Paul Tasker

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Papers by Paul Tasker

Comments on "A new low-noise AlGaAs/GaAs 2DEG FET with a surface undoped layer

IEEE Transactions on Electron Devices, 1987

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IIA-3 enhancement of 2DEG density in GaAs/InGaAs/AlGaAs double heterojunction power MODFET structures by buried superlattice and buried p<sup>+</sup>-GaAs buffer layers

IEEE Transactions on Electron Devices, 1987

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Highly Reflective Load-Pull

IEEE Microwave Magazine, 2011

ABSTRACT This article presented a review of the most common load-pull approaches adopted in the m... more ABSTRACT This article presented a review of the most common load-pull approaches adopted in the measurement and characterization of large-periphery microwave transistor devices. Although the quarterwave transformer technique is simple and very cost-effective, it has serious limitations in terms of scalability, thereby necessitating a separate quarterwave transformer for each device and frequency. Furthermore, due to the limited bandwidth of the quarterwave transformer, its usage in harmonic load-pull applications is severely limited.

Design, Fabrication, and Characterization of an Ultracompact Low-Loss Photonic Crystal Corner Mirror

IEEE Journal of Quantum Electronics, 2007

ABSTRACT An ultracompact, low-loss, and broad-band corner mirror, based on photonic crystals, is ... more ABSTRACT An ultracompact, low-loss, and broad-band corner mirror, based on photonic crystals, is investigated in this paper. Based on the theoretical analysis of the loss mechanism, the boundary layers of the photonic crystal region are revised to improve the extra losses, and the transmission characteristics are evaluated by using the 3-D finite-difference time-domain method. The device with optimized structure was fabricated on silicon-on- insulator substrate by using electron-beam lithography and inductively coupled plasma etching. The measured extra losses are about 1.1plusmn0.4 dB per corner mirror for transverse-electronic polarization for the scanning wavelength range of 1510-1630 nm. Dimensions of the achieved PC corner mirror are less than 7times7 mum2, which are only about one tenth of conventional waveguide corner mirrors.

Direct extraction of large-signal table-based behavioural models from time-domain voltage and current waveforms

High Frequency Postgraduate Student Colloquium, 2005

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Inverse class-FJ: Experimental validation of a new PA voltage waveform family

This paper presents for the first time an experimental validation of the continuous inverse class... more This paper presents for the first time an experimental validation of the continuous inverse class-F mode with varying the voltage waveforms, also known as inverse class-FJ. Starting from the standard inverse class-F condition and varying fundamental and third harmonic impedances whilst maintaining an open-circuit second harmonic load it will be demonstrated that output power and drain efficiency can be maintained

Robust Extraction of Cardiff Model Parameters from Appropriately Tailored Measured Load-Pull Data

2020 IEEE BiCMOS and Compound Semiconductor Integrated Circuits and Technology Symposium (BCICTS), 2020

In the design of power amplifiers the ideal methodology would be a CAD based design cycle using a... more In the design of power amplifiers the ideal methodology would be a CAD based design cycle using a physics-based state-function (I-V, Q-V) non-linear model. In practice state-function models are often more measurement-based than physics-based and by design very general, which does limit their accuracy. Behavioral models extracted directly from measured data provide a complementary methodology, that should address the accuracy limitations of state function models. However, their success in achieving this is highly dependent on the user's behavioral model complexity selection and their measurement dataset choice. In this paper, it will be shown that this issue for the Cardiff Model can be resolved via the design of appropriately tailored measurement datasets.

AlGaInP/GaInAs/GaAs Modfet Devices With Self-Aligned P+-GaAs Gate Structure

MRS Proceedings, 1993

A self-aligned fabrication scheme of a novel AlGaInP/GaInAs/GaAs-MODFET device has been developed... more A self-aligned fabrication scheme of a novel AlGaInP/GaInAs/GaAs-MODFET device has been developed. Two characteristic features have been incorporated in the device structure: An AIGaInP barrier which provides a larger conduction band offset than the commonly used AlGaAs and a highly carbon-doped p-type GaAs gate structure which supports a very simple fabrication scheme. Using 1/am optical lithography we have fabricated first demonstrator devices with a current gain cutoff frequency of 60 GHz and a power gain cutoff frequency of 140 GHz. In addition, the devices show large gate-drain diode breakdown voltages in excess of 30 V and gate currents as low as 50 nA even at gatesource voltages of-5 V.

