Low-Complexity 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. This paper presents a new Time-to-Digital Converter (TDC) 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 methods which control coarse/fine operations. We also present skew compensation circuits which can de-skew off-chip signals based on the skew calibration. The TDC occupies a small area, making it suitable for implementation in a Built-Off Test (BOT) chip.The circuits were implemented using a 130nm technology in a Built-Off Test Interface (BOTI) developed for 800Mbps DDR2 memory functional test.