A 22.5–31.2-GHz Continuously Tuning Frequency Synthesizer With 8.7-GHz Chirp for FMCW Applications

Abstract

This letter presents a fractional-N frequency synthesizer with an ultrawideband continuously tuning range of 32.4% centered at 26.85- and 8.7-GHz chirp for frequency-modulated continuous-wave (FMCW) radars. The synthesizer uses a fractional-N 9-GHz charge-pump phase-locked loop (CPPLL) cascaded by an injection-locked frequency tripler (ILFT). A voltage-controlled oscillator (VCO) with transformer (TFM) coupling for an enhanced linear control voltage range, a better quality factor and good isolation from the load seen by the resonator, and a wide output voltage range charge-pump (CP) are used to achieve the ultrawideband CPPLL. The ILFT is implemented using a weakly coupled TFM for broadband locking range and 3-dB output power. The synthesizer is fabricated in the 40-nm CMOS technology and consumes 28.5 mW. The phase noise (PN) of the synthesizer at 27 GHz is -97.87 dBc/Hz at 1 MHz and the prototype is capable of generating a triangle or sawtooth chirp of 8.7-GHz modulation bandwidth with an rms FM error of 0.04% of BWchirp.