Application of Laplace to Circuits

download Application of Laplace to Circuits

of 45

Transcript of Application of Laplace to Circuits

  • 7/30/2019 Application of Laplace to Circuits

    1/45

    1

    APPLICATION OF THE LAPLACE TRANSFORM

    TO CIRCUIT ANALYSISLEARNING GOALS

    Laplace circuit solutionsShowing the usefulness of the Laplace transform

    Circuit Element ModelsTransforming circuits into the Laplace domain

    Analysis Techniques

    All standard analysis techniques, KVL, KCL, node,loop analysis, Thevenins theorem are applicable

    Transfer FunctionThe concept is revisited and given a formal meaning

    Pole-Zero Plots/Bode PlotsEstablishing the connection between them

    Steady State Response

    AC analysis revisited

  • 7/30/2019 Application of Laplace to Circuits

    2/45

    2

    LAPLACE CIRCUIT SOLUTIONS

    We compare a conventional approach to solve differential equations with atechnique using the Laplace transform

    )()()( tdt

    diLtRitvS +=:KVL

    tCC

    CC eKtit

    dt

    diLtRi ==+ )(0)()(

    equationaryComplement

    pC iii +=

    LeLKeRK

    tC

    tC ==+

    0)(

    pp Kti =)(

    casethisforsolutionParticular

    pS RKv ==1

    tL

    R

    CeKti

    +=1)(

    0000 =

    =

    teR

    tit

    L

    R

    Take Laplace transform of the equation

    +=dt

    diLsRIsVS L)()(

    )()0()( ssIissIdt

    di==

    L

    )()(1 sLsIsRIs

    +=)(

    1)(LsRs

    sI+

    =

    LRs

    K

    s

    K

    sLRs

    LsI

    /)/(

    /1)( 21

    ++=

    +=

    RsILRsK

    RssIK

    LRs

    s

    1|)()/(

    1

    |)(

    /2

    01

    =+=

    ==

    =

    =

    0;11)( >

    =

    teR

    tit

    L

    R

    )()()( tdt

    diLtRitvS +=

    LInitial conditionsare automatically

    included

    No need tosearch forparticularor comple-mentarysolutions

    Only algebrais needed

    P

    ar

    ticul

    ar

    Complementary

  • 7/30/2019 Application of Laplace to Circuits

    3/45

    3

    LEARNING BY DOING 0),( >ttvFind

    KCLusingModel

    dt

    dvC

    R

    vv S

    Sv

    0=

    +vv

    dt

    dvC S

    Svvdt

    dv

    RC=+

    L)()( sVsV

    dt

    dvRC S=+

    L

    )()0()( ssVvssVdt

    dv==

    L

    ssVtuv SS1)()( ==

    0)0(0,0)( =

  • 7/30/2019 Application of Laplace to Circuits

    4/45

    4

    CIRCUIT ELEMENT MODELS

    The method used so far follows the steps:

    1. Write the differential equation model2. Use Laplace transform to convert the model to an algebraic form

    For a more efficient approach:1. Develop s-domain models for circuit elements

    2. Draw the Laplace equivalent circuit keeping the interconnections and replacing

    the elements by their s-domain models3. Analyze the Laplace equivalent circuit. All usual circuit tools are applicable and all

    equations are algebraic.

    Resistor

    )()()()( sRIsVtitv ==

    )()(

    )()(

    sIti

    sVtv

    SS

    SS

    sourcestIndependen

    ...

