On chip ZQ calibration resistor trimming

摘要

Techniques for trimming an on chip ZQ calibration resistor are disclosed. The on chip ZQ calibration resistor alleviates the need for an external ZQ calibration resistor. The on chip ZQ calibration resistor allows for a faster ZQ calibration. The trimming of on chip ZQ calibration resistor may be used to account for process variation. A correction mechanism may be used to account for temperature variation. Some of the circuitry that is used for ZQ calibration is also used for trimming the on-chip calibration resistor. This circuitry may include operational amplifiers, current mirrors, transistors, etc. The dual use of the circuitry can eliminate offset errors in an operational amplifier. The dual use can eliminate current mirror mismatch. Therefore, the trimming accuracy may be improved. The dual use also reduces the amount of circuitry that is needed for trimming the on chip ZQ calibration resistor. Thus, transistor count and chip size is reduced.

主权项

1. An apparatus comprising:
an on-chip calibration resistor; a variable impedance circuit coupled to a calibration node; circuitry configured to establish a voltage at the calibration node based on a current in the on-chip calibration resistor and a reference current when the apparatus is in a first mode; circuitry configured to establish a voltage at the calibration node based on a current in the on-chip calibration resistor and an impedance of the variable impedance circuit when the apparatus is in a second mode; a comparator configured to compare the voltage at the calibration node with a reference voltage when the apparatus is in the first mode and in the second mode; circuitry configured to trim the on-chip calibration resistor based on the comparison of the voltage at the calibration node with the reference voltage when the apparatus is in the first mode; and circuitry configured to perform a ZQ calibration based on the comparison of the voltage at the calibration node with the reference voltage when the apparatus is in the second mode.