GHz DPI Fixture

To investigate the conducted immunity of SOIC8-packaged ICs at centimeter wavelengths, we developed a universal test PCB. One can press any IC on it, and have access to all 8 pins by SMA connectors. To perform a Direct Power Injection (DPI), bias tees or blocking capacitors can be connected external to the board. The connector and coplanar traces have an insertion loss better than 1.9 dB at 20 GHz. [1]

SOIC8 DPI fixture
GHz DPI fixture with an LM7805 voltage regulator pressed onto it. Input and output pins are connectorised, all other pins are shorted to the ground.

Generated Layout

The PCB and the corresponding calibration kit were not entered manually into a CAD tool, but generated by a Python script. This way, stitching vias could be placed consistently along curved traces. Furthermore, this guaranteed that the layout was the same for all traces. Finally, it promotes ‘playing around’ with the layout by avoiding tedious and error-prone manual steps.

Reproduce!

You are invited to reproduce, falsify and improve upon our research. The Python script, as well as the Gerber files and Eurocircuits order details can be downloaded as zip archive. You only need Python 2.7 to run the script:

Y:\Python\centimeterlayout\src>python main.py
Stroke font provided courtesy Altium Ltd.
Creating output directory Y:\Python\centimeterlayout\output

You can now view the Gerber and Excellon files in the output directory, for example with the free Pentalogix ViewMate. In ViewMate:

  1. Choose ‘File→Import→Gerber…’, select all *.gbr files by holding down the shift key, and click ‘Import’
  2. Select an empty layer and choose  ‘File→Import→Drill & Rout…’, select both *.drl files by holding down the shift key, and click ‘Import’

You should now see something like this:

ViewMate preview of the GHz DPI fixture

If you send this order to Eurocircuits with the order details and panelisation instructions found in the order_information directory, you should get something like this:
The next step is to solder Johnson Emerson 142-0771-831 connectors on the calibration kit, following the manufacturers instructions, using the 140-0000-973 soldering tool. The load standard should be fitted with an Vishay CH0402-50RGF 50 Ohm resistor. The [latex]S_{21}[/latex] parameter of the thru standard should measure something like this (between both SMA reference planes):

Thru standard S21 parameter
Measured insertion loss of the thru standard between both SMA reference planes (curve). The different markers are simulated results.

To clamp an IC onto the SOIC8 fixture, one needs a spring: we used an old-fashioned, stainless steel ruler. Two 3 mm holes then must be drilled: one to fix the spring to the board, one for a nylon bolt that presses upon the IC under test (see photo above). To short pads to the ground, we used a CircuitWorks 2200MTP conductive coating dispenser.

React

Please let us know if you have any problems reproducing above results. Questions, remarks and insults are welcomed at sjoerd.optland@eseo.fr.

Electromagnetic Compatibility