Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

This paper presents an octave-bandwidth load modulated balanced amplifier (LMBA) that operates directly on a single modulated RF input. The architecture is based on the recently proposed LMBA technique, in which a control signal applied at the output isolation port of a balanced amplifier is used to modulate the apparent load impedance of the two devices comprising the balanced amplifier. In our approach, the injected control signal is used both as an active match and to dynamically load modulate the main devices to provide efficiency enhancement at back-off, thus extending the dynamic range compared to the original LMBA formulation. In this paper, we introduce a phase-compensation technique through which the active matching and load modulation tracks the frequency-dependent optimal loading trajectory of a packaged device. The result is a load-modulation power amplifier architecture able to perform an active, modulated match over an octave bandwidth. The technique is demonstrated over 1.8–3.8 GHz using packaged devices and an off-the-shelf hybrid coupler. The proof-of-concept octave RF-input LMBA has a peak CW output power of 44 dBm, with power added efficiency (PAE) over the 1.8–3.8 GHz operating frequency range of 37%–59% at peak power and 29%–45% at 6-dB output backoff. The RF-input nature of this architecture enables straightforward measurement with modulated signals; a W-CDMA signal at 3.8 GHz with 9-dB (measured) peak to average power ratio is demonstrated with adjacent channel leakage ratio of −30 dBc and average PAE of 18% for a 31-dBm average output power (2-dB backoff).

RF-Input Load Modulated Balanced Amplifier With Octave Bandwidth

The unique material properties of GaN, wide bandgap, high thermal conductivity, high breakdown voltage, high electron mobility and the device properties of GaN HEMT (High Electron Mobility Transistor) namely low parasitic capacitance, low turn on resistance and high cut off frequencies make it a good choice to use in a power amplifier. During this era of wire- less communication with complex modulation schemes having high peak to average power ratio, maintaining the efficiency and linearity of power amplifier is a tough task. In this paper an extensive review of GaN HEMT based power amplifier is presented. First of all, GaN technology is described and compared with other semiconductor technologies. The different classes of power amplifier like class B, C, D, E, F and J with GaN is discussed. Efficiency and linearity enhancement techniques like envelope tracking, Doherty power amplifier and digital predistortion used in applications with high PAPR waveforms is described. The advantages of GaN MMIC (Microwave Monolithic Integrated Circuit) are reviewed. Finally different thermal management solutions used for GaN power amplifier to cope with its self heating phenomenon are explained.

A review of GaN HEMT broadband power amplifiers

(Ba,La)SnO3 is a wide bandgap semiconducting perovskite oxide with high electron mobility and excellent oxygen stability. The carrier modulation of (Ba,La)SnO3 channel by field effect on perovskite SrTiO3 substrates has been demonstrated in the recent reports. Here we report that (Ba,La)SnO3 on non-perovskite MgO substrate can also exhibit a high electron mobility and excellent carrier modulation by field, an important step towards scaling up for wafer-size processing. We optimized the undoped buffer layer thickness and measured the transport properties as a function of the La doping. The maximum mobility is 97.2 cm2/Vs at 2.53×1020/cm3. The transmission electron microscope images show that the films are epitaxial with about 2×1011/cm2 threading dislocation density. The field effect device based on the (Ba,La)SnO3 channel on MgO substrates is modulated with a high mobility of 43.9 cm2/Vs and Ion/Ioff of about 3.0×107.

High mobility BaSnO3 films and field effect transistors on non-perovskite MgO substrate

This paper presents a monolithic microwave integrated circuit multifunction chip implemented using a 0.25- $\mu \text{m}$ gallium arsenide pseudomorphic high-electron-mobility transistor process for use in a phased array jammer transmitter. This chip, which operates in the frequency range of 6–18 GHz, provides several functions including 8-bit true time delay (TTD), 7-bit attenuation, wideband amplification, and digital serial-to-parallel conversion for 15-bit control. The TTD and attenuation coverage are 255 ps with a step of 1 ps and 31.75 dB with a step of 0.25 dB, respectively. The TTD employing an artificial transmission line configuration demonstrates a root-mean-square delay error of less than 1.7 ps in the operating frequency range. The chip has a compact size of $4\,\,\hbox {mm} \times 5$ mm and exhibits a typical gain of 12 dB and an output P1dB of 16.5 dBm over a frequency range of 6–18 GHz.

A 6–18-GHz GaAs Multifunction Chip With 8-bit True Time Delay and 7-bit Amplitude Control

Non-Foster matching is applied to design a multi- octave broadband GaN power amplifier (PA) in this paper. The bandwidth limitation from high-Q interstage matching is overcome through the use of negative capacitor, which is realized with a negative impedance converter (NIC) using the cross-coupled GaN FETs. For high power operation over the entire bandwidth, the natural interstage matching is optimized for the upper subfrequency band and the lower subfrequency band is compensated for by the negative capacitance presented by non-Foster circuit (NFC). Detailed analysis is presented to understand the frequency and power limits of NIC circuits for PA applications. Two negative impedance matched PAs (NMPAs) are fabricated with 0.25- $\mu$ m GaN pHEMT process. The implemented PA with $2{\times}$ combining shows the output powers of 35.7–37.5 dBm with the power added efficiencies of 13–21% from 6 to 18 GHz. The $4{\times}$ combining PA achieves over 5 W output power from 7 to 17 GHz. The NFC boosts the efficiencies and power below 12 GHz to achieve broadband performance without using any lossy matching or negative feedback. To our knowledge, this is the first demonstration of NIC-based broadband amplifiers with multi-watt-level output power.

