Patent ID: 6829353
Filing Date: 2004-12-07
Classification: H04M

Abstract:
For use with a subscriber line interface circuit (SLIC) having tip and ring ports adapted to be coupled to a telecommunication wireline, and an auxiliary port adapted to be coupled to auxiliary signals in a frequency band different that of voice/data signals, a method of effectively compensating for distortion associated with the differential impedance between said SLIC and said telecommunication wireline at the frequency band of said auxiliary signals, said method comprising the steps of:(a) sensing signals applied to said auxiliary port of said SLIC including said auxiliary signals; (b) generating a signal current representative of said auxiliary signals sensed in step (a), including said auxiliary signals, and exclusive of voice/data signals; and (c) feeding only said signal current generated in step (b) to a transmission channel path of said SLIC in a manner that effectively cancels a reflected component of said auxiliary signal flowing through an impedance circuit of said transmission channel of said SLIC, wherein step (b) comprises coupling said signals sensed in step (a), including said auxiliary signals, to a transconductance amplifier circuit configured as a unity gain buffer and including an operational amplifier having a first, non-inverting input coupled to a reference voltage, and a second, inverting input to which said auxiliary signals sensed in step (a) are coupled, and an output stage coupled in a first current flow path between a first current mirror circuit coupled to a first voltage supply and a second current mirror circuit coupled to a second voltage supply, said output stage having an input terminal to which an input signal is applied, and being coupled by way of a feedback path to said second input of said operational amplifier, a first output port coupled to a second current flow path between said first and second current mirror circuits and providing a first output current having a first direction of current flow relative to said first output port, a third current mirror circuit cross-coupled between said first voltage supply and said second current mirror circuit, and a fourth current mirror circuit cross-coupled between said second voltage supply and said first current mirror circuit, a second output port coupled to a third current flow path between said third and fourth current mirror circuits and providing a second output current equal to said first output current and having a second direction of current flow relative to said second output port that is opposite to said first direction of current flow relative to said first output port, one of said first and second output currents providing said signal current representative of said auxiliary signals.