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1562 results in RF and microwave engineering

Page 10 of 79

  • 9 - Power Management

  • from Part III - Challenges, Approaches, and Emerging Topics
  • Dinh Thai Hoang, University of Technology, Sydney, Dusit Niyato, Nanyang Technological University, Singapore, Dong In Kim, Sungkyunkwan University, Seoul, Nguyen Van Huynh, University of Technology, Sydney, Shimin Gong
  • Book:
    Ambient Backscatter Communication Networks
    Published online:
    24 April 2020
    Print publication:
    30 April 2020, pp 245-274

  • Summary

    In this chapter, we introduce power management issues for ambient backscattercommunication systems (ABCSs). We first present the reduction of power consumption for backscatter communication in components perspective. Then, typical prototypes and circuit designs of ABCSs are presented. After presenting protocols and strategies for ambient backscatter communication in radio-frequency-powered cognitive radio networks and wireless-powered communication networks, we discuss two representative backscatter communication protocols: hybrid backscatter communication and backscatter-based cooperative communication in wireless-powered heterogeneous networks. Finally, challenges and future research directions are given with concluding remarks.

Ambient Backscatter Communication Networks
  • Dinh Thai Hoang, Dusit Niyato, Dong In Kim, Nguyen Van Huynh, Shimin Gong
  • Published online:
    24 April 2020
    Print publication:
    30 April 2020
  • Understand the fundamental principles and applications of ambient backscatter technology with this authoritative review. Covering both theory and practical engineering, leading researchers describe and explain hardware design, network design, and signal processing, and discuss architectures, protocols, communication methods, open research issues, emerging applications, and advanced system models with innovative solutions. This is an essential tool for graduate students, researchers, engineers, developers, and entrepreneurs.

  • 12 - Audio Signal Processing and Anti-aliasing Filters

  • Muzaffer Ahmad Siddiqi
  • Book:
    Continuous Time Active Analog Filters
    Published online:
    24 December 2019
    Print publication:
    26 March 2020, pp 360-397

  • Summary

    Introduction

    Two important areas of analog filter applications are included in this chapter: audio signal processing (ASP) and study of anti-aliasing/reconstruction (AA/ReF) filters.

    In ASP, the frequency range of operation is from a few Hz to around 20 kHz. All the different types of filters, that is, LP (low pass), BP (band pass), HP (high pass), BE (band elimination) and AP (all pass) filters, can be used. Hence, in most applications, general purpose OAs (operational amplifiers) may be used while taking care of noise signals. Generally, order of the filters may not be very high; whereas, in AA/ReF, only LPFs are used for which the frequency range of operation depends on specific applications. Hence, the selection of OA is to be considered carefully. Order of the filter can also be high.

    One of the major objectives in ASP is to improve audio signals employing different approaches. Section 12.2 discusses this aspect in terms of crossover networks and filters eliminating infrasonic and ultrasonic undesired signals. Section 12.3 discusses a specific case which addresses the unequal power output requirements of the satellite speaker and the subwoofer speaker system. Equalization using mid treble boost/cut and mid bass boost/cut, which are part of programmable equalizers are studied in Section 12.4. Section 12.5 takes up certain aspects of the Record Industry Association of America (RIAA) in brief. An application of phase approximated filters in ASP is explained in Section 12.6.

    The essential nature of AA/ReF filters is described in Section 12.7 citing the example of a filter design for a 12-bit ADC. A detailed case is presented in Sections 12.8 and 12.9 showing the application of high frequency AA and ReF filters used in video signal processing.

    Improvement in Audio Performance

    Problems in the frequency response of audio systems and loudspeakers are resolved using active analog audio filters. Of course, the ways these filters are used depend on the required end result. For example, in some cases, filters are required to produce a response which is nearly the inverse of the response of the (say) loudspeaker or any other audio speaker. Hence, when the two responses are combined, it results in a nearly flat response.

