In a mobile communication device, a power amplifier amplifies the power of a signal to be transmitted. A transmitter filter limits the frequency band of the amplified signal to a predetermined frequency band for transmission. The signal limited in frequency band is transmitted via an antenna. Output power control circuitry controls the output power of the signal to be transmitted and has an output power sensor and an automatic power control circuit. The output power sensor succeeds the transmitter filter in the direction of flow of the signal to be transmitted, and senses the output power of the signal. The automatic power control circuit controls the gain of the power amplifier such that the output power sensed by the output power sensor coincides with a preselected reference value.

The present invention provides an output level control circuit for a transmitter of an automobile telephone system which can output a transmission output signal of an output level indicated by a level setting signal with a high degree of accuracy. First and second level control circuits function for a low-level side and a high-level side, respectively, of the detection output of a detection circuit and perform weighting such that the outputs vary with linearity relative to the output signal of the amplifier. A control signal generation circuit causes a selection circuit to select a first or second error signal of a first or second comparison circuit, respectively. The first and second comparison circuits receive the output of the first or second level control circuit, respectively, and these control circuits process the detection output corresponding to the output level of the output signal of the amplifier indicated by a level setting signal. An amplifier control circuit supplies the amplifier with a level control voltage in response to the first or second error signal output selected by the selection circuit and controls the amplifier so that the amplifier may output an output signal of the output level indicated by the level setting signal.

A foldable mobile telephone which is constituted of a main body and a lid being open/close-able and is able to detect open/close state of the lid is provided. The main body provides a receiver for ultrasonic wave and the lid provides a microphone for ultrasonic wave. An ultrasonic oscillator intermittently generates an ultrasonic signal at each fixed interval and gives the ultrasonic signal to the receiver for ultrasonic wave. The receiver for ultrasonic wave receives the ultrasonic signal from the ultrasonic oscillator and generates an ultrasonic wave. The microphone for ultrasonic wave receives the ultrasonic wave generated by the receiver for ultrasonic wave and generates an ultrasonic detecting signal. An ultrasonic level judging circuit receives the ultrasonic detecting signal from the microphone for ultrasonic wave and judges whether the level of this ultrasonic detecting signal is higher or lower than a decided level and judges the open/close state of the lid and generates a judging signal. With this construction, the detecting the open/close state of the lid becomes possible and the ultrasonic wave is applied for this constitution, therefore the outside magnetic field does not influence this operation.

A transmission line coupler (115) for a transmitter output signal (123) generated by an RF signal amplifier (103) includes a through-path transmission line (201) and a coupled-path transmission line (202) electromagnetically coupled thereto by multiple serpentine-like portions (such as portions 641, 642, 643 and 644 in FIG. 6), which are disposed on opposite sides of the through-path transmission line (201) for enhancing coupling sensitivity and eliminating degradation in the amount of coupling due to variations in the transmission line plating registration. Offset portions (641, 643) on one side of the through-path transmission line (201) provide substantially the same amount of coupling as the offset portions (642, 643) on the other side of the through-path transmission line (201). The transmission line coupler (115) is embedded in the output match of the final amplifier (103) and includes complex impedances (212 and 210, 222) at each port of the coupled-path transmission line (202) for substantially eliminating undesired reflections. The coupled port of the coupled-path transmission line (202) is coupled by an inductor (211) to a hot-carrier diode (206) for enhancing the detection sensitivity thereof.

The invention relates to a reception method and a receiver used in a TDMA radio system. The receiver receives signals placed in time slots allowing the receiver to establish connections. The receiver receives the signals, which are placed in time slots and vary in strength. The receiver comprises amplification means amplifying the received signals with an amplification coefficient of a particular size. The receiver is arranged to receive connection establishing signals from time slots and to form at least two sets of time slots from the time slots, and the amplification means amplify the signals in different sets of time slots with an amplification coefficient of a different size. The amplification means amplify the signals in the same set of time slots with an amplification coefficient of the same size. The receiver comprises measurement means for measuring the strength of the signal received by the receiver, and placing means for placing the connection establishing signal into the set of time slots based on the strength measurement performed for the received signal.