Intel 315889-002 manual A.3 VTT Zf Measurement Method, A.4 Results

Z(f) Constant Output Impedance Design

Figure A-4. Time Domain Responses and Corresponding Fourier Spectra of Voltage, Current and Impedance

A.3 VTT Z(f) Measurement Method

An electronic load that has the capability to change the repetition rate up to 3 MHz of the load step is needed. The Intel LGA771/775V2 VTT by Cascade Systems Design, will meet this requirement. By monitoring the VTT current and voltage waveforms with an oscilloscope capable of executing an FFT on these waveforms, the platform impedance is found. A complete impedance profile is then generated by sweeping the input waveform frequency across the range of interest. In order to automate the data collection process, Intel has modified the VTT control software and a GPIB controlled oscilloscope is used along with software supplied with the VTT.

These utilities allow the user to automatically display and collect the magnitude and phase of the motherboard impedance in a Microsoft Excel* compatible data file. The total time it takes to extract the impedance profile using this method is about 1-2 minutes. This technique is very useful in investigating and assuring MB performance based on its stack up.

For more information on the measurement method and theory, see the paper Microprocessor Platform Impedance Characterization using VTT Tools by K. Aygun, S. Chickamenahalli, K. Eilert, M. Hill, K. Radhakrishnan and E. Stanford published at the IEEE Applied Power Electronics Conference, 2005.

A.4 Results

As an example, Figure A-5shows the test platform with 10 560 μF Al-Poly bulk capacitors and 10 10 μF and 8 22 μF high frequency MLCC capacitors in the socket cavity. Figure A-6is the measured impedance profile of the board shown in Figure A-5as capacitors are removed. The VID setting for this measurement was 1.35 V and load

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