Design of quadrature CMOS VCO using source degeneration resistor

A new schematic of quadrature voltage controlled oscillator (QVCO) is designed and fabricated. To obtain the quadrature characteristic and low phase noise simultaneously, two differential VCOs are forced to run in quadrature mode by using cross-coupled transistors, each with a source degeneration resistor, which is optimized to obtain quadrature accuracy with minimum phase noise. The designed QVCO was fabricated in standard CMOS technology. The measured performance shows the phase noise below -120 dBc/Hz at 1 MHz frequency offset, tuning bandwidth of 210 MHz from 2.34 GHz to 2.55 GHz with a tuning voltage varying from 0 to 1.8 V. Quadrature error of 0.5° and amplitude error of 0.2 dB were measured in conjunction with a low-IF mixer. The fabricated QVCO requires 19 mA, including 5 mA in the VCO core part, from a 1.8 V supply.