Contents I. Introduction
Voltage-controlled oscillators are critical building blocks in all modern microwave radar systems and satellite transceivers. They represent the basic microwave energy source for radars. The rapid growth of digital satellite communications systems and microwave radars has created a great demand for low phase noise VCOs. Modern microwaves VCOs use the hetero-junction bipolar transistors (HBTs) or low-noise HEMTs as active devices for achieving low phase-noise performance [1], [2]. A considerable amount of publications has been devoted to the GaAs FET microwave oscillators [3] – [5]. These oscillators are related to the class of negative impedance oscillators having negative real part in the input impedance [6]. Another class of microwave oscillators is based on the Gunn and tunnel diodes [7], [8], which have an NDR region in the -type I-V characteristic. Locating the operating point in the NDR region results in creating a negative resistance induced into the tank circuit for compensating its losses. The -type I-V characteristic can be obtained artificially by using an electronic circuit, which generally consists of a FET with negative gate source voltage and a current mirror (CM) [9]. In this paper a HEMT VCO with improved Wilson PMOST CM is analyzed and designed. The VCO performance characteristics were simulated by ADS software. The theoretical outlines are verified by implementing a 275.87MHz oscillator.
