26.1 A Self-Calibrated 16GHz Subsampling-PLL-Based 30s Fast Chirp FMCW Modulator with 1.5GHz Bandwidth and 100kHz rms Error

Frequency-modulated continuous-wave (FMCW) radars are critical for autonomous-driving applications. Sawtooth waveforms with short chirp time $( \lt; 50 \mu \mathrm {s})$ are desired to eliminate the speed-range ambiguity. The chirp signal needs to be linear to avoid spurious tones in the receiver baseband, which result in false detections. Furthermore, a wide chirping bandwidth (BW $_{chirp}\, \gt;4$ GHz) improves the range resolution to 3.75cm. To meet these requirements, fractionalN PLLs with two-point-modulation (TPM) scheme are presented in [1]–[3] with a relative rms FM error of 0.05% when normalized to the chirping bandwidth. In conventional FMCW PLLs, the lowpass signal injection is implemented through division ratio modulation in the PLL feedback path. However, the divider power consumption and noise are not negligible. In [4], a subsampling GMSK modulator improves the EVM. By using a high-resolution DTC, the divider quantization noise contribution to the PM/FM error is eliminated. In this work, the frequency modulation bandwidth is extended to GHz range and a 16GHz subsampling PLL (SS-PLL) is used for fast-chirp generation. Thanks to the TPM technique and selfcalibration, this PLL takes $30 \mu \mathrm {s}$ to chirp a sawtooth waveform with a 1.5GHz BW $( \sim 9.5$% of the carrier frequency). The rms FM error is 100kHz, which is 0.007% of BW$_{chirp}$.