Fuji Crystal

Home

About Fuji Crystal



Company

News

Low Jitter VCXO Oscillators for SONET Clocking and High-Speed Networks

Release time:

2025-05-28 16:16

As high-speed communications and synchronous optical networks demand greater timing precision, the role of VCXO oscillators has grown increasingly critical. A Voltage-Controlled Crystal Oscillator (VCXO) offers both the stability of crystal timing and the flexibility of fine-tuning through voltage control. In jitter-sensitive systems such as SONET/SDH, FPGA interfaces, jitter-cleaning PLLs, and data converters, low jitter VCXOs serve as essential timing components.

What Is a VCXO Oscillator?

A VCXO is a crystal oscillator whose output frequency can be slightly adjusted with a control voltage. Internally, it includes a quartz resonator and a varactor diode. These oscillators are used in PLL circuits and enable precise frequency alignment, jitter reduction, and clock recovery.

VCXO Structure in Telecom Systems

Unlike standard XOs, VCXOs maintain frequency stability while supporting real-time tuning, making them ideal for telecom, video synchronization, and wireless modules.

Low Jitter Performance in VCXO Design

Jitter refers to short-term variations in clock signal timing. In digital systems, jitter directly impacts bit error rate (BER) and synchronization accuracy. Low jitter VCXOs typically achieve RMS jitter levels as low as 0.5ps to 0.6ps (12kHz–20MHz), making them indispensable for SONET, Ethernet, high-speed ADCs, and RF systems.

VCXO in SONET/SDH and Telecom Applications

In SONET/SDH systems, VCXOs play a crucial role in maintaining timing alignment across network nodes. Standard frequencies include 19.44MHz, 38.88MHz, and 155.52MHz. These VCXOs are used in PLLs or clock distribution ICs that must comply with GR-1244-CORE and ITU-T G.813 standards.

VCXO Application Examples and Frequency Matching

Recommended Applications and VCXO Selection

SONET/SDH Equipment: 19.44MHz, 38.88MHz, 155.52MHz with IDT 8V97051, TI CDCE925
High-Speed ADC/DAC Systems: 50–125MHz with AD9680, DAC38RFxx
FPGA Clocking & Jitter Cleaning: 80–160MHz with Xilinx Ultrascale+, Intel Stratix 10
Telecom Jitter Cleaning Modules: 25MHz, 100MHz with Silicon Labs Si5345, Microchip ZL30250

Trends in VCXO Technology

VCXOs are evolving toward tighter jitter specs (<0.3ps), larger pull ranges (>±100ppm), and compact packages (2520, 3225 sizes). Advanced models now support I²C configuration, thermal stability (±25ppm over -40°C to +85°C), and built-in diagnostics. These are increasingly used in dense optical modules, edge computing, and 5G systems.

Conclusion

VCXO oscillators combine high precision with dynamic adjustability, making them essential for modern synchronous systems. Their role in clock distribution, jitter filtering, and timing alignment continues to expand across telecom, data converters, and high-speed logic platforms.

Key words:

application

Fcom

Automotive Electronics

Fire-fighting

Quartz Crystal

OCXO