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This work deals with multi-level switching amplifiers, in the context of high-efficiency power amplification for signal tracking applications. In particular, this paper evaluates the reduction in the error signal's power due to multi-level power amplification (compared to conventional two-level amplifiers) and compares the performance of two multi-level pulse modulations: PWM and Asynchronous ${{Sigma}} {{Delta}}$ Modulation. First the intrinsic bandwidth limits of multi-level switching amplifiers are inferred, to clearly state the advantages and limitations of multi-level power amplification. From the existing analyses of Pulse Width Modulation already reported in the literature, PWM is herein extended to multiple levels based on an equivalent representation, which allows to derive a closed expression for the power spectrum of multi-level PWM in bandlimited signal tracking. The Asynchronous ${{Sigma}} {{Delta}}$ Modulation is extended to multiple levels and the resulting multi-level encoding algorithm is analyzed in both time and frequency domains. The performance of both modulations is characterized and compared at different operating frequencies and using different number of levels. The main outcomes of this in-depth characterization show that, if the switching frequency is high enough, the tracking error is independent of the modulation and the switching frequency, i.e., it only depends upon the number of levels, which points out the suitability of asynchronous modulations for relatively low switching frequencies (compared to the number of levels)., Peer Reviewed, Postprint (published version)

A mixed-signal continuous-time-processing standard CMOS implementation of an asynchronous sigma-delta modulator aimed to drive a switching amplifier operating as an on-chip wideband adaptive power supply is presented in this work. The paper first briefly discusses the fundamental limit tracking capabilities of a two-level switching signal to inband-error-free track a bandlimited signal with minimum average switching frequency. It is argued the adequacy of an adaptive asynchronous sigma-delta modulator (AAΣΔ) to approximate such fundamental characteristics. The second part of the paper presents mixed-signal design details of the various subcircuits implementing a CMOS low-power digitally-programmable AAΣΔ modulator, with 7 MHz average switching frequency operation and 1000 µm × 640 µm area occupancy., Peer Reviewed, Postprint (published version)

This paper explores the modulation bandwidth limits for switching amplifiers, by analyzing the fundamental tracking capabilities of two-level switching signals. With this aim, this work synthesizes two-level switching signals by obtaining the distribution of switching events providing both minimum average switching frequency and inband-error-free encoding, targeting to minimize the amplifier switching losses when tracking a generic bandlimited signal. This analysis also provides a framework reference to characterize the deviation from such limit in modulations used in actual amplifiers., Peer Reviewed, Postprint (published version)

This work presents a switching converter topology which can boost and step down the supply voltage and can deliver both positive and negative voltages to a grounded load (bipolar converter topology with non-floating output). This topology, which uses five switches to perform the power conversion, is mostly intended for switching amplifiers, especially for applications which require both boosting and inverting the supply voltage (to supply bipolar voltage signals), and/or EMI-sensitive applications. Using a single-stage switching amplifier based on this 5-switch topology, it is feasible to supply a grounded load with a symmetrical bipolar voltage signal whose magnitude extends up to several times the magnitude of the supply voltage., Peer Reviewed, Postprint (published version)

