Voltage Controlled Oscillator Primer
Voltage Controlled Oscillators (VCOs) are a key component to many tunable communications, radio, radar, sensing, and measurement systems. Essentially, a VCO is an oscillator that can be controlled by an input voltage, usually analog. Hence, adjusting the tuning voltage across its range also changes the VCOs output RF signal, proportionally. VCOs are used as key components in Phase Locked Loops, Function Generators, Frequency Synthesizers, radar, Local Oscillators (LOs), and test and measurement equipment that require a frequency generator with an adjustable frequency.
As the applications that leverage VCOs are very diverse, so is the performance range of these devices. There are VCOs that exhibit output RF frequencies over a range of several megahertz, and some that have bandwidths of several gigahertz and operate in the millimeter-wave spectrum.
The key performance parameters for VCOs are tuning voltage, frequency range, noise floor, phase noise, output power, harmonics, and load impedance. Secondary performance parameters include supply voltage, supply current, tuning sensitivity, pushing, pulling, tuning port capacitance, and mechanical considerations. Tuning sensitivity describes the variation in output frequency induced by a changing in the tuning voltage (MHz/V).
It is important to note that the output power and the power of the harmonics is related to the input DC power and the tuning voltage, which may not be a linear relationship. Most VCO designs with analog voltage inputs have roughly linear output frequency versus tuning voltage performance, but this does not account for the combined effects of input voltage, input current, loading, and tuning voltage on the output power and frequency behavior. These effects are described by the pushing (VCO frequency change versus power supply voltage) and pulling (the VCO frequency change versus load on the output).
VCOs come in a wide variety of package, and are commonly assembled in surface mount packages or coaxial connectorized packages. In many cases these packages are ruggedized, hermetically sealed, or otherwise built to harsh environment and high reliability standards, either industrial, commercial, or military. Hence, the types of plating and packaging materials/technologies are often dictated by military standards for operating temperature range, humidity, shock, and vibration.
Common Voltage Controlled Oscillator Applications
• Phase Locked Loops
• Function Generators
• Frequency Synthesizers
• Tunable Receivers
• Electronic Jamming
• Local Oscillator
• Wireless Communications
• Optical Communications
• Electronic Warfare
• Electronic Countermeasures
• Microwave Radio
• Medical Instruments
• Test & Measurement Equipment
Learn more about Pasternack’s line of Voltage Controlled Oscillators: