DesignCon 2003
High-Performance System Design Conference Decomposition of Coplanar and Multilayer Interconnect Structures with Split Power Distribution Planes for Hybrid Circuit–Field Analysis
Neven Orhanovic
Dileep Divekar
Norio Matsui
Applied Simulation Technology
Abstract
A novel technique for decomposing complex interconnect systems into signal propagation and power distribution parts is prented. The decomposition is performed around the discontinuities in the signal or return current paths. The decompod structure is ideally suited for hybrid analysis where one part of the problem is modeled using circuit methods and the cond part is analyzed using field solvers. The method significantly extends the available decomposition techniques in its generality and its applic
ability to a wide range of structures, including coplanar structures as well as structures containing conductive planes with voids such as splits, slits, or gaps. The decompod structure offers the possibility of more efficient analysis compared to the analysis of the non-decompod structure. Author(s) Biography
Neven Orhanovic
Neven Orhanovic received his B.S. degree in Electrical Engineering from the University of Zagreb, Croatia and his M.S. and Ph. D. degrees in Electrical and Computer Engineering from Oregon State University, Corvallis. From 1992 until 1999, he was with Interconnectix and Mentor Graphics Corp. developing numerical methods and simulation software in the area of interconnect analysis and interconnect synthesis. He is currently with Applied Simulation Technology working mainly on full-wave analysis methods.
Dileep Divekar
Dileep Divekar obtained a B.S. in Electrical Engineering from Pune University, Pune, India and M.S. and Ph.D. in Electrical Engineering from Stanford University, Stanford, CA. He has worked in the areas of circuit simulation, miconductor device modeling, static timing analysis and signal integrity.
He is currently with Applied Simulation Technology.
Norio Matsui
Norio Matsui holds a Ph. D. from Wada University, Tokyo and was a rearcher in NTT Labs for over 16 years. During this period he developed noi simulation tools for Signal and Power Integrity as well as physical designs for high speed tele-switching systems. Apart from authoring numerous papers, he also lectured at Chiba University. He is currently President of Applied Simulation Technology and is actively involved in Power Integrity, Signal Integrity, and EMI/EMC solutions.
钣Introduction
像天堂的悬崖The interconnect structures found in today’s printed circuit boards (PCBs) support veral fundamental types of wave propagation. The fundamental modes of propagation can be parated into two categories: 1) modes that require two or more conductors to support the propagating waves; 2) modes of propagation that can be supported by single conductor containing a cavity or a void. The conductors that support the propagation can further have different shapes with widely varying dimensions and aspect ratios. Some of the condu ctors or voids in the conductors are thin and narrow and support mainly one dimensional (1D) propagation along the tangential (or longitudinal) di
rection. The 1D conductors or voids can usually be modeled accurately and efficiently using multiconductor transmission line models and conventional lumped element discontinuity models (Figure 1). Other conductors or voids are wide or thick and they can support more complex propagation in two or three dimensions (2D/3D). In most digital systems, the conductors ud for signal propagation are mainly 1D while the conductors ud for power distribution are 2D/3D. The 2D/3D conductors require more complex analysis techniques, which involve direct or indirect solutions of partial differential equations or integral equ ations in two or three space dimensions.
阽危Figure 1: Simple structure supporting mainly 1D propagation on the left and mainly 2D propagation on the right. For this example, the decomposition into 1D and 2D partitions is trivial (b). Although the same techniques ud for the analysis of 2D/3D systems of conductors can be applied to 1D conductors, the procedure is inefficient in general. The main reason for the inefficiency of 2D/3D analysis methods when applied to 1D problems is in the prence of both very large and very small features in the structure. The ratio of the sizes of the smallest and larges features in the structure is directly related to the efficiency of 2D/3D analysis methods. A particular class of analysis approaches usually works best for a particular type of structures. It is therefore highly advantageous to decompo
the structure into parts that support one type of propagation each, and to analyze the constituent parts using parate analysis methods.
The 1D and 2D/3D types of conductors and voids can typically be mixed freely in the interconnect system. As a result, the overall system will support a number of different 1D and 2D/3D modes of propagation simultaneously. The exact modes of propagation will depend on th e details of the structure as well as on the details of the excitations. Furthermore, the supported modes of propagation can be tightly coupled. A mode propagating in a region of the structure can excite a diffe
rent mode in the same region. Conquently, the decomposition of the interconnect system into parts, such that each part supports one fundamental mode of propagation, is not a trivial problem.
