Design Experiences of a CMOS LNA for mm-waves

This paper describes some of the design experiences achieved during the design, simulation and characterization of a Complementary Metal-Oxide Semiconductor (CMOS) LNA which has been designed for 24GHz and fabricated in a standard 0.180 µm technology. More specifically, some technological limitations of the CMOS process for mm-wave applications are considered, before showing the outcomes of the schematic and post-layout simulations as well as the measurements and discussing the reasons for the difference between simulations and measurements. It is shown that the simulation results can be significantly improved using Electro-Magnetic (EM) post-layout simulations. Moreover, a post-layout simulation methodology allowing a straightforward integration of the EM simulations into the workflow is proposed.

Power line communications

Emmanuel Marthe

With the deregulation of the electricity and telecommunications markets, a great deal of new operators providing some innovative services have appeared. In the telecommunications' field, the promise of broadband Internet access with easy installation procedure at low cost may help to win new customers. The Power Line Communications (PLC) technology is a way to fulfil this function. PLC uses the low voltage (LV) and the medium voltage (MV) networks as communication support. It consists in an additional signal carrying data information and superimposed to the 50 Hz power wave. As PLC is easy to install, it can be used to extend the Internet coverage to areas that are still badly covered by the other broadband technologies, or to provide high speed Internet access to every power socket of a building. This thesis, done as a part of research project called Digital Power Line Access, is devoted to the study of electromagnetic compatibility (EMC) aspects involved with the PLC. There are still a certain number of problems due to the fact that PLC, which is a quite recent technology, has not been regulated yet. Among these problems, all the aspects associated with the radiation created by the transmission of PLC signals over unshielded conductors and their potential disturbances are very significant. The aim of this thesis is the analysis of PLC data transmission over the low voltage network and the related EMC problems, mainly the radiation due to the transmission of PLC signals. The measurement and the analysis of these radiations lead us to develop a method to reduce these radiations. The mitigation of radiation created by the use of PLC within buildings is still an important EMC challenge, because there are no possibilities for network conditioning. The first two chapters of this thesis present a state of the art of PLC, its regulation and the related EMC problems. The second chapter describes the working of PLC and emphasizes the hostile nature of its environment. The problems (filtering, attenuation, generation of noise,...) caused by the use of a signal in the [1 – 30 MHz] band over a channel designed for a 50 Hz power wave are presented. On the other hand, the various technologies used to allow the PLC to work (suitable modulation scheme, use of repeater,...) are illustrated. An analysis of the different PLC concepts and of the successful and unfruitful commercial deployment ends this chapter. In the third chapter, we present the technical criterion (use of the PLC as a multi-purpose port: as a main port and as a telecommunication port) that we have to consider and the evolution of the conducted and radiated limits that we have to respect. The pollution of the radio amateur band, which could be the result of a massive deployment of PLC, is the subject of tremendous discussions and proves that if according to some persons the current limits are too permissive, for the PLC manufacturer they are already too restrictive. The coexistence of the PLC with other broadband technologies (xDSL, CA-TV, Wireless,...) is also addressed and we show that only the coexistence with an alternative of the DSL – VDSL – could be problematic. The main original contributions of this thesis are presented in chapters 4 to 6. We concentrated on the problems related to the electromagnetic radiations associated with PLC signals, especially in indoor environment. The reason for this is that the emission of electromagnetic noise, which can interfere with services such as public and amateur radio, remains an obstacle to the development of PLC. Furthermore, to the best of our knowledge, the mitigation of indoor radiation has not been addressed in the literature. In chapter 4, we present a complete characterization of the problems resulting from the use of PLC in an indoor environment. Two approaches are presented for the measurement of electromagnetic fields. The first one consists in the injection of a reference signal in the network and the measurement of the resulting radiations. The second one deals with the measurements of interferences due to the work of real PLC equipments. These two approaches enlight several aspects. The main aspect is the strong dispersion of the measurements, resulting from the influence of the position of the observation point and of the power network load. Measurements on real PLC networks show excessive radiations, which confirm that the limits are, at this time, too restrictive. We also present and discuss PLC radiated emissions in typical indoor environments. In particular, we analyze the field levels resulting from PLC signals with magnitudes given by EN55022/CISPR22 limits and compare them with various proposals for PLC radiated field limits. Thus, we show that the resulting fields exceed, for a wide range of frequencies, some of the current emission limits such as the German NB30, which is considered as a very strict limit. In this same chapter, we present a technique for the analysis of power line communication (PLC) signals, based on the formalism of the scattering parameters. This technique allows an efficient and fast characterization of any transmission medium of a power network. The analysis of the variations of the magnitude and phase of the scattering parameters gives useful insights on the increasing of the losses with frequency and confirm the need of a technique to reduce impedance mismatch at both injection and reception ports. The chapter 5 presents the modelling of the PLC environment and the computation of its radiations using a commercial code, the Numerical Electromagnetics Code (NEC), which solves the electric field integral equation in the frequency domain using the method of moments. We present some comparisons between the NEC simulations and the experimental data for the total magnetic field presented in the previous chapter. The simulations of simple models give results in good agreement with the experimental data and therefore allow the validation of certain principles. Unfortunately, the simulations on a model of increasing complexity give less satisfactory results. Because of the difficulty to respect the topology of the network and to take into account all of the components of the network coupled with the constraints of NEC, it is extremely difficult to obtain accurate results on the complete PLC band. The strong electromagnetic radiations appeared as the major problem of this technology. Therefore, the development of a method of mitigation was the logical continuation of this work, especially because there is still no solution to this problem. We developed a technique, which is presented in chapter 6, aiming at reducing the electromagnetic field radiated by indoor PLC signals. This technique is the major original contribution of this thesis and led us to file a patent. The central idea is to take advantage of the additional ground conductor and inject a signal similar to the PLC signal into the ground-neutral line, but with a reversed phase. As a result, the overall antenna mode current is significantly reduced, as well as the radiated electromagnetic fields. The method is specifically developed for indoor applications and applies to uni-directional and bi-directional data transmission systems with an implementation using switches. Experimental data obtained on a test network have shown that the use of the proposed technique implies a significant reduction (up to 20 dB) of the PLC electromagnetic radiation in the considered frequency range. It is also shown that the performance of the proposed technique increases when the ground-neutral line is terminated by an impedance equal to the one of the PLC modem. Other tests performed on 230 V network confirm this trend but show that further work is needed in this direction. This work could consist in the development of a system allowing the synchronisation of the real PLC signal and the auxiliary signal according to the behavior of the PLC channel, in order to optimise the performances for any frequency used by the PLC.

