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In this paper, a mixed topology for high efficiency, broadband Doherty power amplifier (DPA) is proposed. The transistor gate biases are set to deep Class-AB for the carrier device and deep Class-C for the peaking device, which enable the DPA to achieve its high efficiency. However, this biasing scheme leads to an inadequate back-off range, which in the past limited applicability. To compensate for this reduced back-off range, a “ $\pi $ -type” harmonic injection network (HIN) is integrated into the DPA thereby allowing the second harmonic to be injected between the two active devices. This achieves waveform engineering, which enhances the output power of the peaking amplifier. However, the use of this HIN leads to a reduction in bandwidth due to a mismatch at the fundamental frequency. A bandwidth compensation technique is then proposed, thereby reducing the peaking device drain impedance variation. This mitigates the reduction in bandwidth as a result of the HIN. A high-efficiency DPA is prototyped based on two identical 10-W gallium nitride HEMTs. Measurement results show that a drain efficiency of greater than 60% is achieved at 5.3–6-dB output back-off power from 1.4 to 2.1 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a novel Doherty power amplifier (DPA) configuration with an auxiliary transformer is proposed for broadband operation. Theoretical analysis reveals that the proposed design can offer enhanced power utilization factor (PUF) and wideband Doherty behavior. The optimal design of the auxiliary transformer is identified with an aim to provide good impedance matching and minimal group delay. Based on the proposed theory, a 1.6–2.4-GHz 20-W DPA with improved PUF is designed, simulated, and measured. Under continuous wave excitation, measurement results indicate that the proposed DPA can achieve a PUF of 0.9, good Doherty behavior over the entire frequency band with a 6-dB back-off efficiency of 55%–64%, and saturated efficiency of 68%–76%. In addition, by the use of single-carrier WCDMA signal (centered at 2 GHz) with peak-to-average power ratio of 6.6 dB and at an average output power of 37 dBm, an average drain efficiency of 56% is obtained with adjacent channel leakage power ratio of better than -37 dBc. [ABSTRACT FROM PUBLISHER]

In this paper, a novel Doherty power amplifier (DPA) configuration with a complex combining load (CCL) is presented to extend the high-efficiency range of the amplifier. Theoretical analysis of dynamic load span, current ratio, and drain efficiency reveals that CCL can offer a new degree of freedom to boost the output back-off (OBO) of the DPA. For verification, a 2-GHz equal-cell GaN HEMT-based DPA is simulated, prototyped, and measured with both complex and resistive combining loads (RCLs). Under continuous wave (CW) excitation, measurement results show that the proposed DPA can attain an OBO of 9.1 dB, which is 3.6 dB higher than that of the RCL design. In addition, by the use of single-carrier WCDMA signal with peak-to-average power ratio of 9.6 dB and at an average output power of 33.2 dBm, the proposed design is found to deliver an average drain efficiency of 57.4%. In the absence of multi-cell or enlarged auxiliary device, this approach offers a low-cost and simple DPA solution with extended OBO, as well as good Doherty behavior. [ABSTRACT FROM AUTHOR]

Investigates the multistage amplifier linearization based on the generalized low-frequency signal-injection technique. Block diagram of the amplifying system; Intermodulation distortion components; Effects of gain error.

Presents a linearization scheme for radio frequency amplifiers based on simultaneous harmonic and baseband signal injection. Incorporation of second-order frequency components into the input of the main amplifier; Presentation of the analytical formulation of baseband, harmonic and the proposed injection techniques; Limitation of the proposed method.