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A voltage-controlled oscillator (VCO) is an electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determines the instantaneous oscillation frequency. Consequently, a VCO can be used for frequency modulation (FM) or phase modulation (PM) by applying a modulating signal to the
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In a direct-conversion receiver, the VFO is tuned to the same frequency as the incoming radio frequency and = Hz. Demodulation takes place at baseband using low-pass filters and amplifiers . In a radio frequency (RF) transmitter , VFOs are often used to tune the frequency of the output signal, often indirectly through a heterodyning process ...
A phase-locked loop (PLL) uses a reference frequency to generate a multiple of that frequency. A voltage controlled oscillator (VCO) is initially tuned roughly to the range of the desired frequency multiple. The signal from the VCO is divided down using frequency dividers by the multiplication factor. The divided signal and the reference ...
The non-sinusoidal output is not suitable for use as a radio-frequency local oscillator, but it can serve as a timing generator, to power lights, LEDs, EL wire, or small neon indicators. If the output is used as an audio signal, the simple tones are also sufficient for applications such as alarms or a Morse code practice device.
Vackář describes a VFO design using this circuit that covers a modest frequency range of 1:1.17. [14] Vackář then describes a variation of the Radioslavia circuit that can cover a frequency range of 1:2.5 [15] or even 1:3. [16] This circuit tries to compensate for some variation in Q over the useful range of the VCO. [17]
A phase frequency detector (PFD) is an asynchronous circuit originally made of four flip-flops (i.e., the phase-frequency detectors found in both the RCA CD4046 and the motorola MC4344 ICs introduced in the 1970s). The logic determines which of the two signals has a zero-crossing earlier or more often.
Figure 3: Practical common-gate Colpitts oscillator with an oscillation frequency of ~10 MHz. Fig. 3 shows an example with component values. [6] Instead of field-effect transistors, other active components such as bipolar junction transistors or vacuum tubes, capable of producing gain at the desired frequency, could be used.