Microprocessor platform impedance characterization using VTT tools

This paper presents a method to extract the impedance profile of Intel processor platforms in frequency domain using custom, high di/dt electronic loads referred as VTT tools. Although currently followed time domain characterization yields the voltage response of the motherboard (MBD) to the current profile generated by the VTT tool, it does not directly provide the MBD impedance as a function of frequency. Without knowledge of the impedance profile it is difficult to fully understand the impact motherboard layout and decoupling capacitor filter configurations have on the overall power delivery system performance. Theory of the method, VTT tool modifications and platform waveform results discussed. Internally developed computer scripts that process the ratio of the measured voltage and current FFT´s as the platform impedance over frequency are described. Correlation of simulation models is provided. Steps towards generalization of the method for maximum industry adoption are identified