Design of reconfigurable multi-mode RF circuits

Wireless communication systems and devices have been developing at a much faster pace in the past few years. With the introduction of new applications and services and the increasing demand for higher data rate comes the need for new frequency bands and new standards. One critical issue for next generation wireless devices is how to support all of the existing and emerging bands while not increasing the cost and power consumption. A feasible solution is the concept of the software-defined radio where a single receiver can be reconfigured to operate in different modes, each of which supports one or several bands and/or standards. To implement such a reconfigurable receiver, reconfigurable RF building blocks, such as the LNA, mixer, VCO, etc., are required. This dissertation focuses on two key blocks: the low noise amplifier (LNA) and the voltage controlled oscillator (VCO). First the design, modeling and characterization of a multi-tap transformer are discussed. Simple mathematical calculations are utilized to estimate the inductances and coupling coefficients from the physical parameters of a multi-tap transformer. The design method is verified with several designed multi-tap transformers that are characterized up to 10 GHz using Momentum simulation results. The effect of switch loss on a switched multi-tap transformer is explored and a broadband lumped-element model of the multi-tap transformer is also proposed. Next a reconfigurable multimode LNA capable of single-band, concurrent dual-band, and ultra-wideband operation is presented. The multimode operation is realized by incorporating a switched multi-tap transformer into the input matching network of an inductively degenerated common source amplifier. The proposed LNA achieves single band matching at 2.8, 3.3, and 4.6 GHz; concurrent dual-band matching at 2.05 and 5.65 GHz; and ultra-wideband matching from 4.3 to 10.8 GHz. The chip was fabricated in a 0.13 m CMOS process, and occupies an area of 0.72 mm2, and has a power dissipation of 6.4 mW from a 1.2-V supply. Finally, a triple-mode VCO using a transformer-based 4th order tank with tunable transconductance cells coupling the primary and secondary inductor is introduced. The tank impedance can be re-shaped by the transconductance cells through the tuning of their biasing currents. With the control of biasing current, VCO is configured in three modes, capable of generating a single frequency in 3- and 5- GHz bands, respectively, and two frequencies in both 3- and 5- GHz bands simultaneously. The triple-mode VCO was fabricated in a 0.13 μm CMOS process, occupies an area of 0.16 mm2, and dissipates 5.6 mW from a 1.2-V supply

Oscillation modes in multiresonant oscillator circuits

An in-depth analysis of the oscillation modes in free-running oscillators loaded with multiresonance networks is presented. The analysis illustrates the mechanisms for the generation and stabilization of the various periodic modes and establishes the conditions for existence of a single stable periodic mode in distinct regions of the parameter plane. The mechanisms for the generation and stabilization of quasi-periodic regimes, with two concurrent oscillations, are also analyzed, considering different situations in terms of two relevant poles. The stability analysis of quasi-periodic solutions, derived in terms of admittance functions, can be applied to circuits simulated with harmonic balance, under the assumption of high quality factor resonators. The impact of the transistor biasing on the stability properties of the quasi-periodic regimes has been analyzed, demonstrating that it can be used to isolate the quasi-periodic solution from the periodic ones. The analysis procedures have been applied to a practical oscillator based on two cross-coupled transistors at the two frequencies 900 MHz and 2.5 GHz. The case of two independent oscillations operating in a synchronized regime is also analyzed, as well as its impact on the phase-noise behavior.This work has been funded by the Spanish Government under contract TEC2014-60283-C3-1-R, the European Regional Development Fund (ERDF/FEDER) and the Parliament of Cantabria (12.JP02.64069)

Double functionality concurrent dual-band self-oscillating mixer

A concurrent dual-band self-oscillating mixer (SOM), based on a ring-shaped stepped-impedance resonator, is proposed and analyzed in detail. Taking advantage of the ring even and odd resonances, the circuit can operate in concurrent dual quasi-periodic mode and injection-locked mode. In the second case, it behaves as a dual-band zero-intermediate-frequency (IF) mixer. Initially, an analytical study of the SOM behavior in the two modes is presented. Then a variety of accurate numerical methods are used for an in-depth investigation of the main aspects of its performance, including stability, conversion gain, linearity, and phase noise. The recently proposed contour-intersection technique and the outer-tier perturbation analysis are suitably adapted to the SOM case. A method is also presented to distinguish the parameter intervals leading to heterodyne and to zero-IF operation at both the lower and upper frequency bands. In the zero-IF SOM, the possible instantaneous unlocking in the presence of modulated input signals is investigated and avoided. The methods have been applied to a dual mixer at the frequencies 2.4 and 4.1 GHz.This work was supported by the Spanish Ministry of Economy and Competitiveness through the European Regional Development Fund (ERDF)/ Fondo Europeo de Desarrollo Regional (FEDER) and under Project TEC2017-88242-C3-(1/2)-R

Oscillation modes in free-running oscillators loaded with multi-resonant networks

An in-depth investigation of oscillation modes in free-running oscillators loaded with multi-resonance networks is presented. It focuses on the mechanisms leading to the coexistence of stable oscillation modes, which may give rise to uncertainty in the physical behaviour. The multiple periodic and quasi-periodic solutions are detected and related to the stability properties of the dc solution and each of the periodic modes. Two different types of Hopf-bifurcation loci enable a global understanding of the circuit operation. The investigation is initially carried out with an analytical formulation and then extended to harmonic-balance simulations. The results have been experimentally validated through their application to a HEMT-based cross-coupled oscillator, at 0.65 and 2.4 GHz.This work has been supported by the Spanish Ministry of Economy and Competitiveness under project TEC2014-60283-C3-1-R and the Parliament of Cantabria (12.JP02.64069). The authors would like to thank S. Pana, University of Cantabria, for her assistance with the manufacturing process

Analysis and design of a concurrent dual-band self-oscillating mixer

A concurrent dual–band self–oscillating mixer, based on a ring resonator, is proposed and analyzed in detail. Taking advantage of the ring even and odd resonances, it is able to operate in concurrent dual quasi–periodic mode and in an injection–locked regime. In the second case, it behaves as a dual frequency zero–IF mixer. The stability properties are analyzed with a reduced–order determinant function that overcomes the problem of limited observability due to a high isolation between different circuit sections. Various procedures, enabling the calculation of the conversion gain, injection–locking bandwidths and phase–noise spectral density, have been applied to a dual mixer at the frequencies 2.3 GHz and 4.1 GHz.Work supported by the Spanish Ministry of Science and Innovation (ERDF/FEDER) project TEC2017-88242-C3-1-R

Information-Based Approaches of Noninvasive Transcranial Brain Stimulation

Progress in cognitive neuroscience relies on methodological developments to increase the specificity of knowledge obtained regarding brain function. For example, in functional neuroimaging the current trend is to study the type of information carried by brain regions rather than simply compare activation levels induced by task manipulations. In this context noninvasive transcranial brain stimulation (NTBS) in the study of cognitive functions may appear coarse and old fashioned in its conventional uses. However, in their multitude of parameters, and by coupling them with behavioral manipulations, NTBS protocols can reach the specificity of imaging techniques. Here we review the different paradigms that have aimed to accomplish this in both basic science and clinical settings and follow the general philosophy of information-based approach