From Complete PCB Design Using OrCad Capture and Layout

Desirable electrical characteristics of a circuit and its PCB include low noise, low distortion, low cross talk, and low radiated emissions, to name a few. The purpose of this chapter is to introduce the issues that cause PCB performance problems and how to route the PCB to minimize them and maximize signal integrity.

Circuit Design Issues Not Related to PCB Layout

Circuit design constraints are primarily the responsibility of the circuit design engineer and will not be covered in detail here, but some of the issues will be mentioned briefly since the symptoms of poor circuit design can be confused with PCB design problems.

Noise

Noise generally refers to any signal that interferes with or degrades a signal of interest. It is often used with an adjective for problems, such as phase noise, switching noise, cross-talk noise, and reflection noise. In this text we will limit the term noise to mean random or pseudo-random, natural signals, which are generally not a result of the PCB design. Functional problems such as cross talk or ringing (which are PCB-related problems) will be named as such. From this perspective there are two basic categories of noise: background noise and intrinsic component noise. These noise problems are generally addressed by the circuit designer, not the PCB designer, but are discussed here briefly for completeness.

Background noise

Background noise is an uncontrolled signal that originates from the system or environment your board is working in. For example, if your circuit is an audio amplifier that...

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Products & Services
ESR/EPR Tubes
ESR/EPR tubes hold samples in ESR or EPR spectrometers. They are thin glass walled tubes, uniformly thick, that produce low background noise.
Spectrum Analyzers and Signal Analyzers
Spectrum analyzers and signal analyzers display raw, unprocessed signal information such as voltage, power, period, wave shape, sidebands, and frequency. They can provide the user with a clear and precise window into the frequency spectrum.
Capacitors
Capacitors are electronic components used for storing charge and energy. In their simplest form, capacitors consist of two conducting plates separated by an insulating material called the dielectric.
Noise Standards
Noise standards are used to calibrate other noise instruments.

Topics of Interest

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Desirable electrical characteristics of a circuit and its PCB include low noise, low distortion, low cross talk, and low radiated emissions, to name a few. The purpose of this chapter is to introduce...

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8.1 Introduction to Noise Noise is unwanted fluctuation superimposed upon a desired signal. It determines the accuracy and repeatability with which we can measure the signal. During the past few...