DESIGN OF DUAL-BAND COLPITTS VCO BY SWITCHED NEGATIVE RESISTANCE SHAPING

摘要

A switched negative resistance shaping technique is proposed to design a dual-band Colpitts VCO. By making use of the Miller effect, the negative resistance of the Colpitts oscillator can be shaped with an additional switchable inductor-capacitor (LC) resonator placed between the base and the collector of the bipolar transistor. The shaping of the negative resistance guarantees oscillation to start at only the selected resonant mode when a multimode resonator is used at the input of the Colpitts oscillator. Using the proposed technique, a dualband VCO is designed with center frequencies of 440 and 640 MHz. The measured continuous frequency tuning range is 15.8 and 16.3% for the lower band and the upper band, respectively.