Choosing appropriate configuration parameters for the Si8000/Si9000's sensitivity analysis

Using Si8000 and Si9000's sensitivity analysis

The Sensitivity Analysis tab of the Si8000m and Si9000e field solvers allows you to graph the effect of a range of changing parameter values. This example will chart the effects of changing the upper substrate height for a range of trace widths for the offset stripline structure below.

Select the Lossless Calculation tab, choose the units as Microns and enter the parameters below; click Impedance Calculate; you should see the impedance result – 49.93 Ohms.

Charting impedance against changing trace width

Switch to the Sensitivity Analysis tab and in the Impedance vs Changing Parameters pane choose the W1 parameter and set the Range Start value to 180 and the Range Finish value to 200; set the Increment to 5 microns and click Calculate.

The Si8000 graphs the change in impedance as trace width (W1) varies between 180 and 200 microns.

Click the Results tab to view the results in tabular form.

Varying parameters while the impedance is held constant

Next, from the Constant Impedance vs Changing Parameters, select H2, specify the target impedance as 50 Ohms and set the Process Window minimum and maximum values to 42.5 and 57.5 Ohms respectively. Click Calculate.

The Si8000 charts the variation in the upper dielectric height (H2) against W1 of 180 and 200 microns for impedances of 42.5 Ohms, 50 Ohms and 57.5 Ohms; results in tabular form are shown below:

50 Ohms results

42.5 Ohm results

57.5 Ohm results

You can copy the tabular results to the Windows clipboard for export to Microsoft Excel – use the Edit|Copy Current Results Tab to Clipboard and paste into the worksheet:

Ensuring successful calculations

On occasions, when using the Si8000 sensitivity analysis you may specify a set of parameters that will not allow you to produce successful calculations. The result will be a blank graph. Check the results tables – the Calculation Success column items where calculations have failed are shown in pink.

When this occurs, to help locate the error, try checking the parameters using the Lossless Calculation tab; for this example, enter the parameters below (derived from the top row of the results table) and goal seek on H2 for a 50 Ohm target impedance.

In this case, the Si8000 reports that the "trace is not embedded within its substrate - [Substrate2]".

Substrate2, for the offset stripline structure above, is H2. Notice that the trace thickness is 18 micron, so the minimum value for H2 to calculate/goal seek successfully will be 19 micron. A quick glance at the Parameter Configuration table will reveal the problem – the minimum value for H2 has been set to 1 micron.

Change the minimum value for H2 to 19 micron and recalculate – the plot is displayed below.

It is sometimes necessary to change the Configuration|Parameters minimum and maximum values to ensure they are appropriate for the selected structure. Note, though, that the H1, H2, H3, H4 values are used differently depending on the structure chosen, so the same minimum and maximum values may not be suitable for all structures and may, therefore, need to be adjusted.

More information:

PCB Impedance Field Solver Si8000m

Insertion Loss GHz PCB Transmission Line Field Solver Si9000e