High-efficiency S-band harmonic tuning GaN amplifier

: A key component of microwave telecommunication systems is the power amplifier (PA). The design parameters of a communication system, such as link performance, power budget, and thermal design are typically driven by the power amplifier's linearity, output power, and efficiency. These design parameters of PA are the key to ensuring an efficient system because the PA is the most power-consuming circuit in the communication system. In an effort to have students involved in this research area, the International Microwave Symposium (IMS) sponsored by IEEE Microwave Theory and Technique Society (MTT-S) has introduced a High Efficiency Power Amplifier Design Competition. In this report, we present a 2.8-GHz, 5-W, highly efficient PA based on a wide bandgap gallium nitride (GaN) high electron mobility transistor (HEMT) device (CGH 40010f from CREE). The PA design was presented at the 2010 IMS Student Design Competition and achieved the competition goal of output power greater than 5 W with a measured power added efficiency (PAE) of 61% at 2.8 GHz.

In this paper, a high-power amplifier integrated circuit (IC) in gallium-nitride (GaN) on silicon (Si) technology is presented at a W-band (75–110 GHz). In order to mitigate the losses caused by relatively high loss tangent of Si substrate compared to silicon carbide (SiC), low-impedance microstrip lines (20–30 Ω) are adopted in the impedance matching networks. They allow for the impedance transformation between 50 Ω and very low impedances of the wide-gate transistors used for high power generation. Each stage is matched to produce enough power to drive the next stage. A Lange coupler is employed to combine two three-stage common source amplifiers, providing high output power and good input/output return loss. The designed power amplifier IC was fabricated in the commercially available 60 nm GaN-on-Si high electron mobility transistor (HEMT) foundry. From on-wafer probe measurements, it exhibits the output power higher than 26.5 dBm and power added efficiency (PAE) higher than 8.5% from 88 to 93 GHz with a large-signal gain > 10.5 dB. Peak output power is measured to be 28.9 dBm with a PAE of 13.3% and a gain of 9.9 dB at 90 GHz, which corresponds to the power density of 1.94 W/mm. To the best of the authors’ knowledge, this result belongs to the highest output power and power density among the reported power amplifier ICs in GaN-on-Si HEMT technologies operating at the W-band.

The power, efficiency, and bandwidth performance improvements demonstrated by gallium nitride (GaN) material and technology are currently being utilized by state-of-the-art microwave power amplifiers in the latest generation of radar systems. High-power wide bandgap semiconductors play an important role in radar performance. For example, in a phased array radar, the RF energy is distributed to each element, phase shifted, and then amplified before being radiated. Throughout the 1990s, gallium arsenide (GaAs) had been the semiconductor of choice for efficiently amplifying this signal; however, as the performance requirements of these systems continued to increase to meet ever-growing threats, the industry began turning to GaN as an alternative semiconductor of choice.GaN has a significantly wider bandgap compared to GaAs, and GaN has a higher saturation velocity, a higher breakdown electric field, and better thermal conductivity in comparison to GaAs. As a result, GaN produces a 5× increase in output power over GaAs that enables radars to search 5× the volume in the same time, increase their effective range by 50%, or reduce their size by 50% depending on the specific application. AlGaN/GaN high electron mobility transistors (HEMTs) became the early heterostructure of choice providing RF output densities >6 W/mm at microwave and millimeter wave frequencies and high conductivity SiC substrates with a 7-8× improvement in thermal conductivity became the early substrate of choice. However, significant material and substrate issues needed to be solved before the reliability and yield of GaN transistors were sufficient to meet the stringent needs required in defense systems.Today, GaN power amplifier technology continues to evolve as solutions to push performance higher are sought through material choices resulting in larger current densities, through design changes enabling higher operating voltages, through process and transistor designs providing more efficient operation, and through various material advances to improve heat dissipation. In this presentation we will provide an overview of GaN technology development at Raytheon covering the early motivation, material challenges, and insertions as they relate to the issues faced today.

This paper presents a high efficiency class-E power amplifier (PA) suitable for wireless transmitters operating at 2 GHz. Compact impedance transformation network is designed, using micro-strip transmission lines, so that it simultaneously achieves fundamental load transformation and harmonic impedance control using only two open-circuit stubs (2fo, 3fo). The dimensions of the network’s elements were determined in order to concurrently attain a high harmonic suppression, minimum loss and high power added efficiency. The measurement results of the PA prototype, which is designed using a 10 W Gallium Nitride (GaN) HEMT transistor, showed state-of-the-art drain and power added efficiency (PAE). The achieved PAE, power gain and output power, when the drain is biased at 50V, were equal to 74%, 12.6 dB and 11.4W respectively. In addition, a second and third harmonic suppression in excess of −40 dBc and −75 dBc, respectively, is achieved without extra circuit tuning or additional filtering.

