Granted Patent
Utility
US 6,587,559 · App. 09/159,143
Cross-frame dual tone multifrequency detector
Inventor:
John G. Bartkowiak
Patented Case
View Patent ↗
Granted: Jul 1, 2003
Filed: Sep 23, 1998
Inventor
John G. Bartkowiak
Assignee (at issue)
Legerity, 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.