  • 4 - Delay: Approximation and Optimization

  • Muzaffer Ahmad Siddiqi
  • Book:
    Continuous Time Active Analog Filters
    Published online:
    24 December 2019
    Print publication:
    26 March 2020, pp 101-124

  • Summary

    Introduction

    While studying magnitude approximations in Chapter 3, real rational functions were selected in order to achieve desirable attenuation in the stop band and pass band. Not much attention was paid on the unintentional occurrence of phase shift or delay. It has been observed that this delay is neither the same for different approximations nor is it constant. In fact, filter delay is highly dependent on the type of approximation, order of the filter and its parameters. As an example, normalized delay for a fourth-order maximally flat, Chebyshev, inverse Chebyshev and Cauer or elliptic filter, with equal order of pass band attenuation in each case, is shown in Figure 4.1. It can be observed that the delay performance in the maximally flat case is the closest to the ideal requirement of constant delay with frequency. Performance is the worst for the elliptic filter and intermediate for the Chebyshev and the inverse Chebyshev cases. It is important to note that though Figure 4.1 is only a representative sketch, the nature of the functions remain the same: maxima of the delay occur near the pass band edge and relative maxima are dependent on filter specifications in the pass and stop bands.

    It is important to have the group delay as constant or the phase response of the filter as linear with frequency. This requirement for filters is necessary in order to process the magnitude and because in many applications, the amount of delay needs to be controlled at the same time. For example, in a telephonic conversation through satellite, generally, the communication channel is active one way and the listener speaks only when the speaker from the other side stops. However, if the delay is too large, two-way conversation will become difficult and sometimes overlapping.

    From this brief discussion, it is clear that in order to avoid distortion due to different phase/group delay in a filter, an ideal transfer function should have its delay constant with frequency.

    In Section 4.2, delay is defined. Its relation with the phase change in a filter section and the normalized transfer function of a filter realizing delay are also discussed in detail.

  • 10 - Cascade Approach: Optimization and Tuning

  • Muzaffer Ahmad Siddiqi
  • Book:
    Continuous Time Active Analog Filters
    Published online:
    24 December 2019
    Print publication:
    26 March 2020, pp 299-333

  • Summary

    Introduction

    In Chapter 2, a number of first-order active filters were realized along with the basic configuration of bilinear functions. Chapters 7 and 8 were devoted to the development of second-order filter sections using one or more than one OA (operational amplifier). However, as mentioned earlier, all filter specifications are not achievable only through second-order sections; higher-order filters become necessary. For the realization of higher-order filters, ladder simulation techniques through element (inductor/frequency dependent negative resistor: FDNR) substitution was discussed in Chapter 9. Ladder simulation using signal flow graph technique, which is better known as the operationally simulated method was also discussed in Chapter 9. The present chapter deals with another basic method of realizing higher-order filter sections known as the cascade design method.

    Section 10.2 will discuss the basics of cascade design and the conditions to be satisfied by first- or second-order sections in order that these could be used for cascading and obtaining higher-order filters. After taking up some examples of cascade design, the importance of cascade optimization will be discussed in Section 10.3 through an example section. While cascading a number of second-order sections, a proper combination of poles and zeroes (Section 10.3.1), correct assignment of gain for each section (Section 10.3.2) and their proper order (Section 10.3.2) play a very crucial role. Hence, all the three aspects will be discussed in some details.

    It is well-known that due to the tolerance associated with passive elements as well as with the parameters of the active elements, and their possible variation due to the change in the biasing voltage and operating temperature, filter parameters gets deviated. Therefore, it is imperative to provide on-chip tuning of the parameters, especially the pole frequency ωo and pole-Q of the individual second-order sections used in the cascade. This chapter introduces the idea of filter parameter tuning. In Section 10.4, we get a better insight into the cascade design method of filter design.

    Cascade Design Basics

    To realize higher-order filters, cascading of second-order sections finds considerable favour in the eyes of a majority of filter designers; a first-order section is also cascaded in case of an oddorder filter. It will be shown later that such a technique has few advantages like the ability to tune filter parameters easily, and that it possess controlled tunability of the filter parameters with respect to the elements used.

