A 77-GHz Mixed-Mode FMCW Signal Generator Based on Bang-Bang Phase Detector

A 77-GHz frequency-modulated continuous-wave (FMCW) signal generator is presented for automobile millimeter-wave (mm-wave) radar applications. The reconfigurable chirp is generated by a mixed-mode synthesizer operating at 38.5 GHz, in which the frequency doubling scheme is used to improve the chirp bandwidth and simplify the design. The bang-bang phase detector (BBPD) is employed for phase detection in the synthesizer, avoiding complicated linear time-to-digital converter (TDC) as well as reducing design complexity and power consumption. A 1-bit third-order single-loop ΔΣ modulator (SLDSM3), combining with the hybrid finite-impulse-response (FIR) filtering technique, significantly suppresses the BBPD induced quantization noise. A type-III slope estimator with a switchable polarity is embedded in the digital loop filter (DLF) to improve the linearity around the chirp turning-around points (TAPs). Two infinite-impulse-response (IIR) filtering stages smoothen the generated chirp waveform by reducing the instant variation of the DLF's output. Implemented in 65-nm CMOS, the proposed FMCW signal generator consumes 43.1-mW power and occupies 2-mm
²
die area, including testing pads. The measured phase noise from the 38.5-GHz carrier is -87.7 dBc/Hz at 1-MHz offset. The measured root-mean-square (rms) frequency errors of the generated triangle chirps over the 1-ms period are 189 and 336 kHz, with 0.914- and 1.827-GHz chirp bandwidth, respectively.