RFIC Layout Analysis Using Sonnet EM with ... - Sonnet Software

View Current DensityIt is also interesting to observe the currentdensity as a function of frequency.Calculating the current density addsminimal EM simulation overhead, but it isvery useful to gain insight into how acircuit works and what cell size isappropriate.Current density at 0.1GHz is shown in thefigure to the right. Since skin effect at thislow frequency is much thicker than themetal, current is relatively evenlydistributed across the width of thetransmission lines, and the conductivelosses dominate the current spreadingeffects.Current density at 15GHz is shown in thesecond picture. In this case, skin effectlosses will dominate the spiral Q, as theskin effect is much thinner than the metal.In addition, current crowding is observedbelow (where current tends to have amaximum on the edges of thetransmission lines). Current crowdingoccurs at higher frequencies where theself-reactance of the transmission lines iscomparable to or greater than theconductive loss. Note the high edgecurrent that Sonnet conformal meshingshows very accurately. This edge currentmust be modeled very accurately by anyEM analysis tool in order to correctlyassess the losses in the device thatcontribute to the Q.Back annotating results to ADSYou can easily back annotate EM simulation results to ADS, to use it in a model based simulation. In the Sonnet plotting tool emGraph,select the data set which you want to export, then use Output > S/Y/Z Parameter File from the menu. This brings up a dialogwhere you can save model data in Touchstone (S2P), MDIF and other file formats. That data can be used easily in ADS as black boxdata, just like measurement results.The Ebridge plug-in also offers a menu item Import MDIF to assist you in reading MDIF swept parameter results created by a sweptparameterEM analysis in Sonnet into an ADS schematic.11