transmission lines

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Day 3, Session 3: Intro to Transmission LinesStar-Hspice Basic Training 2000

Introduction to Transmission Lines

l Overview

q What is a transmission line?

q Who benefits from using transmission line analysis?

q Key circuits for digital systems analysis

l The components

q Ideal transmission lines

q Lossy elements

� Types of lossy elements

� Syntax

� Physical levels

� Electrical levels

� Geophysical microstrips

� RCLG microstrip equivalent circuit

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Transmission Lines

l What is a transmission line ?

q A transmission line is a device intended to deliver an output signal at a distancefrom the point of signal input.

q Any conductive pathway can show transmission line effects at high enoughfrequencies and/or long enough lengths.

q Examples include:

� Microstrips

� Coaxial cables

� Ribbon cables

� IC package interconnect

� PC board traces

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Transmission Lines

l Who benefits from using transmission line analysis ?

q System designers

q IC designers

� High-speed digital

� High-frequency analog

� Interconnect

q PC board designers

q Anyone concerned about cross-talk and signal integrity

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Transmission Lines

l Some key circuits for digital systems analysis

q Pin package models ( for low pin count products )

� 14-64 pin DIP, PLCC, TSOP

� RAM, ROM, EPROM, TTL, Glue-logic

q Driver and receiver models

q PGA package models ( for high pin count applications )

� 100-600 pin gate arrays, uP’s

q PCB trace models (single and coupled lines)

� Variable length model for standard trace widths

� Top layer (microstrip)

� Mid-layer (stripline)

q Cable models - coax, twisted pair, ribbon, power

q Miscellaneous models - chip decoupling capacitors, tantalum capacitor, resistors

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Transmission Lines

l Some of the unwelcome effects caused by transmission line effects are:

q Pulse rounding / distortion

q Propagation delays

q Crosstalk

q Ringing

q Ground bounce

q Attenuation

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Supported Elements

l Hspice supports 3 transmission line elements:

q T: lossless, single signal only

q U: lossy, allows up to 5 signal lines

q W:lossy, more robust & accurate than U, allow more than 5 signal lines.

l Recommend user to use W element

l T and U elements are supported solely for backward compatibility

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Ideal Transmission Lines: T-Element

l The ideal LOSSLESS transmission line

Txxx in inref out outref ZO=val TD=val L=val <IC=V1, I1, V2, I2>orTxxx in inref out outref ZO=val (Ohms) F=val <NL=val> <IC=V1, I1, V2, I2>

l Efficient at simulating long delay times

l Defined by impedance and delay

l Input difference delayed (differential mode only)

l Cannot be coupled

l Common mode is NOT modeled

l Td(min)=Td*L*SCALE (Caution -can cause extremely long analysis times)

Vint = V(out-refout)

t-TD + (iout x Zo)

t-TDVout

t = V(in-refin)

t-TD + (iin x Zo)

t-TD+ +- -

in out

inref outref

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Lossy Transmission Lines: U-Element

l Lossy transmission line syntax

q Uxxx in inref out outref model_name L=val

l Physical model levels (PLEV)

q Coax, twinlead, microstrip, stripline

l Electrical sub-levels of physical model

q Geometric, external field-solver entry, electrical

l Useful for short time delays

l Ground references are treated like the signal line

l Can be coupled ( 5 lines max.)

l Automatic lumping, including resistive loss, mutual coupling

N lumps

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l Syntax for U model

q .model Umodel_name U level=3 plev=x elev=x keyname=val

l Transmission lines are ALL level 3, and there are combinations of physical levels andelectrical levels. The number of conductors in the element is determined by the model(NL=val).

l Have a reference point if analysis is critical (field solver)

l There are three electrical levels:

q elev=1 Geophysical (geometry based calculation of RCLK)

q elev=2 RCLK values entered from field solver

q elev=3 Electro-physical parameters (impedance / delay / attenuation)

� Calculation of RCLG elements

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l Physical levels of U model

q For each electrical level, there are physical levels corresponding to different kindsof transmission line construction.

� plev=1 Microstrip of 2 to 5 conductors plus a ground plane

� plev=2 Coaxial cable

� plev=3 Twinlead cable - 2 symmetric conductors (can be shielded)

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l Electrical levels of U elements

q elev=1: Transmission line described in terms of physical constants and geometric construction

q 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

q elev=3: T-line described in terms of electrical parameters (attenuation, capacitance,impedance)

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Transmission Lines

l The geo-physical microstrip

q elev=1, plev=1

� dlev=0 microstrip in a sea of dielectric

� dlev=1 microstrip in dual dielectric

� dlev=2 stripline dual reference plane

� dlev=3 overlay dielectric - planar conductor with a single reference plane and

an overlay of dielectric material covering the conductor

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Transmission Lines

l ELEV=1 (Geometric/Physical)

q PLEV=1

q PLEV=2

q PLEV=3, DLEV=0,1,2

q PLEV=3, DLEV=3

l ELEV=2 (Pre-computed)

q PLEV=1

q PLEV=2, 3 (Not available in Star-Hspice)

l ELEV=3 (Measured data)

q PLEV=1,2

q PLEV=3

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Star-Hspice’s W Element

l Based on a novel state-of-the-art transmission-line simulation method, veryfast, accurate, and robust

l Inputs frequency-dependent RLGC matrices

l No limit on the number of coupled conductors

l No restrictions on the structure of input RLGC matrices, all matrices can befull.

l Frequency-dependent loss is accurately modeled in the transient analysis.

l Accuracy does not depend on the transient speed, line length, or amount ofloss, coupling, or frequency dependence.

l Requires no manual adjustments (such as the number of lumps in the Uelement). Gives accurate results with large timestep.

