Application of SG3225EEN in PAM4 optical modules and 400G, QSFP-DD optical modules

May 10,2024
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The application of Epson crystal oscillator SG3225EEN, 156.25MHz in PAM4 optical modules and QSFP-DD optical modules. The optical module market has developed to 400G optical modules, so what are the differences between PAM4 optical modules and 400G QSFPDD optical modules? How is SG3225EEN applied in PAM4 optical modules and QSFP-DD optical modules?

The first thing to introduce is the PAM4 optical module: PAM4 is a type of PAM (pulse amplitude modulation) modulation technology. PAM signal is a popular signal transmission technology after NRZ, and also a representative of multi-stage modulation technology. It has been widely used in the field of high-speed signal interconnection. From 4G to 5G, traffic growth is very rapid, and how to reduce the imbalance between traffic and revenue is a major pain point faced by operators. The most effective measure to reduce the scissors gap is to reduce costs. In the cost composition of mobile carrier network equipment, the proportion of optical modules is increasing. If the cost of optical modules can be effectively reduced, it will undoubtedly play a crucial role in reducing the cost of the entire network equipment. The 400 GE/200 GE/50GE based on single channel 50 GPAM4 technology can well adapt to the network cost and performance demands of 5G, and build the optimal solution from access, aggregation to the core network. Given that PAM4 optical modules currently have 50G, 100G, 400G, etc., among which 400G optical modules are the development trend, and many mainstream manufacturers choose QSFP-DD as the packaging for 400 optical modules, so it is also known as QSFP-DD optical modules in the industry.

At present, OSFP and QSFP-DD are the two mainstream modes of 400G optical modules. QSFP-DD is backward compatible with QSFP, while OSFP is not compatible. Therefore, the 400G QSFP-DD optical module is currently the mainstream solution. The QSFP-DD dual density four channel small pluggable package is a high-speed pluggable module package defined by the QSFP-DD MSA group. It is the preferred packaging for 400G optical modules, allowing data centers to effectively grow and expand cloud capacity as needed. Adopting an 8-channel electrical interface, each channel has a speed of up to 25Gb/s (NRZ modulation) or 50Gb/s (PAM4 modulation), providing a solution for aggregation up to 200Gb/s or 400Gb/s. The QSFP-DD optical module can achieve an aggregated bandwidth of up to 14.4Tb/s in a single switch slot. The characteristics of QSFP-DD optical modules mentioned above have unparalleled advantages in 400G applications (such as data center interconnection). It is expected that the world's leading large-scale data centers will soon deploy 400G, and QSFP-DD may become the mainstream packaging.

Considering the current 400G QSFP The packaging and structural dimensions of the DD optical module require a crystal oscillator/crystal combination for the clock generator, and the power consumption is not small, which will also occupy a large design space. Therefore, researchers directly choose small packaging, high-performance, and low-power crystal oscillators. We recommend SG3225EEN, 156.25MHz small package crystal oscillator. The RMS jitter of SG3225EEN can reach 0.05 ps (156.25MHz), with a maximum frequency stability of+25ppm and an optional output frequency between 25M and 200M. It directly supports the LVPECL format level output required by PAM4 optical modules. SG3225EEN is packaged in metal and supports a maximum operating temperature of 105 ℃, with consistent indicators across the entire temperature range. It is very suitable for the design of line side optical modules such as 400G QSFP-DD.