In phase-shift keying (PSK) modulation, a voltage-controlled oscillator (VCO) is typically used to generate the carrier signal with varying phase shifts to transmit digital information. The voltage threshold for triggering a VCO in PSK modulation is not a fixed value and can vary based on the specific design of the modulation scheme and the characteristics of the VCO itself.
PSK modulation involves changing the phase of the carrier signal to represent different symbols or bits of digital data. The VCO's output frequency is directly related to its control voltage, and this voltage is adjusted to achieve the desired phase shifts corresponding to the modulation scheme being used (e.g., BPSK, QPSK, etc.).
The voltage threshold for triggering the VCO might refer to the point at which the control voltage needs to be adjusted to transition between different phase states. This threshold could vary based on factors like the modulation index, the desired phase shifts, and the VCO's specifications (e.g., tuning range, linearity, etc.).
In some cases, the voltage threshold might be predetermined based on the modulation scheme's requirements and the specific characteristics of the VCO, such as its tuning sensitivity. However, it's important to note that the exact voltage threshold can depend on the implementation details of the modulation system and the VCO circuit.
For a specific PSK modulation scheme, it's advisable to refer to relevant documentation, standards, or application notes that provide guidelines on the voltage levels and thresholds needed to properly drive the VCO and achieve the desired phase shifts.