ABSTRACT
This chapter examines the distinction between noise and coherent interference. Noise is considered to arise in a circuit or measurement system from completely random phenomena. Sources of noise in signal conditioning systems can be separated into two major categories: noise from passive resistors and noise from active circuit elements such as bipolar junction transistors, field effect transistors, and vacuum tubes. The chapter discusses common sources of coherent interference and various means of minimizing its input to a measurement system. Coherent interference, unlike random noise, has narrowband Power density spectrum, often with harmonic peaks at integral multiples of the fundamental frequency. Probably the single most important principle of reducing the pickup of coherent noise from internal sources in an electronic system is good grounding practice. The chapter also examines a rule for the design of low-noise signal conditioning systems. It also discusses some of the more common means of mitigating coherent interference and analyzes equivalent circuits relevant to those means.
