[SI-LIST] Re: DDR delay & skew
- From: Vinu Arumugham <vinu@xxxxxxxxx>
- To: ched_chang@xxxxxxxxxxx
- Date: Tue, 10 Dec 2002 09:24:18 -0800
Measure flight time from driver signal crossing Vref while driving the
reference load to receiver signal crossing Vref.
Use crossing point instead of Vref for differential signals.
Thanks,
Vinu
Ched-Chang Chai wrote:
> Dear all,
>
> I am confused about how to measure the DDR-SDRAM delay.
> I was told that there are 2 different methods in measuring the delays:
> Method 1:
> - L->H : from Vref of the driver signal to Vinh of the receiver signal
> - H->L : from Vref of the driver signal to Vinl of the receiver signal
> Method 2:
> - L->H & H->L : from Vtt of the driver signal to Vref of the receiver signal
>
> [Note: L->H means signal transitions from LOW to HIGH and the other way
> round for H->L]
>
> Can I know which method is correct or is there any other standard method?
>
> What about the delay for DDR differential clock? I measure delays from the
> crossing point of the driver signals to the crossing point of the receiver
> signals. Is this correct?
>
> And lastly, how to calculate the skew requirement from the Controller/DDR
> data sheets?
>
> Thank you very much in advance.
> --
> Regards,
> Chai
>
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