Differential termination with calibration for differential signaling

摘要

A system for calibrating an adjustable termination resistor for a low voltage differential signaling (LVDS) system is provided. The system includes an adjustable termination resistor located on a chip and a reference termination resistor located off the chip. A bias circuit coupled to the adjustable termination resistor and the reference termination resistor causes the same current to flow through the adjustable termination resistor and the reference termination resistor. A comparator is configured to compare a first voltage drop across the adjustable termination resistor and a second voltage drop across the reference termination resistor. A control circuit is coupled to receive an output signal from the comparator. If the output signal indicates that the adjustable termination resistor has a desirable value with respect to the reference termination resistor, then the control circuit stops the calibration operation. Otherwise, the control circuit modifies the adjustable termination resistor and repeats the calibration cycle.