No, a voltage-controlled oscillator (VCO) does not directly change the amplitude of an input signal. A VCO is an electronic oscillator that generates an output signal whose frequency is controlled by an input voltage. The VCO typically consists of a resonant circuit, such as an LC (inductor-capacitor) tank circuit or a quartz crystal, and a control circuit that adjusts the resonant frequency based on the input voltage.
The primary function of a VCO is to vary the frequency of the output signal in response to changes in the control voltage. The amplitude of the input signal generally remains unaffected by the VCO.
However, it's worth noting that the amplitude of the VCO's output signal may vary depending on the design and implementation of the specific VCO circuit. Factors such as the supply voltage, biasing, gain stages, and nonlinearities in the circuit can introduce amplitude variations. Additionally, the VCO's output may be further amplified or attenuated by subsequent stages in a system, which could indirectly affect the overall amplitude of the signal.
But in terms of the inherent operation of a VCO itself, its primary role is to generate an output signal with a frequency that is modulated by the control voltage, while typically leaving the input signal's amplitude unchanged.