Introduction to Transmission Lines

Transcription

1 Introduction to Transmission Lines Overview What is a transmission line? Who benefits from using transmission line analysis? Key circuits for digital systems analysis The components Ideal transmission lines Lossy elements Types of lossy elements Syntax Physical levels Electrical levels Geophysical microstrips RCLG microstrip equivalent circuit 1

2 What is a transmission line? Transmission Lines A transmission line is a device intended to deliver an output signal at a distance from the point of signal input. Any conductive pathway can show transmission line effects at high enough frequencies and/or long enough lengths. Examples include: Microstrips Coaxial cables Ribbon cables IC package interconnect PC board traces 2

3 Transmission Lines Who benefits from using transmission line analysis? System designers IC designers High-speed digital High-frequency analog Interconnect PC board designers Anyone concerned about cross-talk and signal integrity 3

4 Transmission Lines Some key circuits for digital systems analysis Pin package models ( for low pin count products ) pin DIP, PLCC, TSOP RAM, ROM, EPROM, TTL, Glue-logic Driver and receiver models PGA package models ( for high pin count applications ) pin gate arrays, up s PCB trace models (single and coupled lines) Variable length model for standard trace widths Top layer (microstrip) Mid-layer (stripline) Cable models - coax, twisted pair, ribbon, power Miscellaneous models - chip decoupling capacitors, tantalum capacitor, resistors 4

5 Transmission Lines Some of the unwelcome effects caused by transmission line effects are: Pulse rounding / distortion Propagation delays Crosstalk Ringing Ground bounce Attenuation 5

6 Supported Elements Hspice supports 3 transmission line elements: T: lossless, single signal only U: lossy, allows up to 5 signal lines W:lossy, more robust & accurate than U, allow more than 5 signal lines. Recommend user to use W element T and U elements are supported solely for backward compatibility 6

7 Ideal Transmission Lines: T-Element The ideal LOSSLESS transmission line Txxx in inref out outref ZO=val TD=val L=val <IC=V1, I1, V2, I2> or Txxx in inref out outref ZO=val (Ohms) F=val <NL=val> <IC=V1, I1, V2, I2> Efficient at simulating long delay times Defined by impedance and delay Input difference delayed (differential mode only) Cannot be coupled Common mode is NOT modeled Td(min)=Td*L*SCALE (Caution -can cause extremely long analysis times) Vin t = V(out-refout) t-td + (iout x Zo) t-td in inref out Vout t = V(in-refin) t-td + (iin x Zo) t-td outref

8 Lossy Transmission Lines: U-Element Lossy transmission line syntax Uxxx in inref out outref model_name L=val Physical model levels (PLEV) Coax, twinlead, microstrip, stripline Electrical sub-levels of physical model Geometric, external field-solver entry, electrical Useful for short time delays Ground references are treated like the signal line Can be coupled ( 5 lines max.) Automatic lumping, including resistive loss, mutual coupling N lumps 8

9 Syntax for U model Lossy Transmission Lines: U-Element.model Umodel_name U level=3 plev=x elev=x keyname=val Transmission lines are ALL level 3, and there are combinations of physical levels and electrical levels. The number of conductors in the element is determined by the model (NL=val). Have a reference point if analysis is critical (field solver) There are three electrical levels: elev=1 elev=2 elev=3 Geophysical (geometry based calculation of RCLK) RCLK values entered from field solver Electro-physical parameters (impedance / delay / attenuation) Calculation of RCLG elements 9

10 Lossy Transmission Lines: U-Element Physical levels of U model For each electrical level, there are physical levels corresponding to different kinds of transmission line construction. plev=1 plev=2 plev=3 Microstrip of 2 to 5 conductors plus a ground plane Coaxial cable Twinlead cable - 2 symmetric conductors (can be shielded) 10

11 Lossy Transmission Lines: U-Element Electrical levels of U elements elev=1: Transmission line described in terms of physical constants and geometric construction elev=2: T-line described via previously computed RCLK values Ilev=0 Ground or shield conductor is purely resistive Ilev=2 Ground plane and common mode L and C are included elev=3: T-line described in terms of electrical parameters (attenuation, capacitance, impedance) 11

