Impedance and PCB-Pool, Part 2

In my last post I talked about about the challenges of routing 50 Ohm traces using PCB-Pool's prototype stackup. In this post I'm going to talk a bit more about using the MMTL Electromagnetic Simulator.

With MMTL you can model a PCB stack-up by drawing objects that represent each layer of either a conductor or a dielectric (insulator). Figure 1 shows an example of a model for the outer layer traces. The top yellow rectangle represents copper traces on an outer layer (ie. the top or bottom layer). The green space below the copper trace is the 0.2mm dielectric layer that separates the top layer from the first inner layer. The blue object below the dielectric is the nearest inner plane. In this case we use the nearest inner plane as a ground plane.

Figure 1. MMTL Model of the Top Two Layers with a 0.2mm Dielectric.

One of MMTL's best features is the ability to sweep a parameter. Below are the results from a 100 iteration sweep of the trace width. I used this output to determine that 0.366mm (14.4mil) wide traces were required on the top layer to achieve 50 impedance traces. Next week I'll post routing examples from my ECP5 DDR3 route.

____ # iterations:  100 ___
Write: "C:/Program Files (x86)/tnt-1.2.2/examples/pcbpooltop.xsctn.temp"
----------------------------------------
::Top width = 9.5e-005
::TopR0   Impedance = 90.4255
____________________________________________________
::Top width = 9.80808080808e-005
::TopR0   Impedance = 89.4904
____________________________________________________
::Top width = 0.000101161616162
::TopR0   Impedance = 88.5816
____________________________________________________
::Top width = 0.000104242424242
::TopR0   Impedance = 87.6974
____________________________________________________
::Top width = 0.000107323232323
::TopR0   Impedance = 86.8369
____________________________________________________
::Top width = 0.000110404040404
::TopR0   Impedance = 85.9987
____________________________________________________
::Top width = 0.000113484848485
::TopR0   Impedance = 85.1817
____________________________________________________
::Top width = 0.000116565656566
::TopR0   Impedance = 84.385
____________________________________________________
::Top width = 0.000119646464646
::TopR0   Impedance = 83.6075
____________________________________________________
::Top width = 0.000122727272727
::TopR0   Impedance = 82.8486
____________________________________________________
::Top width = 0.000125808080808
::TopR0   Impedance = 82.1071
____________________________________________________
::Top width = 0.000128888888889
::TopR0   Impedance = 81.3827
____________________________________________________
::Top width = 0.00013196969697
::TopR0   Impedance = 80.6743
____________________________________________________
::Top width = 0.000135050505051
::TopR0   Impedance = 79.9815
____________________________________________________
::Top width = 0.000138131313131
::TopR0   Impedance = 79.3036
____________________________________________________
::Top width = 0.000141212121212
::TopR0   Impedance = 78.6399
____________________________________________________
::Top width = 0.000144292929293
::TopR0   Impedance = 77.7666
____________________________________________________
::Top width = 0.000147373737374
::TopR0   Impedance = 77.1325
____________________________________________________
::Top width = 0.000150454545455
::TopR0   Impedance = 76.5111
____________________________________________________
::Top width = 0.000153535353535
::TopR0   Impedance = 75.9021
____________________________________________________
::Top width = 0.000156616161616
::TopR0   Impedance = 75.3048
____________________________________________________
::Top width = 0.000159696969697
::TopR0   Impedance = 74.719
____________________________________________________
::Top width = 0.000162777777778
::TopR0   Impedance = 74.1442
____________________________________________________
::Top width = 0.000165858585859
::TopR0   Impedance = 73.58
____________________________________________________
::Top width = 0.000168939393939
::TopR0   Impedance = 73.0262
____________________________________________________
::Top width = 0.00017202020202
::TopR0   Impedance = 72.4823
____________________________________________________
::Top width = 0.000175101010101
::TopR0   Impedance = 71.948
____________________________________________________
::Top width = 0.000178181818182
::TopR0   Impedance = 71.4231
____________________________________________________
::Top width = 0.000181262626263
::TopR0   Impedance = 70.9073
____________________________________________________
::Top width = 0.000184343434343
::TopR0   Impedance = 70.4002
____________________________________________________
::Top width = 0.000187424242424
::TopR0   Impedance = 69.9016
____________________________________________________
::Top width = 0.000190505050505
::TopR0   Impedance = 69.4113
____________________________________________________
::Top width = 0.000193585858586
::TopR0   Impedance = 68.9291
____________________________________________________
::Top width = 0.000196666666667
::TopR0   Impedance = 68.4546
____________________________________________________
::Top width = 0.000199747474748
::TopR0   Impedance = 67.9876
____________________________________________________
::Top width = 0.000202828282828
::TopR0   Impedance = 67.5281
____________________________________________________
::Top width = 0.000205909090909
::TopR0   Impedance = 67.0756
____________________________________________________
::Top width = 0.00020898989899
::TopR0   Impedance = 66.6302
____________________________________________________
::Top width = 0.000212070707071
::TopR0   Impedance = 66.1915
____________________________________________________
::Top width = 0.000215151515152
::TopR0   Impedance = 65.7594
____________________________________________________
::Top width = 0.000218232323232
::TopR0   Impedance = 65.3337
____________________________________________________
::Top width = 0.000221313131313
::TopR0   Impedance = 64.9143
____________________________________________________
::Top width = 0.000224393939394
::TopR0   Impedance = 64.501
____________________________________________________
::Top width = 0.000227474747475
::TopR0   Impedance = 64.0936
____________________________________________________
::Top width = 0.000230555555556
::TopR0   Impedance = 63.6921
