Takeaways From the First Workshop on Modeling and Optimization for Active Devices [Young Professionals]

The first IEEE Young Professional Workshop on Modeling and Optimization for Active Devices took place on 25 October 2022, as a virtual event on Zoom

Experimental evaluation of sub-sampling IQ detection for low-level RF control in particle accelerator systems

The low-level radio frequency (LLRF) control system is one of the fundamental parts of a particle accelerator, ensuring the stability of the electro-magnetic (EM) field inside the resonant cavities. It leverages on the precise measurement of the field by in-phase/quadrature (IQ) detection of an RF probe signal from the cavities, usually performed using analogue downconversion. This approach requires a local oscillator (LO) and is subject to hardware non-idealities like mixer nonlinearity and long-term temperature drifts. In this work, we experimentally evaluate IQ detection by direct sampling for the LLRF system of the Polish free electron laser (PolFEL) now under development at the National Centre for Nuclear Research (NCBJ) in Poland. We study the impact of the sampling scheme and of the clock phase noise for a 1.3-GHz input sub-sampled by a 400-MSa/s analogue-to-digital converter (ADC), estimating amplitude and phase stability below 0.01% and nearly 0.01◦, respectively. The results are in line with state-of-the-art implementations, and demonstrate the feasibility of direct sampling for GHz-range LLRF systems

Automatic Optimization of Input Split and Bias Voltage in Digitally Controlled Dual-Input Doherty RF PAs

Digitally controlled Dual-Input Doherty Power Amplifiers (DIDPAs) are becoming in-creasingly popular due to the flexible input signal splitting between the main and auxiliary stages. Nevertheless, the presence of many degrees of freedom, e.g., input amplitude split and phase dis-placement as well as biasing for multiple stages, often involves inefficient trial-and-error procedures to reach a suitable PA performance. This article presents automated parameter setting based on coordinate descent or Bayesian optimizations, demonstrating an improvement in the performance in terms of RF output power and power-added efficiency (PAE) in the presence of broadband-modulated signals, yet maintaining suitable linear behavior for, e.g., communications applications

Combined Wideband Active Load-Pull and Modulation Distortion Characterization with a Vector Network Analyzer

We present a demonstrator set-up for amplifier error-vector magnitude (EVM) characterization in the presence of wideband load termination arbitrarily set by the user through active modulated signal injection. In the proposed implementation, both the EVM characterization and the wideband active load-pull (WALP) technique are solely based on iso-frequency ratioed measurements obtainable with legacy vector network analyzer (VNA) technology. By avoiding broadband signal demodulation, this approach allows to remove any receiver bandwidth limitation, thus enhancing measurement accuracy and enabling realistic modulation distortion assessment across arbitrarily-wide test bandwidths. The method is tested on a packaged power amplifier circuit for 5 and 30 MHz modulation bandwidths around 1.2 GHz

RF GaN-HEMT Technology Evaluation Framework Based on Drain Current Transient Measurements

A comprehensive framework is proposed for the extraction of RF GaN HEMT trap-related parameters (gate/drain lag, thermal resistance, trap activation energy, cross-section, and reduction of the 2DEG charge density due to trapping) from a small set of drain current transient (DCT) waveforms at a few different gate/drain voltage levels. The alternative identification of gate/drain lag and thermal resistance based on single-pulsed I-V (SPIV) characterization is shown to provide the same results, whereas the other trapping-related parameters cannot be extracted with a traditional SPIV approach, making the proposed DCT-based framework a more complete yet straightforward procedure for the comparative assessment of GaN HEMT process technologies

Automated Measurement Set-Up for the Electro-Mechanical Characterization of Piezoelectric Harvesters

This paper presents an automated measurement setup for the electro-mechanical characterization of piezoelectric energy harvesters in cantilever configuration. The setup provides a mechanical stimulus to the harvester and concurrently acquires mechanical and electrical quantities to characterize the electro-mechanical properties of the device under test in open-circuit conditions. The setup, composed by an electrodynamic shaker, a waveform analyzer, and two laser-based positioning sensors, is fully controlled via MATLAB. The use of two laser heads allows to measure the movement of the base, so to automatically consider artefacts due to the non-ideal response of the electrodynamic shaker. The proposed measurement system is compatible with any generic piezoelectric-cantilever harvesters, and it can be exploited for advanced modelling techniques that requires extensive experimental data. The proposed measurement setup was validated through the characterization of a commercial Piezo Protection Advantage (PPA) transducer up to 300 Hz

Large-signal GaN transistor characterization and modeling including charge trapping nonlinear dynamics

A double-pulse technique for the I/V characterization of GaN-based transistors is adopted for the nonlinear modeling of a 0.25 \u3bcm AlGaN/GaN on SiC FET. Experimental validation is provided by means of large-signal PA performance prediction both at low-frequency, in order to outline the role played by the resistive drain current source, and at microwaves. Improved prediction accuracy is demonstrated with respect to the use of standard single-pulse I/V characteristics

Nonlinear charge trapping effects on pulsed I/V characteristics of GaN FETs

Nonlinear dynamic characterization of 1-mm GaN FETs is carried out by means of pulsed waveform excitations, applied through a recently proposed measurement setup. Due to fast trap capture phenomena, standard narrow-pulsed I/V characteristics are found to deviate from the ideal behavior. In this paper, the effects of the nonlinear charge trapping on pulsed I/V characteristics are experimentally observed thanks to a particular feature of the adopted measurement setup, which allows the monitoring of the DC drain current components of the pulses. In addition, the progressive degradation of the device performance due to charge trapping phenomena at increasing excitation amplitudes is shown by means of a new pulsing procedure. \ua9 2013 European Microwave Association

Comparison of quantitative flow ratio, Pd/Pa, and diastolic hyperaemia-free ratio vs. fractional flow reserve in non-culprit lesion of patients with non-ST-segment elevation myocardial infarction

Abstract Aims To investigate the correlation between quantitative flow ratio (QFR), Pd/Pa, diastolic hyperaemia-free ratio (DFR), and fractional flow reserve (FFR, gold standard) in non-culprit lesion (NCL) of patients with non ST-segment elevation myocardial infarction (NSTEMI). The non-hyperemic pressure ratio (NHPR) and the angiography-based indexes have been developed to overcome the limitation of the use of the FFR. Methods and results Between January and December 2019, 184 NCL from 116 NSTEMI patients underwent physiologic assessment and were included in the study. NCLs were investigated with QFR, Pd/Pa, DFR, and FFR. Mean values of QFR, Pd/Pa, DFR, and FFR were 0.85 ± 0.10, 0.92 ± 0.07, 0.93 ± 0.05, and 0.84 ± 0.07, respectively. DFR and FFR showed a good correlation (r = 0.76). Bland and Altman plot showed a mean difference of 0.080. DFR diagnostic accuracy was 88%. The area under the ROC curve (AUC) for DFR was 0.946 (95% CI: 0.90–0.97, P = 0.0001). Similar findings were reported for Pd/Pa [r = 0.73; mean difference 0.095, diagnostic accuracy 84%, AUC 0.909 (95% CI: 0.85–0.94, P = 0.0001)] and QFR [r = 0.68; mean difference: 0.01; diagnostic accuracy: 88%, AUC: 0.964 (95% CI: 0.91–0.98, P = 0.0001)]. FFR, QFR, Pd/Pa, and DFR identified 31%, 32%, 30%, and 32% potentially flow-limiting lesions, respectively. Conclusions In NSTEMI patients, QFR, Pd/Pa, and DFR showed equivalence as compared to gold standard FFR in the discrimination of non-culprit lesions requiring revascularization