Customized zero frequency control for hybrid FIR noise filtering in ΣΔ fractional-N PLL

This paper describes a method to control the zeroes in the frequency response of hybrid finite impulse response (FIR) filter in SigmaDelta fractional-N PLL for quantization noise reduction. By adjusting the current allocation in different branches of the charge pump, transfer function of the FIR filter can be customized to meet various system requirements. Simulation results shows that the proposed method effectively adds flexibility to the hybrid FIR noise filtering technique while it also helps to reduce the hardware complexity.