Fifth generation communication networks promise extremely high data throughputs, low latencies, and ultra-high reliability by employing small cells in high density networks. This will increase the use of highly inefficient microwave power amplifiers, that exhibit efficiencies sometimes as low as 10% for advanced multi-carrier waveforms. To overcome these inefficiencies and enable next generation technology development, the internal distributed behaviour of the packaged microwave power transistor has to be fully characterised, which is impossible using conventional port-based measurements. In this dissertation, the development of a set of multiphysics measurement techniques that capture the distributed electrical, electromagnetic, and thermal device behaviour is described. These new multiphysics measurement techniques enable the characterisation and direct visualisation of the inefficient device performance, providing a basis for future design optimisation. The techniques combine a non-linear vector network analyser, electro-optic, load-pull and thermoreflectance measurement systems that enable large signal time-domain electrical, distributed multi-harmonic vector electric field (E-field), and transient and steady-state thermal measurements. The multiphysics measurement set-up was used to characterise various transistors and PAs including 260 W silicon (Si) laterally diffused metal oxide semiconductor (LDMOS) field effect transistors in both air-cavity ceramic and plastic packages, 25 W gallium nitride (GaN) on silicon carbide high electron mobility transistors (HEMTs), 250 W GaN HEMT and 360 W Si LDMOS Doherty power amplifiers. The E-field measurements enabled the first ever imaging of parametric odd-mode oscillations within multi-die packaged high-power microwave transistors. Additionally, the measurement system was used to verify the effectiveness of in-package oscillation suppression circuits. As high-resolution E-field measurements can be slow, a surrogate modelling-based measurement algorithm was implemented to accelerate measurements 10-fold. Transient thermal measurements helped to identify abnormal transistor finger-to-finger heating in GaN HEMTs and revealed thermal differences along the gate width in GaN-based asymmetric transistors for Doherty power amplifier applications.

This paper presents a power amplifier (PA) Monolithic Microwave Integrated Circuit (MMIC) based on GaN High Electron Mobility Transistor (HEMT) at 110 GHz. A parallel cascade class AB power amplifier is used in order to increase linearity and efficiency. This single-ended three-stage power amplifier provides 19.6dBm output power (Pout) with large signal gain of 7.6dB and power added efficiency (PAE) of 5.7% at 110GHz. The proposed power amplifier exhibits output power of 18.7dBm at 1dB compression point (P 1dB ).

Recent advances in both high power millimeter wave (mmW) Gallium Nitride (GaN) technology and high-speed System on Chip (SoC) modem technology has enabled the development, fabrication, and field testing of a high speed, long range wireless datalink with fiber equivalent speed. The link exhibited nearly an 80 Gbps bi-directional data rate (40 Gbps in each direction) over a range of 16km. This was accomplished by using a combination of frequency and polarization multiplexing to combine a total of eight ∼10 Gbps modem channels on the lower (71–76 GHz) and upper (81–86 GHz) E-band channels. Each modem channel was separately up-converted and amplified with a Gallium Nitride (GaN) power amplifier. Frequency multiplexing was accomplished at E-band (post-amplification) to maintain high Power Added Efficiency (PAE) in the power amplifiers.

A millimeter-wave (mmWave) gallium nitride (GaN) high-power amplifier (HPA) monolithic microwave-integrated circuit (MMIC) was implemented, considering a source via effect. In this paper, we introduce guidelines for designing GaN HPA MMICs, from device sizing to meeting high-power specifications, power matching considering source via effects, schematic design of three-stage amplifier structures, and electromagnetic (EM) simulation. Based on the results of load pull simulation and small-signal maximum stable gain (MSG) simulation, the GaN high-electron-mobility transistor (HEMT) size was selected to be 8 × 70 μm. However, since the source via model provided by the foundry was significantly different from the EM results, it was necessary to readjust the power matching considering this. Additionally, when selecting the source via size, the larger the size, the easier the matching, but since the layout of the peripheral bias circuit is not possible, a compromise was required considering the actual layout. To prevent in-band oscillation, an RC parallel circuit was added to the input matching circuit, and low-frequency oscillation was solved by adding a gate resistor on the PCB module. The proposed PA was fabricated with a commercial 0.1 μm GaN HEMT MMIC process. It exhibited 38.56 to 39.71 dBm output power (Pout), 14.2 to 16.7 dB linear gain, and 14.1% to 18.2% power-added efficiency (PAE) in the upper Ka band. The fabricated GaN power amplifier MMIC shows competitive Pout in the upper Ka band above 33 GHz.

This paper presents a novel design approach of CMOS power amplifier (PA) using 50Ω matched coplanar waveguide component which improves the power efficiency for K-band applications. This new technique of designing PA also enhances the data transmission rate and achieves saturated output power in the desired frequency band. A two stage CMOS PA is designed in which coplanar waveguide line is used in order to provide broadband multi-section matching networks which could improve bandwidth, output power, power gain and power added efficiency (PAE). A two-stage CMOS PA design is simulated using predictive technology model (PTM) 65nm CMOS process in ADS.v.12. A simulation result of PA achieves a reflection parameter of −43.06dB at 23GHz with forward gain of 15.6dB over the frequency band of 20.5–24.5GHz. The best achievement of design is to achieve PAE of 58% using the concept of coplanar waveguide.