    )()()()()()()()(

    sBVsItBvtisAIsVtAitv

    CDCD

    CDCD

    ==

    ==

    sourcesDependent

  • 7/30/2019 Application of Laplace to Circuits

    5/45

    5

    Capacitor: Model 1

    svsI

    CssV )0()(1)( +=)0()(1)(

    0

    vdxxiC

    tvt

    +=

    Capacitor: Model 2

    )0()(1)(0

    vdxxiC

    tvt

    +=

    Cs

    )0()()( CvsCsVsI =

    Source transformation

    )0(1

    )0(Cv

    Cs

    sv

    Ieq ==

    Impedance in serieswith voltage source

    Impedance in parallelwith current source

    s

    sIdxxi

    t)(

    )(

    0

    =

    L

  • 7/30/2019 Application of Laplace to Circuits

    6/45

    6

    Inductor Models

    ))0()(()()()( issILsVtdt

    diLtv ==

    )0()( issIdtdi =L

    s

    i

    Ls

    sVsI

    )0()()( +=

    s

    i

    Ls

    sVsI

    )0()()( +=)0()()( LisLsIsV =

  • 7/30/2019 Application of Laplace to Circuits

    7/45

    7

    )0()()0()()(

    )0()()0()()(

    22112

    2211111

    LisLsIMisMsIsV

    MisMsIiLssILsV

    +=

    +=

    Mutual Inductance

    )()()(

    )()()(

    22

    12

    2111

    tdt

    diLt

    dt

    diMtv

    tdt

    diMt

    dt

    diLtv

    +=

    +=

    Combine into a single source in the primary

    Single source in the secondary

  • 7/30/2019 Application of Laplace to Circuits

    8/45

    8

    LEARNING BY DOING

    Ai 1)0( =

    Determine the model in the s-domain and the expression forthe voltage across the inductor

    Inductor with

    initial current

    Equivalent circuit ins-domain

    1

    1

    )()(1)( +== ssVsIsV

    LawsOhm'

    )()1(1 sIs+=:KVL

    Steady state for t

  • 7/30/2019 Application of Laplace to Circuits

    9/45

    9

    ANALYSIS TECHNIQUES

    All the analysis techniques are applicable in the s-domain

    LEARNING EXAMPLE Draw the s-domain equivalent and find the voltage in boths-domain and time domain

    0)0(0,0)( =

  • 7/30/2019 Application of Laplace to Circuits

    10/45

    10

    LEARNING EXAMPLE Write the loop equations in the s-domain

    =+ )0()0()0()( 1121 iLs

    vs

    vsVA

    1Loop

    ))()(())()((1

    )(1

    )( 211212

    1

    1

    11 sIsIsLsIsIsC

    sIsC

    sIR +++

    =+ )()0()0(

    )0( 222

    11 sViLs

    viL B

    2Loop

    )()())()((

    1

    ))()(( 222122

    121 sIRsLsIsIsCsIsIsL +++

    Do not increasenumber of loops

  • 7/30/2019 Application of Laplace to Circuits

    11/45

    11

    LEARNING EXAMPLE Write the node equations in the s-domain

    =+s

    ivC

    s

    isIA

    )0()0(

    )0()( 2111

    1VNode

    )(1)(11 212

    11

    21

    1 sVsCsL

    sVsCsLsL

    G +

    +++

    )(1

    )(1

    1

    2

    12

    2

    122 sVsL

    sCsVsL

    sCsCG

    +

    +++

    =+s

    ivCvCsIB

    )0()0()0()( 21122

    2VNode

    Do not increase number

    of nodes

  • 7/30/2019 Application of Laplace to Circuits

    12/45

    12

    LEARNING EXAMPLE

    theorem.sNorton'andsThevenin'tion,transformasource

    ion,superpositanalysis,loopanalysis,nodeusingFind )(tvo

    Assume all initial conditions are zero

    Node Analysis

    01

    )()(

    12)(

    4 11

    =

    +

    +

    s

    sVsV

    s

    ssV

    s

    o

    1V@KCL

    01

    )()(

    2

    )( 1=

    +

    s

    sVsVsV oo

    oKCL@V

    s

    2

    0)()21()(2

    124)()()1(

    1

    21

    2

    =++

    +=+

    sVsssV

    s

    ssVssVs

    o

    o

    )1(2

    s+

    s2

    2)1(

    )3(8)(

    s

    ssVo

    +

    +=

    Could haveused voltage

    divider here

    s

    sV

    12

    )(1

    +

  • 7/30/2019 Application of Laplace to Circuits

    13/45

    13

    Loop Analysis

    s

    sI4)(1 =

    1Loop

    ssIsI

    ssIsIs

    12)(2)(

    1))()(( 2212 =++

    2Loop

    22)1()3(4)(

    ++=

    sssI

    22)1(

    )3(8)(2)(

    +

    +==

    s

    ssIsVo

  • 7/30/2019 Application of Laplace to Circuits

    14/45

    14

    Source Superposition Applying current source

    Current divider

    '2I

    s

    s

    ssVo

    4

    212

    2)('

