Circuit designers often encounter the adverse effects of common-mode noise on a design. Once a common-mode problem is identified, there are several ways that it can be resolved. However, common-mode interference manifests itself in many ways; therefore, it may be hard to determine whether or not this is the cause of your circuit’s misbehavior. If a system is connected and running but only produces erroneous data, common-mode noise may be the reason. This application note describes sources of common-mode problems, presents possible solutions, and concludes with a description of Avago Technologies’ approach to addressing common-mode noise. Common-mode noise problems exist in many electrical circuits. Any device or system with either its input or its output floating may be susceptible to common-mode noise. A common-mode signal is a signal that appears common to either set of floating points. It can be either ac or dc. The overall effect is that excessive common-mode noise causes spurious results at the output, disrupting safe, precise measurements.