A Methodology for Predicting Acoustic Noise From Singing Capacitors in Mobile Devices

Multilayer ceramic capacitors (MLCCs) connected to a power distribution network (PDN) can create acoustic noise through a combination of the power rail noise at the MLCCs and the piezoelectric effect of the capacitor's ceramic material. The deformation of the MLCCs brought on by power supply noise creates vibrations which cause the printed circuit board (PCB) to vibrate and generate the audible acoustic noise. In the following paper, a simulation methodology is presented to analyze the acoustic noise created by MLCCs on a PCB. A simulation model for the PCB vibration modal response is built and the modal superposition method is used to analyze the harmonic response of the PCB excited by the capacitor. By multiplying the measured power noise spectrum on the MLCC with the simulated deformation of the PCB found from the harmonic response analysis, the total response is obtained. Simulated results show a good correlation with the measured acoustic noise. The proposed method shows promise for analyzing and predicting the acoustic noise from singing capacitors.