    ++

    =

    Applying voltage source

    Voltage divider

    sss

    sVo12

    12

    2)("

    ++

    =2

    "'

    )1(

    )3(8)()()(

    +

    +=+=

    s

    ssVsVsV

    ooo

  • 7/30/2019 Application of Laplace to Circuits

    15/45

    15

    Source Transformation

    The resistance is redundant

    Combine the sources and use currentdivider

    +

    ++

    =2124

    21

    2)(ss

    ss

    ssVo

    2)1(

    )3(8)(

    +

    +

    =s

    ssVo

  • 7/30/2019 Application of Laplace to Circuits

    16/45

    16

    Using Thevenins Theorem

    Reduce this part

    s

    s

    ss

    ssVOC

    124412)(

    +=+=

    Only independent sources

    s

    ss

    sZ

    Th

    112+

    =+=

    s

    s

    s

    ssVo124

    12

    2

    )( 2+

    ++

    =

    Voltagedivider

    2)1(

    )3(8)(

    +

    +=

    s

    ssVo

  • 7/30/2019 Application of Laplace to Circuits

    17/45

    17

    Using Nortons Theorem

    2

    124/124)(

    s

    s

    s

    s

    ssISC

    +=+=

    Reduce this part

    sZTh =

    2

    124

    21

    2)(s

    s

    s

    s

    ssVo

    +

    ++

    =

    2)1(

    )3(8)(

    +

    +=

    s

    ssVo

    Currentdivision

  • 7/30/2019 Application of Laplace to Circuits

    18/45

    18

    LEARNING EXAMPLE zerobetoconditionsinitialallAssumevoltagetheDetermine ).(tvo

    . Three loops, three non-reference nodes

    . One voltage source between non-referencenodes - supernode

    . One current source. One loop current knownor supermesh

    . If v_2 is known, v_o can be obtained with avoltage divider

    Selecting the analysis technique:

    Transforming the circuit to s-domain

    ssVsV12)()( 12 =:constraintSupernode

    01

    )()(2

    /2

    )(

    2

    )( 211=

    +++

    s

    sVsI

    s

    sVsV:supernodeKCL@

    2

    )()( 1

    sVsI =:variablegControllin

    )(11)( 20 sV

    ssV

    +=:dividerVoltage

    ssVsV /12)()( 21 =:algebratheDoing

    ssVsI /62/)()( 2 +=

    ( )

    0)1/()(

    )/62/)((2/12)()1)(2/1(

    2

    22

    =++

    ++

    ssV

    ssVssVs

    )54(

    )3)(1(12)(

    22++

    ++=

    sss

    sssV

    )54(

    )3(12)(

    2++

    +=

    sss

    ssVo

  • 7/30/2019 Application of Laplace to Circuits

    19/45

    19

    Continued ... theoremsThevenin'usingCompute )(sVo

    -keep dependent source and controlling

    variable in the same sub-circuit

    -Make sub-circuit to be reduced as simpleas possible

    -Try to leave a simple voltage divider afterreduction to Thevenin equivalent

    sVOC /12

    2

    /12'

