PCB设计完整性分析：电磁兼容性指南

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"PCB SI（信号完整性）分析是关于印刷电路板设计的一个重要主题，它在确保电子设备的电磁兼容性（EMC）方面发挥着关键作用。这本书《Printed Circuit Board Design Techniques for EMC Compliance: A Handbook for Designers, Second Edition》由Mark I. Montrose撰写，是该领域的一本权威指南。作者通过本书分享了实现PCB设计EMC合规性的技术和策略，旨在帮助设计师解决设计挑战并避免潜在问题。" PCB设计完整性分析涉及到多个关键知识点： 1. **信号完整性（Signal Integrity, SI）**：SI是衡量电路中信号传输质量的一个指标，包括信号的幅度、速度和时序等特性。良好的信号完整性能确保数据在PCB上的准确传输，减少噪声、反射和串扰等问题。 2. **电磁兼容性（Electromagnetic Compatibility, EMC）**：EMC是指设备或系统在其电磁环境中能够正常工作，同时不对其环境中的其他设备产生不可接受的电磁干扰的能力。PCB设计必须遵循EMC标准，以防止电磁辐射对其他电子设备造成干扰。 3. **PCB设计原则**：这包括选择合适的布线策略（如差分对、屏蔽层）、电源平面布局、过孔设计、阻抗控制以及适当的接地策略。每个设计决策都会影响到信号的完整性和系统的EMC性能。 4. **仿真工具**：现代PCB设计中，使用SI/PI（功率完整性）仿真工具是必不可少的，它们可以帮助预测和优化信号的传播，避免潜在的问题。 5. **EMI（电磁干扰）和RFI（射频干扰）**：理解和管理这些干扰是PCB设计中的重要环节，包括通过滤波器设计、屏蔽和接地来抑制不必要的辐射。 6. **多层板设计**：多层PCB设计可以提高布线密度，但也会增加信号完整性和EMC的复杂性。设计师需要考虑如何有效地分配电源和地平面，以及如何在不同层之间进行布线。 7. **测试与验证**：设计完成后，进行实际测试和验证是确保PCB满足SI和EMC要求的关键步骤。这可能包括实验室测试、眼图分析、谐波电流测量等。 8. **法规与标准**：设计者需要熟悉并遵循各种国际和行业标准，如FCC、CE、ICES等，以确保产品在全球范围内符合电磁兼容要求。通过深入学习和应用这些知识点，设计师可以创建出高效、可靠且符合EMC标准的PCB设计。Mark I. Montrose的这本书提供了一个全面的指南，对理解和实践PCB SI分析以及EMC合规性具有很高的价值。

Personal account | University of Southern Queensland

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Table of Contents

Chapter 1

1.1: FUNDAMENTAL

DEFINITIONS

1.2: ELEMENTS OF THE

ELECTROMAGNETIC

ENVIRONMENT

1.3: NATURE OF

INTERFERENCE

1.4: REGULATORY

REQUIREMENTS—NORTH

MERIC

1.5: REGULATORY

REQUIREMENTS—

WORLDWIDE

1.6: STANDARDS

1.7: EMISSION

REQUIREMENTS

1.8: IMMUNITY

REQUIREMENTS

1.9: ADDITIONAL

REGULATORY

REQUIREMENTS—NORTH

MERIC

1.10: SUPPLEMENTAL

INFORMATION

REFERENCES

Chapter 1 - Introduction

Printed Circuit Board Design Techniques for EMC Compliance: A Handbook for Designers, Second Edition

by Mark I. Montrose

IEEE Press

Recommend this title?

1.3 NATURE OF INTERFERENCE

EMC is grouped into two categories: internal and external. The internal

category is the result of signal degradation along a transmission path,

including parasitic coupling between circuits in addition to field coupling

between internal subassemblies, such as a power supply to a disk drive.

Stated more specifically, the problems are signal losses and reflections

along the path, along with crosstalk between adjacent signal traces.

External problems are divided into emissions and immunity. Emissions

derive primarily from harmonics of clocks or other periodic signals.

Remedies concentrate on containing the periodic signal to as small an area

as possible, blocking parasitic coupling paths to the outside world.

