A UHF low-spur, low- phase noise fractional-N synthesizer in 0.18-µm CMOS

A fully-integrated fractional-N synthesizer (FNS) is designed and implemented, for a single-chip UHF transceiver, using 1P6M 0.18-μm RF CMOS process. The synthesizer provides very low phase-noise and extremely low reference spur RF source covering 880MHz to 1260MHz, incorporating on-chip active loop-filter and dual-stage charge-pump circuits. The measured phase-noise is -116dBc/Hz at 200KHz offset and -142dBc/Hz at 3.3MHz offset while maintaining 20MHz reference spur levels lowers -84dBc over the entire tuning range. The active die area is 2.2mm × 1.8mm. The chip operates over a wide range of supply voltage from 1.6 V to 2.0V and temperature from -25°C to +75°C respectively. The chip draws 47mA current from a +1.8V supply at +25°C.