LNA-Mixer Front-Ends Using Sampling Techniques for 77 GHz Automotive Radar Receivers

This paper investigates the use of sampling and subsampling techniques for frequency conversion in 77GHz automotive radar receivers. Three LNA-mixer front-ends implementing these techniques are presented and compared. The first front-end implements direct sampling at 77GHz using an innovative local oscillator (LO) pulse-shaper. Both other front-ends implement subsampling with a 25.7GHz LO, significantly relaxing LO generation constraints while achieving better performance than conventional subharmonic mixers. All three front-ends were fabricated using a 28-nm FD-SOI CMOS process. The first design demonstrates a state-of-the-art noise / linearity trade-off while reducing power consumption by a factor of three compared to the best-performing CMOS and BiCMOS solutions. It achieves an input-referred 1dB compression point (ICP) of −7.8dBm, a 8.9dB noise figure (NF), and a 11.4dB front-end gain, consuming only 20 mW at 1V. The subsampling front-ends achieve an NF below 12dB and ICP above −12dBm. A complete description of these front-ends is provided, including the LO signal generation circuits and a theoretical analysis of their double-balanced mixer operation, considering the effects of LO transition time on conversion gain.