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:
Jul. 02, 1991
Filed:
Nov. 27, 1989
Rohm Co., Ltd., Kyoto, JP;
Abstract
A side tone preventive circuit for telephones which prevents the output of the transmitter on the speaker's side from being transmitted to the receiver on the same side. The balance of the impedance bridge in a bridge circuit for separating a transmission signal and a reception signal is automatically adjusted in accordance with the circuit impedance at the location at which a telephone is installed. An impedance measuring circuit measures the impedance of the telephone circuit, and a balance adjustment circuit the impedance of which is adjustable is provided in the bridge circuit. The impedance of the telephone circuit is measured at the time of installation of a telephone, and the impedance of the balance adjustment circuit is adjusted in correspondence with the result of measurement. Thus, the impedance balance of the bridge circuit is adjusted in correspondence with the circuit impedance, thereby effectively preventing a side tone.