Fractional-N PLL phase noise effects on baseband signal-to-noise ratio in FMCW radars

摘要

This work presents a model for estimating the effect of the fractional-N phase locked loop (Frac-N PLL) phase noise (PN) on frequency modulated continuous wave (FMCW) radar baseband (BB) signal-to-noise ratio (SNR). The model captures the SNR degradation due to PN in secondary radars as well as the range correlation effect in primary radars which reduces the amount of SNR degradation. Estimates from the proposed model are in good agreement with measurement results from a dual band FMCW radar test chip fabricated on an IBM7WL BiCMOS 0.18 μm technology. In secondary radar mode, a BB SNR of 30.0 and 23.0 dB is achieved at the 2.4 and 5.8 GHz bands respectively while in primary radar mode a BB SNR of 35.0 and 33.7 dB is achieved at the same bands. The fabricated FMCW radar test chips achieved a ranging precision of 5.2 and 0.3 mm in secondary and primary radar modes respectively.