Abstract: The power amplification circuit for a communication device includes an initial-stage amplifier for amplifying a modulation signal of a predetermined frequency band, a first amplification system having a subsequent-stage amplifier and a final-stage amplifier for amplifying power of an amplified output of the initial-stage amplifier without modification and outputting the amplified output as a first transmission signal, and a second amplification system having a frequency conversion circuit composed of a local oscillation circuit and a mixing circuit for converting an amplified output of the initial-stage amplifier into a signal of a frequency band different from that of the first transmission signal and a subsequent-stage amplifier and a final-stage amplifier for amplifying power of an output signal of the frequency conversion circuit and outputting the amplified output as a second transmission signal.

Abstract: A device load variation protection circuit connected to an output side of a device to protected the device from a variation in a load includes a detection circuit, a protection load, and a switch. The detection circuit detects the variation in the load. The protection load is connected to the output side of the device so as to be switchable between connection and disconnection. The switch switches between connection and disconnection of the protection load on the basis of a detection result from the detection circuit.

Abstract: A PLL synthesizer includes a reference oscillator, an controllable oscillator which generates an oscillation signal which varies in frequency according to a control signal, a phase comparator, and a loop filter. The loop filter includes an A/D converter, a digital filter, and a D/A converter. The digital filter removes high-frequency components from the output of the A/D converter according to setting data. The digital filter is set to a filter characteristic depending to a selected frequency of the oscillation signal. The digital output signal of the digital filter is converted to an analog signal which is used as the control signal of the controllable oscillator.

Abstract: In response to a position registration request transmitted from a mobile telephone terminal 1a (or 1b), at least one base station 2.sub.l (or 2.sub.N) selected by the mobile telephone terminal transmits a response signal to the mobile telephone terminal which measures a receiving electric field strength of the received response signal and a time between the transmission of the position registration request and the reception of the response signal. The mobile telephone terminal calculates a distance between it and the base station and a direction to the base station on the basis of the measured electric field strength and the measured time and displays the results of calculation. The mobile telephone terminal reports the results of calculation to a central controller 4 through the base station and a control station 3 to store it in a portion of a subscriber information memory 5 corresponding thereto.

Abstract: A PLL circuit has a feedback loop including a plurality of feedback circuits in parallel and a combining circuit. The feedback circuits receives an output signal of the PLL circuit and produce feedback output signals, respectively. The combining circuit combines the feedback output signals into a feedback signal which is used to be compared to a reference signal. The feedback circuits in parallel each divide a frequency of the output signal by a predetermined number and the combining circuit performs logical OR of the feedback output signals.

Abstract: A calling system includes radio zones, a mobile telephone terminal, a paging terminal unit, a central control unit, and a notifying section. Each radio zone includes a control unit, a memory unit, a relay station, and calling units. The mobile telephone unit determines a response disabled state of a callee and transmits the corresponding information to the control unit. The main control unit has a main memory unit. The notifying section notifies information indicating the absence of the callee to the control unit, the mobile telephone terminal, and the caller.