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if differential can reduce cross talks, why do we use single ended DQ? And we know DQS is differential from DDR2

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DQS is a timing reference and benefits from being differential in noise immunity and edge accuracy. As you noted, differential DQS was introduced with DDR2.

DQ is a data signal, and can tolerate more skew than DQS. There are also a lot more DQ than DQS (8x more); making them all differential would be a pincount problem.

DQ-DQ crosstalk can be a problem. It is managed by good layout that addresses basic signal integrity, and by the provision of termination in the die in the faster DDR variants (called On-Die Termination, or ODT.)

Future memory technology could move to serial connections which are self-clocking. Serial technology is already being used for flash (NVMe, UFS, HFS/SD Card).

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  • \$\begingroup\$ this is perfect! Do you know any reference for why we use unmatched receivers for DDR5 & LP5? Basically i need to know what drives to decide if we need DFE & whether to use matched or unmatched RX. Thanks! \$\endgroup\$ – Navx Jul 22 '19 at 21:11
  • \$\begingroup\$ Can’t really help you there. Your controller IP vendor should have that info. \$\endgroup\$ – hacktastical Jul 22 '19 at 21:46

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