    0'2/2

    /12

    2

    /12

    sVI

    Is

    sVsV

    OC

    OCOC

    =

    =

    +

    ssVOC12)( =

    0'0'2)/2/()'2(' ==+ IIsII

    0)/2/("2""2 = sIIIISC

    +

    s/12

    sI /6"=

    s

    sISC

    )3(6 +=

    3

    2

    )(

    )(

    +==

    ssI

    sVZ

    SC

    OCTH

    s

    ss

    sVo 12

    3

    21

    1)(

    +++

    =

  • 7/30/2019 Application of Laplace to Circuits

    20/45

    20

    Continued Computing the inverse Laplace transform

    Analysis in the s-domain has established that the Laplace transform of the

    output voltage is

    )54(

    )3(12)(

    2++

    +=

    sss

    ssVo

    )12)(12(542 jsjsss +++=++

    )12()12()12)(12(

    )3(12)(

    *11

    js

    K

    js

    K

    s

    K

    jsjss

    ssV oo

    +++

    ++=

    +++

    +=

    )()cos(||2)()(

    11

    *11 tuKteK

    js

    K

    js

    K t+

    +++

    +

    536|)( 0== =soo ssVK

    ==

    =

    +

    +=

    +=+=

    57.16179.343.19879.3)902(43.1535

    45212

    )2)(12(

    )11(12

    12|)()12(

    1

    jj

    jjs

    so

    VjsK

    )(57.161cos(59.75

    36)(

    2 tutetv to

    ++=

    1)2(2++= s

    ( )[ ] 1)2(1)2()2(

    12

    )3(12)(

    2

    2

    2

    1

    2++

    +++

    ++=

    ++

    +=

    s

    C

    s

    sC

    s

    C

    ss

    ssV oo

    )(]sincos[)()(

    )(21222221 tutCtCes

    C

    s

    sCt

    +

    +++

    ++

    + 5/36|)( 0== =soo ssVC

    ])2([)1)2(()3(12 212

    CsCssCs o +++++=+ 5/12610/362122 22 ==== CCCs o

    5/360: 11 =+= CCCo2softscoefficienEquating

    )(sin512)cos1(

    536)( 22 tutetetv tto

    =

    One can also use

    quadratic factors...

  • 7/30/2019 Application of Laplace to Circuits

    21/45

    21

    LEARNING EXTENSION equationsnodeusingFind )(tio

    supernode

    oVSo VV +

    Assume zero initial conditionsImplicit circuit transformation to s-domain

    SV

    KCL at supernode

    02

    )()(2))()(( =+++

    sV

    Ls

    sV

    ssVsVCs ooSo

    2

    )()(,

    12)(

    sVsI

    ssV ooS ==

    1615

    41

    61

    15.0

    61)(

    22

    + +

    =

    ++

    =

    s

    s

    ss

    ssIo

    algebratheDoing

    ++

    +

    +

    =

    ++

    +

    =

    4

    15

    4

    1

    4

    15

    4

    1

    4

    15

    4

    1

    4

    15

    4

    1

    61)(

    *

    1 1

    js

    K

    js

    K

    jsjs

    ssIo

    )()cos(||2)()(

    11

    *11 tuKteK

    js

    K

    js

    K t+

    +++

    +

    4

    152

    4

    15

    4

    161

    |)(415

    41

    4

    15

    4

    11

    j

    j

    sIjsKjs

    o

    +

    =

    +=

    +=

    =

    = 72.15653.6

    9097.0

    72.6633.61K

    =

    72.1564

    15cos06.13)( 4 teti

    t

    o

  • 7/30/2019 Application of Laplace to Circuits

    22/45

    22

    LEARNING EXTENSION equationsloopusingFind )(tvo

    supermesh

    12

    2II

    s=

    sourcetodueconstraint

    0212

    21

    2211 =+++ Is

    sIIIs

    supermeshonKVL

    Solve for I2

    )73.3)(27.0(216

    )14(216)(

    22++

    +=++

    +=sss

    ssss

    ssI

    73.327.0)( 2102

    ++

    ++=

    s

    K

    s

    K

    s

    KsI

    2|)( 020==

    =sssIK

    48.2)73.327.0)(27.0(

    2)27.0(16|)()27.0( 27.021 =

    +

    +=+=

    =ssIsK

    47.4)27.073.3)(73.3(

    2)73.3(16

    |)()73.3( 73.322=

    +

    +=+=

    =ssIsK

    ( ))(2)(

    )(47.448.22)(

    2

    73.327.02

    titv

    tueeti

    o

    tt

    =

    +=

    Determine inverse transform

  • 7/30/2019 Application of Laplace to Circuits

    23/45

    23

    TRANSIENT CIRCUIT ANALYSIS USING LAPLACE TRANSFORM

    For the study of transients, especially transients due to switching, it is importantto determine initial conditions. For this determination, one relies on the properties:

