Abstract
An analytical method to design a power amplifier (PA) with an optimized power added efficiency (PAE) trajectory for envelope tracking (ET) architecture is proposed. To obtain feasible matching solutions for high-efficiency performance of the PA in the dynamic supply operation, hybrid continuous modes (HCM) architecture is introduced. The design space for load impedances of the HCM PAs with nonlinear capacitance is deduced mathematically using the device’s embedding transfer network, without the necessity of using load-pull. The proposed design strategy is verified with the implementation of a GaN PA operating over the frequency range of 1.9 GHz to 2.2 GHz with PAE between 67.8% and 72.4% in the 6.7 dB back-off power region of the ET mode. The ET experimental system was set up to evaluate the application of the PA circuit. Measurement results show that the ET PA at 2.1 GHz reaches the efficiency of 61%, 54%, 44% and an error vector magnitude (EVM) of 0.32%, 0.60%, 0.67% at an average output power of 34.4 dBm, 34.2 dBm, 34.1 dBm for 6.7 dB peak-to-average power ratios (PAPR) signals with 5 MHz, 10 MHz, and 20 MHz bandwidths, respectively. Additionally, tested by a 20 MHz bandwidth 16 quadrature amplitude modulation (QAM) signal, 41.8% to 49.2% efficiency of ET PA is achieved at an average output power of 33.5 dBm to 35.1 dBm from 1.9 GHz to 2.2 GHz.
Highlights
The current wireless communication schemes employ spectrally efficient complex modulation techniques to address the high data throughput demand
Several architectures to improve the efficiency of RF power amplifier (PA) have been investigated, e.g., Doherty, linear amplification with nonlinear components (LINC), envelope elimination and restoration (EER), and envelope tracking (ET) [1,2,3,4]
As for EER, the linearity of the signal is strongly dependent on the supply modulator and dependent on time-alignment between the RF phase signal and the amplitude envelope signal at the output of the PA [5]
Summary
Several architectures to improve the efficiency of RF PA have been investigated, e.g., Doherty, linear amplification with nonlinear components (LINC), envelope elimination and restoration (EER), and envelope tracking (ET) [1,2,3,4]. As for EER, the linearity of the signal is strongly dependent on the supply modulator and dependent on time-alignment between the RF phase signal and the amplitude envelope signal at the output of the PA [5] These issues can be alleviated in envelope tracking (ET) architecture, which utilizes an envelope amplifier (EA) to instantly adjust the PA power supply voltage in synchronism with the envelope of the RF signal to ensure PA is always working at peak efficiencies for different output power levels. Since the EA is independent of the carrier frequency, the ET architecture has demonstrated considerable flexibility in multimode and multiband (MMMB) application scenarios
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