A 5 GHz Differential Colpitts CMOS VCO Using the Bottom PMOS Cross-Coupled Current Source

A low phase noise differential Colpitts voltage-controlled oscillator (VCO) with the bottom series PMOS cross-coupled current source is presented. The core Colpitts VCO adopts a pair of PMOS as the biased current source at the bottom, instead of a conventional NMOS topology, to achieve a better phase noise performance as the PMOS has lower flicker and white noise than those of NMOS and the output power spectral density of PMOS operated in bottom-biased type is further less than that in top-biased one in the same power consumption. The fabricated VCO operates from 4.9 to 5.46 GHz with 10.6% tuning range when the power consumption is below 6.4 mW with a supply voltage of 1.8 V. The measured phase noise at 100 kHz offset is -100.3 dBc/Hz at 5.46 GHz and achieves a good FOM performance of -187 dBc/Hz.