Title :
Near-carrier phase-noise characteristics of narrow band Colpitts oscillators
Author :
Watanabe, Yasuaki ; Komine, Sayaka ; Goka, Shigeyoshi ; Sekimoto, Hitoshi ; Uchida, Takeshi
Author_Institution :
Graduate Sch. of Eng., Tokyo Metropolitan Univ., Japan
Abstract :
A theoretical approach to estimate the near-carrier phase-noise level of narrow band transistor Colpitts oscillators is described. Near carrier phase-noise characteristics of reference oscillators in mobile communication systems constantly need to be improved. We proposed a narrow-band Colpitts oscillator for SC-cut resonators in 1996 FCS. This oscillator uses an AT-cut resonator as a band selection filter, and we showed that the near-carrier phase-noise characteristics of the oscillator were improved over 5 dB compared with conventional transistor Colpitts oscillators. An analysis of the close to carrier phase-noise characteristics of the narrow-band Colpitts oscillators is described. The open-loop impedance, that is, a series including a SC-cut resonator and an oscillator active circuit, is calculated using a linear circuit model with a nonlinear transistor model. We show the loaded Q can be improved by introducing the resonator filter in the oscillation circuit. Based on Leeson´s model, the near carrier phase-noise is estimated using calculated Q values. The results correspond well with previous experiments. We also show that the phase-noise can be greatly improved - under -148 dBc/Hz at 10Hz offset - by using a resonator filter with high Q value.
Keywords :
crystal oscillators; electric impedance; mobile communication; nonlinear network analysis; phase noise; resonator filters; 1996 FCS; AT-cut resonator; Leeson model; SC-cut resonators; band selection filter; linear circuit model; loaded Q; mobile communication systems; narrow band Colpitts oscillators; near-carrier phase-noise level; nonlinear transistor model; open-loop impedance; oscillator active circuit; resonator filter; transistor Colpitts oscillators; Active circuits; Estimation theory; Frequency; Impedance; Mobile communication; Narrowband; Oscillators; Phase estimation; Phase noise; Resonator filters;
Conference_Titel :
Frequency Control Symposium and Exposition, 2004. Proceedings of the 2004 IEEE International
Print_ISBN :
0-7803-8414-8
DOI :
10.1109/FREQ.2004.1418501