A television adapter includes first and second conversion circuits, a switch unit, and a high definition television (HDTV) interface. The first conversion circuit includes a digital to analog (D/A) converter and a coupler. The second conversion circuit includes an analog to digital (A/D) converter and a decoupler. When the switch unit connects the first conversion circuit to the HDTV interface, the D/A converter converts a first digital signal from the HDTV interface into a first analog form data. The coupler couples the first analog form data to a first alternating current (AC) voltage. When the switch unit connects the second conversion circuit to the HDTV interface, the decoupler decouples and separates a second AC voltage into a second analog form data. The A/D converter converts the second analog form data into a second digital signal, and outputs the second digital signal to the HDTV interface.