Evaluation and analysis of electromagnetic noise coupling in a board with a mixed signal IC

In wireless communication terminal such as smart mobile devices, a countermeasure for electromagnetic noise generated by digital circuits becomes more important since it's coupling to an antenna causes degradation of communication performance. To apply an optimum countermeasure, it is very important to find out correctly a noise coupling path. This paper gives evaluation results of noise coupling to an antenna in a test board with a RF and digital mixed IC using the amplitude probability distribution (APD) measurement method. We analytically investigated noise coupling path to an antenna utilizing a correlation coefficient suitable for the APD curve for the test board. Moreover, in order to verify analyzed results the noise coupling path in the test board was evaluated by measurements of In-phase/Quadrature (I/Q) signals.