US Patent 7558132 Implementing calibration of DQS sampling during synchronous DRAM reads

A method and calibration apparatus implement calibration of sampling of a data strobe signal (DQS) during synchronous dynamic random access memory (DRAM) reads. A calibration control is provided to enable calibration testing. A selected one of a received DQS signal and an internal Enable signal is driven onto a data mask (DQM) IO during a DRAM read for calibration testing. The received DQS signal and the internal Enable signal are used to adjust the Enable delay to generally center the preamble time at the DQS receiver.