In phase-shift keying (PSK) demodulation, a voltage-controlled oscillator (VCO) is often used to recover the phase information from the received modulated signal. The VCO generates an output frequency that is proportional to the input voltage it receives. The specific voltage threshold for triggering a VCO in PSK demodulation can vary depending on the implementation and the modulation scheme used.
In general, the VCO in a PSK demodulator will have multiple threshold levels, each corresponding to a different phase shift. For binary PSK (BPSK), where there are two possible phase shifts (0° and 180°), the VCO will typically have a threshold voltage that corresponds to the midpoint between these two phases. When the input voltage crosses this threshold, the VCO output will transition from one frequency to another, indicating a phase shift.
For higher-order PSK schemes like quadrature PSK (QPSK) or 8PSK, where there are more phase shifts, the VCO thresholds will correspond to the boundaries between these phases.
The specific voltage threshold values can be determined based on the modulation index, the desired phase shift points, and the characteristics of the VCO circuitry. In some cases, automatic gain control (AGC) circuits might be employed to dynamically adjust the input voltage to the VCO, ensuring reliable phase detection and demodulation.
It's important to note that the actual implementation details can vary widely based on the specific design and requirements of the PSK demodulator. If you are working on a practical implementation, you would need to consult relevant literature, documentation, or experts in the field to determine the appropriate voltage thresholds for your specific application.