Abstract: A signal amplifying circuit of a communication device is disclosed including: an amplifier comprising a first input terminal, a second input terminal, and an output terminal, wherein the input terminal is coupled with a fixed voltage level; a feedback circuit coupled with the second input terminal and the output terminal of the amplifier; a digital-to-analog converter (DAC); a signal processing circuit; a switch for selectively coupling the second input terminal of the amplifier with the DAC or the signal processing circuit; and a control unit coupled with the switch for controlling the operations of the switch.

Abstract: A multi-screen video playback system includes: a video playback device having a main display, a portable communication device having a screen, and a multi-screen display controlling server. The multi-screen display controlling server transmits a target video to the video playback device via a network so that the video playback device utilizes the main display to display the target video. While the main display displays the target video, if the multi-screen display controlling server received a selection message corresponding to a position of a partial region of the main display, the multi-screen display controlling server dynamically generates a scaled video corresponding to images displayed on the partial region and transmits the scaled video to the portable communication device via a network so that the portable communication device simultaneously displays the scaled video on the screen.