This paper presents a broadband three-stage Doherty power amplifier (DPA) using impedance compensation for bandwidth extension. Different from the conventional design, an impedance-compensating load combiner is proposed to broaden the bandwidth of the three-stage DPA by employing the output impedances of the peaking amplifiers. Considering the load impedance of the peaking branch as an independent design variable, the Doherty load modulations are analyzed in theory, pointing out the optimized solution for the load combiner. To achieve the impedance compensation, the peaking output matching networks are deliberately designed with the dual-impedance matching topology. Experimental results show that a three-stage DPA is realized from 1.6 to 2.6 GHz (48% fractional bandwidth) with a measured efficiency of 50%–53% at 9.5-dB back-off and a saturated output power around 45.5 dBm. When stimulated by the 20- and 40-MHz modulated signals at an average output power of around 36.5 dBm, the proposed DPA can achieve the adjacent channel leakage ratio of −50 dBc over the whole frequency band after linearization, with an average efficiency of higher than 50%.

Improved Three-Stage Doherty Amplifier Design With Impedance Compensation in Load Combiner for Broadband Applications

The analysis and design of an RF-input sequential load modulated balanced power amplifier (SLMBA) are presented in this article. Unlike the existing LMBAs, in this new configuration, an over-driven class-B amplifier is used as the carrier amplifier while the balanced PA pair is biased in class-C mode to serve as the peaking amplifier. It is illustrated that the sequential operation greatly extends the high-efficiency power range and enables the proposed SLMBA to achieve high back-off efficiency across a wide bandwidth. An RF-input SLMBA at 3.05–3.55-GHz band using commercial GaN transistors is designed and implemented to validate the proposed architecture. The fabricated SLMBA attains a measured 9.5–10.3-dB gain and 42.3–43.7-dBm saturated power. Drain efficiency of 50.9–64.9/46.8–60.7/43.2–51.4% is achieved at 6-/8-/10-dB output power back-off within the designed bandwidth. By changing the bias condition of the carrier device, higher than 49.1% drain efficiency can be obtained within the 12.8-dB output power range at 3.3 GHz. When driven by a 40-MHz orthogonal frequency-division multiplexing (OFDM) signal with 8-dB peak-to-average power ratio (PAPR), the proposed SLMBA achieves adjacent channel leakage ratio (ACLR) better than −25 dBc with an average efficiency of 63.2% without digital predistortion (DPD). When excited by a ten-carrier 200-MHz OFDM signal with 10-dB PAPR, the average efficiency can reach 48.2% and −43.9-dBc ACLR can be obtained after DPD.

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Analysis and Design of Highly Efficient Wideband RF-Input Sequential Load Modulated Balanced Power Amplifier

This article presents the theory and design methodology of broadband RF-input continuous-mode load-modulated balanced power amplifier (CM-LMBA) by introducing the CM output-matching networks in the LMBA architecture. It is illustrated that the CM impedance condition can be achieved by properly adjusting the phase difference between the different PA branches in the proposed CM-LMBA during the entire load modulation process. An RF-input CM-LMBA with 1.45–2.45-GHz bandwidth using commercial GaN transistors is designed and implemented to validate the proposed architecture. The fabricated CM-LMBA attains a measured 11.2–13.4-dB gain and around 40-W saturated power. Power-added efficiency (PAE) of 46.4%–56.5% and 43.2%–50.3% is achieved at 6- and 8-dB output power back-offs throughout the designed band. When driven by a 100-MHz OFDM signal with an 8-dB peak-to-average power ratio (PAPR), the proposed CM-LMBA achieves better than −46-dBc adjacent channel leakage ratio (ACLR) and higher than 45% average PAE after digital predistortion at 1.8 and 2.1 GHz.

