What is a VCXO, what are the benefits and what applications is it suited for?

What is a VCXO, what are the benefits and what applications is it suited for?

What is a VCXO?

A voltage-controlled crystal oscillator (VCXO) is a type of crystal oscillator circuit that uses a quartz crystal resonator to generate an output signal with a very stable and low jitter frequency. ?The oscillator frequency is adjusted by a control voltage input. ?This voltage input is typically a DC voltage that is applied to the VCXO through the Voltage control input pin.

The typical VCXO is an AT strip crystal blank mounted in a seam-sealed ceramic SMD package and connected to an internal VCXO ASIC which contains the Vcontrol, Oscillation, and Output buffer circuits.

VCXOs are commonly used in electronic devices that require high-frequency stability and low jitter, such as communication equipment, test and measurement instruments, and digital signal processing applications. They are often used in conjunction with a phase-locked loop (PLL) circuit to provide precise frequency control and synchronisation.?In some FCXO (Frequency Controlled Crystal Oscillator Applications) the VCXO is used to clean up (de-jitter) the signal.

The output frequency of a VCXO can typically be adjusted by a few parts per million (ppm) up to over 100 ppm depending on the design and control voltage range.

Like simple XO (Crystal oscillators) the VCXO can have many output waveform types like CMOS, LVPECL, LVDS, and others.

How does a VCXO work?

The output frequency of a VCXO can be controlled by applying a control voltage to a varactor diode in parallel with the crystal. ?Nowadays this is inside the VCXO ASIC.?The varactor diode changes its capacitance in response to the applied voltage, which in turn alters the resonant frequency of the crystal. This causes the frequency of the output signal to change.

The amount of frequency change per unit of the applied voltage is known as the VCXO's tuning sensitivity or pullability. The tuning sensitivity can be adjusted by changing the DC bias applied to the Vcontrol pin/varactor diode.?The tuning sensitivity is also affected by the actual pullability of the crystal in ppm/pF and the tuning voltage range.

What are the benefits of a VCXO?

A voltage-controlled crystal oscillator (VCXO) has several benefits that make it a popular choice for a wide range of applications. Firstly, its frequency-tuning capability allows for fine-tuning the output frequency to a specific value, making it ideal for applications that require precise frequency control and tuning. Depending on the output waveform type and supply voltage, some VCXOs require very little power to operate.?This makes them suitable for battery-powered applications and other low-power devices.

Another advantage of VCXOs is their high-frequency stability, which ensures that the oscillator output frequency remains highly stable over time and temperature changes. This stability is critical for applications that require high accuracy and precision, such as in the fields of telecommunications, military, aerospace, and scientific research.

Finally, VCXOs also offer low phase noise performance, which is essential for applications such as radio communication, radar systems, and other applications that require high signal quality. The combination of frequency-tuning capability, low power consumption, high-frequency stability, and low phase noise performance makes VCXOs an attractive choice for many applications that require precise and stable frequency control.

What applications is a VCXO suited for?

VCXOs are used in a wide range of applications that require precise frequency control and tuning. Some common applications include:

• Telecommunications: In telecommunications, VCXOs are used to generate stable, precise clock signals that synchronise data transmission and reception between devices. They are particularly useful for applications that require accurate timing, such as wireless communication systems, base stations, and satellite communications.
• Data Communications: Data communication systems require precise clock signals to ensure reliable data transmission. VCXOs can be used in these systems to generate clock signals that are accurate and stable, even in the presence of noise and other disturbances. They are commonly used in applications such as Ethernet switches, routers, and other network equipment.
• Test and Measurement Equipment: In test and measurement equipment, VCXOs are used to generate precise frequency signals that are used to calibrate and test other devices. They are particularly useful in applications that require high accuracy and stability, such as frequency counters, spectrum analysers, and oscilloscopes.
• GPS Receivers: Global Positioning System (GPS) receivers use VCXOs to generate precise timing signals that are used to calculate the receiver's position. The VCXO is used to generate a stable clock signal that is synchronised with the GPS satellite signal.
• Audio and Video Equipment: In audio and video equipment, VCXOs are used to generate clock signals that synchronise the different components of the system. For example, a VCXO can be used to generate the clock signal that synchronises the video signal with the audio signal in a home theatre system.
• Industrial Control Systems: In industrial control systems, VCXOs are used to generate clock signals that synchronise the operation of different components in the system. They are commonly used in applications such as programmable logic controllers (PLCs) and motor control systems.
• Military and Aerospace Systems: Military and aerospace systems require precise timing signals for communication, navigation, and other critical functions. VCXOs are commonly used in these systems to generate stable clock signals that meet the high reliability and accuracy requirements of these applications.
• Medical Equipment: In medical equipment, VCXOs are used to generate clock signals that synchronise different components of the system. They are commonly used in applications such as ultrasound machines, MRI scanners, and other diagnostic equipment that require precise timing and synchronisation.

Raltron's portfolio of VCXO covers frequencies ranging from 10MHz to 1.2GHZ with frequency stability as low as +/-20ppm. Raltron’s XVO clock series is a cutting-edge family of low to high-frequency, low-jitter output, single or multi-frequency voltage-controlled clock oscillators (VCXO). The XVO VCXOs are available in 7.0 x 5.0, 5.0 x 3.2, or 3.2 x 2.5 mm ceramic packages. Its outstanding flexibility significantly reduces design cycle time and overall cost.?The XVO design incorporates a low-frequency crystal along with a low-jitter frequency synthesizer to provide a wide range of frequencies. The XVO VCXOs are available in LVCMOS, LVPECL and LVDS outputs, allowing for a wide variety of applications.

Raltron is one of the fastest-growing manufacturers of frequency components. The company offers one of the broadest lines of quartz crystals and crystal-based products from simple resonators to precision oscillators, such as OCXO, VCXO, and TCXO. In addition, Raltron’s portfolio extends to RF products such as LTCC Filters, Baluns, Band-Pass Filters, and both Chip Antennas and Stub / Patch Antennas.

Raltron offers full technical support with two application engineering teams and failure analysis labs based in Miami and Shenzhen (China).