Granted Patent
Utility
US 5,644,634 · App. 08/563,973
System and method for dual tone multifrequency detection using variable frame widths
Inventors:
Zheng Xie, John G. Bartkowiak
Patented Case
View Patent ↗
Granted: Jul 1, 1997
Filed: Nov 29, 1995
Inventors
Zheng Xie
John G. Bartkowiak
Assignee (at issue)
Advanced Micro Devices, 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.