3-Way Doherty Power Amplifiers: Design Guidelines and MMIC Implementation at 28 GHz

Abstract

This article presents the design strategy and the implementation of a three-way Doherty power amplifier (DPA3W) to enhance the efficiency at deep power back-off. Theoretical design equations are derived, based on which design charts are drawn to explore the available design space, accounting for practical constraints related to the available technology and selected application. The proposed design strategy is demonstrated by the design, fabrication and experimental characterization of a three-way multistage Doherty amplifier optimized for efficiency peaks at 6 and 12 dB back-off. The amplifier is realized on the WIN Semiconductors 150 nm GaN-SiC high-electron-mobility transistor (HEMT) monolithic process at 28 GHz, targeting 5G applications. The prototype achieves saturated output power in excess of 34 dBm and power added efficiency of the order of 15% from 6 to 12 dB back-off, demonstrating competitive performance and a good agreement between simulations and measurements, thus validating the approach.

A Ka-Band Doherty Power Amplifier in a 150 nm GaN-on-SiC Technology for 5G Applications

“…Finally, measurements Finally, Table 1 summarizes the DPA experimental results, while comparing them with the state-of-the-art Ka-band GaN works. A higher PAE performance has been reported by the authors of [12,13], while the authors of [9,11,12] achieved a higher output power level. However, all these works exhibited a much lower gain performance, which greatly increased their pre-amplifier requirements in terms of maximum output power, linearity, and efficiency, thus negatively affecting the system complexity and cost in addition to the overall transmitter performance.…”

“…On the other hand, gallium nitride (GaN) is nowadays the reference technology for the implementation of high-power and efficient power amplifiers. Although, over-W output power mm-wave DPAs in GaN technology have been already demonstrated [9][10][11][12][13][14], these works suffered from a limited gain performance. This means that they require a high input power, thus transferring to the pre-amplifier design requirements, such as output power, linearity, and efficiency.…”

A Two-Way GaN Doherty Amplifier for 5G FR2 With Extended Back-Off Range

“…The output combiner was implemented following the scheme proposed in [13], in which the parasitic elements of the devices were embedded in the structure as in [9]. The transformation from the standard 50-termination to the optimum impedance at the common node of the DPA (10 ) was carried out through a semi-distributed postmatching network realized by a C-L network.…”

“…The need to maximize average efficiency, particularly for OBO ranging from 9 to 12 dB [1], calls for the extension of the existing solutions, such as the 6-dB two-way Doherty power amplifier (DPA) [2], or the development of new topologies such as the load-modulated balanced amplifier (LMBA) [3], distributed efficient power amplifier (DEPA) [4], and N -way DPA [5]. Even if a few examples extend toward high frequency [6], [7], [8], the prototypes presented in the literature mainly operate in the sub-6-GHz frequency bands and are based on single-stage demonstrators, achieving gains of the overall amplifier of the order of 10 dB.…”

“…Furthermore, examples that comprehensively address the extended OBO scenario in FR2 are scarce [7], [8], [9].…”