With the increasing operating speed of electronic devices , interconnect system designed to connect devices , circuit boards, integrated circuits and devices is increasingly becoming the key to the success of the overall system design constraints to high speed and high density PCB design as an example , the signal integrity (SI) problems , power integrity (PI) and electromagnetic compatibility problems (EMC / EMI) has become a core issue which must be addressed in the project design . As technology advances , more and more designers to identify "high-speed design is the high-frequency design ," the new concept , a good interpretation of Figure 1 of this feature .
At present , more and more radio frequency / high frequency design engineer to participate in and guide the high-speed interconnect design , circuit design , and nearly half have found to be high performance SI / PI design , you must use the 3D full-wave models to deal with key Internet issues .
In fact , to achieve high-performance PCB design and simulation in SI / PI / EMI , the simulation tool must have the following key requirements :
First, we must adopt 3D full-wave electromagnetic model , especially for critical high-speed traces , vias, networks, etc. ; Second , can the simulation of complex supply network on the PCB ; Third, the simulator ( including emulators and road simulation games device ) must have high-precision , high-speed , high-capacity characteristics ; fourth , while providing time-domain and frequency-domain simulation results ; fifth , it must be compatible with existing PCB design process.
Ansoft 's electromagnetic field simulation tools coupled with the series of special design and simulation platform DesignerS SI
I, not only to meet the five -point demand , and because of Ansoft tools are made of a unique field of adaptive meshing technology, will greatly reduce the difficulty of the electromagnetic field simulation , simulation has long been its speed, accuracy and capacity are verified, is practical engineering tools. Field of the interconnection system tools to help designers to accurately extract and create a 3D full-wave interconnect system model of the system is then validated in simulation platform Ansoft DesignerSI extracted crosstalk , eye , when the bit error rate , frequency domain information for signal integrity / power integrity and EMC / EMI design and simulation.
Gigabit -speed channel design
Figure 2 is based on Xilinx's Virtex-II Pro X FPGA test evaluation board , its operating signal rates of up to 10Gbps over , Xilinx using Ansoft series of virtual simulation software , completed the design / receive high-speed differential lines on the PCB to optimize packet , high-speed communications. In the initial design stage, according to the actual problem is divided into a high speed serial channel relatively independent sub- sub- structure or , as in this embodiment can be divided into the package , PCB traces and SMA connectors are designed for optimization of each subsystem and extraction, to build a three-dimensional full-wave model , and then on DesignerSI platform through dynamic linking, co-simulation feature to link the modules form a complete channel verified by field analysis of the overall performance . Ansoft do so only through parametric design capabilities to achieve optimization of key structural design, and to maximize the efficiency of the simulation , for example, if you want to adjust some through the optimization of the structure of PCB vias, traces , such as to improve the overall transmission performance , then in the form of this decomposition subsystem can help designers to quickly obtain the required data , avoiding inefficient duplication of effort.
Use Q2D be controlled PCB trace impedance analysis to determine the geometry and the physical parameters of the differential line ; using three-dimensional field simulation tools HFSS extracting package , vias , SMA connectors, such as irregular traces of full-wave electromagnetic model ; in DesignerSI link the channel model in the frequency domain for each authentication system .
Import chip IBIS / Spice models on DesignerSI platform, through the field with a dynamic link Ansoft tools to complete the overall verification entire channel to give eye and comparison with experimental results (see Figure 3 ) .
Mixed- board PI and SI issues
A six PCB, its operating band at 1G or less divided on the power plane 2.5v, 3.3v and 5v three power split , but with a full ground plane. First, as the resonant field analysis in order to understand the power / ground plane in the overall characteristics of the operating band , a plurality of resonance phenomenon occurs found in the operating frequency band (1G or less ) , the resonant frequency with 14 points (Figure 4 ) in the SIwave , It can be observed while the PCB SIwave the resonance frequency in a different voltage (Figure 5 ) . Since the resonance frequency band will not only work to bring power integrity problems such as severe power / ground noise , SSN , etc., but also on the SI will have a serious impact . The cases are considered by the relevant location ( such as a resonant field peak / valley position ) decoupling capacitors to suppress resonance , and thus indirectly improve SI performance. SIwave simulation directly in the process of direct simulation of the impact of decoupling capacitor resonance analysis based on the previous results obtained for the inhibition of this 14 -resonant added 26 points of decoupling capacitors , simulation shows the decoupling capacitors lowest resonant frequency becomes 1.0133G, outside the operating bandwidth . In order to understand the impact of the SI , select a power split across the network to make S-parameter sweep signal analysis and comparison of S-parameters plus decoupling capacitance curves before and after ( Figure 6a / b), after the discovery of decoupling capacitors , 1G or less signal transmission characteristics significantly improved , especially around 700M insertion loss and return loss of 8dB ~ 9dB improvement .
PCB EMI simulation problem
A eight PCB, wherein the yellow line clock signal traces on the PCB , each of the clock lines are connected to an excitation source of electromagnetic radiation in order to understand the characteristics of the PCB , the first set SIwave swept PCB analysis can be clearly observed plate voltage fluctuations on the frequency , as shown in Figure 7.
Then, calculate PCB EMI radiation in space, in the case of SIwave . To 1G , for example, Figure 8 is a positive voltage fluctuations observed in PCB components through dynamic link between Ansoft HFSS and SIwave can calculate the PCB electromagnetic radiation data anywhere in three-dimensional space , in order to achieve virtual EMI testing. Figure 8 also shows the distance the electric field distribution at the PCB about 500mil cloud , contrast and spatial field distribution voltage fluctuation cloud cloud on the PCB can be found: the actual situation on the PCB voltage peaks / troughs near- field radiation corresponding to large values , it also anastomosis . While in SIwave draw directly on the PCB board at each frequency point far zone radiation field distribution according to need .
High-speed PCB board design , whether SI or PI, are very challenging , and the resulting EMI problems are more complex. SIwave V3 outside the SI / PI simulation adds new EMI simulation capabilities , combined with HFSS simulation process improved , further enhancing the overall performance of this important Ansoft EDA tools. Using the method of virtual prototype simulation of alternative trial design to optimize the design of the circuit board can effectively shorten the design cycle and cost -saving design .
