A receiving circuit includes a first channel, a second channel, a third channel and a control circuit, wherein the first channel is arranged to decode and descramble a first data stream to generate first data corresponding to first color information of an image frame, the second channel is arranged to decode and descramble a second data stream to generate second data corresponding to second color information of the image frame, and the third channel is arranged to decode and descramble a third data stream to generate third data corresponding to third color information of the image frame. The control circuit is configured to enable the first channel to make the first channel decode the first data stream, and enable or disable at least part of functions of the second channel and the third channel according to whether or not the image frame is displayed on a display panel.