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1486 results in Circuits and systems

Page 18 of 75

  • 7 - Effects of Jitter in Wireline Applications

  • Nicola Da Dalt, Ali Sheikholeslami, University of Toronto
  • Book:
    Understanding Jitter and Phase Noise
    Published online:
    19 February 2018
    Print publication:
    22 February 2018, pp 143-173

  • Summary

    A wireline communication system sends and receives data based on precise timing. Any deviation from the ideal timing, i.e., jitter, has a direct impact on the bit error rate (BER) at the receiver. Figure 7.1 shows a generic block diagram of a wireline transceiver that consists of a transmitter, a channel, and a receiver. The role of the transmitter is to serialize N binary sequences, generated by the core logic, into one binary sequence DTX, and send it reliably over the channel to the receiver. If we assume, for example, that the core logic produces 16 data sequences (i.e., N = 16), each at 500Mb/s, then the transmitter will produce a single binary sequence at 8Gb/s. The channel could be a few meters of cable (e.g., between a computer and a peripheral), a few inches of PCB trace (e.g., between a microprocessor and a memory module on the same board), or a few millimeters of an interconnect in a multi-chip module. In all these cases, the channel tends to attenuate the high-frequency components of the signal, and degrade the received eye both in the voltage domain (vertical axis) and in the time domain (horizontal axis). The received signal timing is further degraded due to the jitter in the transmitter clock (CKTX), which in turn may be caused by thermal noise in the clock generation circuit or by power supply noise. In the presence of all these jitter components, the receiver must be designed so as to recover the transmit bits reliably, e.g., at a BER better than 10-12 or 10-15. In this chapter, we first review various sources of the jitter that limits the BER, and then provide techniques for jitter characterization, jitter monitoring, and jitter mitigation.

    As mentioned in Chapter 1, jitter does not always work against performance; there are cases where we can use jitter to improve system performance. We provide two such examples later in this chapter.

    Basic Concepts in Wireline Signaling

    A wireline transmitter, in its simplest form, sends a non-return-to-zero (NRZ) binary signal to the receiver. The wireline receiver first equalizes the received signal so as to compensate for the channel loss (or equivalently to remove the channel ISI) and then samples the equalized signal, using a recovered clock at the center of the data eye to see whether the sampled value is above or below a threshold.

  • 2 - Basics of Jitter

  • Nicola Da Dalt, Ali Sheikholeslami, University of Toronto
  • Book:
    Understanding Jitter and Phase Noise
    Published online:
    19 February 2018
    Print publication:
    22 February 2018, pp 15-42

  • Summary

    In the industry as well as in academia, the concept of jitter is sometimes treated using approximations, leading to misunderstandings and possibly to systems which are not optimally designed with respect to jitter performance. This chapter lays the foundation for a thorough and clear understanding of jitter in practice.

    The chapter starts by providing four fundamental definitions of jitter: absolute jitter, relative jitter, period jitter and N-period jitter. It proceeds with an overview of other jitter definitions commonly found in literature. It will be shown that these additional definitions can be expressed in terms of the four fundamental jitter definitions.

    A large part of the chapter handles the important topic of jitter statistics and the estimation of key parameters such as root mean square (RMS) and peak or peak-peak values. This will lead to the classification of jitter based on its distribution, and eventually to the introduction and explanation of the concepts of deterministic jitter, random jitter and total jitter.

    General Jitter Terminology and Definitions

    A variety of terms are commonly used to express the concept of jitter, and several different definitions can be found in the open literature, mostly dependent on the particular background of the author or on the specific application considered. A short and incomplete list of these terms includes period jitter, cycle jitter, cycle-to-cycle jitter, N-period jitter, accumulated jitter, adjacent jitter and long-term jitter. It is not uncommon to find the same term used with different meanings by different authors, leading to possible misunderstandings and confusion.

    In this chapter jitter will be defined according to the way it can be measured, at least in principle. This will not result in jitter definitions that are different from the ones already found in the literature; rather, it will put the existing definitions in a clear and solid framework. These operative definitions of jitter turn out to be very intuitive, simple and of high practical value. Since the definition is connected to a measurement process, it is easier to relate it to a specific application. And, conversely, given a specific application, this approach makes it is easier to find the relevant jitter definition.

