A newphase noise cancelling technique for fractional-N PLL

A novel real-time phase noise cancelling algorithm with dynamic phase adjustment technique is presented in this paper to improve quantization noise cancelling effect for wideband sigma-delta fractional-N phase locked loops (PLLs). The proposed noise cancelling algorithm in cooperation with DAC based current sources adjusts charge pump current to be constant, which varies at steady state due to division ratio variation. PLLs using conventional and the proposed phase noise cancelling techniques are designed and simulated using Simulink, respectively. Noise comparison shows that the proposed technique achieves additional 7dB phase noise reduction.