Home > Articles > Engineering > Communications Engineering

Introduction to Jitter, Noise, and Signal Integrity at High-Speed

This chapter offers basic and high-level introductions to terminology, definitions, and concepts concerning jitter, noise, signal integrity, bit error rate, and working mechanisms for communication link systems. Sources and root causes of jitter, noise, and signal integrity then are discussed, followed by statistical and system views on jitter, noise, and signal integrity. Then we give a historical overview of the evolution of and advancement path for jitter, noise, and signal integrity. This chapter ends by discussing this book's organization and flow.
This chapter is from the book

1.1 Jitter, Noise, and Communication System Basics

The essence of communication is about transmitting and receiving a signal through a medium or channel. An early mathematical model for communication may be tracked back to Claude Shannon's famous 1948 paper.1 Depending on what kind of medium is used to transmit and receive a signal, communication systems are grouped into three basic categories: fiber, copper, and wireless (or free space) (see Figure 1.1). The bandwidths typically are a few THz for fiber and a few GHZ for copper media. Considering the constraints of bandwidth, attenuation, and cost, fiber-based communication is often used for long-distance (> 1 km), high-data-rate (up to > 100 Gb/s per channel) communication. Copper-based communication is used for medium-distance (< 1 km) and medium-high data rates (1 Mb/s to a few Gb/s per channel). Wireless is used for medium distance (~ km) and medium data rates (up to ~100 Mb/s). The choice of a communication medium is largely determined by cost and application requirements. Clearly, fiber has the highest intrinsic bandwidth, so it can deliver the highest data rate possible for a single channel.

Figure 1.1

Figure 1.1 A simple communication system, including three basic building blocks: transmitter, medium, and receiver.

1.1.1 What Are Jitter, Noise, and Signal Integrity?

When a signal is transmitted and received, a physical process called noise is always associated with it. Noise is basically any undesired signals added to the ideal signal. In the context of digital communication, the information is encoded in logical bits of 1 and 0. An ideal signal may be represented by a trapezoid wave with a finite 0 to 1 rise time or 1 to 0 fall time. In the presence of noise, it is the sum of ideal signal, with the noise giving rise to the "net" or actual signal waveform. If no noise is added, the actual signal is identical to the ideal signal waveform. If the noise is added, the actual signal is deviated from the ideal signal, as shown in Figure 1.2.

Figure 1.2

Figure 1.2 An ideal signal versus a noisy signal for a digital waveform.

The deviation of a noisy signal from its ideal can be viewed from two aspects: timing deviation and amplitude deviation. The amplitude of the digital signal for a copper-based system is the voltage, and for a fiber-based or radio frequency (RF) wireless system it is the power. The deviation of the signal amplitude (ΔA) is defined as the amplitude noise (or simply noise), and the deviation of time (Δt) is defined as the timing jitter (or simply jitter). Those definitions will be used throughout this book. The impacts of timing jitter and amplitude noise are not symmetrical, though. Amplitude noise is a constant function and can affect system performance all the time. Timing jitter affects system performance only when an edge transition exists.

Signal integrity generally is defined as any deviation from ideal waveform.2 As such, signal integrity contains both amplitude noise and timing jitter in a broad sense. However, certain signal integrity signatures such as overshoot, undershoot, and ringing (see Figure 1.3) may not be well covered by either noise or jitter alone.

Figure 1.3

Figure 1.3 Some signal integrity key signatures.

1.1.2 How Do Jitter and Noise Impact the Performance of a Communication System?

There is no doubt that jitter, noise, and signal integrity all impact the quality of a communication system. The following sections discuss and illustrate how jitter and noise cause a bit error and under what conditions this bit error occurs. Then the metric that is commonly used to quantify the bit error rate in a communication system is discussed.

1.1.2.1 Bit Error Mechanisms

The impacts of timing jitter and amplitude noise can best be understood from the perspective of a receiver for a communication system.3 A receiver samples the incoming logical 1 pulse data at a sampling time of ts and threshold voltage of vs, as shown in Figure 1.4. For a jitter- and noise-free digital pulse, an ideal receiver samples the data at the center of the incoming pulse. In this context, clearly there is no need to talk about signal integrity, because its effects are covered by jitter and noise. Under such conditions, threshold crossing times for rising and falling edges satisfying the conditions of tr < ts <tf and V1 > vs result in a logical 1 being detected, and the data bit is received correctly (see part (a) of Figure 1.4). In the presence of jitter and noise, the rising and falling edges can move along the time axis, and the voltage level can move along the amplitude axis. As such, the correct bit detection conditions for sampling time and voltage may not be satisfied, resulting in a bit error due to bit 1 being received/detected as bit 0. The violations of those sampling conditions can occur in three scenarios:

  • The crossing time of the rising edge lags behind the sampling time, or tr > ts.
  • The crossing time of the falling edge is ahead of the sampling time, or tf < ts.
  • The logical 1 voltage is below the sampling voltage vs, or V1 < vs.
Figure 1.4

Figure 1.4 A receiver sampling an incoming data bit 1 (a) and 0 (b), where tr and tf are the timings for the 50% crossing (or zero crossing timings) for the rising and falling edges, respectively, and ts and vs are the sampling time and voltage, respectively.

For a zero pulse or bit "0"detection, in the case of part (b) of Figure 1.4, the correct detection condition becomes tr < ts < tf and V0 < vs. Similarly, the violation of correct sampling condition causes a bit error because bit 0 is received as bit 1. The violation scenarios for timing are similar to those of bit 1 pulse (part (a) of Figure 1.4). However, the violation condition for voltage becomes V0 > vs.

1.1.2.2 Bit Error Rate (BER)

We have demonstrated how jitter and noise cause a digital system bit error with a simple example. Because a digital system transmits and receives many bits for a given time, the system's overall performance can best be described by the rate of bit failure—namely, the ratio of the total failed bits Nf to the total bits received N. This ratio is called the bit error rate (BER) or bit error ratio. Bit error ratio is a more precise definition because BER = Nf/N and no normalization of time is as involved as most of the rate definition otherwise required.

BER is the bottom-line metric for determining a good communication system. At multiple Gb/s rates, the BER requirement for most communication standards such as Fibre Channel (FC), Gigabit Ethernet, SONET, and PCI Express is 10–12 or smaller. Larger BER degrades network or link efficiency and, worse, system latency. A simple implication of BER = 10–12 is that with 1012 bits being transmitted/received, only one bit error is allowed. Clearly BER depends on data rate, jitter, and noise in the communication system. The definition of BER implies that BER is a counting statistic so that Poisson statistics may apply.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020