A Broadband GaN pHEMT Power Amplifier Using Non-Foster Matching

In this paper, a switchless dual-band, dual-mode power amplifier (PA) has been developed for multioctave operation. For the switchless dual-band operation, we proposed a new coupled-line-based diplexer structure. The proposed diplexer operates as a balun at high-band frequencies and the coupled line at low-band frequencies. To better understand the proposed diplexer structure, a detailed analysis is performed based on a coupled-line theory. The interstage and output-stage matching networks of the PA are designed by using the proposed diplexer. To maximize the power-added efficiency (PAE) of the designed PA, turn off the unused band PAs and decide the optimum off-state bias condition of transistors. The designed dual-band, dual-mode PA is fabricated with commercial 0.25- $\mu \text{m}$ GaN HEMT process. The fabricated PA shows over 15-dB small-signal gain at 5–11 GHz in the low-band mode and 9–18 GHz in the high-band mode. The measured average output power and PAE are 35 dBm, 23% in the low-band mode and 37 dBm, 26% in the high-band mode.

A 6–18-GHz Switchless Reconfigurable Dual-Band Dual-Mode PA MMIC Using Coupled-Line-Based Diplexer

A commercial 0.25 μm GaN process is used to implement 6–18 GHz wideband power amplifier (PA) monolithic microwave integrated circuits (MMICs). GaN HEMTs are advantageous for enhancing RF power due to high breakdown voltages. However, the large-signal models provided by the foundry service cannot guarantee model accuracy up to frequencies close to their maximum oscillation frequency (Fmax). Generally, the optimum output load point of a PA varies severely according to frequency, which creates difficulties in generating watt-level output power through the octave bandwidth. This study overcomes these issues by the development of in-house large-signal models that include a thermal model and by applying distributed L-C output load matching to reactive matched amplifiers. The proposed GaN PAs have successfully accomplished output power over 5 W through the octave bandwidth.

http://koreascience.or.kr:80/article/JAKO201611639884364.pdf

6-18 GHz Reactive Matched GaN MMIC Power Amplifiers with Distributed L-C Load Matching

Two-stage reactively matched gain cells are proposed to implement a high-gain multioctave distributed power amplifier (DPA). The proposed reactively matched distributed amplifier (RMDA) structure shows high gain and power in a small die size. Detailed analysis is presented to understand the design criteria for interstage matching of reactively matched cells. A shared dc bias network is proposed to simplify the biasing of each section to reduce the DPA die size. The thermal coupling effect of GaN high-power amplifier is minimized by optimizing the chip layout. The theoretical analysis is verified by the simulation and supported by the measured data. Two RMDAs are fabricated with a commercial 0.25- $\mu \text{m}$ GaN HEMT process. The implemented RMDA with the compact transistor layout has been implemented in a small die size of 10.7 mm2 and shows output powers reaching 40.3–43.9 dBm, power added efficiencies (PAEs) of 16–27%, and small-signal gains of 15.3–23.2 dB. The RMDA with the reduced thermal coupling achieves 40.6–43.4 dBm with a peak PAE of 29% in a slightly larger die size of 13.8 mm2. To the best of our knowledge, this is the first demonstration of a GaN DPA using reactively matched gain cells, showing very high gain and efficiency over multioctave bandwidth in a small die size.

A 6–18-GHz GaN Reactively Matched Distributed Power Amplifier Using Simplified Bias Network and Reduced Thermal Coupling

Two-stage reactively matched gain cells are applied to design a high-gain multi-octave distributed power amplifier (DPA) in this paper. The proposed reactively matched distributed amplifier (RMDA) structure shows a high gain and high output power performance within a small die size. The DC bias network of each section is simplified to implement the proposed structure in an MMIC and the design guide for the bias network is provided. A 6–18 GHz GaN DPA fabricated with the commercial 0.25-µm GaN HEMT process shows output power reaching 40.3–43.9 dBm with 16–27% PAE. To the best of our knowledge, this is the first demonstration of a GaN DPA using reactively matched gain cells, and it exhibits excellent small-signal gain and RF power performance capabilities among other reported GaN PAs with a multi-octave bandwidth up to the Ku-band.

Kwangseok Choi

Papers

A Broadband GaN pHEMT Power Amplifier Using Non-Foster Matching

A 6–18-GHz Switchless Reconfigurable Dual-Band Dual-Mode PA MMIC Using Coupled-Line-Based Diplexer

6-18 GHz Reactive Matched GaN MMIC Power Amplifiers with Distributed L-C Load Matching

A 6–18-GHz GaN Reactively Matched Distributed Power Amplifier Using Simplified Bias Network and Reduced Thermal Coupling

A 6–18 GHz GaN distributed power amplifier using reactive matching technique and simplified bias network