Abstract: In a voltage controlled oscillator, a voltage controlled oscillating part includes a resonance circuit, a differential amplifying circuit and an active load. The resonance circuit generates a resonance signal. The differential amplifying circuit feeds back the resonance signal from the resonance circuit and outputs two oscillation signals having a phase difference of 180°. The active load controls gain of the oscillation signals generated in the differential amplifying circuit. Further, an automatic amplitude controlling part converts the oscillation signals into a direct voltage and compares the direct voltage with a preset reference voltage to output a control voltage for determining a resistance value of the active load. The invention effectively adjusts amplitude of the oscillation signals outputted and reduces phase noise resulting from noise components induced by current source in case of switching of the differential amplitude circuit.

Abstract: The invention provides a low divide ratio programmable frequency divider of a fractional-N type applied to a digital MOPLL tuner and a method thereof. In the invention, a divide ratio assigner assigns divide data as a main divide ratio and a pulse swallow value according to a first or a second dividing operation mode in response to a mode selection signal. A prescaler operates on the first or second divide operation mode in response to the mode selection signal. Also, a main counter divides a frequency from the prescaler by the main divide ratio. Further, a pulse swallow counter counts a clock of the main counter while outputting a pulse swallow signal to the prescaler. The pulse swallow signal has a swallow level if a counting value corresponds to the pulse swallow value, and a non-swallow level if the counting value does not correspond to the pulse swallow value.