    Generally speaking, jitter is the deviation of the time instant at which a given event occurs, relative to a reference time frame, which can be chosen arbitrarily.

  • 8 - Phase Noise in Wireless Applications

  • Nicola Da Dalt, Ali Sheikholeslami, University of Toronto
  • Book:
    Understanding Jitter and Phase Noise
    Published online:
    19 February 2018
    Print publication:
    22 February 2018, pp 174-182

  • Summary

    A wireless transceiver typically uses a PLL at the transmitter to up-convert a baseband signal to an RF frequency and uses another PLL at the receiver to down-convert the RF signal back to the baseband. Depending on the quality of the PLL clock, which is often measured by its phase noise, the process of up-conversion and down-conversion produces unwanted signals which often interfere with signals in adjacent channels and deteriorate the SNR at the receiver. In this chapter, we first provide a brief background on the transmitter and receiver concepts, and then discuss the impact of PLL phase noise on transceiver performance.

    Basics of Wireless Transceivers

    Figure 8.1(a) shows the block diagram of a simplified wireless transmitter, in which a baseband signal is up-converted to an RF frequency in a two-step process: first to an intermediate frequency (IF), and then to an RF frequency, using a local oscillator (inside a PLL). The RF signal is then fed to a bandpass filter (BPF) followed by a power amplifier (PA) and the antenna. If the oscillator produces a pure single tone, the up-converted signal will simply contain the baseband signal translated (shifted) in frequency to fRF. If the baseband signal has a bandwidth of B, the RF signal will have a bandwidth of 2B, as shown in Figure 8.1(b). However, due to the phase noise of the oscillator, the up-converted signal will also contain frequency content outside the 2B bandwidth, which may contribute to noise in adjacent receiver channels. The BPF allows the signal and the noise content within the 2B bandwidth to pass but attenuates the phase noise and other noise content that lie outside the 2B bandwidth. The PA amplifies the power of the RF signal so as to extend its reach to the intended receivers.

    A simplified block diagram of a wireless receiver is shown in Figure 8.2(a). The received signal from the antenna is first filtered by an off-chip surface acoustic wave (SAW) filter, then passed to a low noise amplifier (LNA), and subsequently to a mixer that down-converts the RF signal either to an intermediate frequency (IF) or directly to DC for further filtering.

  • 4 - Jitter and Phase Noise in Circuits

  • Nicola Da Dalt, Ali Sheikholeslami, University of Toronto
  • Book:
    Understanding Jitter and Phase Noise
    Published online:
    19 February 2018
    Print publication:
    22 February 2018, pp 69-110

  • Summary

    This chapter will offer an introduction to how jitter and phase noise are generated in the most common oscillator topologies. Starting with the treatment of basic circuits like a current charging a capacitor, or an inverter, we will continue by analyzing jitter and phase noise generation in ring, relaxation, and LC oscillators. Both linear time invariant and linear time variant approaches will be illustrated.

    The chapter will finish with an overview of how jitter is “transformed” by two of the most common frequency processing circuits: a digital frequency divider and an ideal frequency multiplier.

    Jitter in Basic Circuits

    The next sections provide an explanation, both qualitative and quantitative, of how jitter manifests itself in basic oscillator circuits.

    Noisy Current Charging a Capacitor

    As mentioned already in Section 1.3, in integrated circuit design a central element is a current loading a capacitor. Digital gates, clock buffers, delay elements of relaxation and ring oscillators are just few examples of where this element can be found. Due to its ubiquity and importance, it is worth analyzing in some detail from the standpoint of jitter generation. In the following we will revisit the example provided in Section 1.3, and treat it with a complete mathematical analysis. The case of a PMOS transistor charging a capacitor is shown in Figure 4.1. The case of an NMOS discharging the capacitor is identical.

    The goal of this analysis is to derive an expression for the variation of the time instant at which the charging voltage crosses a given threshold V0 (see Figure 4.1). The first step is to recognize that the resulting time deviation is due to two different components. The first is the effect of the noise current in injected into the capacitor by the PMOS during the charging transient. The second is due to the fact that, even if the capacitor is considered discharged at time zero, there is voltage noise present on it due to the circuitry which is used to keep it discharged. This noise can be considered as a random initial vertical offset which will affect the threshold crossing time.

