| 摘要 |
A line powered loudspeaking telephone is implemented entirely from electronic components, eliminating inductors and transformers. A three stage (521, 523, 525, 532) output amplifier is used with the loudspeaker impedance forming the output stage impedance. A feedback network (527, 528, 529, 530) is used between the amplifier input and output stages to provide the desired gain at audio frequencies while forcing the DC gain to unity. The circuit then functions to provide proper gain for audio frequency signals received from the communication line while reflecting onto the communication line the resistive component of the output stage impedance scaled by biasing circuit elements (518, 519) of the amplifier input stage, thereby maintaining the proper voltage-current characteristic of the communication line. |
