Linearity improvement method of fast-chirp signal for PLL by using frequency detector and division ratio modification

A linearity improvement method of a fast-chirp signal for a PLL by using a frequency detector and a division ratio modification is proposed. A fast-chirp signal generated by the PLL is distorted by its transient characteristic. The proposed method measures a frequency difference between the output and an ideal signal, and it modifies the division ratio of the PLL from the measurement result. An iteration of the modification of the division ratio in the proposed method enables higher linearity improvement. Experimental results show that the maximum frequency error decreases by 90.3% after 3 times of iteration compared to that without the proposed method. Measured chirp linearity L, which is defined as division of the maximum frequency error by a modulation speed is 93ns.