A 1.8-GHz self-calibrated phase-locked loop with precise I/Q matching

This paper describes a 1.8-GHz self-calibrated phase-locked loop (PLL) implemented in 0.35-mum CMOS technology, The PLL operates as an edge-combining type fractional-N frequency synthesizer using multiphase clock signals from a ring-type voltage-controlled oscillator (VCO), A self-calibration circuit in the PLL continuously adjusts delay mismatches among delay cells in the ring oscillator, eliminating the fractional spur commonly found in an edge-combing fractional divider due to the delay mismatches. With the calibration loop, the fractional spurs caused hy the delay mismatches are reduced to -55 dBc, and the corresponding maximum phase offsets between the multiphase signals is less than 0.2 degrees, The frequency synthesizer PLL operates from 1.7 to 1.9 GHz and the closed-loop phase noise is -105 dBc/Hz at 100-kHz offset from the carrier. The overall circuit consumes 20 mA from a 3.0-V power supply.