Susceptibility to external influences, such as ESD or radio frequency

interference, is related initially to propagated fields that couple into I/O

lines, which then transfer to the inside of the unit, and secondarily to case

shielding. The principal recipients are high-speed transmission lines and

sensitive adjacent traces, particularly those terminated with edge-triggered

components.

There are five major considerations when performing EMC analysis on a

product or design [1].

Frequency

. Where in the frequency spectrum is the problem

observed?

Amplitude

. How strong is the source energy level, and how great is its

potential to cause harmful interference?

Time

. Is the problem continuous (periodic signals), or does it exist

only during certain cycles of operation (e.g., disk drive write operation

or network burst transmission)?

Impedance

. What is the impedance of both the source and receptor

units, and the impedance of the transfer mechanism between the

two?

Dimensions

. What are the physical dimensions of the emitting device

that cause emissions to occur? RF currents will produce

electromagnetic fields that will exit an enclosure through chassis leaks

that equal significant fractions of a wavelength or significant fractions

of a "rise-time distance." Trace lengths on a PCB have a direct

relationship as transmission paths for RF currents.

Whenever an EMI problem is approached, it is helpful to review this list

based on product application. Understanding these five items will clear up

much of the mystery of how EMI exists within a PCB. Applying these five

considerations teaches us that design techniques make sense in certain

contexts but not in others. For example, single-point grounding is excellent

when applied to low-frequency applications, but it is completely

inappropriate for radio frequency signals, which is where most of the EMI

problems occur. Many engineers blindly apply single-point grounding for all

product designs, without realizing that additional and more complex

problems are created using this grounding methodology.

When designing a PCB, we are concerned with current flow within the

assembly. Current is preferable to voltage for a simple reason: current

always travels around a closed-loop circuit following one or more paths. It

Personal account | University of Southern Queensland

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Table of Contents

Chapter 1

1.1: FUNDAMENTAL

DEFINITIONS

1.2: ELEMENTS OF THE

ELECTROMAGNETIC

ENVIRONMENT

1.3: NATURE OF

INTERFERENCE

1.4: REGULATORY

REQUIREMENTS—NORTH

AMERICA

1.5: REGULATORY

REQUIREMENTS—

WORLDWIDE

1.6: STANDARDS

1.7: EMISSION

REQUIREMENTS

1.8: IMMUNITY

REQUIREMENTS

1.9: ADDITIONAL

REGULATORY

REQUIREMENTS—NORTH

MERIC

1.10: SUPPLEMENTAL

INFORMATION

REFERENCES

Chapter 1 - Introduction

Printed Circuit Board Design Techniques for EMC Compliance: A Handbook for Designers, Second Edition

by Mark I. Montrose

IEEE Press

Recommend this title?

1.4 REGULATORY REQUIREMENTS—NORTH

AMERICA

Electrical and electronic products generate RF energy. Electromagnetic

emission levels are set by rules and regulations mandated by domestic and

international governments or agencies. In the United States, the Federal

Communications Commission (FCC) regulates the use of radio and wire

communications. The FCC is an independent government agency,

responsible for ensuring interstate and international communication by

radio, television, satellite, and cable.

In Canada, Industry Canada (IC) is the agency responsible for regulating

radio and wire communication. Industry Canada performs a function similar

to that of the Federal Communications Commission. Harmonized test

requirements and standards for North America exist between both the FCC

and IC.

The FCC regulates electronic products by specifying technical standards

and operational requirements through the Code of the Federal Register

(CFR), Title 47. The sections within 47CFR that are most applicable to

products discussed herein are Parts 2, 15, 18, and 68. These regulations,

developed over many years, are based on complaints filed with the

Commission. The most prominent FCC Parts are summarized in the

following list. In Canada, the specification equivalent to 47CFR, Part 15, is

SOR 88/475.

1. Part 2 is an administrative section that details aspects of how to

comply with 47CFR. Included are allocated frequency bands, radio

treaty matters, and general rules and regulations. The rules and

regulations include registration requirements, authorization

procedures, definitions, and various processes to ensure that the

federal code is properly administered.

2. Part 15 regulates products that generate unlicensed radio frequency

energy, both intentional and non-intentional. Information Technology

Equipment (ITE) falls within Part 15.

3. Part 18 regulates Industrial, Scientific, and Medical (ISM) equipment.

These devices use radio waves for proper operation.

