The voltage threshold for triggering a Voltage-Controlled Oscillator (VCO) in Amplitude-Shift Keying (ASK) modulation can vary depending on the specific circuit design and the characteristics of the components used. However, I can provide you with a general idea of how this works.
In ASK modulation, the VCO's frequency is controlled by an input voltage. The VCO generates a carrier signal, and its frequency changes based on the amplitude of the input voltage. When implementing ASK modulation, the VCO's voltage threshold is typically set to correspond to one of the binary states (e.g., 0 or 1) of the digital signal you're transmitting.
For example, in binary ASK modulation, you might use a voltage threshold such that when the input voltage is above a certain level (high voltage), the VCO operates at one frequency corresponding to one binary state, and when the input voltage is below that level (low voltage), the VCO operates at a different frequency corresponding to the other binary state.
The actual voltage threshold will depend on factors such as the sensitivity of the VCO to voltage changes, the desired modulation scheme, noise tolerance, and other considerations related to the specific application and circuit design.
To determine the exact voltage threshold for your ASK modulation setup, you would need to refer to the specifications of the VCO you're using, consult the circuit's design parameters, and possibly perform simulations or measurements to fine-tune the threshold for reliable modulation and demodulation.