Electrical noise generated from the microphonic effect in capacitors

Passive components such as capacitors and inductors are often used in high-frequency circuits. EM engineers often model the frequency response of these components by adding "parasitic" components to the circuit model. For instance, parasitic resistors and inductors are added to the model of a capacitor. Some capacitors also exhibit an electrical response when stressed physically. This response can be significant. This response is called the "microphonic effect" because the frequency of the response is often in the audible range. A simple operational amplifier circuit is used to examine this response for several off-the-shelf capacitors. Considerable variation is observed-depending on capacitor type, capacitor size, and physical location.

INTRODUCTION

Passive components such as capacitors, inductors and ferrite beads are often used when designing various high frequency circuits. Unfortunately “real’ passive components have characteristics that deviate from the “ideal” response. For example, the parasitic performance of capacitors is often modeled using additional discrete components, as shown in Figure 1 [1]. By including these “extra” components EMI engineers try to account for the frequency-dependent responses of actual components when the components are subjected to electrical stresses. Figure 1. Equivalent circuit of a typical capacitor