Granted Patent
Utility
US 4,648,019 · App. 06/768,593
High efficiency ringing generator
Inventor:
Douglas C. Stahl
Patented Case
View Patent ↗
Granted: Mar 3, 1987
Filed: Aug 23, 1985
Inventor
Douglas C. Stahl
Assignee (at issue)
GTE Communication Systems Corporation
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.