phone.

Abstract: The invention provides a light emitting device of a portable telephone, for stabilizing the brightness and color tone of the display, which operates by a power of a battery together with a communication circuit, includes plural light emitting elements of which light emission colors are different, which are driven individually by a pulse width modulation method. It also includes a voltage boosting circuit having a smoothing circuit connected to an output side thereof, whose output is supplied to the light emitting elements. Thus, by raising and stabilizing the battery voltage and supplying it to the light emitting elements, the light emitting elements are driven with a margin, and they are also blocked from an influence of the fluctuations of the battery voltage.

Abstract: A cellular phone in which a data storage means can be installed while meeting the requirements for a compact and lightweight design, imposed on the cellular phone, different types of batteries are selectively used on the basis that a battery used in the cellular phone is removable. That is, when a data storage means is to be additionally provided in the cellular phone, a battery having such a specially designed structure that can be installed together with a data storage memory in the cellular phone, is used with the cellular phone. When the cellular phone should preferentially be compact and lightweight, a standard battery conforming to the compact design requirement is used with the cellular phone.

Abstract: An extension phone type cordless telephone comprises a terminating set, a plurality of branch sets, and a plurality of charger stands. The terminating set comprises a terminating set radio communication circuit for performing radio communication with the plurality of branch sets and a terminating set wire communication circuit for performing communication over a commercial power line with the branch sets via a stand wire communication circuit included in the charger stand.

Abstract: A data backup apparatus for temporarily storing the data stored in a volatile memory using an internal battery when the main power is stopped. When the operation of the internal battery is started, the data stored in the volatile memory as a digital signal is converted into an analog signal by a D/A converter, and then it is stored in a magnetic storage unit. When the power supply is restored, the data stored in the magnetic storage unit as the analog signal is read out and converted into the digital signal, and then it is restored to the volatile memory.

Abstract: The present invention provides a modulation/ demodulation circuit and a communication system utilizing the modulation/demodulation circuit. The modulation/ demodulation circuit can be operated in either of a modulation/demodulation mode wherein an input signal is frequency inverted and scrambled or descrambled and a through mode wherein the input signal is directly outputted therefrom without being subject to any processing. In a private communication system, two such modulation/ demodulation circuits are used as a scrambler in the transmission-side and as a descrambler in the reception-side. In order to prevent the low band characteristic of the reception-side output in the through mode from being different from that of the modulation/demodulation mode, the modulation/demodulation circuit may include a high pass filter. The high pass filter a low band cut-off characteristic reciprocal to a low pass filter for removing the upper side band from the output of a double balanced mixer.

Abstract: A side tone preventive circuit for telephones which prevents the output of the transmitter on the speaker's side from being transmitted to the receiver on the same side. The balance of the impedance bridge in a bridge circuit for separating a transmission signal and a reception signal is automatically adjusted in accordance with the circuit impedance at the location at which a telephone is installed. An impedance measuring circuit measures the impedance of the telephone circuit, and a balance adjustment circuit the impedance of which is adjustable is provided in the bridge circuit. The impedance of the telephone circuit is measured at the time of installation of a telephone, and the impedance of the balance adjustment circuit is adjusted in correspondence with the result of measurement. Thus, the impedance balance of the bridge circuit is adjusted in correspondence with the circuit impedance, thereby effectively preventing a side tone.