Cascaded quality factor of ring LC oscillators

This paper analyzes the cascading effect of the quality factors (Qs) under various definitions. Under the appropriate definitions, the effective Q of the filter with cascaded stages, the relationship between the noise rejection of the positive feedback (PFB) oscillator constructed with an identical bandpass gain stages and the cascading effect of Qs have been investigated. Good phase noise performance of around -102 dBc/Hz@ 1 MHz has been measured from a 4-stage 10 GHz PFB ring LC oscillator fabricated in CMOS process, where only low Q passive components are possible to be integrated.