RF IV waveform engineering applied to VSWR sweeps and RF stress testing

This thesis looks at how the Radio Frequency (RF) waveform measurement and engineering techniques developed for Power Amplifier (PA) design can be used to investigate RF reliability. Within this area two major themes are concentrated on – firstly the effect of a load impedance mismatch and secondly an investigation into using the RF IV waveform measurement system for RF stress testing. The initial aim for this work was to investigate the potential for removing the output protection isolator from a PA. It was seen that in doing so there is the potential to cause an impedance mismatch, which results in a portion of the power produced being reflected back. It was shown that the conditions that could be presented to a device as a result of an impedance mismatch can be found by performing a Voltage Standing Wave Ratio (VSWR) sweep. The results of the worst possible case scenario VSWR sweep, when all of the power is reflected back, can be split into three regions. One of high RF drain voltage swings, one of high RF drain currents and a transition region of simultaneously high RF drain currents and voltage swings. Each of these regions presents different operating conditions to the device, and in turn different stresses. The second part of this thesis concentrates on an investigation into Gallium Nitride (GaN) Heterostructure Field Effect Transistor (HFET) reliability, specifically if the RF waveform measurement system can be used to provide detailed information about the state of the device during RF stress testing. A stress testing procedure was developed to allow this, which featured both DC and RF characterisation measurements before and after every stress period. It was shown that the measurements made during the characterisation stages only gives a representation of the degradation seen in the same measurements during the RF stress period

Development of an RF IV waveform based stress test procedure for use on GaN HFETs

This paper reports on the development of an RF IV waveform based stress test procedure. DC and low-voltage RF characterisation was carried out before and after high power RF stress. RF waveform measurements showed that the exact change in the RF load line induced during RF degradation cannot be directly inferred from the DC or low power RF measurement. The RF degradation takes the form of a knee-walkout, a small pinch-off shift consistent with charge trapping and defect generation, and in addition gate leakage occurs once the RF voltage exceeds a critical voltage

125 - 211 GHz low noise MMIC amplifier design for radio astronomy

To achieve the low noise and wide bandwidth required for millimeter wavelength astronomy applications, superconductor-insulator-superconductor (SIS) mixer based receiver systems have typically been used. This paper investigates the performance of high electron mobility transistor (HEMT) based low noise amplifiers (LNAs) as an alternative approach for systems operating in the 125 — 211 GHz frequency range. A four-stage, common-source, unconditionally stable monolithic microwave integrated circuit (MMIC) design is presented using the state-of-the-art 35 nm indium phosphide HEMT process from Northrop Grumman Corporation. The simulated MMIC achieves noise temperature (T_e) lower than 58 K across the operational bandwidth, with average T_e of 38.8 K (corresponding to less than 5 times the quantum limit (hf/k) at 170 GHz) and forward transmission of 20.5 ± 0.85 dB. Input and output reflection coefficients are better than -6 and -12 dB, respectively, across the desired bandwidth. To the authors knowledge, no LNA currently operates across the entirety of this frequency range. Successful fabrication and implementation of this LNA would challenge the dominance SIS mixers have on sub-THz receivers

125 - 211 GHz low noise MMIC amplifier design for radio astronomy

To achieve the low noise and wide bandwidth required for millimeter wavelength astronomy applications, superconductor-insulator-superconductor (SIS) mixer based receiver systems have typically been used. This paper investigates the performance of high electron mobility transistor (HEMT) based low noise amplifiers (LNAs) as an alternative approach for systems operating in the 125 — 211 GHz frequency range. A four-stage, common-source, unconditionally stable monolithic microwave integrated circuit (MMIC) design is presented using the state-of-the-art 35 nm indium phosphide HEMT process from Northrop Grumman Corporation. The simulated MMIC achieves noise temperature (T_e) lower than 58 K across the operational bandwidth, with average T_e of 38.8 K (corresponding to less than 5 times the quantum limit (hf/k) at 170 GHz) and forward transmission of 20.5 ± 0.85 dB. Input and output reflection coefficients are better than -6 and -12 dB, respectively, across the desired bandwidth. To the authors knowledge, no LNA currently operates across the entirety of this frequency range. Successful fabrication and implementation of this LNA would challenge the dominance SIS mixers have on sub-THz receivers

RF waveform investigation of VSWR sweeps on GaN HFETs

Solid state amplifiers are often fitted with an isolator component on the output to protect them from impedance mismatch. GaN based HFET’s could offer the potential to remove the isolator due to their high breakdown voltages and high channel temperature operation. However the absence of an isolator would mean that the transistor would have to be able to withstand any load impedance that could be presented to it. The usual method to test for impedance mismatch is to select a fixed VSWR ratio and then sweep the load phase through 360°. In this paper a range of VSWR sweeps are investigated. The measurements are performed in a system that provides the RF voltage and current waveforms, as a consequence novel impedance contour plots can be generated. These plots can then aid in identifying potential failure mechanisms and load conditions to avoid

125 - 211 GHz low noise MMIC amplifier design for radio astronomy

To achieve the low noise and wide bandwidth required for millimeter wavelength astronomy applications, superconductor-insulator-superconductor (SIS) mixer based receiver systems have typically been used. This paper investigates the performance of high electron mobility transistor (HEMT) based low noise amplifiers (LNAs) as an alternative approach for systems operating in the 125 - 211 GHz frequency range. A four-stage, common-source, unconditionally stable monolithic microwave integrated circuit (MMIC) design is presented using the state-of-the-art 35 nm indium phosphide HEMT process from Northrop Grumman Corporation. The simulated MMIC achieves noise temperature (Te) lower than 58 K across the operational bandwidth, with average Te of 38.8 K (corresponding to less than 5 times the quantum limit (hf/k) at 170 GHz) and forward transmission of 20.5 +/- 0.85 dB. Input and output reflection coefficients are better than -6 and -12 dB, respectively, across the desired bandwidth. To the authors knowledge, no LNA currently operates across the entirety of this frequency range. Successful fabrication and implementation of this LNA would challenge the dominance SIS mixers have on sub-THz receivers.Comment: 8 pages, 3 figures, 1 table. Submitted and accepted in Experimental Astronomy, awaiting publicatio

High-speed device characterization using an active load-pull system and waveform engineering postulator

This paper presents a methodology that provides rapid estimation of the parameters necessary for the high-speed characterization of transistor devices used in modern microwave power amplifiers. The key in achieving this significant measurement speed improvement is the use of a systematic waveform postulation methodology in combination with an active harmonic load-pull measurement system. The methodology is based on a rapid and systematic procedure that initially requires only a few DC measurement parameters to approximate the device's transfer characteristic and boundary conditions. Using these parameters, it is then possible to accurately estimate or `postulate' the idealized output current and voltage waveforms, in this case for a three harmonic Class-F mode. These waveforms are rich in information and provide harmonic load impedances as well as other key postulated parameters that can then be used to `guide' the harmonic active load-pull measurement system resulting in a very time-efficient characterization process