Patent ID: 6313776
Filing Date: 2001-11-06
Classification: H03M,H04L

Abstract:
A line driving circuit comprising:a comparison circuit that senses a differential output voltage, compares the differential output voltage to a reference voltage, and outputs a compare signal that indicates whether the differential output voltage is greater than or less than the reference voltage, the comparison circuit having:a first switch having an input and an output;a second switch having an input and an output, the inputs of the first and second switches being connected to sense the differential output voltage;a capacitor connected across the outputs of the first and second switches;a third switch having an input connected to the output of the first switch, and an output;a fourth switch having an input connected to the output of the second switch, and an output connected to ground;a voltage source; anda comparator having a non-inverting input connected to the output of third switch, and an inverting input connected to the voltage source;a counter that sets an initial count value in response to a load signal, outputs the initial count value as a count, increments the count in response to a count up signal, and decrements the count in response to a count down signal;a state machine connected to the counter and the comparison circuit, the state machine outputting the load signal, the count up signal, the count down signal, and control signals that control the comparison circuit; anda first digital-to-analog converter (DAC) that sources an output calibration current having a magnitude when the count is equal to a first predefined value, and increases the magnitude of the output calibration current when the count changes in a first direction, and that sinks an input calibration current having a magnitude when the count is equal to a second predefined value, and decreases the magnitude of the input calibration current when the count changes in a second direction.