When discussing noise issues with regards to a digital circuit, topics such as transmission line reflection and ground bounce are a few of the primary topics. But generally, digital circuits operate at relatively large signal levels with high noise margins. This makes these types of circuits inherently immune to low level noise pick-up. In the analog domain, where data acquisition is performed, a small amount of external noise can cause significant interference. For instance, a difference of 10mV of noise in the analog ground between a 12-bit A/D converter and the converter’s driver amplifier can cause an 8LSB error. In contrast, digital systems can tolerate hundreds of millivolts of this type of error before intermittent problems start to occur.

Finding the origin and then eliminating interfering noise in the analog domain presents a formidable challenge. Of particular interest is the “slow” sensor system, where designers are easily tempted to ignore problematic, high frequency, noise issues. This paper delves into hardware and firmware noise reduction strategies for signal conditioning paths that have sensors. Noise topics such as conducted noise, device noise and radiated noise will be explored from the analog perspective.