Patent ID: 7274405

Claim:
A cable extension unit having a signal transmitter for receiving input of an image signal and a signal receiver for outputting said image signal received from said signal transmitter through four signal lines, said signal receiver being connected with said signal transmitter through said four signal lines, said cable extension unit for respectively transmitting color signals R, G, B which comprises a RGB signal to said signal receiver through three signal lines of said four signal lines in case where said image signal inputted into said signal transmitter is said RGB signal: said signal transmitter comprising: synchronous signal polarity judging means for judging polarity of a synchronous signal corresponding to said RGB signal inputted into said signal transmitter; synchronous signal polarity inverting means for inverting polarity of said synchronous signal in case where said synchronous signal polarity judging means judged said polarity of said synchronous signal to be positive; synchronous signal overlapping and outputting means for operating so that said synchronous signal overlap any color signal which comprises said RGB signal inputted into said signal transmitter and for outputting said color signal which said synchronous signal overlapped through said signal line corresponding to said color signal; sound signal receiving means for receiving input of a sound signal; polarity information adding means for adding polarity information of said synchronous signal to a non-data area of said sound signal inputted in said sound signal receiving means; and sound signal transmitting means for transmitting said sound signal, said polarity information being added thereto by said polarity information adding means, through one of said four signal lines, through which said RGB signal has not been transmitted, to said signal receiver; said signal receiver comprising: synchronous signal separating means for separating said synchronous signal from said color signal which said synchronous signal overlapped by said synchronous signal overlapping and outputting means, said color signal being transmitted from said signal transmitter through said signal line; polarity information separating means for separating said polarity information from said sound signal, said polarity information being added thereto by said polarity information adding means, said sound signal being transmitted from said signal transmitter through said one signal line, through which said RGB signal has not been transmitted; synchronous signal recovering and outputting means for recovering said synchronous signal inputted in said signal transmitter, corresponding to said RGB signal from said synchronous signal separated by said synchronous signal separating means on the basis of said polarity information separated by said polarity information separating means and for outputting it; and sound signal outputting means for outputting said sound signal, said polarity information being separated therefrom by said polarity information separating means.