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Designers’ Dilemmas: Making the Software Switch
You can’t teach an old dog new tricks, but what about new software? It’s not the easiest thing to pick up and learn a new program after years of experience with another.
Calculating Trace Lengths (Electrically Long Traces)
When defining a transmission line within a PCB, designers need a method that allows quick determination if a trace is too long for signal integrity purposes during the component placement cycle.
Defining Capacitor Functions on a Printed Circuit Board
Within electrical engineering, a descriptive word is used to describe a specific function or operation. The same word may be used to reference different applications thus making it confusing to understand what is being discussed. Three common words related to the use of capacitors are Bulk, Bypassing and Decoupling.
Failure Modes from an ESD Event
Most ESD problems found on a printed circuit board falls within two categories–component damage and operational disruption.
Grounding EMI Filters
Power line filters are used to remove common-mode and/or differential-mode EMI either into or from a system when connected to a facility’s AC mains network. Optimal performance generally depends upon the capacitance of the filter’s design in order to achieve a designated insertion loss, or level of performance.
Hidden Characteristics of Digital Components
When selecting components for a particular application, design engineers are generally interested only in functionality, operating speed, and propagation delay of the internal logic gates as published by the manufacturer in their datasheets.
Overlooked Characteristics of Capacitors
All capacitors contain a finite amount of lead and device body inductance. Loop inductance (including lead inductance) must be minimized at all times. When the inductance of a routed trace between capacitor and component, plus the internal lead inductance from the solder pad to the plates of the capacitor is added together, a high impedance may be present between the capacitor’s pins and a voltage or return (ground) network.
Printed Circuit Board Traces and Transmission Line Theory
A transmission line is a system of conductors, such as wires, waveguides, coaxial cables or PCB traces suitable for transferring an electromagnetic field between two or more locations.
Relative Permittivity (Dielectric Constant)
Before one can understand how signal propagation occurs within a PCB, we must consider the importance of a primary electrical parameter, E ' r, identified as relative permittivity or dielectric constant.
RF Current Density Distribution
Within a transmission line, electromagnetic energy propagates within a transmission line from a source to a load. Faraday’s law states that when a time variant current travels within a transmission line, magnetic flux is created that surrounds the transmission line (Right Hand Rule), and exist within the surrounding dielectric (free space or the physical substrate; core and prepreg).
Slots Within an Image Plane Affecting RF Current Return
An excessive number of through-holes within a power and ground plane creates a situation commonly identified as the Swiss cheese effect. The physical copper between through-hole pins has been removed leaving large areas of discontinuity.
Vias And Their Effects In Solid Power Planes
Use of vias in solid power planes will decrease the total planar capacitance based on the number of vias and the amount of real estate that has been etched out from the planes.
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