Frequency-Locked RF Power Oscillator With 43-dBm Output Power and 58% Efficiency

This article presents the frequency-locked high-power RF oscillator using a gallium nitride (GaN) high electron mobility transistor (HEMT) amplifier and phase-locked loop (PLL) for 2.4-GHz industrial, scientific, and medical (ISM) band applications. The proposed architecture exploits the GaN power amplifier in the positive-feedback loop, whereas the desired phase shift for the target oscillating frequency is regulated from the PLL. To the best of our knowledge, this work is the first to employ the frequency locking scheme for a high-power solid-state RF oscillator. A detailed analysis of the oscillation conditions and the efficiency is provided. The prototype circuit is implemented with hybrid phase shifters and a fractional- $N$ frequency synthesizer. The implemented RF oscillator circuit operates from 2.3 to 2.575 GHz and achieves a low phase noise of −131.8 dBc/Hz at a 1-MHz offset frequency. The power efficiency of the proposed oscillator reaches 58%, and the PLL incurs only 0.2% efficiency degradation.

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