The voltage threshold for triggering a Voltage-Controlled Oscillator (VCO) in phase modulation is not a fixed value, as it can vary based on the specific design and characteristics of the VCO circuit being used. However, I can provide you with a general idea of how VCOs work in phase modulation and how their voltage control might be related.
In phase modulation, the frequency of a VCO is altered by varying the phase of the oscillator's output signal based on an input voltage. The relationship between the input voltage and the resulting frequency change is determined by the design of the VCO and its control voltage input.
VCOs typically have a control voltage input that allows you to adjust the frequency of the oscillator. The control voltage can be a DC voltage, and the VCO's frequency will change linearly or nonlinearly with changes in this voltage.
The specific voltage threshold for triggering the VCO will depend on its design parameters, such as the range of frequencies it can produce, the sensitivity of its frequency response to voltage changes, and any offset voltages. Some VCOs might start oscillating at a very low control voltage, while others might require a higher control voltage to begin oscillation.
To determine the voltage threshold for a particular VCO, you would need to consult the datasheet or technical specifications provided by the manufacturer of the VCO. This information should outline the operating characteristics of the VCO, including the minimum control voltage required to initiate oscillation.
In summary, the voltage threshold for triggering a VCO in phase modulation is not a standard value and can vary based on the specific VCO circuit you are using. It's important to refer to the manufacturer's documentation or datasheet for accurate information about the voltage control characteristics of the VCO you are working with.