RF Design Blogs

In MMSIM 7.2, two new parameters have been added to the Spectre nport primitive: datatrunc and causality. In MMSIM 7.1, passivity checking was added. The nport now has causality correction, passivity checking and enforcement, and the ability to remove small couplings terms from the input s-parameter data.

The datatrunc parameter removes small relative coupling data in your s-parameter file. This improves capability and performance for simulating large scale nport systems. You can adjust this value from the default (0.001) to say 0.01 or 0.1, according to your accuracy requirements to get better performance. However, note that you are trading off accuracy for performance by doing so.

The causality parameter corrects s-parameter data to ensure the system is causal. When causality=no or the parameter is not set, the nport behavior is the same as in previous MMSIM releases. When causality=fmax, Spectre corrects causality up to fmax, specified by the existing nport parameter fmax. When causality=auto, Spectre corrects s-parameter causality up to an automatically optimized fmax and ignores the existing parameter fmax. Note that the auto setting can significantly increase simulation time, therefore causality=fmax is recommended. The parameter usewindow is ignored when causality=fmax or auto.

Two new passivity checking and enforcement parameters were added in the MMSIM 7.1 release. The passivity parameter checks and enforces passivity of s-parameters. Possible values are no (default), check or enforce.

The pabstol parameter specifies the absolute tolerance of passivity criteria. The default is 1e-6.

Tawna Wilsey