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.