  • Appendix A - Review of Random Variables and Processes

  • Nicola Da Dalt, Ali Sheikholeslami, University of Toronto
  • Book:
    Understanding Jitter and Phase Noise
    Published online:
    19 February 2018
    Print publication:
    22 February 2018, pp 220-232

  • Summary

    This appendix reviews in a very compact form the basic concepts of random variables and random processes for the purpose of understanding jitter and phase noise. The goal is not to provide a thorough treatment, but rather to help the reader in recalling the definitions and the meanings of some of the most useful and common concepts. It is assumed that the reader is familiar with the basic concepts of probability. Although not strictly necessary, it is beneficial that the reader has been previously exposed to the theory of random variables and random processes, as can be found in a typical graduate university class. For further reading, or an in-depth analysis of the concepts, such specialized textbooks as [1], [13], [129], and [105] can be consulted.

    Random Variables

    Definition

    Given an experiment with many possible outcomes, a random variable X is defined as a function that assigns a real number to each outcome of this experiment. In order to be called a random variable, the function must satisfy the following condition: the set of outcomes for which X is smaller than or equal to a given real number a, has a given, well-defined probability for any a.

    As an example, let's take as an experiment the toss of a dice. The possible outcomes are each of the six faces of the dice. We can associate with each face the integer numbers 1 to 6, even if there are no numbers (or dots) on the faces of the dice (assuming that we can distinguish each of the faces of the dice somehow). This rule of association can be formalized as a function X which can assume the values 1, 2, 3, 4, 5, 6. Given any real number a, the probability that X < a is always well defined. For instance, the probability that X ≤ 3.4567 is equal to the probability that the dice shows one of the faces associated with the numbers 1 to 3. The probability that X ≤ -1 is obviously zero, since there is no possible outcome associated to numbers below 1. Since the condition stated in the above paragraph is satisfied, X can be called a random variable.

    Note that the name “random variable” is, strictly speaking, a misnomer, since it refers to a function, not to a variable.

  • 1 - Introduction to Jitter

  • Nicola Da Dalt, Ali Sheikholeslami, University of Toronto
  • Book:
    Understanding Jitter and Phase Noise
    Published online:
    19 February 2018
    Print publication:
    22 February 2018, pp 1-14

  • Summary

    Imagine a lunar eclipse is to occur later tonight at around 1:57 am when you are fast asleep. You decide to set your camera to capture the event, but being uncertain of the actual time, you would set the camera to start a few minutes before the nominal time and run it for a few minutes after 1:57 am. In this process, you have included a margin around the nominal time so as to minimize the risk of not capturing the event on your camera.

    Imagine you have an important meeting at 8:00 am sharp, but you are uncertain about your watch being a bit too fast or too slow. Determined not to be late, you decide to arrive by 7:55 am according to your watch, just in case your watch is a bit slow. This is indeed a practical way to deal with uncertainty in time.

    Imagine you have a ticket for the bullet train in Tokyo that leaves the train station at 1:12 pm sharp. You are at the station and on the right platform, and you take the train that leaves the station at 1:12 pm sharp. But a few minutes later, you notice that your watch is two minutes fast compared to the time being displayed on the train, and you realize that you are on the 1:10 pm train and you are moving towards a different destination.

    Missing an event, being late or early, and getting on the wrong train are all consequences of timing uncertainties in our daily lives. In digital circuits, we deal with very similar situations when we try to time events by a clock that has its own timing uncertainty, called jitter, and in doing so we may miss an event, such as not capturing critical data, or cause bit errors, e.g., capturing the wrong data. Our goal, however, is to prevent such errors from occurring, or to minimize their probabilities. We do this first by carefully studying the nature of these uncertainties and modeling their characteristics.

    This chapter provides a few concrete examples from electronic circuits and systems where timing uncertainties have a profound impact on the accuracy of their operation. Our goal here is to qualitatively introduce the concept of jitter and intuitively explain how it should be characterized and dealt with.

