A CMOS 76–81-GHz 2-TX 3-RX FMCW Radar Transceiver Based on Mixed-Mode PLL Chirp Generator

Abstract

A fully integrated 76–81-GHz frequency-modulated, continuous-wave (FMCW) radar transceiver (TRX) in a 65-nm CMOS is presented. Two transmitters (TXs) and three receivers (RXs) are integrated for multiple-input multiple-output (MIMO) processing. A 38.5-GHz mixed-mode phase-locked loop (PLL) with reconfigurable loop bandwidth and a frequency doubling scheme are employed to generate the reconfigurable FMCW chirp waveforms. The coarse-to-fine-segmented current DAC is utilized to support sawtooth FMCW chirps with fast frequency ramping-down capability, and the delay lock loop (DLL)-based delay time calibration is used to improve the linearity of the embedded 2-D Vernier time-to-digital converter (TDC). Passive voltage-mode down-conversion is utilized to improve the RX linearity against TX leakage and short-range interference. A bottom-switching Gilbert-type modulator in the TX is proposed to realize the bi-phase modulation, and the magnetically coupled resonator technique is used to effectively expand the link bandwidth. The measurement results show that the FMCW TRX could generate reconfigurable chirps with the bandwidth from 250 MHz to 4 GHz and the period from 30 $\mu \text{s}$ to 10 ms. The root-mean-square (rms) frequency error is 110 kHz for a sawtooth chirp with 4-GHz bandwidth and 300- $\mu \text{s}$ period. The TX maximum output power is 13.4 dBm and is adjustable within 3 dB by reconfiguring its low dropout regulator (LDO) voltage. The RX achieves a 15.3-dB noise figure at 600-kHz IF and a −8.5-dBm RF input-referred P1dB. The overall power consumption is 921 mW, with two TXs and three RXs powered ON. Based on the proposed TRX chip, prototype hardware and a data process algorithm are developed. Real-time experimental results show that the distance and the angular resolution of the MIMO radar achieved are 5 cm and 9°, respectively.