Flicker Noise in Observer-Controller Digital PLL

The observer-controller loop filter proposed in the author's prior work is extended to include the effect of flicker noise in the digital-controlled oscillator (DCO). We show that the same implementation structure, as in the author's prior work but with modified gain values to account for the effect of flicker noise, can be used to achieve near-ideal jitter performance. A frequency domain analysis of the observer-controller loop filter is presented to provide a more intuitive understanding of the loop filter operation. The analysis shows that a system zero is introduced at dc to filter out the flicker noise and that the observer-controller based digital phase-locked loop (DPLL) remains effectively a second-order system regardless of the transport delay in the digital feedback loop. A comparison with conventional DPLL loop filter is also provided, which shows that in the presence of flicker noise, the jitter performance is even further improved than in the author's prior work.