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Practical waveform engineering

IEEE Microwave Magazine, 2009

RF I-V waveform measurement and engineering systems are now finally enabling practical waveform e... more RF I-V waveform measurement and engineering systems are now finally enabling practical waveform engineering to be directly undertaken with systems capable of supporting continuous wave stimulus reaching a high level of maturity. On-going research and development activities are presently addressing the multitone requirement. The availability of RF I-V measurement and engineering capability extends the characterization opportunities for both high-frequency/speed transistor

Look‐up table method for optimising coupling ratio in broadband sequential power amplifiers

IET Microwaves, Antennas & Propagation

This study reappraises the optimum design parameters for the sequential power amplifier (SPA) whe... more This study reappraises the optimum design parameters for the sequential power amplifier (SPA) when taking relative phase difference into account. By including the phase relationship between the main and peaking amplifiers, a modified efficiency formulation is derived that reveals the impacts of the key design parameters on the SPA efficiency at output power back-off. To optimise a wideband high-efficiency SPA design, a look-up table method is used to predict the required coupling ratio for a wideband directional coupler. To validate the design approach, a 1.5–2.4 GHz SPA is designed and measured, showing drain efficiency higher than 40% at 6 dB back-off across the band. When characterised using a 20 MHz long term evolution (LTE) signal and digital predistortion, the SPA shows good linearity with error vector magnitude <1.3%, and adjacent channel leakage ratio levels better than −45 dBc across the band.

New Formulation of Cardiff Behavioral Model Including DC Bias Voltage Dependence

IEEE Microwave and Wireless Components Letters

A new mathematical formulation for the Cardiff nonlinear behavioral model is presented in this wo... more A new mathematical formulation for the Cardiff nonlinear behavioral model is presented in this work which includes the DC bias voltages (drain and gate) into the model. It has been verified by modelling a GaN on SiC high electron mobility transistor (HEMT) at 3.5 GHz. For the case presented, interpolation of load-pull data has resulted in more than 90 % reduction in the density of the load-pull data required to generate a nonlinear behavioral model over a wide range of DC bias points. Index Terms-Load-pull, Behavioral model, Power amplifier, Nonlinear device modelling I. INTRODUCTION Advancement in large-signal and waveform measurement systems[1], [2] has created an opportunity for direct utilization of measurement data (specifically load-pull measurement) into the computer-aided design (CAD) environment [3]. However, the generality requirement of advanced radiofrequency power amplifier (RFPA) designs demands load-pull data under various variables such as frequency, input power, and DC bias voltage which can be very time-consuming. Therefore, it is critical to adopt a strategy to reduce the measurement intensity and in doing so, reduce measurement time. One approach to reducing the density of the required load-pull data is to use an accurate and reliable nonlinear behavioral model to interpolate the data. Current industry-leading nonlinear behavioral models are Cardiff University's Cardiff behavioral model [4] and Keysight's X-parameters [5]. Regarding the Cardiff model, to enhance its generality, variables such as frequency, transistor size, input power, etc. have been previously included into its mathematical formulation [6], [7]. In terms of DC bias, however, in the current formulation of Cardiff model [8] (and also X-parameters [9]) the DC bias voltages are treated as independent variables; hence, load-pull measurements at each DC bias voltage are required to generate a bias-dependent model. The CAD tools can be allowed perform simple interpolation. Our previous work in [10] identifies the linear relationship between the Cardiff model coefficients and the gate voltage ' ' sweep and proposes a new Cardiff model formulation to include the into the Cardiff model. In this paper, we present a new expansion for the Cardiff model to include both gate ' ' and drain ' ' bias variation while maintating a

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Load-Pull Data Analysis of a GaN on SiC HEMT Targeting Multi Bias Doherty Design

2022 International Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits (INMMiC)

This paper presents an analysis of load-pull measurement data of a GaN on SiC high electron mobil... more This paper presents an analysis of load-pull measurement data of a GaN on SiC high electron mobility transistor (HEMT) at 3.6 GHz, oriented to aid the design of Doherty power amplifiers with multiple DC supply voltages. Fundamental loadpull data in class AB configuration are analyzed to realize the optimum load modulation for the design of the "Main" amplifier at DC bias levels of 28 V and 50 V.

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A de-embedding network at higher frequency and its error analysis

2016 IEEE International Conference on Electronic Information and Communication Technology (ICEICT), 2016

The intrinsic performance of the devices is of great meaning during power amplifiers design. A me... more The intrinsic performance of the devices is of great meaning during power amplifiers design. A method to update de-embedding network at 5.8 GHz for packaged power devices is put forward based on physical modeling idea. The de-embedding network of a packaged GaN HEMT is presented and its errors are analyzed based on waveform engineering. The results may well lead to optimization of the de-embedding network.

A Systematic Investigation of Behavioural Model Complexity Requirements

2018 13th European Microwave Integrated Circuits Conference (EuMIC), 2018

{ 1 mamoure, 3 monica.barciela }@uvigo.es, { 2 casbonma, 4 Tasker }@cardiff.ac.uk design space (o... more { 1 mamoure, 3 monica.barciela }@uvigo.es, { 2 casbonma, 4 Tasker }@cardiff.ac.uk design space (or, if required, analytically extrapolate with respect to A 2i), provided the model complexity chosen addresses the required mixing order necessary. In this paper, a systematic study is undertaken to investigate the complexity required for the Cardiff model to achieve a given precision on the model prediction, which respected to load impedance, for different LP contour defined Smith Chart design regions. The investigation is undertaken on GaN HFETs.