EPFL2005

Electromagnetic modelling of planar circuits in bounded layered media

Pedro Crespo Valero

Printed circuits in bounded media encompass a wide range of practical structures such as discontinuities in waveguides, planar circuits embedded in shielded multilayered media or even two-dimensional printed periodic structures. The Electromagnetic (EM) modeling of printed circuits in layered bounded media is performed via an Integral Equation (IE) technique. Green's functions (GFs) are specially defined to satisfy both the Boundary Conditions (BCs) imposed by the layered media and by the transverse boundary enclosing the entire structure. Finally, a system of IEs on the equivalent sources can be solved numerically by means of the Method of Moments (MoM). Each of the problems enumerated above has already been solved by other authors using IE-MoM techniques. Nevertheless, our formulation introduces a unified approach applicable to all the aforementioned problems. Due to the symmetry presented by a bounded layered media, the GF problem can be reduced into a two-dimensional transverse boundary problem and a one-dimensional transmission line problem in the normal direction. Both problems can be treated independently. This thesis proposes and fully develops an efficient technique that encompasses different laterally bounded multilayered problems with a seamless transition between them. The method is based on a modal representation of the transverse boundary problem and on the expansion of the equivalent surface currents by zero-curl & constant-charge Basis Functions (BFs). It offers a unified and versatile approach that, on one hand eliminates redundancy in the formulation and on the other hand simplifies each particular problem to the evaluation of constant coefficients or basic line integrals. Analytical solutions can be found for the combination of linear subsectional basis functions in rectangular and circular Perfect Electric Conductor (PEC) boundaries as well as for periodic lattices. This thesis then solves the problem of transmission line model in the longitudinal direction by proposing an efficient algorithm that guarantees numerical stability under a variety of known critical conditions where other already known formulations fail. In addition, it introduces alternate equivalent expressions of this formulation that allow new interpretations of the problem. Due to its practical interest, the method is applied for the EM modeling of multilayered boxed printed circuits. This motivated the implementation of a dedicated software tool for the efficient analysis of these topologies including losses. Extensive numerical experiments have been carried out to assess the validity of the aforementioned theory and some properties of test-structures (losses, mesh, etc).

EPFL2007

Computer Modeling of YBCO Fault Current Limiter Strips Lines in Over-Critical Regime With Temperature Dependent Parameters

Joseph Duron, Bertrand Dutoit, Francesco Grilli

We present the results of an advanced numerical model for fault current limiter (FCL) based on HTS thin films in which both thermal and electromagnetic aspects are taken into account. This model allows simulating the behavior of FCL in the over-critical current regime and we used it for studying strip lines of a YBCO/Au FCL on sapphire substrate. The electromagnetic and thermal equations have been implemented in finite-element method (FEM) software in order to obtain a model for investigating the comportment of the superconductor when the current exceeds

I_{c}

. In particular, materials equations have been implemented in order to simulate the electrical behavior of superconducting devices with strong over-critical currents. We report results of simulations in voltage source mode where currents largely exceed

I_{c}

. The global behavior of the FCL is compared with measurements, showing a good agreement. The use of FEM simulations offers the advantage to give access to local variables such as current density or temperature. Studies with this model can replace expensive experiments where very high current density might damage or destroy the FCL device.

2007