Papers by Harald Enzinger
2010 IEEE MTT-S International Microwave Symposium, 2010
ABSTRACT The underlying paper deals with HF RFID systems and the influences of different paramete... more ABSTRACT The underlying paper deals with HF RFID systems and the influences of different parameters on the entire system and the effects for “very high data rates” (VHD) up to 6.7 Mbit/s. After a short introduction to 13.56 MHz RFID systems, characteristic parameters such as Signal to Carrier Ratio, quality factor, bandwidth and energy are pointed out in the context of VHD. Based on that different reader concepts will be evaluated and the implementation of a testplatform will be shown. Finally dynamic effects of the system will be explained, which have to be taken into account for VHD transmissions.
e & i Elektrotechnik und Informationstechnik, 2009
ABSTRACT The underlying paper and investigations deal with the main functionality and physical pa... more ABSTRACT The underlying paper and investigations deal with the main functionality and physical parameters of contactless smartcard and NFC (Near Field Communication) devices. The specific need of impedance matching for reader devices is pointed out in particular, as the correct matching represents a major performance indicator of the system. Therefore, in a first step, the dedicated parameters are analyzed for a reader device. Based on these insights, detailed analysis of the concept, the implementation and the verification of an automatic impedance matching circuit for NFC antennas with a frequency of 13.56MHz is given. Besides an introduction to manual tuning and its issues, the fundamental components of an automatic tuning system are outlined. A lab-scaled prototype is built and demonstrated. Finally, the successful operation of this system is tested with several different antennas. Furthermore, the effects of detuning due to dynamic behavior are pointed out, characterizing the need for further investigations.
A new topology for a low dropout regulator with NMOS pass device is presented. The stability is c... more A new topology for a low dropout regulator with NMOS pass device is presented. The stability is checked by a model derived from symbolic circuit analysis. The startup by use of a pre-charge mechanism and the integrated oscillator and charge pump are described. The regulator is designed for an input voltage range of 1 to 3.6 V, an output voltage of 920 mV and a load current of 1 to 100 μA.
The overall quiescent current is approximately 100 nA.
IEEE International Symposium on Circuits and Systems 2014
A mathematical framework for analytical description of multilevel carrier-based pulse-width modul... more A mathematical framework for analytical description of multilevel carrier-based pulse-width modulation (PWM) is presented. The framework does not make any assumptions on the input signal and is able to model any configuration of periodic, piecewise-linear carrier signals, specified by two line-segments. By using the framework it is shown that analytical equations can be obtained for two practically relevant multilevel PWM schemes. The derived equations simplify spectral analysis, which is exemplified by numerical simulations.
IEEE International Symposium on Circuits and Systems 2016
We present an analytical model of the joint linearityefficiency behavior of radio frequency power... more We present an analytical model of the joint linearityefficiency behavior of radio frequency power amplifiers. The model is derived by Fourier series analysis of a generic amplifier circuit including both strong nonlinearity due to current-clipping as well as weak nonlinearity due to transconductance variation. By selection of the biasing point, common amplifier classes like class A, class B and class AB can be modeled. For numerical evaluation, the model reduces to two lookup-tables, which makes it well suited for high-level system simulations. In an application example we demonstrate how the model can be used to simulate the error-vector-magnitude and the average efficiency for specific single-carrier and multi-carrier modulation schemes.
We present a new approach to identify the parameters of a given digital predistortion (DPD) struc... more We present a new approach to identify the parameters of a given digital predistortion (DPD) structure for power amplifier (PA) linearization. Traditional methods optimize a single objective, typically the time-domain mean squared error. We propose to use a multi-objective optimization algorithm to jointly optimize the in-band and out-of-band performance as quantified by the respective metrics defined in the particular communication standard. Our constrained approach allows for checking standard-compliance at the time of DPD identification. Furthermore, the DPD model is not required to be linear in the parameters. We exemplify our approach with a WLAN simulation using a PA model at low back-off. By jointly optimizing the error vector magnitude (EVM) and spectral mask margin, we achieve significantly better results than the widely-used indirect learning architecture for the same memory polynomial DPD structure.
