A CMOS colpitts voltage controlled oscillator with an enhanced transconductance method

This work presents a technique to enhance the performance of the conventional PMOS Colpitts VCO circuit. This technique is accomplished by adding an NMOS cross-coupled pair under the traditional differential Colpitts VCO to enhance the oscillator startup condition. The signal analysis also supports this viewpoint and presents a device-choosing method to optimize the output power and phase noise. In realization, the circuit in the CMOS 0.18-μm technology, a U-shaped inductor, and thick oxide varactors are adopted in circuit to increase the quality factor of resonant tank. The performance of VCO demonstrates a center frequency of 16.7 GHz, a FOM of -186.2 dBc/Hz, and the phase noise of -110.42 dBc/Hz at the 1 MHz offset from the oscillation frequency.