05014294 is referenced by 30 patents and cites 6 patents.

A unique speakerphone for celluar telephones includes in the transmit audio path between microphone 112 and transmitter 118, a transmitter mute switch which disconnects the audio path to the transmitter from the microphone 112, and a transamit gain amplifier that is controlled to lower the feedback the microphone can pickup from the speaker 110. In the feedback path to the radiotelephone receiver 120 from the cellular base station 122 and the land line telephone system 124, the speakerphone includes the controlled amplifier 106 which is fed into the speaker mute gate, and the speaker 110 to close the feedback loop. De-emphasized audio is sampled by the A/D 102 on both the microphone-to-transmittr side of the loop and the receiver-to-speaker side of the loop. The microcomputer 104 is able to detect and eliminate howl, as well as determine whether howl exists, from the A/D sampling.

Title
Speakerphone for cellular telephones with howl prevention, detection, elimination and determination
Application Number
7/473294
Publication Number
5014294
Application Date
February 1, 1990
Publication Date
May 7, 1991
Inventor
Charles P Binzel
Hoffman Estates
IL
James D Lefebvre
Cary
IL
Susan C Kromenaker
Palatine
IL
Agent
Rolland R Hackbart
Assignee
Motorola
IL, US
IPC
H04B 1/00
H04M 11/00
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