Effect of impedance variation around the fundamentals on PA distortions characteristics under wideband multi-tone stimulus

Characterisation of modern wireless power transistors and amplifies requires wideband-modulated stimuli for realistic performance evaluation. Normally power transistor performance is evaluated using passive load-pull techniques. However, these have some physical realization constraints that influence the amplitude and the phase of the presented impedance at the DUT plane as across the modulated bandwidth. The problem becomes more apparent as modulation bandwidth is increased beyond few MHz. It has been shown recently that a digitally controlled active envelop load-pull (ELP) system can completely address this problem [1], thus allowing for a more systematic investigation of the parameters that may affect the performance of power transistors under wideband-modulated stimuli. In this paper, non ideal multi-tone impedance conditions are purposely introduced for demonstrating their effects on power amplifier performance in order to illustrate the DUT sensitivity to measurement system imperfections at higher modulation bandwidths in excess of few MHz

Wideband active envelope load-pull for robust power amplifier and transistor characterisation

The advent of fourth generation (4G) wireless communication with available modulation bandwidth ranging from 1 MHz to 20 MHz is starting to emerge. The linear modulation technique being employed means that the power amplifiers that support the standards need to have high degree of linearity. By nature, however, all power amplifiers are non-linear. Load-pull measurement system provides anindispensable non-linear tool for the characterization of power amplifier and transistor for linearity enhancement. Conventional passive or active load-pull has delay problem that get worse as the modulation frequency is increased beyond few MHz. Furthermore in order to provide robust non-linear measurement, load-pull system needs to provide bandwidth at least five times the modulation bandwidth by including the fifth-order inter-modulation (IMD5). This thesis presents, for the first time, delay compensation on the unique active envelope load-pull architecture providing constant impedance for bandwidth up to 20 MHz. In doing so, it provides a superior load-pull measurement and also the ability to directly control in-band impedances. Artificial variations imposed on the in-band impedances offer further insight on power amplifier and transistor behaviours under wideband multi-tone stimulus.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Wideband active envelope load-pull for robust power amplifier and transistor characterisation

The advent of fourth generation (4G) wireless communication with available modulation bandwidth ranging from 1 MHz to 20 MHz is starting to emerge. The linear modulation technique being employed means that the power amplifiers that support the standards need to have high degree of linearity. By nature, however, all power amplifiers are non-linear. Load-pull measurement system provides anindispensable non-linear tool for the characterization of power amplifier and transistor for linearity enhancement. Conventional passive or active load-pull has delay problem that get worse as the modulation frequency is increased beyond few MHz. Furthermore in order to provide robust non-linear measurement, load-pull system needs to provide bandwidth at least five times the modulation bandwidth by including the fifth-order inter-modulation (IMD5). This thesis presents, for the first time, delay compensation on the unique active envelope load-pull architecture providing constant impedance for bandwidth up to 20 MHz. In doing so, it provides a superior load-pull measurement and also the ability to directly control in-band impedances. Artificial variations imposed on the in-band impedances offer further insight on power amplifier and transistor behaviours under wideband multi-tone stimulus

An enhanced modulated waveform measurement system

The microwave devices and circuits need to be characterized prior to being employed in the design of systems and components. Unfortunately the measurement systems required to characterize the microwave devices and circuits have not kept pace with the emerging telecommunication technologies demands. This has resulted into a situation where either the circuits being employed in the components are unoptimized or the yield and turn-around of optimized circuits are slow. One of the contributing factors of such situations is the limitations of the existing measurement systems to scale up in performance to fulfil the necessary requirements. This thesis presents an enhanced multi-tone, time domain waveform measurement and engineering system. The presented system allows for a more considered, and scientific process to be adopted in the characterisation and measurement of microwave power devices for modern day communications systems. The main contributions to the field of research come in two areas; firstly developments that allow for accurate time domain measurement of complex modulated signals using commercially available equipment; and secondly in the area of active impedance control, where significant developments were made allowing active control of impedance across a modulated bandwidth. The first research area addressed is the fundamental difficulty in sampling multi-tone waveforms, where the main achievements have been the realisation of a high quality trigger clock for the sampling oscilloscope and a “Time Domain Partitioning” approach to measure and average multi-tone waveforms on-board. This approach allows the efficient collection of high quality vectoral information for all significant distortion terms, for all bands of interest. The second area of research investigated suitable impedance control architectures to comprehensively investigate out-of-band impedance effects on the linearity performance of a device. The ultimate aim was to simultaneously present independent, baseband impedances to all the significant baseband (IF) frequency components and to 2nd harmonic that result from a multi-tone excitation. The main achievement in this area was the ability of the enhanced measurement system to present the broadband impedance. At baseband this has been achieved in the time domain using a single arbitrary waveform generator (AWG) to synthesise the necessary waveforms to allow a specific IF impedance environment to be maintained across a wide IF bandwidth. To engineer the RF out-of-band load terminations at RF frequencies and to emulate specific power amplifier modes, a Tektronix AWG7000 Arbitrary Waveform Generator was used to deliver the desired impedances, practically fulfilling the wideband application requirements for reliable device characterisation under complex modulated excitations.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

