A 21–48 GHz Subharmonic Injection-Locked Fractional-N Frequency Synthesizer for Multiband Point-to-Point

Abstract

This paper presents a mm-wave subharmonic injec- tion-locked (SHIL) fractional-N f requency synthesizer for wireless multiband point-to-point backhaul communications. The SHIL synthesizer implements a low-phase-noise 4.5–6.1 GHz PLL and injects its output to a dual-modulus divider followed by an ultra-wideband injection-lock ed frequency-multiplier (ILFM) chain to achieve excellent phase noise over an ultra-wide frequency tuning range. The proposed ILFM chain employs higher-order LC tanks to generate a rippled phase response around 0 over a wide frequency range to signi ficantly enhance the locking range and to eliminate expensive mm-wave frequency calibration loops. Fabricated in a 65 nm CMOS process, the synthesizer prototype measures a continuous output fre quency range from 20.6 to 48.2 GHz with frequency resolutio n of 220 kHz and output phase noise between 107.0 and 113.9 dBc/Hz at 1 MHz offset while consuming 148 mW and occupying 1850 1130 m .