[SI-LIST] Re: De-rating
- From: "Istvan Nagy" <buenos@xxxxxxxxxxx>
- To: <maxsidhu@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 30 May 2012 15:59:56 -0700
Hi Siddhart,
My understanding about slew-rate derating is:
The SSTL standard AC threshold levels describe the voltage that the waveform
has to reach at nominal slew rate to accumulate enough charge to shurely
switch the input. If our slew rate is different than the nominal, then the
threshold level to cross will be different.
Instead of specifying new AC threshold levels for the given slew rate, the
JEDEC standards handle this by the slew rate derating, by keeping the AC
threshold constant (which is really valid only for the nominal slew rate)
and modifying the input timing requirements, compensating for the extra time
it takes to finish accumulating the charge after the waveform has already
crossed the standard AC threshold. This is what the derating tables specify.
So, the t_SU/t_H would remain actually the same, but the V_AC levels change.
Instead of dealing with the change of the voltage thresholds, we trick the
analysis and force constant voltage thresholds (easier for SI waveform
analysis) and change another parameter. The derating is the change-table for
the chosen "other" parameter: the input setup and hold requirements. It is
like pulling the numbers to the right direction to get the right results.
Regards,
Istvan Nagy
-----Original Message-----
From: Siddharth Rajagopalan
Sent: Wednesday, May 30, 2012 9:32 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] De-rating
Hello everybody,
Can someone please explain me on the relation between
setup time, hold time and de-rating?? i did some ground reading on it and
encountered terms like charge accumulation, dispersion. where does this
happen??how is del(t) calculated??
--
Thanks in advance,
Siddharth Rajagopalan
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