- PCB Design
- - R-L-C -
- Signal
Integrity - T - Lines
- Power
Supplies - EMC/EMI
- Materials
- Networks
- Tools
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PCB Design is an anomaly. The “Printed Circuit Board” part is based on electrical and physical principles. The “Design” part includes some artistry and some ingenuity. The goal is to merge these two together so that it meets the Engineer’s, the Fabricator’s, and the Assembler’s requirements. These pages contain “some useful info” about PCB Design. There are links to resources, tools and forums that you may find helpful as a Designer. This phrase often fits when it comes to PCB Design, “It’s not always what you know, but what you can find.” Perhaps you can find it here. |
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PCB Design Tutorial by David L. Jones Also available in pdf |
![dc-new-logo3[1]](/graphics/pcbdesign/image017.jpg) Useful Electronic Tutorials |
This site provides a series of online textbooks covering electricity and electronics |
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A Practical Guide to High-Speed Printed-Circuit-Board Layout |
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SOCcentral.com focuses its news coverage on SoC/ EDA/ ASIC /FPGA/ IP technology, products, and standards. |
The Hardware Book is a free collection of connector pinouts and cable descriptions |
Electronic Discharge Association |
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Resistors 
A resistor is a two-terminal component that opposes an electric current by producing a voltage drop between its terminals in accordance with Ohm's law: Inductors An inductor is a passive device used in circuits for its property of inductance. Inductance is an effect which results from the magnetic field that forms around a current through a conductor. This magnetic field is proportional to the current. When the current changes, the magnetic field also changes, resulting in an electromagnetic field. This field opposes changes in current. Capacitors
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Walter Fendt’s Java Applets |
VVMLCCModeling Program |
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 Lessons about: Resistors, Capacitors, and Inductors |
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Signal integrity or SI is a measure of the quality of an electrical signal. When considering signals routed across a PCB, the goal is to deliver a signal in an “unimpaired” condition from output source to destination. Some of the main issues that impair signal integrity are: Crosstalk: Higher interconnect density has led to each net having signals that are closer together, thus leading to increased coupling capacitance between neighboring nets. As circuits shrink, problems from reduced noise immunity increase. Ringing: happens when a signal causes the parasitic capacitances and inductances in the circuit to resonate at their characteristic frequency. Ringing can cause unwanted electromagnetic radiation to be emitted and can delay the arrival of the signal at it's destination. Overshoot/Undershoot: Is the transient signal level beyond/in between the steady state level. A circuit is designed to minimize rise time while containing distortion of the signal within acceptable limits. Overshoot represents a distortion of the signal. In circuit design, the goals of minimizing overshoot and of decreasing circuit rise time can conflict. Overshoot often is associated with settling time, how long it takes for the output to reach steady state; see step response. Signal Loss; from the skin resistance in conductors is a factor of high frequency current and the dielectric material. Current tends to crowd to the edges of the conductor, hence the term “Skin Effect”. The easiest ways to increase a trace’s cross sectional perimeter is to widen it. The other way is to use materials with a lower “dielectric loss.” Below are some Links to sites containing information about this subject. |
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One of the ways to maintain signal integrity is by controlling the impedance of traces. For high-speed designs, care must be taken to design and layout traces in such a way that the characteristic impedance of the trace is constant everywhere along the trace. The transmission line is based on the relationship of the following: · There is inductance between traces and the signal return. · There is also some capacitive coupling between the trace and its return. This is a “lumped” model of the wire pair, because we show the capacitors and inductors as lumped components. · Er (εr) – Relative permittivity is a measure of the effect an insulating material has on the capacitance of a conductor embedded in the material or surrounded by it. It is also a measure of the degree to which an electromagnetic wave is slowed down as it travels through the insulating material · Dielectric Thickness and Trace Width – Both of these parameters play a key role in transmission line impedance. Control of each is necessary during fabrication of the board. · Loss Tangent (tan (δ)) – Loss tangent is a measure of how much of the signal pulse will be lost in the dielectric region between copper layers. Loss tangent is a function of the material’s resin type and molecular structure (molecular orientation). · Resistive Losses and Skin Effect – As frequency increases the energy moving in the trace is forced to the outer perimeter by the large magnetic fields present in higher frequency signals. This is known as skin effect because the majority of the energy is forced to the outer skin of the trace. Reflections and other issues may be caused be Impedance Mismatches. These can be eliminated by terminating transmission lines in their characteristic impedance. The most common methods are Thévenin (or parallel) and source (or series) terminations.
