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This article presents a design methodology for an asymmetrical Doherty Power Amplifier (DPA) which achieves a high average efficiency at back off across its operating bandwidth. It is shown that by combining continuous modes with post matching techniques, it is possible to achieve excellent efficiency performance whilst maintaining broadband operation. Analysis is provided on how the knee effect can reduce the effective potential efficiency of Class J and Continuous Inverse Class F modes. An optimum combination of $2\text{nd}$ and $3\text{rd}$ harmonic impedances is then proposed for the carrier PA which can minimise this knee effect impact on efficiency performance. Also, it is shown how the drain supply can be used to improve the bandwidth over which an intrinsic optimum load can be maintained. Based on this analysis, a simple iterative design procedure is then presented which can be directly implemented with standard RF design tools. This design procedure is then verified in the design and manufacture of a prototype DPA using the Wolfspeed CG2H40010F GaN HEMT. The realised PA operates between 2.1 and 3.2 GHz with a peak power output of between 43.9 and 44.5 dBm. The PA achieves a high average drain efficiency of 64.7 % at 8–9 dB of back off. The DPA has been tested with and without digital pre-distortion (DPD) by considering a 60 MHz LTE OFDM signal with 9 dB peak-to-average power ratio (PAPR). When DPD is enabled, the presented DPA achieves a drain efficiency of between 52.1–64.3 with an adjacent channel power ratio (ACPR) of between −42.2– −44.1 dB over the bandwidth of 2.1–3.2 GHz.

This paper presents a design methodology for a load modulated balanced amplifier (LMBA) focusing on AMPM distortion mitigation. By introducing second harmonic control as a degree of design freedom, a complex load trajectory can be selected to compensate for AMPM nonlinearities in the device without substantially affecting efficiency. A mathematical derivation is accompanied by a design procedure based on closed-form equations to fabricate an LMBA based solely on load-pull data. The theory is validated through the measured comparison of three different designs operating at 2.4 GHz in a pseudo-RF-input Doherty-like LMBA configuration, with class-J, -B, and -J* main PAs. The class-J prototype outperforms the other designs with 54% and 49% drain efficiency at peak output power and 6-dB back-off, respectively, and only 4 degrees of AM-PM across this power range. When driven with a 10-MHz, 8.6-dB PAPR LTE signal, 40.5% average efficiency is achieved with better than $-40.5$ dBc ACLR without digital predistortion.

A hybrid dual-band power amplifier (PA) prototype working at two Industrial, Scientific and Medical (ISM) bands, 2.4-2.5 GHz and 5.725-5.875 GHz, was designed for Unmanned Aerial Vehicles (UAVs) communication applications in Spain. Initially, two single-band PA prototypes centered at each band were designed to evaluate the single-band achievable RF performance. In all the PAs, the Gallium Nitride (GaN) Qorvo HEMT TGF2977-SM was used, as well as microstrip transmission lines technology. To achieve wideband, good linearity and efficiency, the PAs were designed in class J. The measured results for the dual-band PA prototype at the 2dB compression point at the lower and higher bands, respectively, are 14.8 dB and 11.2 dB of Transducer Power Gain ( $G_{T}$ ), 35.7 dBm and 34.8 dBm of RF output power (Pout) and 59.2% and 43.5% of Drain Efficiency ( $\eta $ ). At 3dB compression the respective lower and higher bands results are 37.9 dBm and 37 dBm of Pout and 73.9% and 55% of $\eta $ .

The effects of the nonlinear drain-to-source capacitance ($C_{\mathrm {DS}}$), or the varactor effect, on the operation of continuous-mode class-B/J power amplifiers (PAs) are described in terms of the mathematical analysis as well as experimental validation. The nonlinear $C_{\mathrm {DS}}$ generates harmonic current when the class-B/J drain voltage is applied across it, modifying the theoretical load trajectories on the Smith chart. This is shown to significantly deviate from the continuous-mode assertion of constant power and efficiency. A novel measurement approach called voltage–pull is used to investigate the effects of the second harmonic generation by the varactor in a class-B/J PA mode. Theoretical and experimental results showed the nonlinear $C_{\mathrm {DS}}$ degrades the drain efficiency compared to class-B on one half of the class-B/J design space while improving the other half due to the energy upconversion and downconversion, respectively. This paper provides an approach for die nonlinear characteristic optimizations for transistor manufacturers. [ABSTRACT FROM AUTHOR]

A new synthesis method for the design of broadband impedance matching network has been introduced to match the transistor input. The proposed matching network would be a realistic alternative to those that are frequently designed in low-pass structure. Easy-to-use design equations are given for this filter-based matching network. The required impedance of the stubs and the connecting lines can be directly calculated from the equations. This synthesis method simplifies the implementation of the network in the distributed form as compared with the LC low-pass matching network where equivalences are necessarily required in the rough conversion from lumped-to-distributed elements. The high-efficiency mode of operation is guaranteed by the constructed output low-pass matching network, since the LC low-pass network can provide the prescribed load terminations at fundamental frequencies and at harmonics. A commercially available 10-W GaN HEMT device (CGH40010) was used in this investigation. The proposed broadband power amplifier exhibits band-pass Chebyshev response in S-parameter measurements, and yields good gain flatness (±0.5 dB) and input return loss (>13 dB). Power-added efficiency of 58%–72% has been measured in large-signal measurements. After digital predistortion, the measured adjacent channel leakage power ratio is below −50 dBc at ±5- and ±10-MHz offset, when driven by 5- and 10-MHz WCDMA signals at 7-dB power back off. [ABSTRACT FROM AUTHOR]

A purely passive design technique for a class-J power amplifier (PA) is proposed, based on complex terminations at the fundamental frequency and the second harmonic, which increases the bandwidth while maintaining high efficiency. Using combined analytical derivation and numerical simulations, the drain impedance termination locus curve is obtained in the drain efficiency and DC voltage spaces. Successive application of the newly proposed de-normalization technique avoids the drain DC voltage manipulation used elsewhere. This is due to the resulting variable reactance of the output drain-source capacitor, optimal over a wide frequency range. Following the proposed procedure and the obtained optimal parametric space, a GaN HEMT-based PA is designed, fabricated, and tested displaying a very good agreement of the predicted and measured results. [ABSTRACT FROM AUTHOR]

Electroluminescence microscopy and spectroscopy have been used to investigate hot electron concentration and electron temperature during RF operation. Two modes of operation were chosen, Class B and Class J, and compared with DC conditions. Hot electron concentration and temperature were on average lower for both RF modes than under comparative DC conditions. While these average values suggest that degradation due exclusively to hot electrons may be lower for RF than for DC conditions, the peak values in EL intensity and electric field along dynamic load lines have also to be taken into account and these are higher under Class J than Class B. [ABSTRACT FROM AUTHOR]