Low Phase Noise Voltage-Controlled Oscillators for Wide-Band Frequency Synthesis

Abstract

Noise-bandwidth trade-off is a challenge issue in modern voltage-controlled oscillator (VCO) designs. Wide-tuning VCOs usually suffer degraded phase noise. A mixer based tuning range enhancement technology is proposed in this thesis that allows a VCO to be able to generate wideband frequency tuning in the range from 2.4GHz to 8.4GHz without penalizing its phase noise. The wide tuning is achieved by covering three frequency bands centered at 2.5GHz, 5GHz and 7.5GHz, respectively, in which each band obtains 15.4% tuning range. Using the proposed mixer based frequency generation technique, tuning range of the frequency synthesizer can be significantly increased while the phase noise is controlled within a reasonable range. To achieve good phase noise performance, a VCO should be biased at constant current that is compensated against temperature and supply voltage variations. A bandgap reference (BGR) circuit with the 2nd order temperature-coefficient compensation as well as the power supply rejection is thus developed. The VCO radio frequency integrated circuit (RFIC) was implemented in a 0.18 μm SiGe BiCMOS technology. Measured results from the wideband VCO prototypes demonstrate the wide tuning range capability as well as the low phase noise. The phase noise of the proposed VCO was measured as -124.4dBc/Hz, -119.1dBc/Hz and -108.8dBc/Hz at 1 MHz offset, respectively.