  • 16 - Current Conveyors and CDTA (Current Differencing Transconductance Amplifiers) Based Filters

  • Muzaffer Ahmad Siddiqi
  • Book:
    Continuous Time Active Analog Filters
    Published online:
    24 December 2019
    Print publication:
    26 March 2020, pp 493-537

  • Summary

    Introduction

    All conventional analog circuits are voltage mode (VM) circuits, where the performance of the circuit is determined in terms of voltage levels at all nodes including those at the input and output nodes; operational amplifiers (OAs), being the most commonly used active device, is a voltage controlled voltage source (VCVS). Unfortunately, VM circuits do suffer from some limitations: (i) voltages in the circuit cannot change very quickly when input voltage changes suddenly due to parasitic capacitances; (ii) the bandwidth of OA based circuits is usually limited to the audio frequency range unless high bandwidth OAs are used; and (iii) circuits generally do not have high voltage swings and require high supply voltages for better signal-to-noise ratio.

    In the current mode (CM) approach, the circuit description is presented in terms of current. This implies that all signals, including those at the input and the output are taken in terms of current rather than voltage and the active devices used are preferably CM devices. Hence, CM signal processing techniques can be defined as the processing of current signals in an environment where voltage signals become irrelevant in determining circuit performance, although CM devices do generate VM circuits as well [16.1].

    Advancements in IC (integrated circuits) technologies together with the demand for smaller and low power devices have necessitated in the development of monolithic IC filters, not only at audio frequency but at a much higher frequency range. The advent of sub-micron IC processing (0.5 μm and smaller) has facilitated the realization of filters even in the VHF frequency (30–300 MHz) band. Together with its high frequency operation, reduction in power consumption is another advantage of CM filter circuits. In view of this, attention is being paid toward signal processing in terms of current rather than voltage. This new type of signal processing is known as CM signal processing and is evolving into a better alternative to VM signal processing, especially in the high frequency region.

    CM signal processing leads to a higher frequency range of operation because the signal current is delivered to a small (ideally short circuit) load resistance. Due to this small resistance, the parasitic pole frequency becomes very high. As a result, signals are processed without any appreciable deviation for much larger frequencies.

  • 13 - Follow the Leader Feedback Filters

  • Muzaffer Ahmad Siddiqi
  • Book:
    Continuous Time Active Analog Filters
    Published online:
    24 December 2019
    Print publication:
    26 March 2020, pp 398-423

  • Summary

    Introduction

    One of the important issues in filter design is that parameter sensitivity has to be taken into consideration. A doubly terminated ladder is extensively used mainly because of the same reason, that is, parameters of the filter realized through it have low sensitivities. At the same time, an alternate synthesis method using the cascade approach has found favour because of its ability to tune specific pole–zeros in higher-order filters through the utilization of noninteractive second-order sections. However, in the cascade process, sensitivities increase, especially for high-Q filters. Since we know that negative feedback improves the performance of electronic circuits in a number of ways, the same have been applied to obtain what is known as multiple feedback (MF) topologies. An MF topology consists of a network with a single feed-forward path comprising unilateral (active structures are mostly unilateral unlike passive structures which are bilateral) second-order sections, having different kind of feedbacks. The nature of the feedback decides its final topology. One of the topologies is called leap frog and was discussed in Chapter 9. While performing operational simulation, the circuit had a topology shown in Figures 9.22 and 9.24, where it is easy to recognize the structure as a leap frog structure. Another topology under the broad area of MF topologies known as follow the leader feedback (FLF) is the subject of this chapter.

    In Section 13.2, the basic FLF structure and the kind of transfer functions obtained is included. Also included in this section is the derivation of the structure's transfer function when either lossless integrators or lossy integrators are used in the feedback paths. Use of only a feedback block could provide all pole functions. Hence, feed-forward is also included, as will be discussed in Section 13.3, to improve the versatility of the scheme. A slightly modified feed-forward scheme, called the shifted companion structure is discussed in Section 13.4. It was observed that all these schemes were special cases of a general FLF structure that is given in Section 13.5. Without sacrificing the generality, synthesis of the filter becomes a bit easier if the feedback blocks have BP structures with equal value of quality factor, instead of different quality factors. Such a scheme, known as the primary resonator block technique is also discussed in this chapter.

