A Continuous-Adaptive DDRx Interface with Flexible Round-Trip-Time and Full Self Loop-Backed AC Test

Masaru HARAGUCHI  Tokuya OSAWA  Akira YAMAZAKI  Chikayoshi MORISHIMA  Toshinori MORIHARA  Yoshikazu MOROOKA  Yoshihiro OKUNO  Kazutami ARIMOTO  

IEICE TRANSACTIONS on Electronics   Vol.E92-C   No.4   pp.453-459
Publication Date: 2009/04/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E92.C.453
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Low-Leakage, Low-Voltage, Low-Power and High-Speed Technologies for System LSIs in Deep-Submicron Era)
DDR interface,  SoC,  round-trip-time,  loop-backed test,  

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This paper describes new DDRx SDRAM interface architecture suitable for system-on-chip (SOC) implementation. Our test chip fabricated in a 90-nm CMOS process adopts three key schemes and achieves 960 Mb/s/pin operations with 32 bits width. One of new schemes is to suppress timing skew with rising-edge signal transmission I/O circuit and look-up table type impedance calibration circuit. DQS round-trip-time, propagation delay from rising edge of system clock in SOC to arrival of DQS at input PAD of SOC during read operation, becomes longer than one clock cycle time as for DDR2 interface and beyond. Flexible DQS round-trip-time scheme can allow wide range up to N/2 cycles in N bits burst read operation. In addition, full self loop-backed test scheme is also proposed to measure AC timing parameters without high-end tester. The architecture reported in this paper can be continuously adaptive to realize higher data-rate and cost-efficient DDRx-SDRAM interface for various kinds of SOC.