A 77-GHz Mixed-Mode FMCW Generator Based on a Vernier TDC With Dual Rising-Edge Fractional-Phase Detector

A 77-GHz frequency-modulated continuous-wave (FMCW) generator is presented for millimeter-wave (mm-wave) radar applications. The FMCW chirp is provided by a mixed-mode phase-locked loop (PLL). A dual rising-edge fractional-phase detector based on time-to-digital converter (TDC) is proposed to overcome the problem caused by the rising and falling time mismatch. A 2.3 ns detection range, 10 ps resolution Vernier TDC is employed in the detector to cover the two consecutive rising edges with less power consumption. A self-calibrated delay chain is employed in the Vernier TDC to overcome process, voltage and temperature (PVT) variations. Furthermore, sampling-edge selection technique is utilized to avoid the glitch during phase detection. A divider-less frequency error estimator is presented to save area and power. By employing a coarse-fine segmented digital-to-analog converter (DAC), the generator supports triangular and sawtooth-like FMCW chirp with reconfigurable period and bandwidth. An LC voltage- controlled oscillator (VCO) with split varactor is proposed to improve the linear tuning range. Implemented in 65 nm CMOS, the FMCW generator consumes 99 mW power and 0.7 mm x 0.8 mm chip area. The measurement results show that the phase noise from 78.7 GHz carrier is -87.4-dBc/Hz at 1 MHz offset. The measured root-mean-square (RMS) frequency error of a sawtooth-like FMCW chirp with 4 GHz bandwidth and 0.1 ms period is 205 kHz.