Research And Design Of CMOS LC Voltage Controlled Oscillators

Oscillator is one of the important components in the RF transceivers,which is responsible for frequency generation and clock reference.The phase noise performance of oscillator affects the overall performance of the transceiver system.Therefore,research of oscillator phase noise has been a mainstream topic.The influence of tail capacitor on the phase noise of the conventional differential cross-coupled LC oscillator,which is widely used both in academia and industry,is discussed in this thesis.The closed form expression of phase noise is obtained while the tail capacitance is large by adopting the impulse sensitive function(ISF).Besides,a conculsion is also obtained that the tail capacitor not only prevents the noise from the bias current source from generating phase noise,but also improves the current efficiency of the oscillator.Two quadrature local oscillating signals are required in some RF transceivers.Such quadrature local oscillating signals are often obtained by using a quadrature oscillator.The phase noise performance of the quadrature oscillator affects the performance of the whole transceiver system,which is the same as the single oscillator.Moreover,the phase accuracy of the quadrature oscillator also affects the bit error rate of the transceiver system.Therefore,study of both the phase noise and phase accuracy of the quadrature oscillator is a research hotspot.The phase noise of two conventional types of parallel-coupled LC quadrature oscillator is analysised in this thesis.Phase noise contributed by the noise from the bias current sources is obtained by adopting the impulse sensitive function.Besides,the completed closed form expressions of 1/f2 region phase noise are obtained.Analysis of the conventional series-coupled LC quadrature oscillator is also presented in this thesis.An ac-biased series-coupled LC quadrature oscillator is proposed based on the conventional series-coupled LC quadrature oscillator.In the proposed oscillator,the quality factor of the LC resonator is improved by inserting a bias circuit.Meanwhile,the flicker noise of the coupling MOS transistors is prevented from converting to phase noise.Thus,the propoed quadrature oscillator has a better 1/f3 and 1/f2 region phase noise performance than the conventional series-coupled LC quadrature oscillator.The proposed quadrature voltage-controlled oscillator(QVCO)is designed in SMIC 180-nm CMOS process.Post-layout Simulations indicate that the average power dissipation of it is about 10.6 mW under 1.8 V supply voltage.The frequency tuning range varies from 2.24 GHz to 2.69 GHz,The phase noise at 10 kHz and 1 MHz offset from 2.60 GHz is-72.9 dBc/Hz and-127.5 dBc/Hz,respectively.And the figure-of-merit(FoM)of it is 185.5 dBc/Hz.The average phase error is 0.1°.