Behavioral modeling of nonlinear passband systems like radio frequency power amplifiers is mainl... more Behavioral modeling of nonlinear passband systems like radio frequency power amplifiers is mainly based on polynomial baseband models. Motivated by the convolution property of the Fourier transform applied to passband signals, it is common practice to include only odd-order terms in these models. Experimental results show, however, that significant improvements can be achieved by also including even-order terms. In this paper, the fundamental relationship of even-order terms in polynomial passband and baseband models is analyzed, providing a theoretical foundation for the improved modeling accuracy of polynomial baseband models with even-order terms.
Theses by Harald Enzinger
The radio frequency power amplifier (RF-PA) within a digital wireless transmitter is a critical c... more The radio frequency power amplifier (RF-PA) within a digital wireless transmitter is a critical component regarding both the energy consumption and the signal quality. Especially due to today's broadband multicarrier modulation methods that generate signals with high peak-to-average power ratio, it is very hard to construct RF-PAs that achieve good energy efficiency and fulfill the strict linearity requirements imposed by the standard. Because of this, the digital predistortion (DPD) of RF-PAs has become a key technique for implementing energy efficient, high data rate wireless transmitters.
This thesis investigates theoretical foundations and practical methods for the behavioral modeling and DPD of RF-PAs. The main contributions are a semi-physical model of the joint linearity-efficiency characteristics of RF-PAs, a detailed analysis of polynomial baseband models of RF-PAs focusing on the often neglected even-order terms in baseband, and a collection of practical methods for the dual-band DPD of RF-PAs.
The trade-off between the linearity and efficiency of RF-PAs is investigated based on the semi-physical RF-PA model. For this purpose, linearity and efficiency quantification methods are introduced and applied to the model. Furthermore, an overview on highly efficient RF-PA operation modes and efficiency enhancement methods is given.
A central result regarding polynomial baseband models is the first formal justification of even-order terms in baseband. This is achieved by deriving explicit passband-baseband pairs for the quasi-memoryless polynomial and the Volterra series, which show that even-order terms in baseband correspond to modified basis functionals in passband.
Another central result of the presented analysis of polynomial baseband models is the formulation and proof of the phase homogeneity requirement, which represents a necessary symmetry of all complex baseband models of time-invariant passband systems.
The practical methods for the dual-band DPD of RF-PAs include a method for dual-band crest factor reduction by clipping and error-filtering, a dual-band DPD model based on a vector-switched generalized memory polynomial, and a dual-band DPD training algorithm based on the indirect and direct learning architectures. These methods were implemented in MATLAB and validated at the 2017 DPD competition at the IEEE International Microwave Symposium, reaching the first place within the competition.
This thesis describes the analysis and design of an ultra low power linear voltage regulator that... more This thesis describes the analysis and design of an ultra low power linear voltage regulator that is targeted for the application in a wireless sensor node. In the introductory chapter, the concepts of wireless sensor nodes, power management and ultra low power design are summarized. The second chapter contains fundamental considerations concerning the design of linear voltage regulators. A small signal model of the control loop is presented and methodologies for stability analysis and performance measures are introduced. The AC characteristics of both NMOS and PMOS pass device transistors are investigated by analytical calculations. A symbolic circuit analysis methodology is introduced that allows the analytical treatment of larger circuits. This methodology is applied to derive analytical models of the power supply rejection of simple CMOS OTAs. In the third chapter, the design of the voltage regulator based on an NMOS pass device is described. A new circuit topology for the control loop is presented that allows the biasing of the pass device for low dropout operation. The proposed topology is analytically investigated concerning stability, power supply rejection and output impedance. Additional circuit blocks like an oscillator, a charge pump and a startup circuit are described. The fourth chapter contains simulation results of the complete system. The functionality is shown by transient simulations and parameter variations are considered. Finally in the last chapter a conclusion of the presented results is given.
