Abstract: A dual mode mobile telephone apparatus includes an echo canceler. In a hands-free conversation mode, a received speech output from a loudspeaker is input to a microphone by circulate cross talk and transmitted to the destination side so that an acoustic echo may be generated. The echo canceler cancels the acoustic echo. A center clipper for eliminating a residual echo signal having a level lower than a preset level is provided at the output side of the echo canceler. Enabling/disabling operations of the center clipper are controlled in accordance with a volume control level for a reception signal and transmission/reception state detection signal from a voice switching circuit which controls gains of reception channel and transmission channel in the opposite directions.

Abstract: A digital radio telephone apparatus adaptively employs an equalizer for compensating for signal distortion of received signals. A switch may be provided at an output terminal of the equalizer so that the equalized signals are selectively applied to the decoder. The equalizer may be rendered to be operative when the quality of received radio frequency signals is lower than a prescribed level and rendered to be inoperative when the quality of received radio frequency signals is not lower than the prescribed level. The equalizer may be rendered to be inoperative for a predetermined time period from the time a digital speech radio link establishment operation is initiated. In the event that a radio link is established by TDMA (Time Division Multiple Access), the equalizer may be rendered to be operative in synchronization with a time slot assigned to the apparatus. The equalizer is not suppled with electric power or clock while the equalizer is rendered to be inoperative.