Patent ID: 6873703
Filing Date: 2005-03-29
Classification: H04M

Abstract:
1. A transmission channel for a subscriber line interface circuit comprising: a current-sensing transimpedance stage, having tip and ring ports adapted to be coupled to tip and ring paths of a telecommunication wireline pair, and being operative to transform differentially sensed tip and ring input currents of said telecommunication wireline pair into a single ended voltage; and a transconductance amplifier gain stage coupled to receive said single ended voltage output by said current-sensing transimpedance stage, and being operative to produce an output voltage for application to downstream voltage-fed circuitry, wherein said transimpedance stage includes an operational amplifier having first and second complementary polarity inputs and an output; a tip path sense resistor coupled to said tip port; a first differential coupling circuit coupled between said tip path sense resistor and said first and second complementary polarity inputs of said operational amplifier, and being operative to apply a first differential input current to said first and second complementary polarity inputs of said operational amplifier in accordance with a first voltage across said tip path sense resistor; a ring path sense resistor coupled to said ring port; a second differential coupling circuit coupled between said ring path sense resistor and said first and second complementary polarity inputs of said operational amplifier, and being operative to apply a second differential input current to said first and second complementary polarity inputs of said operational amplifier in accordance with a second voltage across said ring path sense resistor; and a linearity compensator circuit coupled between a supply voltage node and said first and second complementary polarity inputs of said operational amplifier, and being operative to close a negative feedback path from said output of said operational amplifier to said first input of said operational amplifier, relative to a voltage balancing path coupled to said second input of said operational amplifier, and equalize voltages applied thereby to said first and second complementary polarity inputs of said operational amplifier, irrespective of variations in currents through said tip path and ring path sense resistors.