25.4 A 1/f noise upconversion reduction technique applied to Class-D and Class-F oscillators

The 1/f (flicker) noise upconversion degrades the close-in spectrum of CMOS RF oscillators. The resulting 1/f³ phase noise (PN) can be an issue in PLLs with a loop bandwidth of <;1MHz, which practically implies all cellular phones. A previously published noise-filtering technique [1] and adding resistors in series with g_m-device drains [2] have shown significant reduction of the 1/f³ oscillator PN corner. However, the former needs an additional tunable inductor and the latter degrades PN in the 20dB/dec region.