1. Field of the Invention
The present invention relates to a speaker telephone, and particularly to such a device wherein the microphone and loudspeaker may be situated in a single housing.
2. Description of the Prior Art
Speaker telephones offer the convenience of "no hands" operation. The incoming signal is amplified and reproduced by a loudspeaker. The user's voice is picked up by a microphone and amplified for transmission to the line. Appropriate circuitry provides voice responsive operation, isolates the outgoing and incoming signals, and prevents audio feedback from the loudspeaker to the microphone.
Signal isolation and feedback prevention have been particularly difficult in the past. Electrical isolation between outgoing and incoming signals typically required use of a hybrid network. Elimination of acoustic feedback generally necessitated separate housings for the loudspeaker and the microphone. If these were placed in the same housing, loud speech from the speaker would cause the microphone output signal to be so large as to leak through the outgoing amplification circuitry and into the incoming signal path, causing feedback.
An object of the present invention is to provide a speaker telephone in which the microphone and loudspeaker may be situated in a single housing. Another object is to provide a speaker telephone in which no hybrid network or other isolation means is required between the loudspeaker and microphone circuits. A further object is to provide a speaker telephone in which the loudspeaker and microphone circuits are alternately, sequentially actuated and disabled to accomplish mode switching.