Understanding Jitter and Phase Noise
  • A Circuits and Systems Perspective
  • Nicola Da Dalt, Ali Sheikholeslami
  • Published online:
    19 February 2018
    Print publication:
    22 February 2018
  • Gain an intuitive understanding of jitter and phase noise with this authoritative guide. Leading researchers provide expert insights on a wide range of topics, from general theory and the effects of jitter on circuits and systems, to key statistical properties and numerical techniques. Using the tools provided in this book, you will learn how and when jitter and phase noise occur, their relationship with one another, how they can degrade circuit performance, and how to mitigate their effects - all in the context of the most recent research in the field. Examine the impact of jitter in key application areas, including digital circuits and systems, data converters, wirelines, and wireless systems, and learn how to simulate it using the accompanying Matlab code. Supported by additional examples and exercises online, this is a one-stop guide for graduate students and practicing engineers interested in improving the performance of modern electronic circuits and systems.

  • Preface

  • Andrew G. Webb
  • Book:
    Principles of Biomedical Instrumentation
    Published online:
    11 August 2019
    Print publication:
    11 January 2018, pp xi-xv

  • Summary

    The main aim of this textbook is to provide the tools to understand the function and design of different biomedical instruments and devices, and for the reader to be able to use these tools to envision new and improved future technology and designs. Throughout the book the terms medical and biomedical are used interchangeably, and similarly with the terms device and instrument. With several thousand instruments and devices on the market it is clearly impossible to consider more than a handful in detail. Instead, this book concentrates on the following general approach.

  • (i) What is the clinically relevant measurement that needs to be made?

  • (ii) What are the pathophysiological mechanisms that give rise to the clinical condition?

  • (iii) What are the characteristics (e.g. magnitude, frequency, bandwidth) of the signal to be measured? How accurate and reproducible does the measurement have to be? What are the interfering signals that have to be suppressed?

  • (iv) What are the recommended instrumental specifications for the particular device? How does one design the device to meet these specifications?

  • (v) How does one test the biocompatibility and electrical safety of such a device, whether it is external or implanted, so that it can operate safely for a number of years?

    • Traditionally, most of these instruments and devices have been located in a hospital, and patients travel to the clinics for the measurements to be performed by trained personnel. However, this model is changing and nowadays there is an increasing role for what is termed mobile health (m-health), which involves a much greater degree of healthcare being performed by the patients themselves at home. This means that a biomedical device must operate in the patient's home environment without specialized training, as well as transmit the data wirelessly and securely to the physician. This model of continuous patient monitoring not only provides a much more complete assessment of the patient's health, but also reduces the number of visits that a patient has to make to the hospital.

    The main areas of technological development that have enabled the rapid incorporation of m-health into the healthcare infrastructure are wearable and implantable devices that can transmit data to the physician via mobile phone networks.

  • 9 - Safety of Biomedical Instruments and Devices

  • Andrew G. Webb
  • Book:
    Principles of Biomedical Instrumentation
    Published online:
    11 August 2019
    Print publication:
    11 January 2018, pp 271-307

  • Summary

    Introduction

    Every year many thousands of patients receive some form of electrical shock from medical devices and instruments. These are typically not fatal and do not cause serious injury, but rather result in significant discomfort to the patient and may cause effects such as ventricular fibrillation. There are many incidents of physicians and nurses also receiving electric shocks. These events occur despite strict regulations to ensure the electrical safety of all medical devices. Although some events occur due to a design flaw in a particular device, the most common situation in which electrical shocks occur is one in which a patient is hooked up to many different devices in the operating room (OR), as shown in Figure 9.1. These devices might include defibrillators, pacemakers, ultrasound scanning equipment, cardiac catheters and EEG equipment to monitor anaesthesia. In addition, there are a number of ancillary devices such as high intensity lights and intravenous lines, which are attached to, or close to, the patient. Conductive body fluids also result in unintended conduction paths close to the patient or in the medical device itself if these fluids come into contact with the equipment. In general, medical equipment, and particularly the power cords and power cables feeding the equipment, see many years of use, and it is estimated that over 70% of electrical ‘incidents’ occur due to wear and tear on the power cords, which are regularly run over or mechanically stressed. The electrical insulation around equipment also becomes damaged over time during normal operation. In order to govern the design of medical equipment, regulatory bodies have produced documents to safeguard patients, and the IEC has produced a standard, the IEC 60601 Medical Electrical Equipment – Part 1: General Requirements for Safety and Essential Performance. A brief description of the tests that must be performed before installation, and for regular maintenance, is covered in section 9.5 of this chapter.

    One can analyze the different potential danger points in terms of the possibility that multiples of these are present, and can cause a potential electrical shock to the patient or physician, as shown in Figure 9.2.

