Speakerphone

  
This circuit consists of two audio channels, a control circuit, and a hybrid irlterface circuit. The gain of each audio channel is con· trolled by the control circuitry, with the use of a voltage controlled amplifier (VCA). The inputs to the control circuit are obtained from each of the audio channels. The hybrid interface circuit performs three important functions. First, it couples the Tx channel signal to the telephone line.
Speakerphone - schematic

Second, it couples the signal on the telephone line to the Rx channels. And, finally, it cancels a majority of the Tx signal that can couple into the Rx channel. The amount of Tx signal that appears on the Rx channel is called sidetone.




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