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MOS Battery Feed Circuit for Subscriber Line Interface Equipment

IP.com Disclosure Number: IPCOM000048199D
Original Publication Date: 1981-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Delaporte, F: AUTHOR [+4]

Abstract

This article describes a subscriber line interface circuit comprising a battery feed circuit using VMOS transistors and in which battery noise is fully rejected. Hybrid conversion is also described.

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MOS Battery Feed Circuit for Subscriber Line Interface Equipment

This article describes a subscriber line interface circuit comprising a battery feed circuit using VMOS transistors and in which battery noise is fully rejected. Hybrid conversion is also described.

The battery feed circuit, which supplies DC power to the subscriber loop connected to terminals a and b, basically comprises an input resistor network (R1-R4), a VMOS current source (CS1), a VMOS current sink (CS2), and a constant current generator (CG). CS1 comprises VMOS transistor Q1 controlled by operational amplifier A1. MOS technology matches very well with the current source functions because MOS transistors exhibit high drain to source breakdown voltage and low saturation voltage, end have no gate current even when saturated. When the telephone set is off hook, I(D)=30 mA and V(DS) greater than 0. When it is on hook, I(D)=0 mA, V(DS) approximately equal to 0, and very weak dissipation within the MOS transistor is obtained.

The value of resistor R7 is selected to be R7=R6+R5 as to provide a bridged configuration which, in cooperation with the biasing CG that isolates CS1 from CS2, fully rejects battery noise. CS2 is a symmetrical version of CSl, and the value of resistor R10 is selected to be R10=R8+R9 for battery noise rejection.

Hybrid conversion is provided by operational amplifiers A3, A4 and A5 and a balancing network (BN). Transmit AC signals are applied to the inverting input of amplifier A...