Calibration Methods and Circuits to Calibrate Drive Current and Termination Impedance

A method for calibrating a resistance of an on-die termination (ODT) resistor against an off-die resistor using a single comparator, the method comprising:

• drawing a reference-resistor current through the off-die resistor to develop a reference-resistor voltage;
• comparing, with the single comparator, the reference-resistor voltage to a reference voltage;
• adjusting the reference-resistor current through the off-die resistor responsive to an output of the single comparator until the reference-resistor voltage matches the reference voltage to produce a calibrated reference-resistor current and a calibrated reference-resistor voltage;
• creating a calibrated ODT current proportional to the calibrated reference-resistor current;
• drawing the calibrated ODT current through the ODT resistor to develop an ODT voltage;
• and
• adjusting the resistance of the ODT resistor responsive to the output of the single comparator until the ODT voltage matches the calibrated reference-resistor voltage and the reference voltage.

An on-die termination (ODT) control circuit comprising:

• a comparator having:
• a first comparator input;
• a second comparator input;
• and
• a comparator output;
• a multiplexer having:
• a first multiplexer input;
• a second multiplexer input;
• and
• a multiplexer output coupled to the second comparator input;
• an adjustable ODT element having:
• a first current-handling terminal;
• a second current-handling terminal coupled to the second multiplexer input;
• and
• an ODT control input;
• and
• circuitry coupled between the comparator output and the ODT control input of the adjustable ODT element, the circuitry to provide a digital value to the ODT control input to calibrate an impedance through the adjustable ODT element.