Granted Patent
Utility
US 4,646,347 · App. 06/729,955
Ringing signal reformatting circuit
Inventor:
Thomas Liu
Patented Case
View Patent ↗
Granted: Feb 24, 1987
Filed: May 2, 1985
Inventor
Thomas Liu
Assignees (at issue)
American Telephone and Telegraph, Co.
AT&T Information Systems Inc.
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.