In amplitude-shift keying (ASK) demodulation, a voltage-controlled oscillator (VCO) is often used to recover the modulating signal from the ASK-modulated carrier waveform. The VCO generates an output frequency that is proportional to the input voltage it receives.
The voltage threshold for triggering a VCO in ASK demodulation depends on the specific design and characteristics of the demodulation circuit. Generally, the VCO's threshold voltage is set to correspond to the midpoint of the amplitude levels used in the ASK modulation scheme.
In binary ASK (BASK), for example, two different amplitudes are typically used to represent binary symbols (0 and 1). The threshold voltage for the VCO would ideally be set to the midpoint voltage between these two amplitudes. This ensures that the VCO transitions between its output frequencies when the received ASK signal crosses this threshold.
However, it's important to note that in practical scenarios, factors such as noise, signal distortion, and circuit imperfections can affect the demodulation process. In some cases, adaptive or automatic threshold adjustment techniques might be employed to ensure reliable demodulation even in the presence of these factors.
The exact threshold voltage value will depend on the specific modulation index, signal-to-noise ratio (SNR), and circuit characteristics, and it's usually determined through simulation, testing, and calibration for a given demodulation setup.