Methods for memory interface calibration

Abstract

Integrated circuits with memory interface circuitry may be provided. Prior to calibration, a number of samples may be determined by computing probability density function curves as a function of timing window edge asymmetry for different degrees of oversampling. During calibration, duty cycle distortion in data strobe signals may be corrected by selectively delaying the data strobe rising or falling edges. A data clock signal that is used for generating data signals may also suffer from duty cycle distortion. The rising and falling edges of the data clock signal may be selectively delayed to correct for duty cycle distortion. The data path through which the data signals are routed may be adjusted to equalize rising and falling transitions to minimize data path duty cycle distortion. Multi-rank calibration may be performed by calibrating to an intersection of successful settings that allow each memory rank to pass memory operation tests.