Wideband monolithic integrated voltage controlled oscillator for adaptive RF applications

Abstract

The major research issue in this thesis is on the design and implementation of wideband microwave monolithic integrated circuit(MMIC) voltage controlled oscillator(VCO) adaptably tunable to the frequency between 2.5 to 6 GHz for portable intelligent RF applications. Two different approaches have been proposed and tried for tunability extension and low power operation of the MMIC differential VCO employing: (1) varactor coupling between VCO output and load as well as LC tuner and (2) modified active tunable inductance directly connected to negative resistance generator. The MMIC VCOs have been implemented using the InGaP/GaAs Heterojunction Bipolar Transistor (HBT) technology with a compact dimension less than 800 x 900 $um^2$. To overcome the limitation of an active tunable inductor circuit such as high voltage operation and high power consumption, which is related to compensation of the internal loss, this thesis proposes a new integration circuit with an active tunable inductor directly connected with the negative resistance generator by eliminating a capacitance canceling transistor, which results in the reduction of power consumption by a factor of two while using 3.3V operation and by inserting the transistor in the resistive feedback network, resistance can be varied from 30 to 150 ohms, which results in excellent tunability. The monolithic integrated differential VCO with the proposed active tunable inductor circuit reveals 66% tuning range from 3.4GHz to 6.8GHz with single ended output power of -4.85dBm $\pm$ 1.85dB within full oscillation band, and the measured phase noise characteristics of -85.6dBc/Hz at 1MHz offset from 6.3GHz carrier frequency is obtained. To reduce the load pulling effect, the emitter follower buffers are inserted between VCO output and load. This VCO consumes 64mA with 3.3V supply voltage while VCO core consumes only 40mA and control voltage varies from 0.7V to 4.7V. Consequently, for operating active inductor VCO of above 3G...