ISSCC 2001 / SESSION 23 / ANALOG TECHNIQUES / 23 . 4 23 . 4 A Filtering Technique to Lower Oscillator Phase Noise

Wireless applications are pushing the required phase noise in integrated oscillators to ever lower levels. Integrated oscillator circuits published so far use tuning inductors that are either fully integrated, partly integrated, or discrete, with quality factors spanning a large range. However, lacking a clear understanding of the physical processes of phase noise, it is difficult to compare the relative merits of these VCOs in a normalized sense. An LC oscillator consists of a lossy resonator, and an active circuit across it to overcome this loss (Figure 23.4.1). In steady-state, the active circuit presents a large-signal negative resistance equal to the equivalent parallel loss resistance R across the resonator. The phase noise sidebands around the oscillation frequency are given by: