In ultrasonic systems, power amplifiers are one of the most important electronic components used to supply output voltages to ultrasonic devices. If ultrasonic devices have low sensitivity and limited maximum allowable voltages, it can be quite challenging to detect the echo signal in the ultrasonic system itself. Therefore, the class-J power amplifier, which can generate high output power with high efficiency, is proposed for such ultrasonic device applications. The class-J power amplifier developed has a power efficiency of 63.91% and a gain of 28.16 dB at 25 MHz and 13.52 dBm input. The pulse-echo measurement method was used to verify the performance of the electronic components used in the ultrasonic system. The echo signal appearing with the discharged high voltage signal was measured. The amplitude of the first echo signal in the measured echo signal spectrum was 4.4 V and the total-harmonic-distortion (THD), including the fundamental signal and the second harmonic, was 22.35%. The amplitude of the second echo signal was 1.08 V, and the THD, including the fundamental signal and the second harmonic, was 12.45%. These results confirm that a class-J power amplifier can supply a very high output echo signal to an ultrasonic device.

https://www.mdpi.com/1424-8220/20/8/2273/pdf

A Class-J Power Amplifier Implementation for Ultrasound Device Applications.

As wireless communication standard continues to evolve accommodating the demand of high data rate operation, the design of radio frequency (RF) power amplifier (PA) becomes ever challenging. PAs are required to operate more efficiently while maintaining stringent linearity requirement. In this paper, the design concepts of the PA in addressing these challenges are reviewed. The concepts are divided into two main categories, namely the linearization technique and efficiency enhancement technique. The mandatory attempt in realizing a low-cost design is also discussed.

Power Amplifier Design Methodologies for Next Generation Wireless Communications

In MRI systems, RF fields are affected by the presence of the human body in the scanner causing mismatch between the RF coil and the feed cable. A power amplifier incorporating an unconventional Cartesian feedback loop is presented which works to maintain a fixed current in the RF coil against impedance variations. The performance of the system is investigated by model simulation, including stability analysis, linearity improvement and mismatch compensation. A prototype amplifier is measured to verify the model.

/pdf/power-amplifier-for-magnetic-resonance-imaging-using-4q6kgmddtp.pdf

Power amplifier for magnetic resonance imaging using unconventional Cartesian feedback loop

For application in radar and communication systems operating in the frequency range around 250 GHz, a power amplifier (PA) millimeter-wave monolithic integrated circuit (MMIC) has been developed. The amplifier makes use of a novel coupler approach allowing for in-phase and equal-magnitude distribution of an incoming signal to four parallel output ports. This is possible due to a subtle use of grounded coplanar waveguide and air-bridge microstrip transmission lines, providing different propagation constants. With a size of quarter-wavelength, the coupler is very compact and is the key to the presented PA topology. The amplifier exploits the virtual open occurring due to the identical signals for transistor biasing and matching. The amplifier topology is applied to develop an amplifier MMIC. When biased for maximum gain, it shows a 17-GHz 3-dB bandwidth around its center frequency at 248 GHz with a maximum gain of 32.8 dB. When biased for maximum output power, it provides an output power of 10 and 8.5 dBm at 250 and 270 GHz, respectively. At 250 GHz, it demonstrates a state-of-the-art power density of 125 mW/mm. Due to the amplifier topology, the MMIC is very compact $({\hbox{1.25}}\times {\hbox{0.75}}~{\hbox{mm}}^{2})$ .

A Novel 1 $\times$ 4 Coupler for Compact and High-Gain Power Amplifier MMICs Around 250 GHz

Power amplifiers applied in modern active electronically scanned array (AESA) radars and 5G radios should have similar features, especially in terms of phase distortion, which dramatically affects the spectral regrowth and, moreover, they are difficult to be compensated by predistortion algorithms. This paper presents a GaN-based power amplifier design with a reduced level of transmittance distortions, varying in time, without significantly worsening other key features such as output power, efficiency and gain. The test amplifier with GaN-on-Si high electron mobility transistors (HEMT) NPT2018 from MACOM provides more than 17 W of output power at the 62% PAE over a 1.0 GHz to 1.1 GHz frequency range. By applying a proposed design approach, it was possible to decrease phase changes on test pulses from 0.5° to 0.2° and amplitude variation from 0.8 dB to 0.2 dB during the pulse width of 40 µs and 40% duty cycle.

A GaN HEMT Amplifier Design for Phased Array Radars and 5G New Radios

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Handbook Of Rf And Microwave Power Amplifiers