Xilinx, Inc.
Global resistor calibration for transceivers

Abstract:

Apparatus and associated methods relate to a programmable resistor having a resistance iteratively programmed by a calibration control loop. In an illustrative example, the calibration control loop may alternately sample the programmable resistance and a reference resistance by producing a corresponding voltage drop across the resistors. The voltage drops may, for example, be induced by the same constant current source. The calibration control loop may compare the voltage drops with a comparator, for example. In some examples, the comparator may provide a count direction signal to a logic block, generating a calibration code. The calibration code may, for example, be applied to the programmable resistor, such that the resistance of the programmable resistor iteratively approaches the resistance of the reference resistor. Various programmable resistors within a calibration control loop may, for example, substantially improve termination impedances of high-speed transmission lines and may mitigate random resistive mismatch variations.