A fully integrated 1.5-V 5.5-GHz CMOS phase-locked loop

A 1.5-V 5.5-GHz fully integrated phase-locked loop (PLL) has been implemented in a 0.25-μm foundry digital CMOS process. From a 5.5-GHz carrier, the in-band phase noise can be as low as -88 dBc/Hz at a 40-kHz offset, while the phase noise for the free-running VCO is -116 dBc/Hz at an 1-MHz offset. The VCO core current is 4.6 mA. The prescaler is implemented using a variation of the source-coupled logic (SCL) structure to reduce the switching noise, and thus to reduce the PLL side-band spurs. At -18 dBm signal power measured off chip, the switching noise coupled through substrate and metal interconnect generates spurs with power levels less than -99 dBm when the loop is open. A new charge-pump circuit is developed to reduce the current glitch at the output node. By incorporating a voltage doubler, the voltage dynamic range at the charge-pump output and thus the VCO control voltage range is increased from 1.3 to 2.6 V with immeasurable phase noise and spurious level degradation to the PLL. When the loop is closed, the power levels of side-band spurs at the offset frequency equal to the ~43-MHz reference frequency are < -69 dBc. The total power consumption of the PLL including that for the output buffers is ~23 mW