[SI-LIST] Re: Ground, the preferred reference plane

  • From: Chris Cheng <chris.cheng@xxxxxxxxxxxx>
  • To:
  • Date: Thu, 12 Dec 2002 13:48:22 -0800

100% agree but in reality, a lot of PC board doesn't have enough space to
fit so many rpack's. Take a look at most of the reference designs for PC
chipsets, most of them call out generating vref with a DC/DC converter and
terminate with a single resistor.

-----Original Message-----
From: Vinu Arumugham [mailto:vinu@xxxxxxxxx]
Sent: Wednesday, December 11, 2002 11:55 PM
To: chris.cheng@xxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Ground, the preferred reference plane




Chris Cheng wrote:

>Take an example of DDR in most PC design. The vref on receivers is
basically
>the VTT which usually is generated from an external DC/DC converter that
>generates VDDQ/2 and is completely isolated from the driver VDDQ. 
>
That does not sound like a good thing...
The receiver Vref should be driver Vddq/2. We usually generate it with a 
resistor divider from driver Vddq.
This way, Vref will track Vddq better...

Thanks,
Vinu
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