A 20.8-23.2GHz sub-sampling PLL with transformer-coupled VCO feedback loop achieving -47.05 dBc reference spur and -245.9dB FOM in 40nm CMOS Technology

This paper presents a 20.8-23.2GHz integer-N sub-sampling phase-locked loop (SSPLL) with low-reference spur and low-phase noise. A transformer-coupled based voltage controlled oscillator (VCO) is employed and its output is feedback as the input to SSPD in sub-sampling PLL to reduce the reference spur without requiring extra area and power consumption. In addition, a common source feedback circuit is adopted in the proposed sub-sampling charge pump (SSCP) to reduce current mismatch. The proposed sub-sampling PLL is implemented in a 40nm CMOS technology, measured results exhibit a frequency tuning range of 10.9% from 20.8 to 23.2GHz. The measured phase noise is -106.92@1MHz offset, the reference spur is -47.05 dBc. The typical power consumption is 29.1 mW from a 1.1V supply voltage, leading to a PLL FoM of -245.9 dB. The PLL occupies a core area of 1.2mm2.