Off-Chip Skew Measurement and Compensation Module (SMCM) Design for Built-Off Test Chip

Skew calibration and compensation are critical ATE features for reliable functional test, particularly for applications such as memory chips since most mainstream memories use a source-synchronous interface. This paper presents a new Skew Measurement and Compensation Module (SMCM) design for off-chip skew calibration from Time Domain Reflectometry (TDR) measurements. It consists of coarse and fine parts which enable the circuit to detect a large skew range with high resolution. Circuit complexity is reduced through use of the proposed automatic edge detection method which controls coarse/fine operations. We also present skew compensation circuits which can de-skew off-chip signals based on the skew calibration. The SMCM occupies a small area, making it suitable for implementation in a Built-Off Test (BOT) chip. The circuits were implemented using a 130 nm technology in a Built-Off Test Interface (BOTI) developed for 800 Mbps DDR2 memory functional test.