The voltage threshold for triggering a Voltage-Controlled Oscillator (VCO) in Frequency Modulation (FM) demodulation can vary depending on the specific design of the FM demodulation circuit and the characteristics of the VCO being used. However, I can provide you with a general overview of how this process works.
In FM demodulation, the input signal is typically a frequency-modulated waveform. The goal is to recover the modulating signal (the original message signal) from this frequency-modulated carrier signal. One common method to achieve this is by using a Phase-Locked Loop (PLL) circuit, which often includes a VCO.
The VCO's frequency is typically controlled by a voltage input, and it generates an output frequency that is proportional to the input voltage. In FM demodulation using a PLL, the VCO is part of a feedback loop. The input signal is mixed with the output of the VCO, and the resulting difference signal (error signal) is used to adjust the VCO's frequency.
The voltage threshold for triggering the VCO will depend on the desired sensitivity and accuracy of the demodulation process, as well as the characteristics of the input FM signal. A lower voltage threshold can make the demodulation more sensitive to small changes in the input frequency, but it can also introduce more noise and instability into the system.
Designers typically determine the voltage threshold based on factors such as the modulation index of the input FM signal (which relates to the maximum frequency deviation from the carrier), the desired signal-to-noise ratio, the loop filter characteristics, and the overall performance requirements of the demodulation system.
It's important to note that the specific voltage threshold value can't be given without knowing the details of the demodulation circuit and the VCO being used. Designing and optimizing such circuits often involve simulation, testing, and adjustments to achieve the desired demodulation performance.