U.S. Patent No. 2,821,639 - 01/28/1958 - Richard L. Bright and George H. Royer
Comments Concerning the Patent Gerald Stanley 03/03/2003: "Class-D solid-state amp. 1954 saw the creation of a full-bridge class-D amplifier by Richard Bright of Westinghouse. Suited only for servo-class uses, this fundamental design would wait for better semiconductors to again be said to be new."