Voltage-controlled oscillator having three or more varactor diodes

Abstract

In a voltage-controlled oscillator having an LC resonant circuit including a varactor circuit so that resonant frequency is controlled by a D.C. bias or control voltage applied to the varactor circuit, three or more varactors are connected in series in one embodiment so that a high-frequency voltage applied to the varactor circuit is divided into a plurality. The varactors may be connected in the same direction or opposite direction. In another embodiment, a plurality of series circuits of varactors are connected in parallel to provide the varactor circuit, where each series circuit comprises two or more varactors. A series-parallel connection of a plurality of varactors may be arranged in a matrix. In order to reduce undesirable stray capacitance, some or all varactors are attached to a printed circuit board so that they are normal to the plane of the printed circuit board. In one embodiment an auxiliary printed circuit board is employed so that some varactors are spaced from a main circuit board. The voltage-controlled oscillator of the invention shows high carrier-to-noise ratio throughout a wide frequency range.