12 The geo-physical microstrip elev=1, plev=1 Transmission Lines dlev=0 dlev=1 dlev=2 dlev=3 microstrip in a sea of dielectric microstrip in dual dielectric stripline dual reference plane overlay dielectric - planar conductor with a single reference plane and an overlay of dielectric material covering the conductor 12

13 ELEV=1 (Geometric/Physical) PLEV=1 PLEV=2 PLEV=3, DLEV=0,1,2 PLEV=3, DLEV=3 ELEV=2 (Pre-computed) Transmission Lines PLEV=1 PLEV=2, 3 (Not available in Star-Hspice) ELEV=3 (Measured data) PLEV=1,2 PLEV=3 13

14 Star-Hspice s W Element Based on a novel state-of-the-art transmission-line simulation method, very fast, accurate, and robust Inputs frequency-dependent RLGC matrices No limit on the number of coupled conductors No restrictions on the structure of input RLGC matrices, all matrices can be full. Frequency-dependent loss is accurately modeled in the transient analysis. Accuracy does not depend on the transient speed, line length, or amount of loss, coupling, or frequency dependence. Requires no manual adjustments (such as the number of lumps in the U element). Gives accurate results with large timestep. See Star-Hspice User s Manual for more information on W-Element. 14

15 Element Card W xxxx N=num_of_conductors + node1.1 node1.n node1 + node2.1 node2.n node2 + RLGCfile=RLGC_file_name + l=line_length 15

16 RLGC File 16

17 W Element Syntax Wline in1 in2 inn inref out1 out2 outn outref N=<value> L=<value> + <RLGCmodel=name FSmodel= name RLGCfile=name Umodel=name > N: number of signal wires, excluding reference conductor L: length of transmission line (default unit: meter) Require RLGC matrices. Allow four possible formats: RLGCmodel (if RLGC values are already available) Fsmodel (RLGC values unknown, but physical geometry of transmission lines is known) RLGCfile (if RLGC values are already available, syntax is not flexible as RLGCmodel) Umodel (supported for backward compatibility) 17

18 RLGCModel Syntax.MODEL name W MODELTYPE=RLGC + N=<value> + Lo=<matrix_entries> Co=<matrix_entries> + (Ro=<matrix_entries> Go=<matrix_entries> + Rs=<matrix_entries> Gd=<matrix_entries> + Rognd=<matrix_entries> + Rsgnd =<matrix_entries> ) Example: W1 i1 i2 i3 0 o1 o2 o3 0 N=3 L=1 RLGCmodel=sample.model sample W MODELTYPE=RLGC N=3 Lo=2.311e e e e e e-6 Co=2.392e e E e e e-11 18

19 Conversion Table for W-Element Matrices from U Element RLGC Matrices 19

20 W Element Accepts U Model The W-Element is extended to fully accept all U-model modes including: RLGC input for up to five coupled conductors Geometric input (planar, coax, twinlead) Measured parameter input Skin effect MONTE CARLO simulation The above features provide backward compatibility with the U element. 20

21 0.35 Benchmark U element (300 segments) W element Transient Waveforms (V) spurious ringing (U element) Time (ns) 21

22 Benchmark Hspice Transient Runtime, Four-Conductor Line Line Model Relative Runtime Runtime (s) Memory (Kbytes) New model Single lumped resistors Single lumped RLGC segment U element 23,513 3,827 9,354 Spice3 convolution model

23 Parameter Extractor for Transmission Line (PETL) 2-D field solver integrated into Star-Hspice simulator Underlying numerical technique is improved version of boundary element method Highly efficient and accurate Star-Hspice now performs full transmission line analysis for virtually any size interconnect system Supports Star-Hspice optimization and Monte-Carlo statistical analysis 23

24 PETL Parameter Extraction for Transmission Lines Input: geometry information of transmission lines Output: L, C, Ro, Rs, Go, Gs Capabilities Allow arbitrary number of dielectric and conductors Shape of dielectric must be a planar layer Allow arbitrary shape of conductor Conductors must not overlap Magnetic materials are not supported Limitations Proximity and edge effects are not considered so, the resulting Rs matrix is diagonal. For inhomogeneous media, the arithmetic average values of conductivities and loss tangents are used to compute the conductance matrices, Go and Gd. 24

