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Lossy U Element Statement The ideal transmission line only delays the difference between the signal and the reference. Some applications, such as a differential output driving twisted pair cable, require both differential and common mode propagation. Use a U Element, if you need the full signal and reference. You can use approximately two T Elements (as shown in Figure A-6). In this figure, the two lines are completely uncoupled, so that only the delay and impedance values are correctly modeled. Figure A-6: Use of Two T Elements for Full Signal and Reference out in outbar You cannot implement coupled lines with the T Element, so use U Elements for applications requiring two or three coupled conductors. Avant! in-circuit simulation uses a transient timestep that does not exceed half the minimum line delay. Very short transmission lines (relative to the analysis time step) cause long simulation times. You can replace very short lines with a single R, L, or C Element (see Figure A-1 on page A-4). Lossy U Element Statement The U Element models single and coupled lossy transmission lines for various planar, coaxial, and twinlead structures. When a U Element is included in your netlist, simulation creates an internal network of R, L, C, and G Elements to represent up to five lines and their coupling capacitances and inductances. For more information, see Chapter 2, “Using Passive Device Models”. True-Hspice Device Models Reference Manual, Release 2001.4, revision A A-11