  • 8 - Mobile Health, Wearable Health Technology and Wireless Implanted Devices

  • Andrew G. Webb
  • Book:
    Principles of Biomedical Instrumentation
    Published online:
    11 August 2019
    Print publication:
    11 January 2018, pp 235-270

  • Summary

    Introduction

    The standard model of healthcare is that a patient with disease symptoms visits a general practitioner, who refers the case to a specialized physician at a hospital. The patient then visits the specialist who orders a battery of tests and scans. Some time later, when the results of the tests and scans have been interpreted, the patient revisits the hospital and the appropriate therapeutic course is prescribed. At regular periods the patient may be asked to revisit the hospital, whereupon updated tests are performed, progress assessed and any necessary changes to the medication are implemented.

    There are several obvious inefficiencies in this process. First is the lack of any prior information that can be transmitted to the general practitioner before the patient's initial visit. Second is the requirement for the patient to visit the hospital multiple times. Perhaps the most important limitation is the lack of continuous monitoring of the patient's situation after therapy has started. Infrequent visits to the hospital provide only a snapshot of the entire treatment process. While the process may merely be inconvenient in the developed world, the entire concept breaks down in many developing countries.

    This chapter considers the design of software and hardware that can be used to provide continuous information from a patient to a physician and vice versa, as well as from a device to the patient and the physician, all without the patient being required to be physically present at the hospital. Figure 8.1 schematically represents different ways in which information transfer can be achieved. In order of increasing complexity, the general areas covered are:

  • (i) the use of mobile/smartphone utilities for information dissemination and patient reminders: this comes under the general description of mobile health

  • (ii) the design of wearable activity monitors that can wirelessly upload data to the patient and physician

  • (iii) the application of physical patches that can be attached to the skin and record heart rate, blood pressure, sweat, temperature etc. and can wirelessly send data to the hospital

  • (iv) the design and operation of implanted monitoring devices such as continuous glucose monitors, which can wirelessly transmit data through the body to a recording device that provides feedback to the patient and the physician, and

  • 5 - Electrocardiography

  • Andrew G. Webb
  • Book:
    Principles of Biomedical Instrumentation
    Published online:
    11 August 2019
    Print publication:
    11 January 2018, pp 140-168

  • Summary

    Introduction

    An ECG, also sometimes referred to as an EKG from the original German word ‘electrokardiogram’, measures the electrical activity of the heart [1]. This electrical activity produces the contractions and relaxations of the cardiac muscles required to pump blood around the body. An ECG is recorded over a series of cardiac cycles (heartbeats) and shows the different phases of the cardiac cycle. The ECG indirectly measures transmembrane voltages in myocardial cells that depolarize and repolarize within each cardiac cycle. These depolarization and repolarization events produce ionic currents within the body, and these are transduced into voltages by electrodes (described in Chapter 2) placed on the surface of the chest and thorax, as shown in Figures 5.1(a) and (b). Up to twelve different lead voltages are recorded, with the magnitude of the voltages being in the low mV range, Figure 5.1(c), and a frequency spectrum between 0 and 30 Hz, as shown in Figure 5.1(d). The ECG signal has many distinct features, such as the P-wave, QRS-complex and T-wave, illustrated in Figure 5.1(c). The amplitude, shape and relative timing of these features can be used to diagnose different clinical conditions.

    An ECG is an essential part of diagnosing and treating patients with acute coronary syndromes and is the most accurate method of diagnosing ventricular conduction disturbances and cardiac arrhythmias. It is also used to diagnose heart conditions such as myocardial infarcts, atrial enlargements, ventricular hypertrophies and blocks of the various bundle branches. An ECG is universally used to monitor a patient's cardiac activity during surgery.

    Most ECG machines are now digital and automated, meaning that the data is analyzed automatically. Software algorithms measure different aspects (such as delays, durations and slopes) of the ECG waveform and provide a set of keyword interpretations of the scan such as ‘abnormal ECG’ or more specific suggested diagnoses such as ‘possible sinoatrial malfunction’. The most common software package is the University of Glasgow algorithm, which is outlined in detail in section 5.4.1. The major interference signals are caused by electromagnetic coupling from external sources such as power lines, which must be removed by appropriate filtering.

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