Measurement of power distribution network impedance using an error analysis approach

In order to achieve power integrity (PI), power distribution network (PDN) impedance has been designed lower than calculated target impedance in frequency domain. However, with PDN impedance scaling down milliohm order, its measurement accuracy has been limited by the inevitable uncertainty from vector network analyzer (VNA). In this paper, we investigate the uncertainty effects in three impedance measurement methods using an error analysis approach. Impedance error rate is proposed as a function of variable uncertainty and the impedance of device under test (DUT), to represent the measurement accuracy. By analysis, we find that three methods have different accuracy for different DUT impedance ranges, and the appropriate method should be employed for different DUT measurements. Taking a fabricated power ground plane board (a special PDN) as case study, the measured results from three methods are compared with the simulated results from cavity model method and EM simulations in Computer Simulation Technology (CST) Microwave Studio, and the comparison results correlate well with our error analysis results. It´s proven that the two-port method based on scattering parameter (S parameter) S₂₁ performs best with highest accuracy for measuring the PDN impedance scaling down to milliohm order.