Microcontroller applications often have low-level sensor signals and moderate power-drive circuitry, in addition to the microcontrollers. A peaceful coexistence with these three extremes requires a careful power and ground distribution design. This paper will discuss sources of noise and the paths by which the noise travels. We will cover the theory behind good layout practices and their impact on noise. Any designer who struggles to keep digital and power noise out of sensitive input circuits will find this paper useful.