Hi Scott, Thank you Sir for patiently clarifying my doubts. Regards, Ben --- Scott McMorrow <scott@xxxxxxxxxxxxxxxx> wrote: > > Ben, > > Here are the answers to your questions. > > >How is impedance control dependent on whether > >they are loosely/tightly coupled. > > > With loosely coupled differential pairs, > manufacturing etch contol > affects the width of the traces, which alters the > impedance. For > tightly coupled differential pairs, the width > between the pairs is also > greatly altered by the etch dimensions. Impedance > of a differential > pair trace is controled by the width of the trace > and the separation of > the edges. The percentage change for both is higher > with a tightly > coupled differential pair. > > >What is even mode return loss and how is coupling > >affecting this. > > > Even mode return loss is S11 for the common mode > signal (the part of the > signal that is not differential and is caused by > driver and delay skew) > and is the reflected energy that returns back to the > driver. Higher > return loss means more common mode energy is > bouncing around. This is > usually due to impedance mismatch in the system. > Tighter trace coupling > causes a larger divergence in odd and even mode > impedances. If the > system is matched for odd mode (differential > transmission) then the even > mode suffers greater mismatch and return loss. This > can become a > problem when the even mode return loss sets up > unwanted resonance > conditions in the system. > > >How is insertion loss affected by coupling. > > > To achieve the same differential impedances, > conductor width must be > smaller for tightly coupled differential pairs, when > compared to loosely > coupled differential pairs. This smaller width > causes higher DC > conductor loss and higher AC losses at high > frequencies due to skin > effect. In addition, a larger percentage of the > fields for tightly > coupled differential pairs are concentrated towards > the edge of the > pair, increasing the field concentration here and > thereby increasing the > conductor losses. > > >Are you experts there driving gigabit links > >through 2mm open pin field connectors! > >Its very hard to believe. Or is it controlled > >impedance connectors. But then are there any > >controlled impedance 2mm connectors. Any > >inputs on what connectors you are using and > >the highest data rate. > > > Teradyne, Molex, Tyco, FCI, Erni and many others > make a number of > varieties of 2 mm connectors which have controlled > impedance for 50 ohm > single-ended and 100 ohm differential signals. > We've used them > successfully for 2.5 and 3.125 Gbps system > backplanes. Some of the > newer connectors are capable of supporting nearly 10 > Gbps data transmission. > > >How is impedance variation at connector, BGA > >escapes and via transitions affected by > >coupling. > > > Tightly coupled differenential pair separation must > be widened at the > point of insertion into these strucures. Changing > the separation of the > pairs causes a change in impedance. > > >What resonance are you refering to, could you > >please elaborate. > > > Whenever an impedance mismatch occurs a resonance > structure is formed. > Quarter-wave and half-wave resonance structures are > created by these > mismatches. These resonance modes can cause > degradation in signal > waveshape and can couple to other similar resonance > structures across > the board. I'd refer you to the book: Microwave > Engineering by Pozar > for more information on resonance. > > > Good questions, Ben. > > > > regards, > > scott > > -- > Scott McMorrow > Principal Engineer > SiQual Interconnect Engineering > 18735 SW Boones Ferry Road > Tualatin, OR 97062-3090 > (503) 885-1231 > http://www.siqual.com > > > > ------------------------------------------------------------------ > 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 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 > > __________________________________________________ Do You Yahoo!? Yahoo! Sports - Coverage of the 2002 Olympic Games http://sports.yahoo.com ------------------------------------------------------------------ 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 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