Study And Design Of Wideband And Low Phase Noise Voltage-Controlled Oscillator

The LC voltage-controlled oscillators are widely used in clock synthesizer and frequency synthesizer.With the development of the communication system,the bandwidth and close-in phase noise performance of voltage-controlled oscillator are called for higher standards.On the other hand,in a contemporary voltage-controlled oscillator,the on-chip inductor is typically implemented with spiral turns.This on-chip spiral inductor has a low quality-factor,small inductance value per unit area and non-tunable inductance.In order to solve these problems,the method of reducing the AM-PM conversion coefficient to improve the close-in phase noise,and improving the quality-factor of the active inductor is investigated in this paper.This paper investigates the influence of the device size of the cross-coupled differential pair on AM-PM conversion in integrated LC voltage controlled oscillators.The AM-PM conversion coefficient is obtained by figuring the drain-bulk parasitic capacitance and gate-drain parasitic capacitance of the cross-coupled differential pair.The results show that by increasing the device size of the cross-coupled differential pair the AM-PM conversion coefficient increases.Therefore,in the low phase noise voltage controlled oscillator,the device size of the cross-coupled differential pair should be minimized to reduce the AM-PM conversion.The influence of the body effect of the cross-coupled differential pair on AM-PM conversion in integrated LC voltage controlled oscillators is investigated in this paper.By introducing the body effect,the results show that the drain-bulk parasitic capacitance can work in the smooth region of C-V curve,the linear range of cross-coupled differential pair can be improved and the oscillation amplitude and quality factor of oscillator increase.Therefore,the AM-PM conversion coefficient and the phase noise in the 1/f³ region can be reduced,and the Figure-of-Merit for 1/f³ phase noise(FoM^1/f3can be improved by introducing the body effect in the cross-coupled differential pair.Based on the cascode-grounded active inductor circuit topology with a feedback resistor,an on-chip capacitor was applied to this circuit to improve its quality-factor.It is obtained that introducing an on-chip capacitor can substantially improve the equivalent inductance and decrease the equivalent parasitic resistance,so that the maximum quality-factor of the active inductor with on-chip capacitor is significantly improve.In order to realize the high quality-factor of the tunable AI in its whole inductance tuning-range,a circuit topology with a varactor was proposed.The quality-factor can be adjusted by controlling the capacitance of the varactor.Finally,a voltage controlled oscillator with this active inductor instead of passive inductor is designed.Using the TSMC 0.18-?m process,the layout design and simulation are achieved with the assistance of Cadence Virtuoso.The proposed design achieves a tuning range of 136% and the phase noise is–112.5 dBc/Hz at a 1 MHz frequency offset.