A 6.5∼7.5-GHz CMOS Wideband FMCW Radar Transmitter based on Synthetic Bandwidth Technique

A fully integrated wideband FMCW radar transmitter based on synthetic bandwidth technique has been proposed and implemented in 55-nm CMOS technology. The wideband chirp is synthesized by mixing 500-MHz chirp from low frequency phase locked loop (PLL) with multiple high frequency carriers generated from sub-harmonic injection locking oscillator (SHILO). The fast switching SHILO allows the combination of multiple 500-MHz chirps to form a wideband chirp at high frequency. In the design, a wideband fractional-N PLL with randomized phase interpolation, covering 1.8 similar to 2.3 GHz, is employed to generate the desired 500-MHz chirp while achieving low in-band phase noise of -115 similar to 120 dBc/Hz. The high frequency SHILO also attains similar low in-band phase noise thanks to the injection locking property while achieving fast switching time less than 14 ns. The proposed transmitter achieves final chirp bandwidth of 1 GHz with good phase noise performance. The technique can be easily extended for wider chirp bandwidth by increasing the number of output carriers from SHILO. The transmitter supports pulse repetition period ranging from 0.3 to 6.3 ms. It consumes 84 mW, while occupying a total active area of 2.24 mm(2).