[SI-LIST] Re: DDR2 simulation with multiple loads.
- From: "Beal, Weston" <Weston_Beal@xxxxxxxxxx>
- To: Arvind Reddy <arvindnreddy@xxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 9 Aug 2011 19:39:57 +0000
The most important measurement is the setup time. If the signal at all the DRAM
devices is stable before the required setup time, then the other issues are
secondary. The non-monotonic signal could create an EMC problem, but not
always. You need to simulate the ACC signals along with the clock signal and
measure the timing margins.
Regards,
Weston
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Arvind Reddy
Sent: Monday, August 08, 2011 11:30 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] DDR2 simulation with multiple loads.
Hi Experts,
We have a DDR2 interface in our board interfaced to a Freescale processor with
5 loads. Address/Command/Control signals are routed star topology, with a pull
up termination of 50ohms placed in the star point where the signals branches.
my pre-layout simulation were pretty good.
I am facing an issue in my post layout simulation for address/Command/Control
signals.since we have 5 DDR2 devices on board.
For Address/Command/Control signal group the number of branches used in this
topology for each layer are balanced except for one DDR2 device.
Due to the constraints on the board we are not able achieve symmetric
topology(The number of vias for all four DDR2 are four with 2 BGA fanouts but
the 5th ddr has only one via with 2 BGA fanouts)
Hence my post layout simulation for 5Th devices is not satisfactory, the signal
is suffering with non monotonic and no noise margin (-54.87 mV).
So, tried to compensate the via effect by simulating the signals,added 3pF cap
connected to ground near the 5th DDR devices.
I found the signal quality with improved noise margin.
So,I seek experts suggestion for added caps near the 5th receiver device.since
I have not come across any documents or technical notes related.
Thanks
Arvind.
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