    1. Voltage across capacitors cannot change discontinuously2. Current through inductors cannot change discontinuously

    LEARNING EXAMPLE 0),( >ttvoDetermine

    AiVv LC 1)0(,1)0( ==

    itshortcircuareinductors

    circuitopenarecapacitorscaseDCFor

    Assume steady state for t0

  • 7/30/2019 Application of Laplace to Circuits

    24/45

    24

    Circuit for t>0Laplace

    Use mesh analysis

    14

    )1( 21 +=+s

    sIIs

    11

    )21( 21 =+++

    sI

    sssI

    Solve for I2s

    )1( + s

    232

    12)(

    22

    ++

    =

    ss

    ssI

    s

    sI

    s

    sVo1)(

    2)( 2 +=

    232

    72)(

    2++

    +=

    ss

    ssVo

    Now determine the inverse transform

    rootsconjugatecomplex

  • 7/30/2019 Application of Laplace to Circuits

    25/45

    25

    LEARNING EXTENSION 0),(1 >ttiDetermine

    Initial current through inductor

    Aii LL 1)0()0(=+=

    12

    6 s2s1)(1 sI

    ss

    ssI

    1

    182

    2)(1

    +

    =Current

    divider

    )()(

    9

    )(9

    11 tueti

    s

    ssI t=

    +

    =

  • 7/30/2019 Application of Laplace to Circuits

    26/45

    26

    LEARNING EXTENSION 0),( >ttvoDetermine

    Determine initial current through inductor

    )0(LiUse sourcesuperposition

    Ai V 212=

    Ai V3

    24 =

    AiL

    3

    4)0( =

    s2

    +

    V38

    +

    )(sVo

    divider)(voltage +

    +=

    3812

    242)(

    sssVo

    =+

    +=

    )2(3

    )368()(

    ss

    ssVo

    2

    21

    ++

    s

    K

    s

    K

    6|)( 01 == =so ssVK

    3

    10|)()2( 22 =+= =so sVsK

    )(3

    86)(

    2 tuetv t

    o

    =

  • 7/30/2019 Application of Laplace to Circuits

    27/45

    27

    TRANSFER FUNCTION

    )(sX )(sYSystem with allinitial conditionsset to zero

    )(

    )()(

    sX

    sYsH =

    xadtdxa

    dtxda

    dtxda

    ybdt

    dyb

    dt

    ydb

    dt

    ydb

    om

    m

    mm

    m

    m

    on

    n

    nn

    n

    n

    ++++=

    ++++

    11

    1

    1

    11

    1

    1

    ...

    ...

    equationaldifferentiaissystemtheformodeltheIf

    )(sYs

    dt

    yd kk

    k

    =

    L

    zeroareconditionsinitialallIf

    )()(...)(

    )()(...)(

    01

    01

    sXassXasXsa

    sYbssYbsYsb

    mm

    nn

    +++=

    +++

    )(...

    ...

    )(01

    01

    sXasasa

    bsbsb

    sY mm

    nn

    +++

    +++

    =

    01

    01

    ...

    ...)(

    asasa

    bsbsbsH

    mm

    nn

    +++

    +++=

    1)()()( == sXttx

    functionimpulsetheFor

    The inverse transform of H(s) is alsocalled the impulse response of the system

    If the impulse response is known then onecan determine the response of the systemto ANY other input

    H(s) can also be interpreted as the Laplace

    transform of the output when the input isan impulse and all initial conditions are zero

  • 7/30/2019 Application of Laplace to Circuits

    28/45

    28

    LEARNING EXAMPLE responseimpulsehasnetworkA u(t)eth t=)(

    )(10)()(2 tuetvtv tio

    =inputthefor,response,theDetermine

    In the Laplace domain, Y(s)=H(s)X(s)

