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# Two Slope Resistive Feeder for Telephone Line Interface Circuits

IP.com Disclosure Number: IPCOM000045651D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 30K

IBM

## Related People

Ballatore, D: AUTHOR

## Abstract

This article describes a two-slope linear resistive feeder which supplies more current for a high resistance telephone line and less current for a low resistance telephone line than does a simple resistive feeder.

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Two Slope Resistive Feeder for Telephone Line Interface Circuits

This article describes a two-slope linear resistive feeder which supplies more current for a high resistance telephone line and less current for a low resistance telephone line than does a simple resistive feeder.

Referring to Fig. 1, the feeder comprises transistor T which has its collector connected to battery voltage source E and its emitter connected to the feeder output through resistor r. The base of transistor T is connected to voltage source E through resistor R1.

Capacitor C is connected between the feeder output and the base of transistor T. Series-connected Zener diode DZ and resistor R2 are connected in parallel with capacitor C1.

In the DC mode of operation and since Vbe and Ib can be neglected, as long as the output current I is less than Vz/r, where Vz is the voltage drop across diode DZ, the latter does not conduct, and the output voltage V is given by: V = E - rI

The feeder behaves as a resistive feeder with a slope equal to l/r (see Fig. 2). When output current I is higher than Vz/r, diode DZ conducts, and output voltage V is given by: V = E + R1/R2 Vz - r (1 + R1/R2) I

The feeder behaves as a resistive feeder with a slope equal to l/r (1 + R1/R2).

In the AC mode of operation, the feeder exhibits impedence Z given by:

Z = (1 + R1/R2) + r.R1.Cp where p is the Laplace transform operator. The feeder behaves as a voltage source series connected with a high value inductor (r.R1.C) and r...