AN INVESTIGATION OF THE HIGH-FREQUENCY LIMIT OF A MINIATURIZED COMMERCIAL VOLTAGE-CONTROLLED OSCILLATOR USED IN 900-MHZ-BAND MOBILE-COMMUNICATION HANDSET

The 900-MHz-band voltage-controlled oscillator (VCO) currently used in a commercial mobile-communication handset has the features of light w eight, small size, low phase noise, and low de current consumption. Th is paper investigates the problems that may occur when these types of VCO's are employed in next-generation high-frequency mobile-communicat ion handsets. The results show that oscillation may not commence above frequency f(T)/2 root R-eq/r(bb), which is significantly below the f( max) of the device itself, due to the effects of the circuit elements. In addition, a new formula is proposed which provides a practical gui deline for selection of the active devices. The procedure for extracti on of the small-signal model required by the proposed formula is also described in detail. The results obtained with the formula are in good agreement with those obtained from the measured S-parameters.