This article presents a novel method of extending the high-efficiency range of Doherty power amplifiers (DPAs) by utilizing multiple output power back-off (OBO) parameters. The OBO extension techniques of the DPAs, such as complex combining load (CCL), virtual stub (VS), and out-phased current combining (OCC) methods, were defined, and a general expression for these OBO extension techniques was derived. Using the general expression, three OBO extension methods were comparatively and comprehensively analyzed. Based on the analysis, the DPA with an extended OBO can be designed by simultaneously employing multiple back-off techniques with a high degree of freedom. To verify the general expression and its analysis, a DPA design for the frequency band of 3.45–3.75 GHz with GaN HEMTs was conducted using multiple OBO extension techniques of VS and OCC methods for a large OBO of 8.5 dB. Using a long-term evolution (LTE) signal with a signal bandwidth of 20 MHz and a peak-to-average power ratio (PAPR) of 8 dB, the drain efficiency (DE) of 38.9%–56.8% was achieved at the average output power levels of 34.4–36.8 dBm while satisfying ACLR of no larger than −45 dBc with digital predistortion (DPD) linearization. Under excitation of a 5G new radio (NR) signal with a signal bandwidth of 100 MHz and a PAPR of 8 dB, the DE of 38.5%–50.2% was achieved at the average output power levels of 34.6–36.8 dBm with an ACLR of under −24.6 dBc without DPD linearization.

The load networks of advanced Doherty power amplifiers (DPAs) have traditionally been designed according to the ABCD parameters. In this paper, design conditions as an impedance transformation condition and an effective electrical length were used to design the output matching networks (OMNs) for the carrier and peaking amplifiers of the virtual-stub DPAs (VS-DPAs). An optimization method for the effective electrical length was proposed that was specifically constructed for the load impedances of the carrier amplifier at the low power level to have broadband characteristics through the load-pull simulation. Using the optimized design conditions for broadband design, compact OMNs for the carrier and peaking amplifiers were designed using quasi-lumped components. Moreover, an asymmetric structure with an increased power capacity of the peaking amplifier for the VS-DPA was proposed to compensate for a relatively low peak fundamental current of the peaking amplifier due to its deep class-C operation as well as the extended output back-off (OBO) range of the VS-DPA. To verify the proposed load network, a broadband asymmetric VS-DPA for the 3.3 - 4.2 GHz band was designed and implemented using GaN HEMTs with power capacities of 6 and 10 W. Using a 5G new radio (5G NR) signal with a signal bandwidth of 100 MHz and a peak-to-average power ratio (PAPR) of 7.8 dB, power gain of 8.2 - 9.1 dB, DE of 46.0 - 57.0%, ACLR of better than -45 dBc after DPD linearization at an average power of 35.0 dBm were achieved at the broad frequency range of 3.3 - 4.2 GHz.

A new load modulation combiner (LMC) having the capability of back-off control is proposed for a Doherty power amplifier (DPA). The proposed LMC consists of two transmission lines tied at the combining node, and a shunt element across the other ends of the transmission lines. The shunt element of the LMC becomes virtually open-circuited at the peak power level and allows the carrier amplifier to have an arbitrary load impedance at the low power level. The operating principle and circuit structure of the DPA based on the proposed LMC are presented in detail. The proposed DPA was implemented using GaN-HEMT for the 3.5 - 4.0 GHz band. Using a 5G NR signal with a peak-to-average power ratio (PAPR) of 7.9 dB and signal bandwidth of 100 MHz, the implemented DPA showed drain efficiency (DE) of 49.6 - 54.4% and power gain of 11.1 - 13.0 dB at an average output power of 34.5 dBm. An adjacent channel leakage power ratio (ACLR) was obtained as -50.4 - -45.0 dBc at the average power level with a digital pre-distortion (DPD) technique.

This paper presents a 2.8-3.8 GHz broadband 2-stage fully differential Doherty power amplifier using direct interstage power division based on a 2-μmInGaP/GaAs HBT process for 5G new radio handset applications. A compact transformer-less interstage network is proposed for direct power division for carrier and peaking amplifiers. The power division ratio at the interstage is designed to dynamically vary according to the input power level to provide higher power gain and desired load impedance modulation. By utilizing the non-linear input reactance of the peaking amplifier, broadband dynamic power division circuits were designed for an operating frequency band of as broad as 1 GHz. In addition, active bias circuits for the peaking amplifier were optimized to have sufficient gain expansion, so that the overall AM-AM characteristics is as flat as possible. A broadband load modulation network using one transformer and two quarter-wave transmission lines is proposed. For the off-chip output transformer, impedance trajectory for the wide band impedance matching is presented using a T-equivalent circuit of the transformer. The self-inductance ratio of the transformer is optimized to maximize the bandwidth. Using the 5G new radio uplink signal with a signal bandwidth of 100 MHz, the implemented Doherty PA IC exhibited a power gain of 31.9 to 38.4 dB, PAE of 22.0 to 30.6%, and average output power of 26.0 to 27.8 dBm at a given ACLR of -33.0 dBc without pre-distortion.

This paper presents a two-stage Doherty power amplifier module (PAM) in CMOS SOI and GaAs HBT technologies for 5G handsets. While the driver amplifier is implemented using SOI CMOS for low cost, the carrier and peaking amplifiers are implemented using InGaP/GaAs HBT for high efficiency and linearity. The proposed Doherty PAM has a differential driver whose two output terminals are connected to the input ports of the carrier and peaking amplifiers, respectively. For the 3.35 GHz continuous-wave (CW) signal, the proposed PAM exhibited a power-added efficiency (PAE) of 30.3% and a power gain of 29.8 dB at a peak output power of 32.2 dBm. Using the 5G New Radio (NR) signal with a peak-to-average power ratio (PAPR) of 9.7 dB and a signal bandwidth of 100 MHz, a linear gain of more than 19.5 dB and a linear output power of more than 17 dBm in the range of from 3.15- to 4.15 GHz with a supply voltage of 4.5 V.

This letter presents a broadband interstage network for a two-stage Doherty power amplifier (DPA) with dual-drive amplifiers. The broadband interstage network consists of a load matching network of the drive stage, an input matching network of the main stage, and an optimized length of the transmission line between them. Both the matching networks are designed with simple L-section structure for the reference impedance 50 $\Omega$ . Then, the 50- $\Omega$ transmission line with an optimized length between them matches the frequency deviations of the two matching networks over a broad frequency band. For verification of the broadband interstage network, a (3.4–3.8)-GHz two-stage DPA was designed and implemented as a hybrid circuit for the sub-6-GHz 5G NR band. The core size of the DPA is 25 $\times$ 40 mm, and a drain efficiency of (40.7%–47.0%), power gain of (27.5–27.7) dB, and adjacent-channel leakage power ratio (ACLR) of ( $-$ 46.4 to $-$ 40.4) dBc after digital predistortion (DPD) were obtained at an average output power of 37.5 dBm using the 5G NR signal with a signal bandwidth of 100 MHz and a peak-to-average power ratio (PAPR) of 9.3 dB.