Oscillator phase-noise reduction using low-noise high-Q active resonators

This paper describes a method for the design of a low phase-noise planar oscillator based on a compact low-noise active elliptic filter for its frequency stabilization. The phase-noise of the oscillator is significantly reduced by taking advantage of the high frequency-selectivity and low-noise characteristics of the active filter. The filter occupies a relatively small area due to its two-pole dual-mode structure, making it suitable for the fabrication of very compact low phase-noise oscillators. As a proof of concept, a X-band oscillator using a packaged SiGe HBT transistor is designed and tested. The oscillator, operating at 8.1 GHz, achieves a measured phase-noise of -150 dBc/Hz at 1 MHz frequency offset with 10 dBm output power. To the best of our knowledge, the oscillator demonstrated in this paper presents the lowest phase-noise among published planar oscillators, to date.