Specifying the timebase and line length settings for Delta-L insertion loss tests

Delta-L insertion loss tests

Polar's Atlas PCB insertion loss test sytem includes the Delta-L technique which uses long-line short-line measurement combined with innovative via de-embedding techniques for removing the via effects from differential (mixed mode) s-parameters when characterising raw PCBs for insertion loss.

To create a new loss test choose the Insert Test… command from the Board menu and then choose Delta-L.

This will create a new test and display the Delta-L Test Editor with its text and numeric fields in which to specify test parameters for each Delta_L test. Entries in the fields contained in the Test Setup Editor will be available for display in the Test List and Datalog and printed out with the test results.

Supply the settings for theTest Editor dialog to specfy the test description, configuration (single ended or differential) and the board layer along with the number of data points and averages.

Click the Delta-L Iterative Fit check box and use the Test Limits dialog to specify maximum (and optionally, minimum) values for loss at selected frequencies.

The dialog above shows maximum loss limits defined for three frequencies.

Delta-L test parameter default settings

The Delta-L test editor opens with default settings for the number of data points, the number of averages, waveform acquisition start point and intersample period.

Timebase and line lengths

The Timebase and Line Lengths section contains the waveform acquisition start point, intersample period and the lengths of the short and long lines. Specify the short and long line lengths of the test coupon.

The acquisition start point should be set to ensure both short and long line Raw TDT waveforms are contained in the waveform window and to maximise the energy displayed in the Raw TDT waveforms.

The graphic below displays the waveforms with the default acquisition start point value of End of Probe minus 200 picoseconds.

It should normally not be necessary to alter the intersample period setting and it it is recommended that it is left at its default value of 1.25pS.

Use the acquisition start setting to shift the short and long waveforms to display maximum energy in the waveforms – ensure both waveforms are visible in the waveform window.

The graphic below illustrates the short and long waveforms with the acquisition start set to End of Probe plus 200 picoseconds.

In the unlikely event it becomes necessary to consider the intersample period contact your local Polar office for information.