Granted Patent
Utility
US 4,406,926 · App. 06/218,054
Telephone station circuit using digital tone generation
Inventor:
Robert Hume Duncan
Patented Case
View Patent ↗
Granted: Sep 27, 1983
Filed: Dec 19, 1980
Inventor
Robert Hume Duncan
Assignee (at issue)
International Telephone and Telegraph 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.