Most of the wireless systems are built using voltage controlled oscillators to control the movement of the frequency from source to unit. As the name hints two oscillators are used in dual-conversion systems. While one fine tunes all the input channel frequencies other functions at a pre-determined single frequency. They can be used either as an IC, module or discrete component circuit however they are more frequently used as part of an IC or a discrete circuit due to the price constraints.
Discrete-feature of voltage controlled oscillators is that they offer greater freedom to enhance performance of system including phase noise, tuning range, current consumption, output power, cost etc. Usually voltage controlled oscillators cannot be adjusted on as required bases, hence the RF engineer is faced with the challenge to develop a VCO that can be assembled without making any adjustments, such a VCO is called trimless VCO.
Designing a trimless VCO is not easy as it needs combination of design fundamentals and up-to-date RF engineering skills to make sure that the design is properly centered and that the oscillator tunes to the desired frequency as and when variations occur in supply voltage, component values and temperature. Developing a practically feasible RF VCO would mean you need to consider all the different types of oscillator topologies available, but the best and the most profitable topology has been that of Colpitts common-collector topology.
If you want to develop a low cost, flexible and high performance voltage control oscillator then using inductor-capacitor (LC) tank circuit which also includes a low-cost varactor diode and surface mount inductor. Oscillation frequency changes with every change in the inductor or capacitor, parallel resonance circuit in the oscillator tank controls the oscillation frequency. Inductor and varactor can be used to implement parallel- or series-mode network type resonance.
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