A Voltage Controlled Crystal Oscillator or a VCXO is a piece of electronic equipment whose oscillating or output frequency is altered whenever a control potential difference is given to it under a constant supply voltage. A VCXO comes with a crystal oscillator, supporting circuitry, and a varactor diode. The maximum change in the measure of the output frequency of VCXO over the change in control voltage under constant temperature and supply voltage – as said in ppm – is known as Pullability or Total Pulling Range.

Difference between VCXO and VCO

1. In the VCXO an oscillation frequency is generated according to the Crystal Properties while in the VCO it is generated through an electronic circuit.
2. The VCXO has got a narrow range of frequency while the VCO comes with a wide range of frequency.
3. VCXO has got higher stability, on the other hand, VCO has got lower stability.
4. VCXO has a lower phase noise while VCO has a higher phase noise.

Applications of VCXO

VCXOs have found their use in many applications. Here we have some of them:

• Narrowband PLLs – VCXO is used in narrow-band phase-locked loops where the requirement for the change on frequency is very small.
• Temperature Controlled Crystal Oscillators – VCXOs are mainly used in TCXOs, commonly known as Temperature Controlled Crystal Oscillators, where the temperature pay voltage is provided to a control terminal of the VCXO. Thus using this technique reduces the drift to a lot extent. It is to be noted that the use of VCXO is not that much good as a full oven-controlled crystal oscillator but still it can provide a slight up-gradation in its performance level.

VCXOs Specifications:

While specifying VCXOs the following parameters are normally taken into consideration.

1. Package – The voltage-controlled crystal oscillators come in different forms, thus it is important to specify the right package for the right product.

2. Pullability – The pullability is defined as the range of frequency over which the VCXO can be pulled for a defined change in control potential difference. For a given voltage, it is specified in terms of ppm (parts per million). VCXO having a small pullability value offers a lower phase noise and greater stability. While VCXOs with larger pullability value provides a larger tuning range.

3. Voltage Supply – It is important to mention the supply voltage to guarantee that it works inside the unit for which it is proposed. Ideally, it ought to have the option to work outside the normal resistance of the flexibly so that any slight jumble doesn't cause an issue.

4. Frequency – This is generally specified in MHz for all frequencies that are in the range of over 1.0MHz and in KHz for all frequencies that are below this. It is also important to specify the frequency to the right number of decimal spots to empower the producer to have the option to decide the necessary recurrence required.

This was all we have regarding VCXO Oscillators. Hope you liked going through it. Brands that manufacture them are ABRACON, Silicon Labs and, Crystek. Make sure to check them out using the links as provided.

View all our VCXO Oscillators