____________________________________________________
::Top width = 0.000233636363636
::TopR0   Impedance = 63.2961
____________________________________________________
::Top width = 0.000236717171717
::TopR0   Impedance = 62.9058
____________________________________________________
::Top width = 0.000239797979798
::TopR0   Impedance = 62.5208
____________________________________________________
::Top width = 0.000242878787879
::TopR0   Impedance = 62.141
____________________________________________________
::Top width = 0.00024595959596
::TopR0   Impedance = 61.7664
____________________________________________________
::Top width = 0.000249040404041
::TopR0   Impedance = 61.3968
____________________________________________________
::Top width = 0.000252121212121
::TopR0   Impedance = 61.0322
____________________________________________________
::Top width = 0.000255202020202
::TopR0   Impedance = 60.6723
____________________________________________________
::Top width = 0.000258282828283
::TopR0   Impedance = 60.3171
____________________________________________________
::Top width = 0.000261363636364
::TopR0   Impedance = 59.9665
____________________________________________________
::Top width = 0.000264444444445
::TopR0   Impedance = 59.6204
____________________________________________________
::Top width = 0.000267525252525
::TopR0   Impedance = 59.2787
____________________________________________________
::Top width = 0.000270606060606
::TopR0   Impedance = 58.9413
____________________________________________________
::Top width = 0.000273686868687
::TopR0   Impedance = 58.6081
____________________________________________________
::Top width = 0.000276767676768
::TopR0   Impedance = 58.279
____________________________________________________
::Top width = 0.000279848484849
::TopR0   Impedance = 57.954
____________________________________________________
::Top width = 0.000282929292929
::TopR0   Impedance = 57.6328
____________________________________________________
::Top width = 0.00028601010101
::TopR0   Impedance = 57.3156
____________________________________________________
::Top width = 0.000289090909091
::TopR0   Impedance = 57.0022
____________________________________________________
::Top width = 0.000292171717172
::TopR0   Impedance = 56.6925
____________________________________________________
::Top width = 0.000295252525253
::TopR0   Impedance = 56.3863
____________________________________________________
::Top width = 0.000298333333333
::TopR0   Impedance = 56.0839
____________________________________________________
::Top width = 0.000301414141414
::TopR0   Impedance = 55.7849
____________________________________________________
::Top width = 0.000304494949495
::TopR0   Impedance = 55.4893
____________________________________________________
::Top width = 0.000307575757576
::TopR0   Impedance = 55.1971
____________________________________________________
::Top width = 0.000310656565657
::TopR0   Impedance = 54.9083
____________________________________________________
::Top width = 0.000313737373738
::TopR0   Impedance = 54.6227
____________________________________________________
::Top width = 0.000316818181818
::TopR0   Impedance = 54.3402
____________________________________________________
::Top width = 0.000319898989899
::TopR0   Impedance = 54.061
____________________________________________________
::Top width = 0.00032297979798
::TopR0   Impedance = 53.7847
____________________________________________________
::Top width = 0.000326060606061
::TopR0   Impedance = 53.5116
____________________________________________________
::Top width = 0.000329141414142
::TopR0   Impedance = 53.2413
____________________________________________________
::Top width = 0.000332222222222
::TopR0   Impedance = 52.974
____________________________________________________
::Top width = 0.000335303030303
::TopR0   Impedance = 52.7095
____________________________________________________
::Top width = 0.000338383838384
::TopR0   Impedance = 52.4479
____________________________________________________
::Top width = 0.000341464646465
::TopR0   Impedance = 52.189
____________________________________________________
::Top width = 0.000344545454546
::TopR0   Impedance = 51.9328
____________________________________________________
::Top width = 0.000347626262626
::TopR0   Impedance = 51.6793
____________________________________________________
::Top width = 0.000350707070707
::TopR0   Impedance = 51.4285
____________________________________________________
::Top width = 0.000353787878788
::TopR0   Impedance = 51.1802
____________________________________________________
::Top width = 0.000356868686869
::TopR0   Impedance = 50.9345
____________________________________________________
::Top width = 0.00035994949495
::TopR0   Impedance = 50.6912
____________________________________________________
::Top width = 0.00036303030303
::TopR0   Impedance = 50.4504
____________________________________________________
::Top width = 0.000366111111111
::TopR0   Impedance = 50.2121
____________________________________________________
::Top width = 0.000369191919192
::TopR0   Impedance = 49.976
____________________________________________________
::Top width = 0.000372272727273
::TopR0   Impedance = 49.7424
____________________________________________________
::Top width = 0.000375353535354
::TopR0   Impedance = 49.5111
____________________________________________________
::Top width = 0.000378434343435
::TopR0   Impedance = 49.282
____________________________________________________
::Top width = 0.000381515151515
::TopR0   Impedance = 49.0552
____________________________________________________
::Top width = 0.000384595959596
::TopR0   Impedance = 48.8305
____________________________________________________
::Top width = 0.000387676767677
::TopR0   Impedance = 48.608
____________________________________________________
::Top width = 0.000390757575758
::TopR0   Impedance = 48.3876
____________________________________________________
::Top width = 0.000393838383839
::TopR0   Impedance = 48.1693
____________________________________________________
::Top width = 0.000396919191919
::TopR0   Impedance = 47.9532
____________________________________________________
::Top width = 0.0004
::TopR0   Impedance = 47.739
____________________________________________________
Set the display values to the data prior to the simulations.