Design Of Low Power Quadrature Voltage Controlled Oscillator

Global navigation satellite system(GNSS)has been widely used all over the world,such as BDS of China,GLONASS of Russian,GPS of the USA and GALILEO of European Union.As the critical module of PLL system in satellite navigation receiver,the power consumption of voltage controlled oscillator(VCO)affects the performance of the whole system.The method of reducing power supply voltage is the focus of solving power consumption problem.How to design a low voltage VCO who covers the main frequencies of GNSS is one of the emphases and difficulties in the research.The ring VCO with four single-ended delay cells is designed to meet the requirements of low power and four quadrature outputs simultaneously.In order to satisfy the criteria of Barkhausen,four feedforward paths are added.Therefore,the low voltage feedforward single-ended delay cell,who has direct path and feedforward path,has been improved in the thesis.The feedforward path is made up of an inverter with resistive enhancement.The resistor can increase the overdrive voltage of PMOS transistor,so that the rise time of the inverter has been reduced and the turnover rate of output signal has been accelerated.Besides,the formula of frequency and startup condition for the oscillator are derived.It is concluded that adjusting the ratio of the trans-conductance of two paths can change the frequency.Moreover,the oscillating current of this four stage QRVCO keeps in balance in the positive and negative half cycles.It greatly reduces the native jitter and is beneficial to improve phase noise.The four quadrature outputs are able to drive the after mixer directly without buffer,which cuts down the total power consumption of system.A low power feedforward QRVCO for GNSS using SMIC 40 nm CMOS process is designed and verified by tape-out.Experimental results show that the highest frequency of QRVCO is merely 802 MHz,while dissipating about 0.933 mA at 0.70 V.The increase of parasitic capacitance in layout and the reduction of current decline the frequency.With the power supply rising to 0.85 V,the operating current rises to the range of 1.64 mA to 1.75 mA.Furthermore,the QRVCO can work properly from 1.24 GHz to 1.70 GHz and the phase noise is-94.02dBc/Hz at 1 MHz offset from carrier(1.576GHz),for a figure-of-merit of-156.4dBc/Hz.