The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 04, 1990
Filed:
Mar. 08, 1988
Applicant:
Inventors:
Hisashi Fujisaki, Tokyo, JP;
Keiko Shimada, Tokyo, JP;
Assignee:
NEC Corporation, , JP;
Attorney:
Primary Examiner:
Assistant Examiner:
Int. Cl.
CPC ...
H04M / ;
U.S. Cl.
CPC ...
379390 ; 379388 ; 381 94 ;
Abstract
A loud speaking telephone has separate volume level control circuits positioned in the transmit and receive paths, respectively. The frequency is shifted in at least one of the paths to provide a signal which is less likely to produce echos or singing. A comparator compares the levels in the send and receive paths to produce a control signal. The control signal adjusts the volume level controls to prevent singing.