手绘画Figure 2 shows a simple homogeneous stripline example where two fundamental propagation modes exist simultaneously: the TEM stripline mode and the TEM parallel plate mode. This simple structure can be decompod into stripline and parallel plate parts only if an appropriate mode coupling mechanism is introduced.
Figure 2: Simple homogeneous stripline structure for which the 1D and 2D propagation regions overlap.
The decomposition of the structure into 1D and 2D propagation partitions requires an
appropriate mode transformation network.
A number of structure decomposition techniques have been propod in the literature (e.g., [1–8]). Some of the methods perform simple geometrical parations of the structure into non-overlapping parts [1–3]. As each part of a general structure can support more than one form of fundamental propagatio n, the methods do not always take full advantage of analysis technique specialization for each constituent part. Others, decompo the circuit around via discontinuities [4–6]. The technique propod in [6]
decompos a stripline structure filled with a homogenous dielectric medium into a parallel plate structure and a transmission line. The decomposition is performed around a via discontinuity. The method handles the two parated structures efficiently, but it is applicable to a class of very special structures. In [7] the method of [6] is generalized for an arbitrary system of coupled planar conductors around arbitrary vertical discontinuities using a dependent voltage and current source mo
de coupling circuit. This method is still not general enough to deal with all of the structures prent in complex PCBs and IC packages. The generalization to [6] propod in [8] promis applicability to a wider range of cas, including magnetically coupled structures. However, this generalization comes with the pena lty of additional implementation complexity and larger storage and computational requirements.
The purpo of this paper is to propo a method for parating the 1D propagation network from the
2D/3D propagation partition at the discontinuities in the horizontal return plane. The paper extends the decomposition propod in [7] and makes it applicable to planar discontinuities such as various voids in the signal return planes. The 1D part of the decompod structure is solved using circuit simulation methods while the 2D/3D part can be solved using any of a number of analysis approaches. The generalization for the analysis of 2D partitions described in [8] can also be ud in conjunction with [7] and our propod decomposition method. The method is exemplified on microstrip examples containing voids in the return plane as well as on a coplanar structure.
Decomposition Approach for Microstrips
醋溜绿豆芽
The propod decomposition is first explained for a microstrip structure. Figure 3 shows a microstrip line passing over a split in the return plane.
εr = 1
Top boundary of the field partition
Figure 3: Example structure ud to illustrate the decomposition around a slit in the return plane.微信视频下载
The split can reprent a slit or gap in a single plane or two parated power planes with different DC voltage levels. The structure is decompod into two microstrip lines on either side of the split and the split model. The difficulties in the accurate modeling of the structure of Fig. 3(a) ari due to the prence of the split. Conversion of propagation modes occurs around the split where the dominant quasi-TEM mode of the microstrip couples with the dominant slotline mode of the split. The split or gap can also have an irregular shape or it can couple to other oddly shaped gaps in the same plane or in nearby planes.
立式升降台铣床A general and efficient approach to modeling such structures is to decompo the structure into the 2D propagation partition and the signal propagation partition. The 2D propagation partition, consisting of the original structure without the signal trace, can be analyzed using field analysis methods. The signal propagation partition can be analyzed using transmission line models. The two partitions are connected in the area of the discontinuity underneath the signal trace. If the analysis of the planes is performed in the time domain using FDTD, the connection between the two parts can be made using FDTD–SPICE interfacing methods ([9–14]). The placement of the FDTD to SPICE interface port is shown in Fig. 3(b).
A similar connection approach can be ud if other field analysis methods are ud [15]. Since the traces are not included in the part of the structure that is analyzed using field solution methods, the amount of detail and the discretization requirements for this part of the m odel are reduced significantly compared to tho of the original structure.
Figure 4 compares the results obtained by using FDTD–SPICE on the decompod structure to tho obtained using FDTD on the non-decompod structure that includes the signal trace. The voltages at the trace input and output are shown along with the voltages at the two ends of the split. Good agreement is obrved. The simulation of the decompod structure was more than ten times faster than for the corresponding non-decompod structure. For complex multilayer boards with coupled thin traces, the computational advantages of the decomposition are usually larger.
Figure 4. Voltage respon of microstrip trace over open split in the return plane: propod method (solid lines) and FDTD analysis of original structure without decomposition (dashed lines).鹌鹑好养吗
