This paper presents a continuous frequency switching zig-zag voltage-controlled oscillator (VCO) to overcome the frequency discontinuity problem during the band switching process in multi-band wideband VCOs. Complementary PMOS and NMOS varactors are explored to realize opposite VCO tuning gains with high linearity. The VCO reduces the nonlinearity of the transmitted chirp in frequency-modulated continuous-wave (FMCW) radars, improving the range resolution. Implemented in a 40-nm CMOS technology, the proposed zig-zag multi-band VCO shows a simulated maximum peak frequency error of 10 MHz over 23.4-27.6 GHz frequency range, a −106.6 dBc/Hz phase noise at 1 MHz offset, and a −183.1 dBc/Hz FoM while consuming 12.69 mW power.

This brief presents a 24 GHz dual-mode frequency synthesizer designed in a 55-nm CMOS technology supporting both Doppler and frequency modulated continuous wave (FMCW) radars. The effects of chirp linearity and delta-sigma modulation (DSM) resolution on the rms FM error is analyzed. A design procedure for the PLL loop bandwidth and time interval of the frequency step to reduce the rms FM error is proposed. A voltage-controlled oscillator (VCO) featuring a four-coil transformer load is developed providing differential local oscillation (LO) signals for the transmitter (TX) and quadrature LO signals for the 2-channel receiver (RX). The prototype is designed with a loop bandwidth of 350 kHz, a frequency step time interval of $2 ~\mu s$ , and a VCO tuning linearity of 26%. In the FMCW mode, it achieved an rms FM error of 68.8 kHz over a 1.25 GHz chirp bandwidth. In the Doppler mode, the VCO operates in the free-running mode to save power consumption. An 8-bit digital-to-analog converter (DAC) is used to provide the VCO control voltage compensating process and voltage variations. The free-running VCO operates at a 24.125 GHz and has a frequency error of less than 1 MHz.

This paper presents a mmW voltage-controlled oscillator (VCO) employing stacked-coupled switched differential inductor (SSDI) and hybrid analog-digital varactor array (HVA) to simultaneously achieve wide tuning range and low phase noise. A frequency co-tuned VCO buffer is also developed to minimize the VCO output power variation. Fabricated in a 55-nm CMOS process, the VCO achieves an ultra-wide frequency tuning range of 41.14% (24.48 to 37.16 GHz) and a low phase noise of -124.91 dBc/Hz at 10 MHz offset. The FoM(T) is -192.67 dBc/Hz and the output powervariation is less than 3 dB over the entire tuning range.