ADS学习第三课下8a_MomentumAdvanced_2010

ADS学习第三课下8a_MomentumAdvanced_2010 Agenda - Why do Post-layout simulations? - PCIe 3.0 example • Momentum Simulation • Compare with Pre-layout simulation • What is causing bad results? o TDR Front Panel o Current Visualization - Eye diagram and Xtalk analysis Why do Post-layout Simulations? What assumptions are made in Pre-layout Simulations? Typical Pre-layout Simulation - Lines are always parallel - Spacing is always constant - Return path is ideal It is very important to know when these assumptions break down and what impact they have on the design Lab-1: Import Allegro layout & check geometry - Copy Project called Mom_wkshop_Feb2010_prj - From ADS main window: - File -> Copy Project - Open design called PEX_ - From ADS Schematic window: - File -> Open Design -> PEX_strip Lab-1: Use 3D Viewer to better understand the geometry - View the geometry in 3D Viewer - Tools -> View 3D Connectivity - Click Query - Select any object on gnd plane - Click “View” in 3D connectivity Note that there is split pwr and gnd plane What is the impact of the split planes? Lab-1: Momentum Simulation Results Pre vs. Post Layout - Open Design PCI_PreLayout_ - Using 2D-Fieldsolver Multilayer model for Pre Layout Simulation Thissetup transforms Single-Ended data to Differential Ø Run the simulation to compare Pre vs. Post Layout results Lab-1: Momentum Simulation Results Pre vs. Post Layout - Open Design PCI_PreLayout_ - Using 2D-Fieldsolver Multilayer model for Pre Layout Simulation Double-click on S16P model and selected Momentum Simulation dataset -> PEX_strip_sim_mom_ Thissetup transforms Single-Ended data to Differential Ø Run the simulation to compare Pre vs. Post Layout results Lab-1: Momentum Simulation Results Pre vs. Post Layout Ø Return Loss is Terrible -> significant energy is reflecting back -> causing huge Insertion Loss Ø Open design PEX_strip_sim_ Ø MomentumRF -> Post-Processing -> Visualization Ø Select “Solution Setup” Ø Port Setup -> Multiple Mode Excitation Ø Set Port 1 & 2 to 1. Also set Port 2 phase to 180 Ø Thissets up differential excitation Ø Select solution freq of 9.45 GHz Ø Go to “Plot Properties” tab and Ø Why is Return loss so high? Ø Use TDR Front Panel to Investigate Ø From Data Display Window -> Open sp_tdr_ Ø Thislab demonstrated: Ø Post-layout simulation is critical for High-speed Design Ø There can be significant differences between Pre-and-Post layout simulation Ø Momentum can do accurate post-layout simulation Ø Modeling Return-path-discontinuities Ø Split Planes Ø Voids in the planes Ø Momentum can do fast post-layout simulation Ø NlogN Solver for simulating very large geometries Ø Memory Efficient Ø Multi-threading at NO extra $$$