    )()()( sVsHsV io =

    1

    1)()()(

    +==

    ssHtueth t

    2

    10)()(10)(

    2

    +==

    ssVtuetv i

    ti

    )2)(1(

    10

    )( ++= sssVo

    21

    21

    +++= s

    K

    s

    K

    10|)()1( 11 =+= =so sVsK

    10|)()2( 22 =+= =so sVs

    )(10)(2

    tueetvtt

    o

    =

  • 7/30/2019 Application of Laplace to Circuits

    29/45

    29

    Impulse response of first and second order systems

    First order system

    t

    Keths

    KsH

    =

    +

    = )(1

    )(

    Normalized second order system

    2

    00

    2

    20

    2

    )(

    ++

    =

    ss

    sH

    12

    002,1 = s:poles

    tt

    eKeKth

    )1(

    2

    )1(

    1

    200

    200

    )(

    ++=

    >

    networkOverdamped:1:1Case

    networkdUnderdampe:1:2Case

  • 7/30/2019 Application of Laplace to Circuits

    30/45

    30

    LEARNING EXAMPLE

    )(

    )()(

    sV

    sVsH

    i

    o=functiontransfertheDetermine

    Transform the circuit to the Laplacedomain. All initial conditions set to zero

    Mesh analysis

    212)( IIsVi =

    21

    110 I

    sCsI

    +++=

    )(sVi

    )(1)( 2 sI

    sCsVo =

    Css

    C

    sVo /1)2/1(

    )2/1(

    )( 2 ++=

    25.025.02,1s == :poles8FCa)

    25.02,1 == s:poles16FCb)

    073.0,427.02,1 == s:poles32FCc)

    D t i th t f f ti th t f d i d th

  • 7/30/2019 Application of Laplace to Circuits

    31/45

    31

    LEARNING EXAMPLE Determine the transfer function, the type of damping and the

    unit step response

    Transform the circuit to the Laplacedomain. All initial conditions set to zero

    0=+

    V

    01

    )(

    1

    )(1=+

    s

    sVsV o

    01

    )()(

    1

    )(

    1

    )(

    1

    )()( 01111=

    +++

    sVsVsV

    s

    sVsVsV S

    = )()(1 ssVsV o

    16

    1

    2

    132

    1

    )(

    )(

    2++

    =

    ss

    sV

    sV

    S

    o

    25.002

    =o

    o2 1=

    ssVS1)( =responsestepUnit

    2

    4

    1

    )32/1()(

    +

    =

    ss

    sVo 21211

    )25.0(25.0 ++

    ++=

    s

    K

    s

    K

    s

    Ko

    5.0|)( 0== =soo ssVK

    125.0|)()25.0( 25.02

    12 =+= =so sVsK[ ]

    5.0)(

    25.0

    2

    11 ==

    =s

    o

    ds

    sVsdK

    ( )( ) )(5.0125.05.0)( 25.0 tuettv to +=

  • 7/30/2019 Application of Laplace to Circuits

    32/45

    32

    LEARNING EXTENSION

    84

    10)(2

    ++

    +=

    ss

    ssH

    Determine the pole-zero plot, the type of damping and theunit step response

    10-z =:zero

    22084 2,12

    jsss ==++

    :poles

    x

    x

    2

    2O

    10

    842

    ++ ss

    2o

    o22

    2=

    )84(

    101)()( 2

    ++

    +

    ==sss

    s

    ssHsY

    2222

    )(*221

    js

    K

    js

    K

    s

    KsY

    ++

    +

    +

    +=

    )22)(22(842 jsjsss +++=++

    8

    10|)( 01 == =sssYK

    )4)(22(

    28|)()22( 222

    jjsVjsK jso

    +

    +=+=

    +=

    )()cos(||2)()(

    11

    *11 tuKteK

    js

    K

    js

    K t+

    +++

    +

    =

    = 21173.0

    90413583.2

    1425.82K

    += )2112cos(46.1

    8

    10)( ttvo

  • 7/30/2019 Application of Laplace to Circuits

    33/45

    33

    Second order networks: variation of poles with damping ratio

    Normalized second order system

    200

    2

    20

    2)(

    ++=

    sssH

    12

    002,1 = s:poles

    networkdUnderdampe:1:2Case

  • 7/30/2019 Application of Laplace to Circuits

    34/45

    34

    LEARNING EXAMPLE The Tacoma Narrows Bridge Revisited

    Previously the eventwas modeled as a

    resonance problem.More detailed studiesshow that a modelwith a wind-dependentdamping ratio provides

    a better explanation

    022

    2

    2

    =++

    oodt

    d

    dt

    d

    (mph)speedwind=

    =

    U

    U00013.00046.0

    Torsional ResonanceModel

    45mincollapsetotime

    12twist

    42mphspeedwindfailureatConditions

    =

    =

    =

    Problem: Develop a circuit that models this event

    2 integrator

    adder

  • 7/30/2019 Application of Laplace to Circuits

    35/45

    35

    model02

    2

    2

    2

    =++

    oodt

    d

    dt

    d

    )2(02 2...