Aquesta tesi tracta sobre amplificació de potència d'alt rendiment de senyals variables en el temps; concretament, tracta sobre conversió de potència eficient (amb mínimes pèrdues) de tensions DC continues en senyals de tensió no constants. Aquest tipus de conversió de potència està present en la majoria de dispositius electrònics d'ús quotidià, com ara telèfons mòbils i reproductors de música portàtils, així com també en dispositius d'alta potència com amplificadors d'àudio i estacions base de telefonia mòbil. Generalment l'energia està disponible en forma de tensió DC contínua (d'una bateria o d'una font d'alimentació). D'acord amb la informació a transmetre, aquesta energia s'ha de processar o transformar en un senyal variable en el temps de manera que, per exemple, es pugui convertir en àudio per un altaveu . La tendència de mercat és a reduir la mida i el pes dels dispositius electrònics i a oferir noves funcionalitats, incloent una llarga autonomia en dispositius alimentats per bateries. Millorar l'eficiència dels amplificadors de potència no només n'estendria l'autonomia, sinó que també permetria utilitzar dissipadors més petits i lleugers. Altres aplicacions com les d'alta potència o integrades també es beneficiarien de millores en l'eficiència dels amplificadors de potència. Els dispositius electrònics de processament de potència més eficients són els amplificadors commutats. Aquests utilitzen components reactius (bàsicament bobines i condensadors) per dur a terme un processament de potència idealment sense pèrdues, així com dispositius actius (transistors) controlats com interruptors (o bé tancats o bé oberts), per tal de controlar aquest procés. Tot i que es poden assolir eficiències molt altes amb amplificadors commutats, la precisió de seguiment pot no ser gaire bona. Es pot millorar la precisió de seguiment senzillament incrementant la freqüència de commutació (la freqüència a la qual es fan commutar els interruptors), tot i que, com que es requereix u, This thesis is about power amplification of time-varying signals; more precisely, it is about efficient power conversion, i.e. with minimum losses, of DC constant voltages into non-constant voltage signals. This kind of power conversion is quite common in power-management circuits and electronics in general. It is present in most everyday use electronic devices, including mobile phones, portable audio players and routers, as well as in high-power devices such as audio amplifiers and wireless base stations. In most electronic devices, whether portable or not, the energy is available as DC constant voltage (typically from a battery or a power supply). According to the information to transmit, this energy must be processed or transformed into a time-varying analogue signal so that, for instance, it can be directly converted into audio by a speaker or radiated by an antenna. The market trend is to reduce the size and weight of electronic devices whilst offering new or enhanced functionalities, including long autonomy in battery-powered devices (mainly portable). Improving the efficiency of power amplifiers not only extends the autonomy, but also allows using smaller and lighter heatsinks. Other applications such as high-power or embedded would also benefit from efficiency improvements of switching amplifiers. The most efficient power-processing electronic devices are switching amplifiers. Switching amplifiers use reactive components (mainly inductors and capacitors) to perform an ideally lossless power processing, and active devices (transistors) driven as switches, either ON or OFF, to control this process. Whilst very high efficiencies can be achieved with switching amplifiers, their tracking fidelity may not be very high. The tracking fidelity can be improved by simply increasing the switching frequency (i.e. the frequency at which the active devices are driven), although, provided that a certain amount of energy is required to switch the state of each active device, Postprint (published version)

This work extends the Asynchronous ΣΔ Modulator and its Adaptive version to multi-level modulators, targeting wideband high-efficiency switching power amplifiers. The performance of these modulators is compared with the multi-level Pulse Width Modulator, the most common modulator in multilevel switching power amplifiers. Behavioural model simulation results show that, unlike the multi-level PWM (which can only be used at high switching frequencies), the Asynchronous ΣΔ Modulators can also be used at average switching frequencies close to the signal bandwidth. At high switching frequencies, the performance of all the modulators is similar. The Asynchronous ΣΔ Modulators have further and more important advantages, such as high PSRR (even at the input signal frequency), the ability of handling non-regular distributed voltage levels, or a low ratio between the average switching frequency and the maximum instantaneous switching frequency., Peer Reviewed, Postprint (published version)

This work proposes a switching policy for multi-level fullbridge switching power converters and analyses their performance by driving them with a multi-level PWM modulation, targeting highefficiency power amplifiers. Unlike conventional policies, which generate the output voltage levels only from the values of the supply voltages, this enhanced policy also uses the values of the voltage difference between supply voltages to generate additional output voltage levels, therefore maximising the number of output voltage levels for a given set of supply voltages and connection switches. Simulation results show that, when tracking a band-limited signal, the proposed switching policy can reduce the power of the high-frequency spectral content from 21% to 11% by upgrading a 5-level amplifier to a 7-level amplifier without adding supply voltages or connection switches., Peer Reviewed, Postprint (published version)