Low power and high efficiency vco and quadrature vco circuits constructed with transconductance-enhanced colpitts oscillator feature

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 and its efficiency. The analytics also support this viewpoint and present a device-choosing method to optimize the output power and phase noise. This new VCO can also be applied to realize the QVCO circuit, because the coupling transistors can be placed in parallel, connecting with the transistors in the NMOS cross-coupled pair, to achieve the proper coupling between individual VCOs. To verify the proposed design concept, two prototypes, which are VCO and QVCO operated at 2.4 GHz and fabricated in CMOS 0.25-μm technology, are designed and tested. The measurement results show that the performance of VCO demonstrates a FOM of about 180dBC/Hz, and the phase noise of QVCO is -116 dBc/Hz at the 1 MHz offset from oscillation frequency.