This work deals with the development of a new standard for enhanced transmission rates for contac... more This work deals with the development of a new standard for enhanced transmission rates for contactless smartcard systems according to ISO 14443. The aim is to achieve data rates that are significantly above today’s maximum of 848 kbit/s. Contactless smartcards are a form of chipcards that can be accessed over a radio frequency field. The communication is based on inductive coupling and uses a carrier frequency of 13:56 MHz. For the downlink (card to reader) the concept of load modulation is used. Because of the close relation to RFID the first chapter of this work contains an overview on RFID systems. The state of the art of contactless smartcards is presented and an introduction on Very High Data Rates is given. In the second chapter the physical, mathematical, and technical fundamentals of inductively coupled transmission systems are described. This is followed by the presentation of a Matlab based system model in the third chapter. The system modeling contains a description of the channels for up- and downlink by transfer functions and an evaluation of the dependencies on the operation point. The impact of load modulation on the amplitude and phase of the carrier is calculated. The conception of the Very High Data Rate Test Platform is presented in the fourth chapter. It is a hardware setup that allows the generation of various modulation schemes and can be used to validate transmit- and receive concepts. The analog and digital developments for the Test Platform are described in the fifth and sixed chapter. The seventh chapter contains results of measurements that were carried out to validate the functionality of the Test Platform and to characterize the transmissions of up- and downlink. In the final chapter a recapitulation of the achieved results is presented and the next steps in the development process are outlined.
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Papers by Harald Enzinger
The overall quiescent current is approximately 100 nA.
Theses by Harald Enzinger
This thesis investigates theoretical foundations and practical methods for the behavioral modeling and DPD of RF-PAs. The main contributions are a semi-physical model of the joint linearity-efficiency characteristics of RF-PAs, a detailed analysis of polynomial baseband models of RF-PAs focusing on the often neglected even-order terms in baseband, and a collection of practical methods for the dual-band DPD of RF-PAs.
The trade-off between the linearity and efficiency of RF-PAs is investigated based on the semi-physical RF-PA model. For this purpose, linearity and efficiency quantification methods are introduced and applied to the model. Furthermore, an overview on highly efficient RF-PA operation modes and efficiency enhancement methods is given.
A central result regarding polynomial baseband models is the first formal justification of even-order terms in baseband. This is achieved by deriving explicit passband-baseband pairs for the quasi-memoryless polynomial and the Volterra series, which show that even-order terms in baseband correspond to modified basis functionals in passband.
Another central result of the presented analysis of polynomial baseband models is the formulation and proof of the phase homogeneity requirement, which represents a necessary symmetry of all complex baseband models of time-invariant passband systems.
The practical methods for the dual-band DPD of RF-PAs include a method for dual-band crest factor reduction by clipping and error-filtering, a dual-band DPD model based on a vector-switched generalized memory polynomial, and a dual-band DPD training algorithm based on the indirect and direct learning architectures. These methods were implemented in MATLAB and validated at the 2017 DPD competition at the IEEE International Microwave Symposium, reaching the first place within the competition.
The overall quiescent current is approximately 100 nA.
This thesis investigates theoretical foundations and practical methods for the behavioral modeling and DPD of RF-PAs. The main contributions are a semi-physical model of the joint linearity-efficiency characteristics of RF-PAs, a detailed analysis of polynomial baseband models of RF-PAs focusing on the often neglected even-order terms in baseband, and a collection of practical methods for the dual-band DPD of RF-PAs.
The trade-off between the linearity and efficiency of RF-PAs is investigated based on the semi-physical RF-PA model. For this purpose, linearity and efficiency quantification methods are introduced and applied to the model. Furthermore, an overview on highly efficient RF-PA operation modes and efficiency enhancement methods is given.
A central result regarding polynomial baseband models is the first formal justification of even-order terms in baseband. This is achieved by deriving explicit passband-baseband pairs for the quasi-memoryless polynomial and the Volterra series, which show that even-order terms in baseband correspond to modified basis functionals in passband.
Another central result of the presented analysis of polynomial baseband models is the formulation and proof of the phase homogeneity requirement, which represents a necessary symmetry of all complex baseband models of time-invariant passband systems.
The practical methods for the dual-band DPD of RF-PAs include a method for dual-band crest factor reduction by clipping and error-filtering, a dual-band DPD model based on a vector-switched generalized memory polynomial, and a dual-band DPD training algorithm based on the indirect and direct learning architectures. These methods were implemented in MATLAB and validated at the 2017 DPD competition at the IEEE International Microwave Symposium, reaching the first place within the competition.