Telephone line circuit
AssigneeU.S. Philips Corporation
InventorsAloysius J. Nijman, Franciscus A. C. M. Schoofs
Life of this patent
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Abstract
The line circuit comprises at least a driver stage 1 having an amplifier. This amplifier is provided with a feedback circuit for forming a virtual output impedance which functions as a supply resistor so that additional collector space is created for the amplifier output transistor. In addition, the line circuit comprises a controlled supply source 5 connected to the amplifier output transistor for eliminating this additional collector space, which results in a low-dissipation line circuit.
Claims11
A telephone line circuit comprising at least one driver stage which comprises a first signal input for the connection to an a.c. source and a linear amplifier having an output transistor, the output transistor being coupled to a first terminal for the connection to a subscriber's line and also to a supply source for applying a direct current to the terminal via the main current path of the output transistor, characterized in that the driver stage comprises a feedback circuit connected between a current path through which the current of the main current path of the output transistor flows and an input of the amplifier for applying to the input of the amplifier a voltage which is proportional to the current in the main current path of the output transistor for establishing at least a partly virtual predetermined output impedance, which represents the line supply resistor and wherein said supply source comprises a controlled supply source.
A line circuit as claimed in any one of the preceding claims, characterized in that the controlled supply comprises a voltage source having an internal impedance which is substantially proportional to the said output impedance.
Dependencies are inferred from the claim text.