A 12-GHz All-Digital Calibration-Free FMCW Signal Generator Based on a Retiming Fractional Frequency Divider

摘要

A 12-GHz all-digital calibration-free frequency-modulated continuous-wave (FMCW) signal generator is presented in this paper based on a retiming fractional frequency divider (FFD). Instead of modulating a multi-modulus divider (MMD) by a $DeltaSigma$ modulator, a fractional divider is utilized to release the narrow loop bandwidth limitation and achieve better phase noise without active noise cancellation techniques. Thus, the FMCW signal generator can achieve low root-mean-square (RMS) frequency error under a fast chirp slop. A calibration-free retiming FFD architecture which is not sensitive to process, voltage and temperature (PVT) variations is proposed to avoid complex and slow calibration process. Implemented in 40-nm CMOS, the generator consumes 33.8 mW power and 0.32 mm² chip area. Measurement results show that the generator achieves 78 $mathrm{MHz}/mumathrm{s}$ maximum chirp slope and 6.0 kHz RMS frequency error when 300 MHz frequency is swept in 2 ms. The phase noise from 12 GHz carrier is -113.6 dBc/Hz at 1 MHz offset.