4. Part 68 regulates electronic equipment connected to a telephone

network. This part provides a uniform standard for protecting the

telephone network from harm caused by connection of terminal

equipment.

The FCC defines a digital device as

An unintentional radiator (device or system) that generates and

uses timing signal or pulses at a rate in excess of 9,000 pulses

(cycles) per second and uses digital techniques; inclusive of

telephone equipment that uses digital techniques or any device or

system that generates and uses radio frequency energy for the

purpose of performing data processing functions, such as

electronic computations, operations, transformation, recording,

filing, sorting, storage, retrieval or transfer.

Digital computing products are classified into two categories: Class A and

B. The FCC and IC use the same definitions.

Personal account | University of Southern Queensland

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Table of Contents

Chapter 1

1.1: FUNDAMENTAL

DEFINITIONS

1.2: ELEMENTS OF THE

ELECTROMAGNETIC

ENVIRONMENT

1.3: NATURE OF

INTERFERENCE

1.4: REGULATORY

REQUIREMENTS—NORTH

MERIC

1.5: REGULATORY

REQUIREMENTS—

WORLDWIDE

1.6: STANDARDS

1.7: EMISSION

REQUIREMENTS

1.8: IMMUNITY

REQUIREMENTS

1.9: ADDITIONAL

REGULATORY

REQUIREMENTS—NORTH

MERIC

1.10: SUPPLEMENTAL

INFORMATION

REFERENCES

Chapter 1 - Introduction

Printed Circuit Board Design Techniques for EMC Compliance: A Handbook for Designers, Second Edition

by Mark I. Montrose

IEEE Press

Recommend this title?

1.5 REGULATORY REQUIREMENTS—WORLDWIDE

Test requirements, standards, and procedures have been harmonized on a

worldwide basis. The principles discussed herein will allow regulatory

compliance to be achieved with minimal development cost and shorter

design cycles. The harmonization process is based on the work of expert

technical committees reporting to the International Electrotechnical

Commission (IEC).

The IEC works closely with the International Standards Organization (ISO),

which is chartered by the United Nations. Many countries throughout the

world are members. The IEC oversees the work of technical committees

working on a particular product sector. The IEC's objectives are to

"promote international co-operation on all questions of standardization ...

achieved by issuing publications including recommendations in the form of

international standards."

Two IEC technical committees work on EMC standards. The first is TC77,

Electromagnetic compatibility between equipment including networks

. The

second committee is

International Special Committee on Radio

Interference

(Comité International Spécial des Perturbations

Radioélectriques or CISPR). CISPR publications deal primarily with limits

and measurements of the radio interference characteristics of potentially

disturbing sources or emissions. CISPR and IEC standards coexist to

define most technical aspects related to EMC compliance.

The IEC publications themselves have no legal requirements. National

committees do not have to adopt them, although several countries outside

of Europe have incorporated them into their national laws. The important

aspect of IEC standards is that they have been adopted and harmonized

as a European standard for all members of the European Union. Once

published as a harmonized document, a legal requirement now exists.

A separate organization, the Committee for European Electrotechnical

Standardization (Comité Européen de Normalisation Electrotechnique, or

CENELEC), is responsible for developing European standards for electrical

equipment. CENELEC received its charter from the Parliamentary

Commission of the European Union and produces EMC standards for use

with the EMC Directive, usually based on IEC and CISPR publications.

For telecommunications equipment, the European Telecommunications

Standards Institute, or ETSI, is the standards-making body. ETSI develops

standards for telecommunications network equipment not supplied to the

subscriber, in addition to radio communication equipment and broadcast

transmitters.

CENELEC and ETSI adopt IEC and CISPR publications, whenever

possible, as a basis for preparing a formal standard. The CENELEC

committee responsible for preparing EMC standards is TC110. Technical

Committee TC110 has several subcommittees, including SC110A, which is

responsible for immunity requirements of Information Technology

Equipment (ITE).

International EMC publications are commonly referred to as CISPR or IEC,

when in fact the real standard, after adoption and publication by the

European Commission, is prefixed with an EN (European Normalization)

number. To summarize, the European Commission adopts into law

requirements developed by CISPR and the IEC, as well as other European

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