An enhanced modulated waveform measurement system

The microwave devices and circuits need to be characterized prior to being employed in the design of systems and components. Unfortunately the measurement systems required to characterize the microwave devices and circuits have not kept pace with the emerging telecommunication technologies demands. This has resulted into a situation where either the circuits being employed in the components are unoptimized or the yield and turn-around of optimized circuits are slow. One of the contributing factors of such situations is the limitations of the existing measurement systems to scale up in performance to fulfil the necessary requirements. This thesis presents an enhanced multi-tone, time domain waveform measurement and engineering system. The presented system allows for a more considered, and scientific process to be adopted in the characterisation and measurement of microwave power devices for modern day communications systems. The main contributions to the field of research come in two areas; firstly developments that allow for accurate time domain measurement of complex modulated signals using commercially available equipment; and secondly in the area of active impedance control, where significant developments were made allowing active control of impedance across a modulated bandwidth. The first research area addressed is the fundamental difficulty in sampling multi-tone waveforms, where the main achievements have been the realisation of a high quality trigger clock for the sampling oscilloscope and a “Time Domain Partitioning” approach to measure and average multi-tone waveforms on-board. This approach allows the efficient collection of high quality vectoral information for all significant distortion terms, for all bands of interest. The second area of research investigated suitable impedance control architectures to comprehensively investigate out-of-band impedance effects on the linearity performance of a device. The ultimate aim was to simultaneously present independent, baseband impedances to all the significant baseband (IF) frequency components and to 2nd harmonic that result from a multi-tone excitation. The main achievement in this area was the ability of the enhanced measurement system to present the broadband impedance. At baseband this has been achieved in the time domain using a single arbitrary waveform generator (AWG) to synthesise the necessary waveforms to allow a specific IF impedance environment to be maintained across a wide IF bandwidth. To engineer the RF out-of-band load terminations at RF frequencies and to emulate specific power amplifier modes, a Tektronix AWG7000 Arbitrary Waveform Generator was used to deliver the desired impedances, practically fulfilling the wideband application requirements for reliable device characterisation under complex modulated excitations

Novel power amplifier design using non-linear microwave characterisation and measurement techniques

This thesis, addresses some aspects of the well-known, problem, experienced by designer of radio frequency power amplifiers (RFPA): the efficiency/linearity trade-off. The thesis is focused on finding and documenting solution to linearity problem than can be used to advance the performance of radio frequency (RF) and microwave systems used by the wireless communication industry. The research work, this was undertaken by performing a detailed investigation of the behaviour of transistors, under complex modulation, when subjected to time varying baseband signals at their output terminal: This is what in this thesis will be referred to as “baseband injection”. To undertake this study a new approach to the characterisation of non-linear devices (NLD) in the radio frequency (RF) region, such as transistors, designated as device-under-test (DUT), subjected to time varying baseband signals at its output terminal, was implemented. The study was focused on transistors that are used in implementing RF power amplifiers (RFPA) for base station applications. The nonlinear device under test (NL-DUT) is a generalisation to include transistors and other nonlinear devices under test. Throughout this thesis, transistors will be referred to as ‘device’ or ‘radio frequency power amplifier (RFPA) device’. During baseband injection investigations the device is perturbed by multi-tone modulated RF signals of different complexities. The wireless communication industry is very familiar with these kinds of devices and signals. Also familiar to the industry are the effects that arise when these kind of signal perturb these devices, such as inter-modulation distortion and linearity, power consumption/dissipation and efficiency, spectral re-growth and spectral efficiency, memory effects and trapping effects. While the concept of using baseband injection to linearize RFPAs is not new the mathematical framework introduced and applied in this work is novel. This novel approach NOVEL POWER AMPLIFIER DESIGN USING NON-LINEAR MICROWAVE CHARACTERISATION AND MEASUREMENT TECHNIQUES CARDIFF UNIVERISTY - UK ABSTRACT vi has provided new insight to this very complex problem and highlighted solutions to how it could be a usable technique in practical amplifiers. In this thesis a very rigorous and complex investigative mathematical and measurement analysis on RFPA response to applied complex stimulus in a special domain called the envelope domain was conducted. A novel generic formulation that can ‘engineer’ signal waveforms by using special control keys with which to provide solution to some of the problems highlighted above is presented. The formulation is based on specific background principles, identified from the result of both mathematical theoretical analysis and detailed experimental device characterisation

