Connection arrangement for a telephone microphone amplifier with power supply connected to the output side of the amplifier

Claim 2

Amplifier means for telephone microphones having a power supply connected to the output side of the amplifier means, comprising: a differential transistor amplifier having feedback constituting a first stage including means for receiving the output of a microphone, a Darlington connection transistor amplifier constituting an output stage for said differential amplifier, a plurality of semiconductor diodes connected in series across the output of said Darlington amplifier, said diodes being connected in the forward direction with respect to said power supply and means connecting said Darlington amplifier output, said diodes and said differential amplifier for supplying direct currents to said differential amplifier, for providing a signal feedback from said output stage to said first stage thereby degenerating any changes in output by reason of fluctuations in the power supply and for determining the operating points of the amplifier means, said connecting means being arranged with respect to said diodes and the transistors in said amplifiers in such a way that the terminals of the transistors in the quiescent state are maintained at whole number multiples of the threshold voltage of a PN junction operated in the forward direction in one of said transistors.

Claim 3

The apparatus of claim 1 in which said amplifier has input terminals for connection to a microphone, and output terminals for connection to a telephone line and said diodes are three in number connected in series between a first and second one of the output terminals of the differential amplifier, with the junction between a first and second one of the diodes connected to one input terminal, and resistively connected to the bases of the differential transistor amplifier, the base of one of the transistors being connected to the other input terminal and the base of the other transistor of the differential amplifier being resistively connected to said second output terminal, the emitters of said two transistors being connected together and their junction resistively connected to said second output terminal, and the collectors of said two transistors being resistively connected to said first output terminal, the input transistor of the Darlington amplifier having its base connected directly to the collector of said one transistor of the differential amplifier and its collector resistively connected to the base of said other transistor thereof, the output transistor of the Darlington amplifier having its emitter connected to said second output terminal and its collector connected with said first output terminal.