Zhangkun All of your DDR DQS, DQ, and DM signals should be routed overtop of a ground plane. This reduces return path effects in the package and connector. Both VDD and VTT should be as small a plane or fill area as possible, to reduce planar resonance effects. For VTT termination resistors, use 8 pin 4 resistors R-paks. Place an outer layer Vtt fill area behind the resistors and for each Rpak use 1 0603 0.1 uF ceramic capacitor directly behind the resistor. This will insure ample decoupling for VTT. For Vdd decoupling you will need to compute the worst case instantaneous current required by your devices and the acceptable noise level, (usually 5%) and from that compute the necessary ESL to accomplish this. Based on the ESL you will then select the number of 0.1 uF capacitors to meet your ESL needs by calculating (or solving for) the mounted inductance of the capacitor, and computing the number in parallel necessary to meet your requirement. regards, scott Zhangkun wrote: >Dear all: >In DDR, there are two power, VDD and VTT. For example, VDD=2.5V and VTT=1.25V. >VDD should be decoupled very well. How about the decoupling of VTT? Is it >important? How to arrange the VDD, VTT and GND? > >Best Regards > >Zhangkun >2004.5.14 > > >------------------------------------------------------------------ >To unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >or to administer your membership from a web page, go to: >//www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >List FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > >List technical documents are available at: > http://www.si-list.org > >List archives are viewable at: > //www.freelists.org/archives/si-list >or at our remote archives: > http://groups.yahoo.com/group/si-list/messages >Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > > -- Scott McMorrow Teraspeed Consulting Group LLC 2926 SE Yamhill St. Portland, OR 97214 (503) 239-5536 http://www.teraspeed.com Teraspeed is the registered service mark of Teraspeed Consulting Group LLC ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu