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A method for design of low phase-noise balanced-Colpitts (BC) fixed-frequency oscillators (FFOs) and wideband voltage-controlled oscillators (VCOs) is presented. Analytical expressions describe how to design an oscillator for best phase noise, given a limited Q factor and a certain active device. The theory needs only two free parameters: the impedance level (Zc) and tapping ratio (n) of the resonator. It is described how to chose ZC and n for low phase noise and large tuning range, respectively. The design method is verified with a low phase-noise FFO and a wideband VCO, both designed in InGaP HBT technology. The BC FFO presents a phase noise of 112 dBc/Hz at 100-kHz offset from a 9.2-GHz carrier. The wideband VCO implemented in the same technology presents a minimum phase noise of 106 dBc/Hz at 100-kHz offset from a 9-GHz carrier. Over the frequency range of 8.4-9.7 GHz, the phase noise is better than 102 dBc/Hz and the output power is 7 0.5 dBm. The wide tuning range, constant output power, and relatively constant and low phase noise are achieved due to double pairs of tuning varactors, one between emitters and one between collectors. To the authors' best knowledge, this type of double-tuned BC VCO topology has not been previously published.
Microwave Theory and Techniques, IEEE Transactions on (Volume:60 , Issue: 11 )
Date of Publication: Nov. 2012