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:
Nov. 28, 2000
Filed:
Nov. 25, 1998
Takuya Kanazumi, Tokyo, JP;
Osamu Kurokawa, Tokyo, JP;
Akira Ishikura, Kawasaki, JP;
Yoshihiro Nomura, Tokyo, JP;
Masakuni Hyodo, Tokyo, JP;
Ken Nakamura, Yokohama, JP;
Kabushiki Kaisha Toshiba, Kawasaki, JP;
Abstract
The present invention provides a cheap handsfree unit which can prevent the howling phenomenon and reduce the input sound from the loud-speaker into the microphone in both the analog and digital modes. A reception side comprises a signal level adjusting circuit constituted by a switch circuit and attenuators, and a transmission side comprises a signal level adjusting circuit constituted by a switch circuit and attenuators, to introduce the attenuation of 15 dB or 30 dB in response to the analog or digital mode. A voice switch is constituted so that the analog reception signal and the analog transmission signal are rectified respectively by rectifiers, the levels of both signals are compared by a comparator, and either switch or switch having a higher input signal level becomes conductive as a result of the comparison. The attenuation is introduced on the basis of the communication mode, only to either the analog reception signal or analog transmission signal having a smaller signal intensity.