Wideband and high-power nonlinear measurement system for the characterisation of GaN amplifiers

Recent RF applications and cellular networks architecture require to use high-power PAs, therefore it is critical to characterise their behaviour under appropriate operating condition with an accurate, reliable, fast, and flexible measurement system. As highpower PAs are typically operated in the pulsed mode, measurement system should be able to apply pulsed excitation and perform different types of characterisation under pulsed condition. Integrating pulsed capability into a measurement system to characterise large-signal behaviour of the device is relatively expensive and rigid in terms of instrumentation. Moreover, the inaccessible software that is used by the traditional systems has made them a vendor-defined system, where their application cannot be amended to scope specific phenomena. This is contrary to the need for a flexible pulsed system that can be extended and modified according to user preferences. This thesis presents a high-speed pulsed measurement system that maintains flexibility, upgradability, accuracy, expanded power, and bandwidth ranges. The system is configured around NI modules to apply DC and RF signals and analyse them by employing vector signal transceiver (VST) with up to 1 GHz bandwidth. Due to employing programable VSTs, and accessibility of measured raw samples, different types of measurements can be performed, and small and large-signal behaviour of the device can be analysed. The aforementioned features of the developed measurement system assist to analyse the time-domain behaviour of the device and characterise the physical phenomenon such as thermal, traps effect on large-signal behaviour of the device. As an application of developed high-power measurement system and operating it under wideband RF stimulus, the trapping effect on the large-signal behaviour of the PA is investigated. Time-domain behaviour represents significant variation in the input and output of the device. These variation leads to change the optimum load impedance of the device in time-domain, which decreases the performance of the device up to 8% and mostly linked to the traps of the device. moreover, linearity of the device in time-domain is analysed and intermodulation distortion levels of the device are extracted in time-domain at various timeslots of RF pulses. Interesting results are achieved by applying various drain-lag levels to the device, which shows linearity of the device increases up to 5 dB in back-off operation regime. In this work, for the first time, a nonlinear behavioural model is provided for the surface traps of GaN device. Developed measurement system utilise Cardiff behavioural model during load-pull measurements to decrease the number of load impedances to find the optimum impedance of the device and increase the speed of process. By applying gate-lag levels and pre-charging the surface traps of the device before conducting active load-pull measurements, relation between the Cardiff behavioural model and gate-lag levels of the device is investigated and a new model is achieved by using quadratic function to incorporate the gate-lag effect into the Cardiff behavioural model. Furthermore Cardiff behavioural model variation in timedomain is also achieved at different gate-lag levels and clarifies pre charging traps can reduce the variation in time-domain

Multi-sines stimulus design for the assessment of non-linear devices

The intention of the work presented is to provide novel, accurate and time-efficient way of designing multi-sines stimulus signal to replace real-life modulated signals prevailing within telecommunication networks, hence providing a novel tool for the development of modern RF measurement and design solution. The work demonstrated that with 50 tones, the multi-sines stimulus excites almost the same level of nonlinearity as real modulated signals do. For this conclusion the investigation of nonlinear behaviour mechanism was taken and a real DUT was measured under designed multi-siness and various types of modulated signals. It is also demonstrated that this multi-sines stimulus is compatible with the advanced RF measurement systems which are capable of measuring the complete RF waveform including the harmonic and base-band frequencies but demanding a periodical stimulus signal. Furthermore, a novel and quick sub-sampling algorithm was proposed to efficiently use the memory of Sampling Oscilloscope and therefore allows for accurate multi-sines capturing. An averaging algorithm for multi-sines stimulus was proposed to “stabilize” the captured waveform and a PCA based phase compensating algorithm was also proposed to tackle the problem of frequency shift under multi-sines excitation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo