The voltage threshold for triggering a Voltage-Controlled Oscillator (VCO) in Phase Modulation (PM) demodulation can vary based on the specific circuit design, the modulation index of the input signal, and the intended application. In PM demodulation, the VCO generates an output frequency that is proportional to the phase of the input signal.
Typically, in PM demodulation using a VCO, the VCO's control voltage is proportional to the phase deviation of the input signal. The control voltage is used to adjust the VCO's frequency. The specific voltage threshold for triggering the VCO will depend on the design parameters and the modulation index of the input signal.
The modulation index of a PM signal determines how much the carrier frequency varies with respect to the amplitude of the modulating signal. In PM, the phase deviation is directly proportional to the amplitude of the modulating signal. Therefore, the larger the modulation index, the greater the phase deviation and consequently, the larger the control voltage required to trigger the VCO.
To determine the voltage threshold, you would need to consider the modulation index, the sensitivity of the VCO to changes in the control voltage (often specified as MHz/V or similar units), and any offset or bias voltage present in the VCO control circuit.
It's important to refer to the datasheet or technical specifications of the specific VCO you are using, as it will provide information about its characteristics, sensitivity, and control voltage range. Additionally, the circuit's overall architecture and the demodulation requirements will also influence the voltage threshold. If you're designing such a circuit, simulation and testing are crucial to determine the exact voltage threshold in your specific setup.