In amplitude modulation (AM), a voltage-controlled oscillator (VCO) is not directly triggered by a voltage threshold as it might be in some other contexts. Instead, the VCO in an AM modulator generates a continuous waveform, typically a sinusoidal carrier signal, at a specific frequency determined by the control voltage applied to it. The amplitude of this carrier signal is modulated based on the amplitude of the modulating signal, such as an audio signal representing the information to be transmitted.
The modulation process involves changing the amplitude of the carrier signal in proportion to the amplitude of the modulating signal. This is achieved by multiplying the carrier signal with the modulating signal. In mathematical terms, the modulated waveform can be represented as:
modulated
(
)
=
(
1
+
⋅
modulating
(
)
)
⋅
carrier
(
)
V
modulated
(t)=(1+k
a
⋅V
modulating
(t))⋅V
carrier
(t)
Where:
modulated
(
)
V
modulated
(t) is the modulated waveform at time
t.
k
a
is the modulation index, representing the sensitivity of the modulation to the amplitude of the modulating signal.
modulating
(
)
V
modulating
(t) is the modulating signal at time
t.
carrier
(
)
V
carrier
(t) is the carrier signal at time
t.
The control voltage applied to the VCO will determine the carrier frequency, but it doesn't directly relate to triggering based on a voltage threshold. Instead, the VCO produces a continuous waveform that varies in frequency according to the control voltage.
If you are referring to a specific circuit or application where a VCO is used in an AM context and triggered by a voltage threshold, please provide more details so that I can offer more accurate information.