This paper presents a novel methodology for designing broadband Doherty power amplifier (DPA) with extended output power back-off (OBO) range. A modified load modulation network (LMN) is proposed to enhance the OBO range and the bandwidth of the DPA simultaneously. Analysis is conducted to explore the relationship between the proposed LMN parameters and the broadband performance under various OBO levels. Generalized design formulas of the LMN parameters are then introduced to offer the broadband solution for arbitrary current ratios and OBO levels. An asymmetric DPA is demonstrated and implemented with Gallium Nitride (GaN) transistors using the proposed approach. The fabricated DPA operates from 1.4 GHz to 2.5 GHz with 9-dB OBO range. The measured drain efficiency reaches 61%-75.5% at saturation and 44.6%-54.6% at 9-dB OBO within the operating bandwidth. When driven by a 60 MHz modulated signal with 9-dB peak-to-average power ratio (PAPR), the fabricated DPA attains 47.4%-53.5% average drain efficiency and better than -45.5 dBc adjacent channel leakage ratio (ACLR) after digital predistortion.
This paper presents the design of continuous mode monolithic microwave integrated circuit (MMIC) power amplifiers (PAs) with bandwidth improvement. The output matching network (OMN) satisfying the continuous mode in broadband can be efficiently constructed with LC resonant circuits. The bandwidth can be further improved through generating the new LC unit in OMN with a minimum number of components added possible. Two prototype MMIC PAs are demonstrated with 0.25µm Gallium Nitride (GaN) MMIC process. The measured drain efficiency is over 39.2% and 38.7% from 4.5 GHz to 6.5 GHz, respectively. When driven by 100-MHz modulated signals, two PAs exhibit great linearity performance with adjacent channel leakage ratio lower than -51.2 dBc and -53.4 dBc with digital predistortion.
This article presents a practical design methodology to construct output matching networks for broadband continuous mode monolithic microwave integrated circuit (MMIC) power amplifiers (PAs). Unlike conventional harmonic manipulation approaches, combinations of parallel and series LC resonant circuits are utilized to build the matching networks as it can generate frequencydependent components and locate the varying impedance of continuous mode. With a proper design, the impedance variation in frequency domain can be mapped to the frequency response of the matching network at the fundamental frequency and the second harmonic simultaneously. Matching network design procedures are demonstrated and results show that the frequency response of the network has very good approximation with the desired continuous mode conditions. A prototype PA is implemented on 0.25-μm gallium nitride (GaN) MMIC process, and tested with both continuous-wave and modulated signals. Measurement results show 50.82% maximum drain efficiency and 8.5 dB gain can be achieved across the operation bandwidth of 5.4 to 6.4 GHz.
This paper presents the analysis and design of a three-stage load modulated power amplifier (PA) in which, three amplifiers, each with different biasing, are connected to a four-port coupler. It is illustrated that, by properly configuring current relationships between the three amplifiers, this new load modulated PA can provide flexible output power back-off (OBO) and achieve high efficiency within a large OBO range. The detailed theoretical analysis and design methodology are given. In this architecture, the OBO level can be adjusted by simply setting bias conditions of the relevant amplifiers that correspond to the current relationships. Therefore, after circuit fabrication, the OBO range can still be reconfigured without redesigning the circuit. To validate the proposed approach, a prototype operating at 3.45 GHz is demonstrated and implemented with Gallium Nitride (GaN) transistors. The measured saturated output power reaches 45 dBm with 70.1% drain efficiency. At 6-/8-/10-dB OBO, the fabricated PA can provide up to 62.1%/53.8%/47.3% drain efficiency, respectively. When driven by a 60 MHz 9-dB PAPR long-term evolution (LTE) signal, the PA provides 34 dBm average output power with 44.3% average efficiency. Moreover, measurement results prove that the PA can offer efficiency enhancement when the OBO is reconfigured to 8-dB or 12-dB after fabrication.
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