## Bypass Array Model

I'll be at DesignCon 2003 next week in San Jose, learning lots of new things as always. Hope to see you at the show. Ralph Cavin has me scheduled to talk on a panel about University Education. I also will appear with Henri Merkelo talking about the new reality of multi-level transceivers for backplane applications.

## Bypass Array Model

Daniel Paradis writes to the si-list:

Is-there a Mathcad model available to calculate the impedance magnitude of a bypass capacitor array?

I am specifically referring to sec 8.2 of "High Speed Digital Design".

Thanks for your interest in High-Speed Digital Design.

This summer I received a very nice Excel spreadsheet based on the approach outlined in section 8.2 equations. The spreadsheet was developed by JP Nicholls of Powerwave UK Ltd.

It takes into account the inductance of your power-supply wiring, any bulk-decoupling capacitors, a uniform bypass capacitor array, and the natural capacitance of your power and ground planes.

JP's spreadsheet produces a beautiful color version of my figure 8.9 showing the impedance of each element and also the composite impedance of all four elements taken in parallel. Once you see how it works you can modify it to do lots of other combinations.

The spreadsheet runs on Windows using Excel 2000. It handles all the calculations quite nicely using the complex-maths functions in Excel.

Save the target of this link to your desktop:

The spreadsheet uses advanced Excel-spreadsheet functions including a call to the function COMPLEX. If this function is not already available to your Excel application, run the Excel Setup program to install the Excel Analysis ToolPak. After you install the Analysis ToolPak, you must enable it by using the Add-Ins command on the Tools menu. Refer to your Excel Help screens (search for the COMPLEX function) for further assistance.

I love the fact that this has been done on an Excel spreadsheet because, as much as I like to use MathCad, I must admit that Excel is much more widely disseminated. Thanks, JP.

Best Regards,
Dr. Howard Johnson