The voltage threshold for triggering a Voltage-Controlled Oscillator (VCO) in Phase-Shift Keying (PSK) modulation can vary depending on the specific design and requirements of the modulation scheme and the VCO itself. However, I can provide you with a general understanding of how this works.
In PSK modulation, the VCO is used to generate a carrier signal whose frequency is controlled by an input voltage. The phase of the carrier signal is then shifted according to the modulation scheme (e.g., binary PSK, quadrature PSK, etc.). The voltage applied to the VCO determines the frequency of the carrier signal and, consequently, the phase of the modulated signal.
The voltage threshold for triggering the VCO essentially corresponds to the point at which the VCO starts to produce a stable output frequency. Below this threshold voltage, the VCO might not produce a usable or reliable carrier signal. As the input voltage surpasses this threshold, the VCO's output frequency will begin to increase or decrease linearly with the applied voltage.
The actual voltage threshold value will depend on various factors, including the design of the VCO circuit, the technology used, the desired frequency range, and the modulation scheme being employed. It is determined through the design and characterization of the specific VCO used in the PSK modulation system.
To determine the voltage threshold for a specific VCO in a PSK modulation scheme, you would need to consult the VCO's datasheet, the modulation system's specifications, and potentially conduct testing or simulation based on the actual components being used.