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mtline physical length

Karev11

Hi,

When the type of input for mtline is s-parameter, simulation shows different results with different physical length as it should intuitively. However, when S-parameter is extracted from a shape, shouldn't the length be fixed already? (length can be made a variable of course, but one s-parameter is still for one length only), then how is the tool able to somehow adjust the s-parameter for different physical length?  could anyone explain

thanks,

Kev

Parents
  • Andrew Beckett

    Hi Kev,

    My understanding is that if you are providing mtline with an s-parameter description, then the physical length of that line must be provided. Since the description is no longer a per-length description (as you might have done if it was per-length RLGC matrices). The length is needed to allow it to properly compute the delay in the line (which is very hard to do from the s-parameters alone, which is why the suggestion is to use mtline rather than nport when you have s-parameters representing a relatively long line). From the "spectre -h mtline" output:

    =====================
    S-Parameter Data File
    =====================

    MTLINE also supports S-parameter data file input describing a transmission line
    system using the `file' parameter. MTLINE will convert the frequency dependent
    S-parameter to frequency dependent RLGC data and store the results in the file
    `%C:t:r_InstanceName.rlgc' for reuse in subsequent simulations.

    If the `file' parameter corresponds to S-parameter data, MTLINE will first
    check the existence of the file `%C:t:r_InstanceName.rlgc' to determine if the
    S-to-RLGC extraction has been performed in a previous simulation.

    The S-parameter data file formats supported include Touchstone, Spectre and
    Citi.

    The physical length of the line must also be specified using the `len'
    parameter.

    The ordering of the S-parameter input file should be in the format of input
    ports followed by the output ports of the transmission line system, or Pin1,
    Pin2, Pin3, ..., Pout1, Pout2, Pout3,

    So you should set the actual physical length of the line rather than expecting mtline to adjust a fixed set of s-parameters to a different length than they actually represent.

    Kind Regards,

    Andrew.

Reply
  • Andrew Beckett

    Hi Kev,

    My understanding is that if you are providing mtline with an s-parameter description, then the physical length of that line must be provided. Since the description is no longer a per-length description (as you might have done if it was per-length RLGC matrices). The length is needed to allow it to properly compute the delay in the line (which is very hard to do from the s-parameters alone, which is why the suggestion is to use mtline rather than nport when you have s-parameters representing a relatively long line). From the "spectre -h mtline" output:

    =====================
    S-Parameter Data File
    =====================

    MTLINE also supports S-parameter data file input describing a transmission line
    system using the `file' parameter. MTLINE will convert the frequency dependent
    S-parameter to frequency dependent RLGC data and store the results in the file
    `%C:t:r_InstanceName.rlgc' for reuse in subsequent simulations.

    If the `file' parameter corresponds to S-parameter data, MTLINE will first
    check the existence of the file `%C:t:r_InstanceName.rlgc' to determine if the
    S-to-RLGC extraction has been performed in a previous simulation.

    The S-parameter data file formats supported include Touchstone, Spectre and
    Citi.

    The physical length of the line must also be specified using the `len'
    parameter.

    The ordering of the S-parameter input file should be in the format of input
    ports followed by the output ports of the transmission line system, or Pin1,
    Pin2, Pin3, ..., Pout1, Pout2, Pout3,

    So you should set the actual physical length of the line rather than expecting mtline to adjust a fixed set of s-parameters to a different length than they actually represent.

    Kind Regards,

    Andrew.

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