[SI-LIST] Re: Fw: About the spacing between GND pad and PCIE traces

Dear Gongxian and Yanfeng,

Thanks for your information. The GND pads, vias or plane outside differential 
pair will help to reduce radiation and enhance SI. But I think there must be a 
condition for it. If the air gap is over 2x trace width between GND pad (or via 
or plane) and differential trace, there will be no doubt that it's helpful for 
SI. 

In case the air gap is less than one trace width. I'm afraid that the 
differential pair will be coupling to GND due to the limited spacing of GND pad 
to trace. Even on the PCIE finger, the spacing between two adjacent pins is 
over 2x trace width.

Thanks,

Peter 
  ----- Original Message ----- 
  From: yu.yanfeng@xxxxxxxxxx 
  To: jgxian@xxxxxxxxxx 
  Cc: pangning2000@xxxxxxxxx ; si-list@xxxxxxxxxxxxx ; 
si-list-bounce@xxxxxxxxxxxxx 
  Sent: Saturday, June 26, 2004 2:51 PM
  Subject: ´ð¸´: [SI-LIST] Re: Fw: About the spacing between GND pad and PCIE 
traces



  Dear Gongxian, 
  I don't agree with your opinion about the gnd pads. In fact, those 
sandwiched-type gnd pads will help to enhance SI. 
  Yanfeng Yu
  Sr. Engineer
  Nanjing R/D center, ZTE Corp.
  63 Gongqingtuan Road, Nanjing 210012
  Phone: 86-25-52872410
  Mobile :13505159475
  Mail: yu.yanfeng@xxxxxxxxxx 


       Jia Gongxian <jgxian@xxxxxxxxxx> 
        ·¢¼þÈË£º si-list-bounce@xxxxxxxxxxxxx 
        2004-06-26 14:35 
        Çë´ð¸´ ¸ø jgxian 
               
                ÊÕ¼þÈË£º        pangning2000@xxxxxxxxx 
                ³­ËÍ£º        si-list@xxxxxxxxxxxxx 
                ´«ÕæÖ£º         
                Ö÷Ì⣺        [SI-LIST] Re: Fw: About the spacing between GND 
pad and PCIE traces 



  Hi Peter,

   Since the the pads between the differential pair is gnd pads, and the PCI 
express signal is differential,  these two pads will have little impact on 
PCIE's SI.By the way,the conditions you mentioned for some kinds of connectors 
such as HS3 is inevitable.

  Jia Gongxian

  ----- Original Message ----- 
  From: "Pang Ning" <pangning2000@xxxxxxxxx>
  To: <si-list@xxxxxxxxxxxxx>
  Sent: Saturday, June 26, 2004 12:37 PM
  Subject: [SI-LIST] Fw: About the spacing between GND pad and PCIE traces


  > Dear Experts,
  > 
  > I have a question about the layout of PCI Express traces. We planned to use 
5mil trace width and 6mil (or 7mil) air gap for each PCIE differential pair. 
But there are two GND pads that are located at the both sides of the 
differential pair (Each differential pair is sandwiched by two GND pads) .  The 
spacing between GND pad and PCIE trace is only 5mil. As PCIE has very high 
swithing frequency, my concerns are if the two GND pads will impact PCIE signal 
quality. Is it possible that PCIE signal will be coupling to GND pads ? Thanks 
for you help.
  > 
  > Best regards,
  > 
  > Peter  
  > 
  >                  
  >        
  >    
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