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When do you need a voltage controlled oscillator?
A tunable type of oscillators is required for some of the wireless applications for which the output frequency is a function of the input. Most commonly a voltage signal is used as control input to vary the output frequency. These type of oscillators are called as Voltage-controlled oscillators or simply VCO.
Which is the most common type of oscillator?
Some of the most common oscillator circuits are LC circuit, Tank circuit etc. A Voltage Controlled Oscillator is an oscillator which produces oscillating signals (waveforms) with variable frequency. The frequency of this waveform is varied by varying the magnitude of the Input voltage.
How is the frequency of a crystal oscillator controlled?
Voltage-controlled crystal oscillators. The frequency of a voltage-controlled crystal oscillator can be varied a few tens of parts per million (ppm) over a control voltage range of typically 0 to 3 volts, because the high Q factor of the crystals allows “pulling” over only a small range of frequencies.
How are voltage controlled oscillators sensitive to RFI?
Voltage-controlled oscillators are sensitive to RFI, especially in the range of 20 to 100 MHz. It has been shown that when a radiating antenna is placed in the vicinity of a VCO, as shown in Figure 3.83, failure can occur at several RF frequencies, and in some cases it was not operational until DC power was recycled.
How is the frequency of a ring oscillator controlled?
The frequency of a ring oscillator is controlled by varying either the supply voltage, the current available to each inverter stage, or the capacitive loading on each stage.
How is the frequency of an oscillator related to the capacitance?
For an RC type oscillator, the frequency of oscillations is inversely proportional to the capacitance (f = 1 / (2πRC)) and for LC oscillator the frequency of oscillations is 1 / (2π√LC). Therefore, as the reverse or control voltage increases the capacitance decreases.
Which is the output of a square wave oscillator?
In case of astable multivibrator VCO, the capacitance charging current on either side of the multivibrator is proportional to the external input voltage. Depending on the capacitor value in the multivibrator frequency range is selected. Square wave is the output of this type of oscillator.