Wide band PLL frequency synthesizer: A survey

Phase Locked Loops are key element in RF and mixed signal ICs. They are used as frequency synthesizers to generate multiple on chip frequencies. The output characteristics of PLL based frequency synthesizer are Tuning Range of frequency, Phase Noise and Frequency Resolution. Ideally output of frequency synthesizer is pure sinusoidal waveform. But practically, its power spectrum shows a peak at desired frequency with sidebands. The uncertainty of a synthesizer's output can be measured by its phase noise or spur level at a certain frequency offset from the desired carrier frequency. Phase noise degrades quality of output waveform and hence careful design is necessary. This paper compares different topologies for low phase noise Integer-N phase locked loop in Ku band (12GHz-18GHz). The best topology suitable for wide band PLL can be selected considering phase noise as primary element and area and power consumption as secondary. The chosen topology should mitigate severe trade off between the channel frequency spacing and frequency switching time.