A Dual-Loop Synthesizer with Fast Frequency Modulation Ability for 77/79 GHz FMCW Automotive Radar Applications

The implementation of wideband mm-wave radars for automotive applications necessitates wideband, fast, and precise linear frequency modulation generation. In this paper, we propose to use dual-loop phase-locked loop (PLL) architecture for this task. The frequency modulation dynamics are analyzed for this architecture. The results are employed to implement a SiGe BiCMOS fully integrated 75-83 GHz frequency-modulated continuous-wave synthesizer. Performance enhancements were achieved by utilizing the bulk-drain parasitic variable capacitance of P-channel transistors, embedded in a gm-boosted Colpitts VCO, for frequency control. This mechanism together with the dual-loop PLL architecture provides low loop bandwidth variation over the whole output frequency range, -97 dBc/Hz phase noise at 1-MHz offset, and maximal modulation rate of 100 GHz/ms.