Title: Telephone transmitter amplifier

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Abstract: A telephone transmitter amplifier circuit is easy to manufacture in integrated circuit form and has a low power consumption. It has a microphone unit, and an operational amplifier including a differential amplifer. A grounded collector transistor is connected to the output of the differential amplifier and a constant-current circuit is connected to the emitter of that transistor. An output stage amplifier has a grounded emitter transistor having its base connected directly to the output terminal of the operational amplifier. A smoothing circuit smooths the voltage which is supplied from the telephone line to the amplifier. A voltage-divider circuit, at the output of the smoothing circuit, presets the operating points of the operational amplifier and the output stage amplifier. The output terminals of the output stage amplifier are connected in common to input terminals of the smoothing circuit.


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