Non-Linearity Effects in PLL Based Automotive Radar Systems

In LFMCW radar systems linearity of the frequency ramp is crucial to obtain a clean IF spectrum. PLL based frequency ramp generation is immune to temperature variations and thus provides a robust solution. However, being a closed loop system, the response of a PLL to a frequency ramp input will contain a transient. In this work it was found that this transient causes a single-sided l/f distortion in the IF spectrum. It was shown that the amount of distortion can be controlled by allowing some time for the PLL to settle and by changing the loop-bandwidth of the PLL.