Calibration methods and circuits to calibrate drive current and termination impedance

摘要

Described are on-die termination (ODT) systems and methods that facilitate high-speed communication between a driver die and a receiver die interconnected via one or more signal transmission lines. An ODT control system in accordance with one embodiment calibrates and maintains termination resistances and drive currents to produce optimal output swing voltages. Comparison circuitry employed to calibrate the reference resistance is also used to calibrate the drive current. Termination elements in some embodiments are divided into two adjustable resistive portions, both of which are designed to minimize capacitive loading. One portion is optimized to produce a relatively high range of adjustment, while the other is optimized for fine-tuning and glitch-free switching.

主权项

1. An integrated circuit comprising:
a reference node operable to receive a first reference; a resistor operable to exhibit an adjustable impedance to current flow responsive to an impedance-control signal; a comparator having a first input coupled to the reference node to receive the first reference, a second input coupled to the resistor, and a comparator output; a transistor disposed in series with the resistor between the second input and a supply terminal, the transistor operable to disable the current flow through the resistor; a counter operatively disposed between the comparator output and the resistor, the counter operable to update the impedance-control signal responsive to the comparator output; wherein the counter is operatively coupled between the comparator and the resistor via a latch, the latch to capture the signal from the comparator output; adjustable termination elements each having a control port coupled to the counter; and a differential amplifier operable to receive a pair of complementary signals via respective first and second signal pads, and wherein each of the signal pads is coupled to a DC voltage via a respective one of the adjustable termination elements.