Phase noise analysis in CMOS LC quadrature VCO

Based on a physical understanding of phase noise mechanisms in CMOS LC Quadrature voltage-controlled oscillator (QVCO), a quantitative analysis of phase noise in QVCO is developed. The noise of the coupling transistor is identified, and the relationship between the phase noise and the ratio of the width of coupling transistor to the width of switching transistor is analyzed. The prediction of the phase noise is in good agreement with the measurement results at 1/f(2) region. As a demonstration, a QVCO is implemented in a 0.25 mu m CMOS process using on-chip spiral inductors. Measurement results show that the QVCO can be tuned between 1.77 and 2.415 GHz, has a phase noise of -117.17 dBc/Hz at 1 MHz frequency offset for a 2.267 GHz carrier, and dissipates 7.5 mW from the 2.5 V power supply.