Hello all, I'm trying to simulate common-mode return loss in hspice, and want to double check my simulation with you because the result showed me was somewhat different than what I expected over 100MHz ~ 10GHz. First of all, below is my simple diagram implemented in the spice deck. Port1 Port2 + -------[[[[[[[[[[[[[[[[[[[[[[[[[[[[[-------+ +----+ dif'l traces +-------+ | +--------[[[[[[[[[[[[[[[[[[[[[[[[[[[[[-------+ | ((V)) common-mode ///// | input voltage source ///// Since I assume that both source impedance and the load impedance are 50ohms, I put 25ohms of Zcm to Rin and Rout variable as shown in the input file below. So, here are my questions to ask. 1. Is my diagram is reasonable for scc11 measurement? 2. What impedance value should both Rin and Rout have in the .NET statement. Is it Zo, Zeven or Zcm? If I set it to Zo(=50ohms), I have 6dB less loss than I expected. My W-elements model was based on dif'l traces having roughly 70ohms of even mode impedance, which is Zcm = Zeven/2 = 35ohms, although the odd mode impedance is ~53ohms. Interestingly, If I set both Rin and Rout in .NET statement to 35ohms(=Zcm of trace), then it resulted in exactly what I expected. So I want to clarify what is the right setting. 3. Is it right to use Sij(db) rather than either Sij(m) or Sij(r) for the simple math like scc11=(s11+s21+s12+s22)/2? *My spice deck Vin vcm_in 0 AC=1 Xline1 vcm_in vcm_in vcm_out vcm_out 0 trace1 Rdummy vcm_out 0 1meg .OPTIONS accurate post=2 probe .NET v(vcm_out) Vin Rin=25 Rout=25 .AC lin 1k 10meg 10000meg .PROBE scc11=par('(s11(db)+s21(db)+s12(db)+s22(db))/2') .SUBCKT trace1 in1 in2 out1 out2 Vss Wline1 in1 in2 Vss out1 out2 Vss +RLGCFILE= 'my_trace.rlc' N=2 L=.049 .ENDS .END Thanks, TK ------------------------------------------------------------------ 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