Performance Analysis of Interconnects Based on Carbon Nanotubes for AMS/RF IC Design

Electrical interconnects are essential elements to transmit electrical current and/or to apply electrical voltage to the electronic devices found in an integrated circuit. With the introduction of carbon nanotubes in electronic applications, efficient and high-speed interconnects have allowed for optimizing the electrical performance of the integrated circuits. Additionally, technical problems, such as electromigration, large values of parasitic elements, large delays, and high thermal dissipation, presented in metallic interconnects based on copper, can be avoided. This chapter presents a performance analysis of interconnects used in AMS/RF IC design based on carbon nanotubes as the physical material where electrical variables are provided.

Optimization-Based Design of RF-VCOs with Tapered Inductors

Voltage-Controlled Oscillators (VCOs) are widely used in wireless transceivers. Due to the stringent specifications regarding phase-noise, LC-VCOs are usually adopted. The need for maximizing phase-noise as well as minimizing the power consumption makes imperious the adoption of optimization-based design methodologies. For the optimization of the LC-VCO characteristics, special attention must be paid to the integrated inductor design, since its quality factor may have a strong influence in the LC-VCO phase-noise. Furthermore, designers must ensure that the higher limit of VCO operating frequency is sufficiently below the inductor resonant frequency. In this chapter, a study on the influence of the quality factor of the inductors on the LC-VCO overall behavior is presented. Then, optimization of integrated inductors by exploring the inductor geometric layout is presented. Finally, results obtained for the design of an LC-VCO in 130nm Technology using a previously optimized inductor are presented.

Synthesis of LC-Oscillators Using Rival Multi-Objective Multi-Constraint Optimization Kernels

This chapter presents a state-of-the-art multi-objective/multi-constraint design automation approach applied to the design of an LC-Voltage Controlled Oscillator and an LC-Oscillator for a 130 nm technology node and leading to sets of design solutions showing figures-of-merit around -192 dBc/Hz and -186 dBc/Hz, respectively. The proposed approach, implemented in AIDA-C, guarantees accuracy by using commercial circuit simulators (HSPICE® and ELDO®) to evaluate the performance of the tentative circuit solutions, where the number of time-consuming circuit simulations is efficiently pruned by the optimization kernel. Three multi-objective optimization algorithms, the NSGA-II, the MOPSO, and the MOSA, are experimented with in the synthesis of the quoted oscillators and compared in terms of performance using statistical results obtained from multiple synthesis runs for each one of the oscillators. The performance of the optimized oscillators is then compared to other state-of-the-art results, showing the benefits of the presented multi-objective design approach.

HEMT for RF Circuits

In this chapter, III-V compound semiconductors MESFET, HBT, and HEMT are described, including papers which report major achievements of the HEMT technologies in the fields of microwave, millimeter-wave, and digital Integrated Circuits (ICs). The important aspects of device physics, small-signal equivalent circuits for GaAs, and GaN-based HEMT are discussed. The authors present a comparative analysis of different analytical modeling techniques and show that the differences reflect the physical and technology differences of the tested microwave transistors. The purpose of this chapter is to facilitate the choice of the most appropriate strategy for each particular case. For that, the authors present a brief but thorough comparative study of analytical techniques developed for modeling different types of advanced microwave transistors: GaAs HEMTs, GaN HEMTs. The chapter shows that a crucial step for a successful modeling is to adapt accurately the small-signal equivalent circuit topology.

Combination of Metaheuristics to the Optimal Design of Analog and RF Circuits

Multi-objective metaheuristics are over and over again used by analog designers. They allow generating a set of non-dominated solutions (i.e. the Pareto front). In this chapter, the authors highlight the fact, via the application of six multi-objective algorithms to the optimization of conflicting performances of four analog and RF circuits, that the generated fronts highly depend on the used algorithm. They propose a solution consisting of combining metaheuristics to generate a “better” front by merging results obtained thanks to different algorithms and the application of a dominance routine. Viability of the proposed idea is shown through examples.

Backtracking ACO for RF-Circuit Design Optimization

Sizing analog, mixed-signal, and particularly radio-frequency circuits generally relies on the experience of the designer. Metaheuristics have been recently proposed, and it has been shown that they can arguably replace the classical iterative simulation-based trial/error approaches. Among the most known metaheuristics, Ant Colony Optimization (ACO) has already successfully been used to deal with analog circuit performance optimization. Despite the fact that ACO is robust and has a good intrinsic intensive research strategy, it suffers from its greedy requirement in computation time. In this chapter, the authors deal with the improvement of the ACO technique by integrating in this algorithm a backtracking search technique that has the role to act on the ratio of the accumulated pheromones, thus reducing the computation time. The new algorithm is called BA-ACO. Performances of BA-ACO are highlighted through some RF-applications. ADS simulation results are given to show the validity of the proposed algorithm.

Stability of Optimization Trajectories for Designing Analog Circuits

In this chapter, the problem of computer time reduction for optimization of large electronic system is discussed. It is one of the essential problems of high-quality improvement of design, and it is defined by means of the generalized methodology for analog network optimization on the basis of the control theory formulation. It is shown that the main conception of this methodology is based on a special control vector which operates process of optimization and gives a solution of optimization problem during the minimal computing time. The problem of creation of a vector of optimal control is solved on the basis of direct Lyapunov method. Lyapunov function of optimization process is proposed to analyze a stability of trajectories of optimization. This function gives the opportunity of the analysis of stability of various strategies and is used as the basis for search of the optimal algorithm of designing.

Radio Frequency Chaotic Circuit Design

In recent decades the design of nonlinear circuits, which are capable of generating chaotic oscillations from audio frequencies up to the optical band, is a great challenge due to their use as sources of chaotic carriers in a variety of applications. Therefore, this chapter is dedicated to this class of circuits. A brief history of the first nonlinear circuits, which were the most important stages in the evolution of chaotic circuits, is given at the beginning of the chapter. Next, one of the most well known nonlinear circuits, the circuit of Colpitts oscillator, and its modifications, operating from a few Hertz up to the microwave region, are described in detail. A novel modification of Colpitts oscillator, which has higher fundamental frequency than the others do and greater Lyapunov dimension is also studied. Finally, some interesting applications of this class of circuits are presented at the end of this chapter.

Thermometer to Gray Encoders

Analog to Digital Converter (ADC) is a key functional block in the design of mixed signal, system on chip, and signal processing applications. An optimized method for the direct conversion of analog signal to Gray code representation is presented. This eliminates the need for binary-to-Gray code conversion in many digital modulation techniques like M-PSK and M-QAM, which uses Gray coding representation to represent the symbols that are modulated. The authors design a low-power and high-speed Thermometer to Gray encoder for Flash ADC, as encoders have been widely utilized in high-performance critical applications which persistently impose special design constraints in terms of high-frequency, low power consumption, and minimal area. In this chapter, they propose a new circuit that converts the Thermometer code to Gray code and also yields minimized power.

Performance Analysis of Electromagnetic Interference Shielding Based on Carbon Nanomaterials Used in AMS/RF IC Design

Integrated circuits are a source of electromagnetic interference whose energy is radiated significantly to other objects around them. Different techniques have been used to avoid such electromagnetic radiation, which can modify the operation of other circuits, such as the use of coatings to produce electromagnetic interference shielding. With the introduction of nanomaterials such as carbon nanotubes and graphene embedded in polymeric matrices, it is possible to increase the efficiency of the shielding to very high frequencies. This chapter presents a performance analysis of the carbon nanomaterials as materials used to produce electromagnetic interference shielding in AMS/RF IC design.