A high efficiency Ka‐band GaN high power amplifier (HPA) utilizing 0.15‐μm gallium nitride (GaN) high electron mobility transistor (HEMT) technology is presented in this letter. The MMIC is designed with load‐pull method, with the final stage matched to compromise between output power and power added efficiency (PAE). An output power of more than 43 dBm and a power added efficiency of more than 30% over the band of 33–37 GHz under a drain voltage of 24 V at 100 μs pulse‐width and 10% duty‐cycle have been achieved. The chip size is 2.8 mm × 3.4 mm (9.52 mm2).

This paper presents a new class of power amplifier (PA) - Class-iF- <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> - resolving the highly nonlinear double inflection characteristics in the conventional Class-F- <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> PA. It is illustrated that, by properly terminating the second harmonic source impedance Z <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2S</inf> from conventional short-circuit to open-circuit, the double inflection nonlinear gain profile can be mitigated in the proposed Class-iF- <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> PA, wherein the same saturation output power is achieved with less gain compression without drain efficiency trade-off. The idea was validated with source/load-pull and a broadband prototype operating from 2.0 to 2.6 GHz was designed using a commercial 10-W Gallium Nitride (GaN) transistor. Under continuous wave (CW) signal test, the proposed Class-iF- <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> PA can achieve 40.1-40.8-dBm output power, 71.2%-77.3% drain efficiency (DE) and 67.4%-74.1 % power added efficiency (PAE) at 3-dB gain compression level over 2.0-2.6 GHz.

Flexible radio frequency (RF) devices are in high demand for wearable electronics; however, they currently do not offer sufficient output power for application in fifth-generation wireless communication systems. This paper reports a bendable gallium nitride (GaN) high-electron-mobility-transistor (HEMT) with state-of-the-art output power in the microwave band. In this study, a fabrication method is proposed, where HEMT is originally grown on silicon carbide (SiC) substrates. After thinning the SiC substrates down to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5~\mu \text{m}$ </tex-math></inline-formula> , HEMT is transferred using a copper film rather than flexible substrates used in other studies. The measurements indicated that the fabricated devices exhibited a saturation output power of 2.65 W, corresponding to a power density of 2.65 W/mm, which was associated with maximum power added efficiency (PAE) of 51% at 3 GHz. The performance of the fabricated device remained stable even with a bending radius of up to 0.6 cm. These results indicated that the proposed fabrication method can potentially be used to realize high-power flexible RF electronics.

This work presents radio-frequency-microelectromechanical-system (RF-MEMS)-based tunable matching networks for a multi-band gallium nitride (GaN) power amplifer (PA) application. In the frequency range from 3.5–8.5 GHz return losses of 5–10 dB were measured for the input network, matching impedances close to the border of the Smith chart. For the output matching network return losses of 10–20 dB and insertion losses of 1.3–2 dB were measured. The matching networks can tune the PA to four different operating frequencies, as well as changing the transistor's mode of operation from maximum delivered-output-power to maximum power-added-efficiency (PAE), while keeping the operating frequency constant. Furthermore, different single pole double throw (SPDT)-switches are designed and characterized, to be used in frequency-agile transmit/receive-modules (T/R modules).

This letter reports a high-efficiency gallium nitride (GaN) high-electron mobility transistor (HEMT) Doherty power amplifier (DPA) based on the class-E topology for wideband code-division multiple-access (WCDMA) applications. The class-E topology is employed as the carrier and peaking cells of the Doherty configuration. For validations, the proposed DPA is designed and implemented with 25-W GaN HEMTs at 2.14 GHz. For the proposed DPA, the power-added efficiency (PAE) and drain efficiency of 56.1% and 61.2% are achieved at 40 dBm (6-dB backoff power from Psat) for a continuous wave. For a 1-carrier WCDMA signal, the PAE of 44.8% is obtained with an adjacent channel leakage ratio (ACLR) of -31 dBc at 37 dBm, which is an 8.9% improvement over the conventional DPA with an ACLR of -36.4 dBc.

We fabricated a wideband gallium nitride (GaN) power amplifier (PA) using a power combiner with impedance transformation function. We designed a four-way planar impedance transformer power combiner based on the transmission line transformer (TLT) technique. The fabricated PA exhibited an average output power (Pout) of 233 W, average power-added-efficiency (PAE) of 42 %, and average drain efficiency (η) of 47% in the frequency range of 0.5 GHz to 2.1 GHz. The fabricated P A exhibits a wider fractional bandwidth (FBW) than a reported P A with an output power of over 200 W.