See Star-Hspice User’s Manual for more information on W-Element.

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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

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RLGC File

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W Element Syntax

Wline in1 in2 … inN inRef out1 out2 … outN outRef N=<value> L=<value>

+ <RLGCmodel=name | FSmodel= name |RLGCfile=name | Umodel=name…>

l N: number of signal wires, excluding reference conductor

l L: length of transmission line (default unit: meter)

l 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)

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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-6 4.14e-7 2.99e-6 8.42e-8 5.27e-7 2.81e-6

Co=2.392e-11 -5.41e-12 2.12E-11 -1.08e-12 -5.72e-12 2.447e-11

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

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W Element Accepts U Model

The W-Element is extended to fully accept all U-model modes including:

q RLGC input for up to five coupled conductors

q Geometric input (planar, coax, twinlead)

q Measured parameter input

q Skin effect

q MONTE CARLO simulation

The above features provide backward compatibility with the U element.

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Benchmark

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 10 20 30 40 50

U element (300 segments)

W element

Time (ns)

Transient W

aveforms (V

)

spurious ringing (U element)

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Benchmark

l Hspice Transient Runtime, Four-Conductor Line

Line Model RelativeRuntime

Runtime(s)

Memory(Kbytes)

New model 1 0.17 23

Single lumpedresistors

0.69 0.12 153

Single lumpedRLGC segment

0.92 0.16 172

U element 23,513 3,827 9,354

Spice3convolutionmodel

687

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Parameter Extractor for Transmission Line (PETL)

l 2-D field solver integrated into Star-Hspice simulator

l Underlying numerical technique is improved version of boundary elementmethod

l Highly efficient and accurate

l Star-Hspice now performs full transmission line analysis for virtually any sizeinterconnect system

l Supports Star-Hspice optimization and Monte-Carlo statistical analysis

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PETL

l Parameter Extraction for Transmission Lines

l Input: geometry information of transmission lines

l Output: L, C, Ro, Rs, Go, Gs

l 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

l 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 tangentsare used to compute the conductance matrices, Go and Gd .

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PETL: Defining Materials

.MATERIAL mname METAL|DIELECTRIC <ER=val> <UR=val>+ <CONDUCTIVITY=val> <LOSSTANGENT=val>

mname Material name

METAL|DIELECTRIC Material type: METAL or DIELECTRIC

ER Dielectric constant (relative permittivity)

UR Relative permeability

CONDUCTIVITY Static field conductivity of conductor or lossy dielectric (S/m)

LOSSTANGENT Alternating field loss tangent of dielectric (tan �)

q The Star-Hspice field solver assigns the following default values for metal: CONDUCTIVITY = -1 (perfectconductor), ER = 1, UR = 1. PEC is a predefined metal name with the default values and cannot beredefined.

q 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 predefineddielectric name with default values and cannot be redefined.

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PETL: Defining Layerstack

.LAYERSTACK sname <BACKGROUND=mname>+ <LAYER=(mname,thickness) ...>

sname Layer stack name

mname Material name

BACKGROUND Background dielectric material name. By default, AIR is assumed for the background.

thickness Layer thickness

q Layers are listed from bottom to top.

q Metal layers (ground planes) are located only at the bottom, top, or both top and bottom.

q Layers are stacked in y-direction, and the bottom of a layer stack is at y=0.

q All conductors must be located above y=0.

q Background material must be dielectric.

q Free space without ground: . LAYERSTACK mystack

q Free space with a (bottom) ground plane: .LAYERSTACK halfSpace PEC 0.1mm

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PETL: Defining Shapes

.SHAPE sname Shape_Descriptor

sname Shape name.

Shape_Descriptor See the following subsections.

l Rectangles

RECTANGLE WIDTH=val HEIGHT=val <NW=val> <NH=val>

WIDTH Width of rectangle (length in x-direction).

HEIGHT Height of rectangle (length in y-direction).

NW Number of segments for the width discretization.

NH Number of segments for the height discretization.

q Normally, it is not necessary to set the values of NW and NH since they are automatically setby the solver depending on the accuracy mode.

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PETL: Defining Shapes (cont.)

CIRCLE RADIUS=val <N=val>

RADIUS Radius of the circle.N Number of segments for discretization.

STRIP WIDTH=val <N=val>

WIDTH Width of strip (length in x-direction).N Number of segments for discretization.

POLYGON VERTEX=(x1 y1 x2 y2 ...) <N=(n1,n2,...)>

VERTEX (x, y) coordinates of vertices. Listed either in clockwise or counter-clockwise direction.

N 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).

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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 Sets the solver accuracy to either LOW , MEDIUM , or HIGH . (Default = HIGH)

GRIDFACTOR Multiplication factor (integer) to determine the final number of segments used in discretization. (Default = 1)

PRINTDATA Specifies that the solver will print output matrices.(Default = NO)

COMPUTEGO Specifies that the solver will compute the static conductancematrix. (Default = YES)

COMPUTEGD Specifies that the solver will compute the dielectric loss matrix. (Default = NO)

COMPUTERO Specifies that the solver will compute the DC resistance matrix. (Default = YES)

COMPUTERS Specifies that the solver will compute the skin-effect resistance matrix. (Default = NO)

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PETL Example

l Three traces immersed in stratified dielectric media

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PETL: Example Input File Listing

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LAB 9

transmission lines

Documents

transmission line elements

transmission line effects

transmission line analysis

lossy transmission lines

transmission linesl

val td

q pulse

q examples