Chirp Generators for Millimeter-Wave FMCW Radars

Abstract

The vast number of radar applications generates the demand for highly-linear, low-noise, fast chirp generators implemented in nanoscale CMOS technologies. Off-the-shelf chirp synthesizers are realized in BiCMOS technologies and demonstrate excellent phase noise performances, though, at high cost and limited modulation speed. This chapter describes a new class of fast and reconfigurable chirp generators based on digital bang-bang phase-locked loops, suitable for integration in modern CMOS processes. After analyzing the impact of the chirp generator impairments on a frequency-modulated continuous-wave (FMCW) radar system, a novel pre-distortion scheme for the linearization of critical blocks is introduced to achieve at the same time low phase noise and fast linear chirps. The chirp generator fabricated in 65-nm CMOS technology demonstrates above-state-of-the-art performance: It is capable of generating chirps around 23-GHz with slopes up to 173 MHz/µs and idle times of less than 200 ns with no over or undershoot after an abrupt frequency step. The circuit consuming 19.7 mA exhibits a phase noise of -100 dBc/Hz at 1 MHz offset from the carrier and a worst case in-band fractional spur level below -58 dBc.