Design of quadrature CMOS VCO using source degeneration resistor

A new schematic of quadrature voltage controlled oscillator(QVCO) is designed and fabricated. To obtain quadrature characteristic and low phase noise simultaneously, two differential VCOs are forced to run in quadrature mode by using cross-coupled transistor 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 showed the phase noise of 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 form 0 to 1.8 V. Quadrature error of 0.5 degree and amplitude error of 0.2 dB was measured with conjunction with low-IF mixer. The fabricated QVCO requires 19 mA including 5 mA in the VCO core part from a 1.8 V supply.