Phase noise improvement and noise modeling of type-I ADPLL with non-linear quantization effects

This paper presents a phase noise improvement method for fine tuning of type-I ADPLL by exploiting its nonlinear quantization effects. When quantization step approaches the same orders of magnitude of standard deviation of input noise, quantization effects become nonlinear, and additive noise modeling of quantization effects is no longer applicable. By proper offsetting the input signals in this case, the feedback loop of ADPLL can be very sensitive to frequency phase deviation. It results in a larger loop bandwidth, and in turn smaller in-band phase noise than in linear quantization case. A theoretic s-domain noise model is proposed to quantify the phase noise in nonlinear case. Results are verified in Modelsim simulations. Proposed method offers possibility of achieving lower phase noise by lower quantization resolution and less circuit design efforts.