Crystal Oscillators for 800G and 1.6T Optical Communications
As AI computing, cloud infrastructure, and high-performance computing (HPC) drive increasing data rates, optical communication systems will need to manage 800G, 1.6T architectures, and soon, multi-terabyte-level transmissions. The precise timing to coordinate the needed high-speed data processing, clock generation, and network synchronization goes well beyond basic signal integrity.
Crystal oscillators provide reference clocks that serve as the foundation for many of these systems, helping establish the frequency stability and timing performance required by digital signal processors (DSPs), serializer/deserializers (SerDes), and phase-locked loops (PLLs).
As data throughput increases, oscillator characteristics such as phase jitter, phase noise, frequency stability, output format, and package size, become even more critical to overall system design. Understanding these parameters is an important step in selecting timing components for high-speed optical transceivers and networking equipment.
Why Are Crystal Oscillators Important in High-Speed Optical Communications?
Transceivers convert electrical data into optical signals for transmission through fiber and convert received signals back into electrical data. Within these modules, DSPs and SerDes devices process high-speed data using clocking architectures that depend on reference frequencies.
Crystal oscillators use quartz resonators to generate predictable frequencies with defined stability and noise characteristics. These properties make them useful reference sources for electronic systems that require precise timing.
As data rates increase, engineers must ensure that the reference oscillator meets the receiving device’s requirements and contributes appropriately to the system’s overall timing budget.
Crystal oscillators are widely used as reference clock sources because they provide predictable frequency generation and can be designed to desired frequency stability, phase noise, and phase jitter specifications. These characteristics ensure clocking systems meet the timing requirements of high-speed electronic interfaces.
How Are 800G and 1.6T Networks Changing Clock Requirements?
Higher network speeds place greater demands on electrical interfaces, signal processing, and clock generation. PAM4 signaling, which uses four signal levels to encode data, enables higher throughput than conventional NRZ signaling at a comparable symbol rate. However, its smaller vertical eye openings make noise and timing margins important design considerations.
| Optical Generation | Main Signaling Technology | Reference Clock Trend | Key Timing Considerations |
|---|---|---|---|
| 100G | NRZ | 156.25 MHz | Frequency stability and basic jitter performance |
| 400G | PAM4 | 156.25 MHz / 312.5 MHz | Lower jitter and improved phase noise |
| 800G | PAM4 | 156.25 MHz / 312.5 MHz | Ultra-low jitter and high-quality DSP / SerDes clocking |
| 1.6T | PAM4 / 224 Gbps-class SerDes | 312.5 MHz / 625 MHz | More stringent phase jitter, phase noise, and timing margin requirements |
Oscillator selection is therefore part of a broader effort to manage timing performance across the transceiver.
Key specifications include:
- Phase jitter: Measures clock timing variation that contributes to the system’s jitter budget
- Phase noise: Describes phase fluctuations across frequency offsets and can affect downstream clock generation
- Frequency stability: Indicates how well the oscillator maintains its specified frequency under defined conditions
- Electrical compatibility: Ensures the output meets the receiving device’s interface requirements
- Power and package size: Affect integration in compact, power-constrained networking equipment
The required parameters depend on the transceiver architecture, DSP, SerDes, PLL, and overall system design.
How Does a 312.5 MHz Oscillator Support High-Speed Networking?
A 312.5 MHz oscillator is used in compatible high-speed networking architectures to provide an external timing source for DSPs, SerDes devices, and associated clock-generation circuitry.
In some PLL architectures, using a 312.5 MHz reference instead of a 156.25 MHz reference can reduce the multiplication ratio needed to generate a particular internal clock frequency. The resulting jitter and phase-noise performance depends on the PLL design and the characteristics of the complete clocking system.
For engineers developing high-speed platforms, the key is selecting an oscillator that meets the reference-frequency and timing requirements of the target device.
Why Do High-Speed Optical Modules Use Differential Clocking?
High-speed optical modules contain dense circuitry, high-speed data traces, switching power supplies, and DSP/SerDes components that can increase EMI and crosstalk challenges.
Differential clocking helps reject common-mode noise and maintain signal integrity in high-speed environments. The interface must still match the clock input requirements of the DSP, ASIC, or SerDes device. Common differential output formats include LVPECL and LVDS.
LVPECL vs. LVDS: How to Select the Right Differential Clock?
LVPECL and LVDS both support high-speed clocking, but differ in signal swing, power consumption, and system requirements.
- LVPECL offers a larger signal swing and fast transitions, making it suitable for high-speed systems with demanding signal integrity and timing requirements.
- LVDS uses a lower signal swing to reduce power consumption while supporting low-noise, high-speed signaling in space- and power-constrained designs.
The best choice depends on the target device’s input specifications, power budget, and phase-jitter requirements. Aker offers multiple differential output options to support different high-speed networking and optical communication designs.
| Characteristic | LVPECL | LVDS | Selection Considerations |
|---|---|---|---|
| Signal Swing | Higher | Lower | LVPECL offers larger swing and higher sensitivity; LVDS features smaller swing, helping reduce high-frequency EMI. |
| Edge Rate | Fast | Fast | Both provide fast transition times suitable for high-frequency clocking. |
| Power Consumption | Relatively higher | Lower | LVPECL provides stronger drive capability with higher power; LVDS consumes less power, ideal for space and power-constrained designs. |
| Noise Immunity | Excellent | Excellent | Both utilize differential signaling to effectively reject common-mode noise and crosstalk in dense modules. |
Applications for Crystal Oscillators in Optical Networking
Crystal oscillators provide reference timing across a range of communication and data infrastructure applications.
- 800G and 1.6T optical transceivers: Reference clocks for compatible DSP, SerDes, and clock-generation architectures.
- AI data center networking: Timing components for switches and equipment connecting servers and accelerators.
- High-speed Ethernet switches: Clock sources for compatible switch ASICs and PHY devices.
- Telecommunications and optical transport: Frequency-control components for optical networking infrastructure.
- High-performance computing: Reference timing for systems requiring stable clock generation and high-speed data movement.
The appropriate oscillator depends on the target architecture, electrical requirements, and system timing budget.
How Does Aker Support High-Speed Optical Communication Applications?
Aker supports high-speed optical communication and networking designs with frequency-control solutions engineered to meet demanding timing, stability, and signal integrity requirements. Our differential oscillator portfolio includes the 312.5 MHz series with LVDS and LVPECL output options, with select models delivering typical RMS phase jitter as low as 27 fs. These options help engineers align clock performance with the requirements of their DSP, ASIC, and SerDes platforms while balancing jitter, power, and integration needs.
Our range of frequency-control options provides engineers with configurations to consider when developing high-speed optical communication and data infrastructure systems.
Contact us today to discuss your timing requirements, request samples, or evaluate the right 312.5MHz series for your next-generation high-speed design.
