Calibration methods and circuits to calibrate drive current and termination impedance

An integrated circuit comprising:

• a transmitter having a termination resistance and supporting a drive current to transmit a signal having a signal swing, wherein the signal swing is a product of the termination resistance and the drive current;
• and
• a calibration circuit coupled to the transmitter, the calibration circuit to establish control values that calibrate the drive current and the termination resistance, the calibration circuit including:
• a comparator having a comparator output terminal that provides a signal exhibiting an offset error;
• a reference current source coupled to the comparator output terminal to pass a reference current proportional to the drive current;
• and
• an adjustable reference resistor coupled to the comparator output terminal to exhibit a reference resistance proportional to the termination resistance, wherein the reference resistance is modified by the signal exhibiting the offset error, such that the reference resistance increases with the signal exhibiting the offset error if the reference current decreases and decreases with the signal exhibiting the offset error if the reference current increases.

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

• a comparator having first and second comparator input terminals and a comparator output terminal;
• a first counter coupled to the comparator output terminal to store a first value representative of an ODT resistance offset;
• and
• a second counter coupled to the comparator output terminal to store a second value representative of a drive-current offset.

A method of calibrating a transmitter on an integrated circuit device, the method comprising:

• drawing a reference current through a reference resistor to produce a first voltage;
• drawing a second current through an external reference termination element to produce a second voltage;
• comparing the first and second voltages to calibrate a reference termination resistance;
• and
• drawing the reference current through a reference resistor to produce a third voltage and comparing the third voltage with a reference voltage to calibrate a driver current of the transmitter;
• wherein offset errors exhibited by the comparator that increase the reference termination resistance decrease the reference current.

An integrated circuit comprising:

• a pad to couple to an external resistor;
• a first current source, coupled to the pad, to develop a first voltage by drawing a first current through the external resistor;
• a first plurality of register bits, coupled to the first current source, to store a first value that calibrates the first current of the first current source, wherein the first value is based on a first comparison between the first voltage and a reference voltage;
• a second current source that is controlled based on the first value;
• a digitally adjustable resistor, coupled to the second current source, wherein a second voltage is developed by drawing a second current through the digitally adjustable resistor and the second current source;
• a second plurality of register bits, coupled to the digitally adjustable resistor, to store a second value that calibrates an impedance setting of the digitally adjustable resistor, wherein the second value is based on a second comparison between the second voltage and the reference voltage;
• and
• a plurality of drivers to transmit data, wherein, for each driver of the plurality of drivers, at least one of a drive current and a termination resistance is set based on the first value and the second value.