/pdf/broadband-rf-input-continuous-mode-load-modulated-balanced-28i8x6zdfg.pdf

Broadband RF-Input Continuous-Mode Load-Modulated Balanced Power Amplifier With Input Phase Adjustment

A novel Doherty power amplifier (DPA) architecture with extended bandwidth is presented in this paper. A modified load modulation network is introduced to provide impedance condition required by the Doherty operation in a wide frequency range. Analytical parameter solutions of the proposed load modulation network and the related load modulation process are presented. A DPA with 2.80-3.55 GHz bandwidth utilizing commercial GaN transistors is implemented. The fabricated DPA attains a measured 9.3-11.1 gain and 43.0-45.0 dBm saturated power. 50.0-60.6% and 66-78% drain efficiency is obtained at 6 dB output power back-off and saturation throughout the designed band, respectively. Moreover, the back-off drain efficiencies are higher than 55% within 700 MHz bandwidth. When driven by a 6-carrier 120 MHz OFDM signal with 7.0 dB peak to average power ratio, the proposed DPA achieves adjacent channel leakage ratio of better than −50 dBc after digital pre-distortion (DPD) at 3.20 GHz with average efficiency of 53.3%.

/pdf/bandwidth-enhancement-of-doherty-power-amplifier-using-4ggpb0uohy.pdf

Bandwidth Enhancement of Doherty Power Amplifier Using Modified Load Modulation Network

A novel architecture to extend the bandwidth of the Doherty power amplifier (DPA) is presented in this article. It is illustrated that two DPA modes at different frequency bands can be realized by simply swapping the gate biases of the transistors without changing the matching circuits, and hence, ultrawide bandwidth can be achieved by using a single load modulation network in DPA. A dual-mode DPA with 2.8–4.1-GHz bandwidth for Mode I and 2.2–2.7-GHz/4.2–4.8-GHz bandwidth for Mode II using commercial GaN transistors is designed and implemented to validate the proposed architecture. The fabricated DPA attains a measured 7.5–11.7-dB gain and 39.2–41-dBm saturated power. 35.0%–49.7% drain efficiency is obtained at 6-dB output power back-off for the designed dual-mode bands. When driven by a ten-carrier 200-MHz OFDM signal with 7.7-dB peak-to-average power ratio, the proposed DPA achieves adjacent channel leakage ratio of better than −50 dBc after digital predistortion at 2.5 GHz/3.5 GHz/4.5 GHz with an average efficiency of 46.0%/35.7%/33.0%. This simple configuration provides a promising solution for 5G, where multiple frequency bands in sub-6 GHz will be deployed.

/pdf/ultra-wideband-dual-mode-doherty-power-amplifier-using-1lzysgpyck.pdf

Ultra-Wideband Dual-Mode Doherty Power Amplifier Using Reciprocal Gate Bias for 5G Applications

In this paper, a broadband continuous-mode Doherty power amplifier (CM-DPA) is realized taking advantage of the noninfinity output impedances of peaking stage Specifically, the carrier PA of the designed DPA operates in a continuous class-J mode when the peaking PA is in the OFF-state, where the output impedance of the peaking PA has some influences on the carrier PA When the peaking transistor is in the OFF-state, the load impedance variation of the carrier transistor versus noninfinity peaking impedance is presented in this contribution The proposed method surmounts the back-off drain efficiency deterioration of DPAs at two side working bands through elaborately processing the noninfinity peaking impedance This paper also presents a method to derive the required OFF-state output impedance of the peaking stage by the carrier PA in a symmetrical broadband DPA A broadband CM-DPA working over 16–27 GHz (bandwidth of 51%) is designed and fabricated for interpreting our theories The simulated load trajectory of the carrier transistor is in line with the design space of continuous class-J mode Under continuous wave excitation, experimental results show the drain efficiencies of 465%–635% at 6-dB output back-off power levels and 56%–753% at peaking power levels The maximum output power of this DPA is 438–452 dBm with a gain of 94–115 dB across the whole working band Furthermore, a 20-MHz LTE modulated signal with a peak-to-average power ratio of 74 dB is also applied to the fabricated CM-DPA at 22 GHz At an average output power of 375 dBm, measurement results show the adjacent channel power ratios of −302 and −501 dBc before and after digital predistortion, respectively

Min Zhang

Papers

Broadband Continuous-Mode Doherty Power Amplifiers With Noninfinity Peaking Impedance