Abstract: A ceramic resonator, a variable reactance circuit, and a limiter circuit are connected to the output of an amplifier having an output that is fed back to the positive phase-sequence input, and the frequency of oscillation is controlled by varying an equivalent capacitance of the reactance circuit with a control voltage applied to the reactance circuit. The limiter circuit ensures a variable frequency range on the high frequency side, and the symmetry of the capture range when this system is applied to a PLL can be improved.

Abstract: A voltage controlled oscillator free from free-run oscillating frequency adjustment is disclosed. This oscillator includes an amplifier having a positive feedback loop, a resonator connected to the output of the amplifier, and a variable reactance circuit connected to the output of the amplifier. The reactance circuit presents a reactance value variable by a control voltage to control an oscillation frequency of the oscillator. There is a further provided a low-pass filter which is connected in cascade to the variable reactance circuit. A high-pass filter is preferably inserted in the positive feedback loop.