Method of measuring disturbances from modular devices by magnetic probe method above 1 GHz

In recent years, personal computers have been constructed by combining modules such as a hard disc drive and memory boards. Although a simple method for measuring disturbances from such modules in the frequency range below 1 GHz has been proposed, device technology progress needs an evaluation method above 1 GHz. This paper describes a method using a magnetic probe for measuring disturbances in the range from 1 GHz to 6 GHz. A test board for use above 1 GHz was developed according to the specifications for use below 1 GHz, and the current distribution and decoupling characteristics were evaluated. The results show that the decoupling factor was less than -11 dB and the maximum current appeared at the nearest point to the decoupling capacitors. Analysis by the finite difference time domain (FDTD) method indicates that the calculated current distribution agrees well with the measured value and that the maximum current could be measured at the nearest point to the decoupling capacitors. Measurement results for a hard disc drive with a USB3.0 port indicate that the disturbance level could be measured at the nearest point to the decoupling capacitor.