An Injection- and Frequency-Locked Loop for Reducing Phase Noise of Wideband Oscillators

High-performance microwave oscillators often exploit feedback loop methods such as those that involve a frequency-locked loop (FLL) or a self-injection-locked loop to improve phase noise. This paper proposes a novel injection- and frequency-locked loop (IFLL) for reducing phase noise of wideband oscillators, which uses an injection-locked oscillator instead of a high-gain amplifier and a variable phase shifter in the FLL to amplify and phase-shift the feedback signal. In this paper, the frequency domain analysis is presented to characterize the proposed IFLL and compared with the experimental results. Consequently, the oscillators that use the IFLL exhibit remarkable phase-noise reduction, which is 5.5-9.3 dB better than that achieved using conventional FLLs at 1-MHz offset frequency, over a wide tuning range of about 53%.