25 PETL: Defining Materials.MATERIAL mname METAL DIELECTRIC <ER=val> <UR=val> + <CONDUCTIVITY=val> <LOSSTANGENT=val> mname METAL DIELECTRIC ER UR CONDUCTIVITY Material name Material type: METAL or DIELECTRIC Dielectric constant (relative permittivity) Relative permeability Static field conductivity of conductor or lossy dielectric (S/m) LOSSTANGENT Alternating field loss tangent of dielectric (tan ) The Star-Hspice field solver assigns the following default values for metal: CONDUCTIVITY = -1 (perfect conductor), ER = 1, UR = 1. PEC is a predefined metal name with the default values and cannot be redefined. The Star-Hspice field solver assigns the following default values for dielectrics: CONDUCTIVITY = 0 (lossless dielectric), LOSSTANGENT = 0 (lossless dielectric), ER = 1, UR = 1. AIR is a predefined dielectric name with default values and cannot be redefined. 25

26 PETL: Defining Layerstack.LAYERSTACK sname <BACKGROUND=mname> + <LAYER=(mname,thickness)...> sname Layer stack name mname BACKGROUND thickness Material name Background dielectric material name. By default, AIR is assumed for the background. Layer thickness Layers are listed from bottom to top. Metal layers (ground planes) are located only at the bottom, top, or both top and bottom. Layers are stacked in y-direction, and the bottom of a layer stack is at y=0. All conductors must be located above y=0. Background material must be dielectric. Free space without ground:. LAYERSTACK mystack Free space with a (bottom) ground plane:.layerstack halfspace PEC 0.1mm 26

27 .SHAPE sname Shape_Descriptor PETL: Defining Shapes sname Shape_Descriptor Shape name. See the following subsections. Rectangles RECTANGLE WIDTH=val HEIGHT=val <NW=val> <NH=val> WIDTH HEIGHT NW NH Width of rectangle (length in x-direction). Height of rectangle (length in y-direction). Number of segments for the width discretization. Number of segments for the height discretization. Normally, it is not necessary to set the values of NW and NH since they are automatically set by the solver depending on the accuracy mode. 27

28 CIRCLE RADIUS=val <N=val> PETL: Defining Shapes (cont.) RADIUS N Radius of the circle. Number of segments for discretization. STRIP WIDTH=val <N=val> WIDTH N Width of strip (length in x-direction). Number of segments for discretization. POLYGON VERTEX=(x1 y1 x2 y2...) <N=(n1,n2,...)> VERTEX N (x, y) coordinates of vertices. Listed either in clockwise or counter-clockwise direction. Number of segments for each edges. If only one value is specified, then this value is used for all edges. The first value of N, n1, corresponds to the number of segments for the edge from (x1 y1) to (x2 y2). 28

29 PETL: Defining Options.FSOPTIONS name <ACCURACY=LOW MEDIUM HIGH> + <GRIDFACTOR=val> <PRINTDATA=YES NO> <COMPUTEG0=YES NO> + <COMPUTEGD=YES NO> <COMPUTERO=YES NO> <COMPUTERS=YES NO> ACCURACY GRIDFACTOR PRINTDATA COMPUTEGO COMPUTEGD COMPUTERO COMPUTERS Sets the solver accuracy to either LOW, MEDIUM, or HIGH. (Default = HIGH) Multiplication factor (integer) to determine the final number of segments used in discretization. (Default = 1) Specifies that the solver will print output matrices. (Default = NO) Specifies that the solver will compute the static conductance matrix. (Default = YES) Specifies that the solver will compute the dielectric loss matrix. (Default = NO) Specifies that the solver will compute the DC resistance matrix. (Default = YES) Specifies that the solver will compute the skin-effect resistance matrix. (Default = NO) 29

30 PETL Example Three traces immersed in stratified dielectric media 30

31 PETL: Example Input File Listing 31

32 LAB 9 32