Browsing by Author "Aras, Yunus Erdem"

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Open Access
Analytical model and design of load modulated balanced amplifier
(2020-02) Aras, Yunus Erdem
RF power ampliﬁers (PA) with high eﬃciency and linearity are in high demand for modern communication systems. Modulated signals having a high peakto-average power ratio (PAPR) require PA’s to maintain these features in the output-back-oﬀ (OBO) region. Since higher linearity always brings the trade-oﬀ in the form of lower eﬃciency, a PA having both high eﬃciency and linearity is challenging requirement for RF designers. Load modulation is one of the promising techniques oﬀering good eﬃciencylinearity trade-oﬀ under OBO conditions for conventional PAs. This work presents an analytical model for the load modulated balanced ampliﬁer (LMBA) using the recently introduced analytical non-linear model of a RF power transistor. We show that it is possible to predict the eﬃciency and nonlinearity of the LMBA reasonably well using this simple transistor model having only a small number of parameters. To test the performance of the analytical model, we designed an LMBA using three identical discrete RF transistors and 3-dB hybrid couplers. The model parameters of the 5-W GaAs PHEMT are determined from the I-V characteristics and load-pull measurements. LMBA works at 1.7 GHz with a peak output power of 37.5 dBm and with a peak eﬃciency of 53%. The eﬃciency is measured to be 47% at 6 dB output-back-oﬀ.
Open Access
Correlation-based study of FEA and IR thermography to reveal the 2DEG temperature of a multi-fingered high-power GaN HEMT
(AIP Publishing LLC, 2022-02-23) Koçer, Hasan; Aras, Yunus Erdem; Soydan, Mahmut Can; Butun, Bayram; Özbay, Ekmel; Durna, Yılmaz
High electron mobility transistors (HEMTs) based on gallium nitride (GaN) with a wide range of application potentials need to be rigorously examined for reliability to take advantage of their intrinsically extraordinary properties. The most vital parameter of the reliability, the hotspot, or Tmax, resides in the two-dimensional electron gas (2DEG) temperature profile inside the device where optical access is often restricted. The device surface temperature can be measured by widespread IR thermography with the limitation of diffraction-based IR transmission losses. However, Tmax on the sub-surface cannot be reached thermographically. Although finite element analysis (FEA)-based thermal simulations can easily reveal the 2DEG temperature profile, accuracy is tightly dependent on the realistic modeling of material/structure parameters. Because these parameters are rather sensitive to fabrication and processing, it is quite difficult to specify them accurately. To overcome these drawbacks, a method integrating both IR thermography and FEA thermal analysis is demonstrated on a fabricated high-power 40 × 360 μm packaged GaN HEMT as a proof-of-concept. Utilizing the simulation and measurement temperature profiles, a correlation algorithm is developed so that accuracy of the FEA thermal simulation is improved by calibrating the parameters specific to fabrication/process conditions by thermographic measurement. Then, it is quantitatively shown that the proposed method is able to find the 2DEG temperature profile and Tmax with an accuracy that best suits the intrinsic and extrinsic characteristics of the device under test. The method sheds light on GaN reliability engineering by providing a feasible and reliable alternative to realistically reveal hotspot information for device lifetime assessments.
Open Access
GaN-based single stage low noise amplifier for X-band applications
(IEEE, 2022-07-18) Çağlar, Gizem Tendürüs; Aras, Yunus Erdem; Urfalı, Emirhan; Yılmaz, Doğan; Özbay, Ekmel; Nazlıbilek, Sedat
Source degenerated HEMTs are used to achieve good noise matching and better input return loss without degrading the noise figure and reducing the stability. This work presents an MMIC design for the frequency band of 8–11 GHz by using HEMTs with source degeneration in 0.15 µm GaN on SiC technology. All design work is done in the Advanced Design System. The LNA delivers more than 6.9 dB gain with better than 8.5 dB and 9.5 dB input and output return losses, respectively. In addition, the gain ripple is around 2.7 dB. The noise figure of the amplifier is achieved below 1.1 dB with P1dB of 17.2 dBm and %12.7 drain efficiency within the operating bandwidth at the bias conditions of 9 V /20 mA.
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(Bilkent University, 2014) Günendi, Sezen; Uysal, Ratipcan; Soydan, Mahmut Can; Aras, Yunus Erdem; Kostak, Gürol
Open Access
Unveiling Tmax inside GaN HEMT based X-band low-noise amplifier by correlating thermal simulations and IR thermographic measurements
(IEEE, 2022-12-20) Zafar, Salahuddin; Durna, Yılmaz; Koçer, Hasan; Akoğlu, Büşra Çankaya; Aras, Yunus Erdem; Odabaşı, Oğuz; Bütün, Bayram; Özbay, Ekmel
This paper presents a method to reveal the channel temperature profile of high electron mobility transistors (HEMTs) in a multi-stage monolithic microwave integrated circuit (MMIC). The device used for this study is a two-stage X-band low-noise amplifier fabricated using 0.15 m GaN-on-SiC technology with 4x50 m and 4x75 m HEMTs at the first and the second stage, respectively. The surface temperature measured through infrared (IR) thermography has a diffraction-limited resolution. Moreover, it is impossible to measure sub-surface Tmax residing inside the two-dimensional electron gas of HEMT using IR thermographic measurements. Finite element analysis (FEA) thermal simulations are performed in this study to acquire the surface and sub-surface temperature profiles of the whole MMIC. IR measurements and FEA simulations are integrated through a correlation-based method verifying the accuracy of the FEA-based temperature profiles. This method leads to accurately finding the hotspots in the MMIC, thus revealing the Tmax of both stages. The correlation method using two filters approach to match the measurements and simulated temperature profiles of all the stages finds its application in MMICs’ high-temperature operating lifetime reliability tests.
Open Access
X-band cascode LNA with bias-invariant noise figure using 0.15 µm GaN-on-SiC technology
(IEEE, 2022-07-18) Nawaz, Muhammad Imran; Aras, Yunus Erdem; Zafar, Salahuddin; Akoğlu, Büşra Çankaya; Tendürüs, Gizem; Özbay, Ekmel
Cascode HEMTs exhibit better stability and broad bandwidths performance as compared with common source HEMTs. This paper presents the design of a single stage broadband low noise amplifier based upon 0.15 um GaN HEMT technology in the frequency range of 8 – 12 GHz. Cascode HEMT with inductive source degeneration is utilized. All the design work is done using PathWave Advanced Design System. The LNA provides 9.5 to 10.6 dB with input return loss better than 10 dB and output return loss better than 8 dB in the whole band. The noise figure of the amplifier is below 1.9 dB. The linearity parameters P1dB and OIP3 are greater than equal to 16 dBm and 28 dBm respectively within operating bandwidth. The noise figure of the amplifier is fairly constant over 30 mA to 60 mA bias currents and 9 V – 18 V operating bias voltage. This is a unique finding which is being reported for the first time to the best of authors' knowledge.