Below are some Links to sites containing information about this subject. |
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Interface Bus Trace Terminations |
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A typical application of a power supply is to convert an AC voltage into a regulated DC voltage, or a DC-DC conversion needed to supply a specific voltage. A simple AC powered linear power supply usually uses a transformer to convert the voltage from to a different, usually a lower voltage. If it is used to produce DC a rectifier circuit is employed. Depending on the requirements of the load, a linear regulator may be used to reduce the ripple sometimes also allowing for adjustment of the output to the desired but lower voltage. A switched-mode power supply (SMPS) works by directly rectifying an AC input to obtaining DC voltage. Then this voltage is changed back to AC by using electronic switches, but with a much higher frequency (typically 10 kHz — 1 MHz). Higher frequencies require smaller transformers. Then on the transformer secondary the AC is again rectified to DC. To keep output voltage constant, the power supply needs a sophisticated feedback controller Distributing power/ground across a board is often accomplished by planes because they are:
Parallel power and ground planes has zero lead inductance and no ESR. Capacitance of a power plane= 0.225 er A / d where:
Below are some Links to sites containing information about this subject. |
SMPS Switching Power Supply guide- circuit design tutorial, schematics, regulator topologies |
Calculators: |
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Mike Harris, Better Boards, Inc |
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Power supply circuit design problems, solutions, tutorials, tips, and resources. |
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SwitcherPro(TM) Online and Desktop Design Creator and Management Software |
In physics, electromagnetics is the study of how waves behave at different frequencies and how materials react in different ways at different frequencies. With pc boards, the terms that deal with electromagnetics are EMC (ElectroMagnetic Compatibility) and EMI (ElectroMagnetic Interference.) Even if your design doesn't have to meet certain requirements, it still has to operate in the intended environment. Problems caused by EMI are discussed in terms of “aggressor” or “victim.” An aggressor radiates energy or creates stray reactive fields. The victim malfunctions due to interference or ambient fields. Besides the victim/aggressor problems, there is also problems caused by noise. Components, signal traces, and planes combine to form noise sources and antennas. These noise sources must have an amplification mechanism to propagate an electromagnetic field out into space. To reduce radiation levels, simply identify each component as either part of the noise source or part of the antenna. Almost everything in the system is part of the antenna. The antenna is a complex mechanism created by IC lead frames, circuit board signal and power traces, and cables. All IC’s potentially generate noise and, therefore radiate to some degree. There are generally two actions to take: 1) spoil the antenna, and 2) suppress the noise at the source. Improved circuit board layout and more effective bypassing can improve EMI performance.
Below are some Links to sites containing information about this subject. Also included are RF/Microwave resources. |
A material is classified as “dielectric” if it has the ability to store energy when an external electric field is applied. Dielectric properties of the materials used in a printed circuit board effects the electrical properties of the circuits on this board. The dielectric properties of the various materials used in fabrication and packaging play an important role in achieving the desired performance. A basic understanding of dielectric properties is therefore needed. A good reference source would be the "High Frequency Circuit Materials Properties Guide" from Rogers Corporation.
Below are some Links to sites containing information about this subject. |
Network: (electronics) a system of interconnected electronic components or circuits.
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SIGCOMM is ACM's professional forum for discussing communications and computer networks. |
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The UNH-IOL offers downloadable networking tutorial documents in the technologies it has tested. |
Below are some Links to sites containing information about Tools.
| Free Tools | |
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PCB is an interactive printed circuit board editor for the X11 window system. |
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