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Frequency Dependance in AC and TRAN Analysis

Discussion in 'CAD' started by [email protected], Jul 17, 2007.

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  1. Guest

    I am trying to model a current clamp in Spice based on a mathematical
    model which uses frequency dependent inductances.

    I have seen various articles on using Laplace code blocks for
    frequency dependent expressions, but these don't seem to behave
    properly when in circuit for AC sweeps,
    and I have tried passing parameters to the inductor value but these
    only seem to work in AC or Transient not both.

    What I am hoping to achieve is an inductor whose inductance is
    selected from a look up table based on the instantaneous frequency of
    the stimulating waveform.

    I have included an example netlist below to show the solution I am
    trying to get working.
    NB I am using ICAP4 which insists on Laplace functions being
    denominator loaded hence the use of "1/s" rather than just "s" to
    extract the frequency.

    V1 1 0 AC=1
    L1 1 2 (v(5))
    R1 2 0 1k

    B1 103 0 V=v(1)
    A1 103 104 LAPLACEA1
    ..MODEL LAPLACEA1 s_xfer( in_offset=0 gain=1 num_coeff=[0 1]
    den_coeff=[1 0] denorm_freq=1)
    A2 104 105 TABLEA2
    ..MODEL TABLEA2 Pwl( xy_array=[<< Table of F v L >>] input_domain=.01
    R2 105 0 1

    When I run the above sort of circuit in AC mode it seems to calculate
    L at the start of the run and keep it constant.
    I need a model that will work in both AC and TRAN as the intention is
    to replicate results from a network analyser to validate the circuit
    model against an actual device and then perform TRAN runs to examine
    the time domain response under varying conditions.
  2. Jim Thompson

    Jim Thompson Guest

    What Spice variant is this? I don't recognize the syntax.

    ...Jim Thompson
  3. The general technique to make a controllable/variable impedance is to use a
    VCCS connected to itself. So, try a VCCS fed from the laplace transfer
    function output with the laplace input connected to the VCCS output.
  4. Shame on you Jim. Its xspice, well maybe a bit modified, the inductor line
    don't make sense in xspice, but the other stuff looks basically ok.

    Kevin Aylward
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