  • 14 - Switched Capacitor Circuits

  • Muzaffer Ahmad Siddiqi
  • Book:
    Continuous Time Active Analog Filters
    Published online:
    24 December 2019
    Print publication:
    26 March 2020, pp 424-452

  • Summary

    Introduction

    To meet the advances in technology, realization of monolithic electronic analog filters became an important issue. In the beginning, the problem of inductance realization was solved through its simulation using active RC circuits. However, integration needed the solution of a few more problems such that the realized filters perform as close to the design as possible. One of the main issues faced while integrating circuits was the amount of tolerance in passive elements; it was too large. This large tolerance resulted in large errors in the realized filter parameters. These errors could be reduced through electronic tuning of components or the tuning of filter parameters, with an obvious increase in circuit complexities. It was observed that the need of electronic tuning could be reduced through schemes in which filter parameters depend on the ratio of passive components, especially capacitors, as capacitor ratio tolerance is much better in integrated circuits. Switched capacitor filter (SCF) realization technique is one such scheme in which all filter parameters depend on capacitor ratios. Equally important is the fact that switched capacitor (SC) schemes do not use external resistors. This saved a large amount of chip area; a highly attractive feature for integrated circuits.

    In this chapter, the basic concepts of SCF realization will be discussed. One important approach is the simulation of grounded and floating resistors using capacitors, switches, and non-overlapping clock signals. Such a realization and its simple applications including integrators are shown in Sections 14.2 and 14.3. As switches and clocks are the basic components of integrated circuits, these are further studied in Section 14.4. The rest of the chapter covers the topic of first- and second-order SCF sections.

    Switched Capacitor Resistor

    Let us examine a simple circuit as shown in Figure 14.1(a), containing two switches and a capacitor CR. The port voltages are v1 and v2, and the two switches become ON and OFF continuously at a certain clock frequency fc. This means that each switch can remain on for a maximum time duration Tc = 1/2 fc. It is further assumed that either voltages v1 or v2 will remain constant during the small duration Tc when either of the switches is ON.

  • 7 - Single Amplifier Second-order Filters

  • Muzaffer Ahmad Siddiqi
  • Book:
    Continuous Time Active Analog Filters
    Published online:
    24 December 2019
    Print publication:
    26 March 2020, pp 170-212

  • Summary

    Introduction

    Depending on the specifications, the required order of the filter may be small or big. For less challenging requirements, a second-order or even a first-order section may be adequate. However, higher-order sections may become necessary in other situations. For higher-order filter requirements, either the direct form approach is used, or a combination of secondorder second sections is used which are connected in a cascade form or in a multiple-loop feedback form. Hence, the study of and realization methods of second-order sections assumes importance as they are used either stand-alone or form the building blocks for higher-order filters. Since the overall performance of the higher-order filter depends on the individual second-order building blocks, it is very important that these building blocks have desirable and attractive properties; the following are some such requirements.

  • (c) Low sensitivities of the two important filter parameters, pole frequency wo and pole-Q, with respect to the circuit elements are highly desirable.

  • (d) Utilization of a lesser number of passive elements (active elements as well, though in present discussion, it is assumed that only one active component is used) makes the realization economical in discrete, as well as in integrated form.

  • (e) Values of the passive components should be in the practical range of integrated circuit (IC) fabrication, and the component spread is preferred to be as small as possible in order to make them attractive in IC form.

  • (f) Independent tunability of the parameters wo and Q is important as analog filters require some tuning.

  • (g) To properly connect the second-order blocks in cascade or in multiple feedback system, their input impedance should be as high as possible and the output impedance as low as possible at all working frequencies. Otherwise, it can change the characteristics of the overall higher-order filter.

    • A large number of second-order active building blocks are available with each one claiming advantages over the others. Study of the development procedure of such sections might help the readers to gain more insight towards selecting the optimal section or help in designing new circuits/improving upon the existing ones.

    Hence, we begin the study of development of second-order sections using a single passive feedback in Section 7.2; the effect of using different types of passive structures in the feedback is also included.