    2

    ...

    oooo +==++

    iv

    ( )

    )(1

    )(

    01

    )()(

    sVsCR

    sV

    Cs

    sV

    R

    sV

    i

    i

    =

    =+

    integrator

    1v

    2v

    adder

    +=

    =++

    2

    2

    1

    1

    2

    2

    1

    1 0

    VR

    RV

    R

    RV

    R

    V

    R

    V

    R

    V

    ff

    f

    dt

    d

    2

    2

    dt

    d

    Simulation usingdependent sources

    579.1)00013001156.0( =

    U

    Using numerical values

    Simulation

    buildingblocks

  • 7/30/2019 Application of Laplace to Circuits

    36/45

    36

    Simulation results

    Wind speed=20mph

    initial torsion=1 degree

    Wind speed=35mphinitial torsion =1degree

    POLE ZERO PLOT/BODE PLOT CONNECTION

  • 7/30/2019 Application of Laplace to Circuits

    37/45

    37

    LCs

    L

    Rs

    LCsV

    sVsG

    in

    o

    1

    1

    )(

    )()(

    2+

    +

    ==

    POLE-ZERO PLOT/BODE PLOT CONNECTION

    Bode plots display magnitude and phase information of jssG =|)(

    They show a cross section of G(s)

    52)(2

    2

    ++=

    ss

    ssG

    Cross sectionshown by Bode

    If the poles get closer toimaginary axis the peaksand valleys are morepronounced

  • 7/30/2019 Application of Laplace to Circuits

    38/45

    38

    Cross section

    Front view

    Due to symmetryshow only positivefrequencies

    Amplitude Bode plot

    Uses log scales

    STEADY STATE RESPONSE

  • 7/30/2019 Application of Laplace to Circuits

    39/45

    39

    STEADY STATE RESPONSE

    )()()( sXsHsY = Response when all initial conditions are zero

    Laplace uses positive time functions. Even for sinusoids the response containstransitory terms

    EXAMPLE ))(][cos)(()(,1

    1)(

    22tuttx

    s

    ssX

    ssH =

    +=

    +=

    jsK

    jsK

    sK

    jsjssssY

    +

    ++

    +=

    ++=

    *221

    1))()(1()(

    )()cos(||2)( 22 tuKtKKetyt

    ++=

    transient Steady state response

    If interested in the steady state responseonly, then dont determine residuesassociated with transient terms

    termstransient++

    +

    =

    ++

    =

    oo

    x

    o

    M

    o

    M

    js

    K

    js

    K

    js

    X

    js

    XsHsY x

    *

    2

    1)()(

    )(2

    1|)()( oMjsox jHXsYjsK o == =

    termstransient++= )cos(||2)( 2KtKty ox

    ))(cos(|)(|)( oooMss HtHXty +=

    ( )

    ++

    =+=

    o

    M

    o

    MtjtjMM

    js

    X

    js

    XsXee

    XtutX

    2

    1)(

    2)(cos

    For the general case))(cos(|)(||)(

    )()cos()(

    ++=

    +=

    oooMss

    oM

    jHtjHXty

    tutXtxIf

    LEARNING EXAMPLE Determine the steady state response

  • 7/30/2019 Application of Laplace to Circuits

    40/45

    40

    LEARNING EXAMPLE Determine the steady state response

    Transform the circuit to the Laplace domain.

