Voltage Controlled Oscillator
A Voltage Controlled Oscillator (VCO) is an oscillating circuit whose output frequency changes in direct proportion to an input voltage. VCOs can be made to oscillate from a few Hertz to hundreds of GHz. Every wireless device in use today has some sort of voltage controlled oscillator inside it. For example, there is a least one VCO inside every cell phone that generates the Radio Frequency (RF) waves that are used to communicate by-directionally to the cell tower.
A Voltage Controlled Oscillator Frequency
A VCO output frequency is stabilized or controlled with a Resonator. The lower the close-in Phase Noise requirement, the higher the Quality Factor (Q) of the Resonator needs to be. A Resonator can be as simple as an Inductor or as complex as a Quartz Crystal. The Table below lists some of the most popular Resonator types with their accompanying typical Q value in ascending order.
| Resonator Type | Quality Factor |
| Inductor | 20~150 |
| Transmission Line | 200~350 |
| Coaxial | 300~600 |
| SAW | ~10K |
| Crystal | 20K~300K |
Voltage Controlled Oscillator Design
There are two main categories of VCO designs. Those built with Monolithic Integrated Circuits (I.Cs) and the other of discrete components. The choice is primarily dictated by the resonator requirement. That is, with today’s technology, a quartz crystal resonator cannot be easily integrated due to the technology mix and size. Consequently, ultra-low phase noise VCOs are of discrete designs using the appropriate resonator type.
Crystek Corporation is a company that designs and sells VCOs using discrete designs using all the resonators listed on the table above. These discrete VCOs will outperform any integrated voltage controlled oscillator design due to the very high Q afforded by the resonator.
View the complete line of Crystek Voltage Controlled Oscillators by Clicking Here