  • 11 - Amplification and Filtering in Biomedical Applications

  • Muzaffer Ahmad Siddiqi
  • Book:
    Continuous Time Active Analog Filters
    Published online:
    24 December 2019
    Print publication:
    26 March 2020, pp 334-359

  • Summary

    Introduction

    There has been a lot of development in the use of biomedical equipment for diagnostic and treatment purposes in recent times. A good amount of literature has come from the interdisciplinary area of medical engineering, medical instrumentation, and so on, making medical electronics a specialized field of study. An important constituent of electronics engineering is the study of analog filters. Hence, the design and application of analog filters finds a place in the books and literature on medical engineering and medical instrumentation too. The design of analog filters especially the continuous-time types requires special attention. However, the available books on analog filter design do not adequately relate filter design with biomedical applications. A few simple examples included in this chapter will try to bridge the gap between theoretical design and the application of analog filters in this important field.

    We have already studied the basics of continuous-time analog filter in the previous chapters. In this chapter, we will first connect the design of a filter to its utilization in the field of biomedical electronics.

    It is a well-known fact that cells in the human body have different element (Na+, K+, Ca++, Cl-) ion concentrations inside and outside the membrane. This difference in ion concentration creates a small electric potential called biopotential. When there is a disturbance in a biopotential, an action potential is generated which is the result of depolarization and repolarization of the cells in the human body. It is the action potential at the location (nodes) on the body which is detectable and can be processed using biomedical circuits. When such signals generated by the heart are collected, it makes up the electrocardiogram (ECG). ECG detectors use electrodes to collect these signals, which are amplified, filtered and displayed for data analysis. ECG signals require filtering and amplification to produce high-quality signals. Not only are different stages of amplification used, specific signal processing is also required. Therefore, instead of a simple (DA) differential amplifier, instrumentation amplifiers (inst-amp) are used. Section 11.2 discusses the the necessity of converting DA into an inst-amp. Transformation of the inst-amp into a biopotential amplifier and as integrated circuit inst-amps especially suitable in medical instruments and devices are discussed in Section 11.3 along with a case study on a piezoelectric transducer.

  • 17 - Active R and Active C Filters

  • Muzaffer Ahmad Siddiqi
  • Book:
    Continuous Time Active Analog Filters
    Published online:
    24 December 2019
    Print publication:
    26 March 2020, pp 538-592

  • Summary

    Introduction

    Conventionally, the design of OA-RC (operational amplifiers with resistors and capacitors) circuits assumes that OAs are ideal, having a large frequency independent gain. However, a commercially integrated OA is a non-ideal device, whose gain is frequency dependent and exhibits a LP (low pass) characteristic. A simple model for OAs, given in Chapter 1, is repeated here depicting its frequency dependent gain nature.

    In equation (17.1), ωa is its first pole, Ao is the gain at dc and B = Aowa is gain bandwidth product. This effect of the gain bandwidth product, B, being finite, its effect on the magnitude and phase responses of the filter became important criterion for comparison of the performance of filters. Finite B restricts the frequency range of the operation of OA-RC filters to mostly the audio frequency range, particularly when commercially economical OAs, such as OA 741, are used. In fact, in some topologies, product of pole-Q and center frequency wo has to be much less than B to avoid undesirable enhancement in Q, and likely instability. Consequently, suitable compensating schemes were developed to design filters with lesser dependence on OA gain characteristics, like those shown for integrators in Chapter 2; in other cases, specially designed but costly OAs were used.

    In an alternative approach, instead of considering the frequency dependent gain of the OA as undesirable, it has been exploited by using it directly in the design itself. This approach increases the frequency range of operation, and also reduces or completely eliminates the requirement of external capacitors. In this context, networks which use only OAs and resistors, with no external capacitors in their implementation, and derive their response from the internal dynamics of the OAs, are known as active R circuits [17.1], [17.2].

    Similar to active R, active C networks have also been designed. They utilize the frequency dependent model of the OAs, but use only capacitances, mostly in ratio form. It results in an extended frequency range; the use of small value capacitors in ratio form provides related advantages.

    Basic Techniques in Active R Synthesis

    Active R synthesis is an off-shoot of the active RC synthesis, where external capacitors were eliminated. Hence, the techniques used in the active RC synthesis are only tailored to suit active R realizations; these are briefly discussed in this section.

Page 10 of 79