    Assume all initial conditions are zero

    0

    1222: 111 =

    +

    ++

    s

    VVVV i

    1

    KCL@V

    1

    12

    1V

    s

    Vo+

    =:dividerVoltage

    443)()(443)( 2

    2

    2

    2

    ++=

    ++=

    ss

    s

    sHsVss

    s

    sV io

    10,2 == Mo X

    =++

    = 45354.04)2(4)2(3

    )2()2(

    2

    2

    jj

    jjH

    ))(cos(|)(||)(

    )()cos()(

    ++=

    +=

    oooMss

    oM

    jHtjHXty

    tutXtxIf

    Vttys )452cos(54.3)( +=

    LEARNING EXTENSION 0),( >ttvossDetermine

  • 7/30/2019 Application of Laplace to Circuits

    41/45

    41

    LEARNING EXTENSION )(oss

    ))(cos(|)(||)(

    )()cos()(

    ++=

    +=

    oooMss

    oM

    jHtjHXty

    tutXtxIf

    12,2 == Mo X

    Transform circuit to Laplace domain.Assume all initial conditions are zero

    s

    s

    1

    )(sVi

    Thevenin

    )(1

    1

    )(11

    1

    )( sVssV

    s

    ssV iiOC +=

    +=

    1

    1

    1

    1||1,1||)(

    2

    +

    ++=

    ++=+=

    s

    ss

    ss

    sssZTh

    )()(2

    2)( sV

    sZsV OC

    Th

    o+

    =

    )(33

    2)(2

    sVss

    sV io++

    =

    )(sH

    =

    +=

    ++=

    46.9908.6

    2

    61

    2

    364

    2)2(

    jjjH

    )(

    1

    1

    112

    2)(

    2sV

    ss

    ss

    sV io

    +

    ++++

    =

    )46.992cos(08.6

    212)( = ttvoss

    LEARNING BY APPLICATION De-emphasize bass

  • 7/30/2019 Application of Laplace to Circuits

    42/45

    42

    G C O De-emphasize bass

    Enhances bass to original level

    )1(

    )1)(1()( 21

    p

    zzvR

    s

    ssKsG

    +

    ++=

    filterrecordingRIAA

    s

    s

    s

    p

    z

    z

    318

    3180

    75

    2

    1

    =

    =

    =

    1|)(| 10002 == jssKG

    ]500[/1346,3

    ]50[/46.313

    ],12.2[/33.13

    Hzsr

    Hzsr

    kHzskr

    =

    =

    =

    p

    z1

    z1

    :pole

    :zeros

    Pole-zero map for )(sGvR

    The playback filter is the reciprocal

    )(

    1

    )( sGsG rpvp

    =

    Pole/zero of playback filter cancelspole/zero of recording filter

    LEARNING BY DESIGN Filtering noise in a data transmission line

  • 7/30/2019 Application of Laplace to Circuits

    43/45

    43

    Data bits at 1000bps Noise source is 100kHz

    SOLUTION: Insert a second order low-passfilter in the path. Should not affect datasignal and should attenuate noise

    Proposed filter

    1V

    0=V

    0)/1(

    3

    1

    2

    1

    1

    1

    1

    1=

    +++

    R

    VV

    R

    V

    sC

    V

    R

    VV odata

    0)/1( 22

    1=+

    sC

    V

    R

    V o

    2132131211

    2

    21321

    3

    1111

    1

    )(

    )(

    CCRRCRCRCRss

    CCRRR

    R

    sV

    sV

    data

    o

    +

    +++

    =

    22

    2 ooss ++

    Below 100k

    Well below 100kabove 1k

    Filter designcriteria 1>

    1

    2

    21

    3212

    3,

    1

    C

    C

    CCRRRR o ====

    Design equations

    Selected pole location or filter

  • 7/30/2019 Application of Laplace to Circuits

    44/45

    44

    Selected pole location or filter

    nFCnFC

    kR

    33.1,75.0

    .2,000,25,40

    21

    0

    ==

    ===

    determineandequationsdesignUse

    Select

    Circuit simulating the filter

    noise

    5102 =

    The filter eliminates noise

    but smooths data pulse

    25kbpsdata transferrate

    Filtered signalis useless

    REDESIGN!

    N l l ti 1

  • 7/30/2019 Application of Laplace to Circuits

    45/45

    45

    New pole-zero selection 1=

    Simulation for 25kbps

    1

    2

    210

    2

    31

    000,40

    1

    000,150

    C

    C

    CC

    ==

    ==

    equationsDesign

    APPLI CATI ONAPPLI CATI ONAPPLI CATI ONAPPLI CATI ON

    LAPLACELAPLACELAPLACELAPLACE