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Study of Drain Injected Breakdown Mechanisms in AlGaN/GaN-on-SiC HEMTs

IEEE Transactions on Electron Devices, 2022

Breakdown mechanism in 0.25 μm gate length AlGaN/GaN-on-SiC iron doped HEMTs with background carb... more Breakdown mechanism in 0.25 μm gate length AlGaN/GaN-on-SiC iron doped HEMTs with background carbon is investigated through the drain current injection technique. The measurement results reveal that it can be divided into two distinct stages according to the gate voltage levels. The first stage of the measured drain injected breakdown is mainly due to the initiation of the punch-through process under the gate, and the second stage of breakdown is associated with the potential barrier between the unintentionally doped GaN and the Fe doped p-type GaN buffer layer which also has a higher carbon density. The electroluminescence (EL) results suggest that the first stage shows uniform punch-through current flow, but localized leakage current flow associated with a snapback breakdown mechanism replaces the uniform punch-through current flow and dominates the second stage. A 2D-TCAD simulation has been implemented and shows the current paths under uniform flow conditions.

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Optimising Linearity of Envelope Tracking Power Amplifier Using Baseband Linearisation Approach

2020 International Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits (INMMiC), 2020

The aim of this paper is to improve the linearity of an envelope tracking (ET) power amplifier (P... more The aim of this paper is to improve the linearity of an envelope tracking (ET) power amplifier (PA) using a simple baseband linearisation approach (BLA), which releases the requirement for the ET-customised digital predistortion (DPD) techniques. The proposed BLA is verified through the comparative study on a Gallium Nitride (GaN) PA with ET and a 28V supply voltage. A two-tone signal and a 20MHz modulated signal are used in the measurement, which demonstrates that in contrast to the 28 V case, the ET PA using BLA can simultaneously achieve higher efficiency and better linearity. To investigate the linearity improvement of using BLA, the constellation diagrams, AM/AM and AM/PM characteristics with and without generalized memory polynomial (GMP)-based DPD are measured and analysed.

Investigation of transport phenomena in pseudomorphic modfets

A Novel Modulated Rapid Load Pull System for the Emulation of Envelope Tracking Power Amplifiers

Electronics Letters, 2020

This Letter presents a novel characterisation system that is able to fully emulate a complete env... more This Letter presents a novel characterisation system that is able to fully emulate a complete envelope tracking power amplifier (ET-PA) environment, with modulated impedance synthesis and dynamic supply voltage generation while using industry-standard modulated signals and digital pre-distortion. The system is used to characterise a 10 W GaN device and provide impedance control over the signal and distortion bandwidths, in response to a 10 MHz long-term evolution signal. A National Instruments PXI-based measurement system is utilised to apply tracking signals to a bespoke supply modulator and successfully improve the average power added efficiency by ~18 percentage points. Three different shaping functions are implemented, and their efficiency and linearity performance evaluated. In addition, digital pre-distortion (DPD) is used to linearise the PA while operating with the three different tracking trajectories. Experimental results demonstrate that when applying shaping functions, a trade-off needs to be made between efficiency and linearity. Even though a constant gain shaping function provides lower efficiency, it achieves good raw linearity performance without DPD, which is a good option if local linearisation is not available. This novel system is a useful tool in the design of ET-PAs, to more completely investigate the performance of the device.

Broadband non-linear FET behavioral model defined in the admittance domain

2016 11th European Microwave Integrated Circuits Conference (EuMIC), 2016

Cit ati o n f or p u blis h e d v ersi o n: Cit ati o n f or p u blis h e d v ersi o n: M. R. M o... more Cit ati o n f or p u blis h e d v ersi o n: Cit ati o n f or p u blis h e d v ersi o n: M. R. M o ur e, M. F er n a n d ez-B ar ci el a, M. C as b o n a n d P. J. T as k er, " Br o a d b a n d n o nli n e ar F E T b e h a vi or al m o d el d efi n e d i n t h e a d mitt a n c e d o m ai n," 2 0 1 6 1 1t h E ur o p e a n Mi cr o w a v e I nt e gr at e d Cir c uits C o nf er e n c e (E u MI C),

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A practicable de-embedding network at higher frequency of a packaged GaN device

2016 IEEE MTT-S International Wireless Symposium (IWS), 2016

The intrinsic performance of the devices is of great meaning during power amplifiers design. A me... more The intrinsic performance of the devices is of great meaning during power amplifiers design. A method to update de-embedding network at higher frequency for packaged power devices is put forward based on physical modeling idea. The de-embedding network at 5.8 GHz of a packaged GaN HEMT is presented and its practicability is verified through error analysis. This method is prospected to be applied to other packaged microwave devices.

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