400G PAM4 Ethernet Transceivers – Introduction
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400G PAM4 Ethernet Transceivers - Introduction
Pulse Amplitude Modulation 4-level or PAM4 has been widely adopted for 400G Ethernet used in data centers. In this newsletter, we shall share with you the technologies for 400G PAM4 Ethernet and the 400G QSFP56-DD transceivers.
What is 400G PAM4 Ethernet?
PAM4 uses data transmission with four distinct signal levels (or symbols) to convey information. Each symbol period represents 2 bits of logical information, effectively doubling data throughput within the same bandwidth. By efficiently encoding two bits per symbol, PAM4 halves the signal bandwidth requirement, facilitating higher data. 400Gbps Ethernet is achieved by utilizing four lanes of PAM4, each operating at 50Gbps, hence 400G PAM4 Ethernet.
Figure 1 shows an example of a PAM-4 waveform, along with an eye diagram for PAM-4 data. When a signal is referred to as “50G PAM-4”, or “100G PAM-4” it means the signal is carrying data at a rate of 50Gbps or 100Gbps respectively, using PAM-4 modulation.
Figure 1: PAM-4 waveform
400G QSFP 56-DD Transceiver
The QSFP56-DD stands for “Quad Small Form-factor Pluggable (QSFP) – Double Density (DD)”. The electrical interface of a QSFP-DD connector has 8 electrical lanes, running at 50Gbps each with PAM4 modulation (8x50G PAM), for a total bandwidth of 400Gbps.
Figure 2: Form factor of 400G QSFP56-DD transceiver
Multimode SR8: “SR” refers to 100m reach using multi-mode fiber, and “8” implies there are 8 optical channels. Each of the 8 optical channels from an SR8 module are carried on separate fibers, resulting in a total of 16 fibers (8 Tx and 8 Rx). Each optical channel operates at 50Gbps. The SR8 module uses an MPO-16 connector to connect to 8 fiber pairs or a 2 row MPO-12 connector to connect to 8 fiber pairs. The most common implementations use 2 row MPO-12
Figure 3: Multimode SR8 400G QSFP56-DD transceiver
For 400G single mode, they can be divided in two groups. One group operates optical 8x50G PAM4 channels, while the other group operates optical 4x100G PAM4 channels. The 8x50G offers improved link budgets in some scenarios, but on the flip side the total laser cost is higher per module (8 instead of 4). The 4x100G transceivers have lower power consumption and simpler thermal handling, and is the current market focus.
Figure 4: Single mode 400G QSFP56-DD transceiver
Transceiver Types
The suffixes of 400GBASE-SR8, DR4, FR4, LR4, LR8, and ER8 are defined by the fiber optic type, transmission distance and the number of optical channels. For example, DR4: “DR” refers to 500m reach using single-mode fiber, and “4” implies there are 4 optical channels. Each of the 4 optical channels from a DR4 module are carried on separate fibers, resulting in a total of 8 fibers (4 Tx and 4 Rx). Each optical channel operates at 100Gbps. Each lane operates at 1310nm and requires one fiber; thus, the transceiver interface needs to have 8 fibers. The DR4 and DR4+ modules use MPO-12 connector to connect to 4 fiber pairs.
Figure 5: 400GBASE-DR4 or DR4+ transceiver
Longer reach module uses 4 or 8 wavelengths (CWDM grid) and a multiplexer is added to combine these signals together. By this, the number of required fibers is reduced to 2 (TX + RX). The transceivers have duplex LC interfaces, and are commonly referred as FR4 for 2km, LR4 or LR8 for 10km, and ER8 for 40km.
Figure 6: 400GBASE-FR4/ LR4/ LR8/ ER8 transceiver
Starview offers the various 400G transceivers shown in the table below:
Transceiver Type | Datasheet | Type | Interface | Distance | Lanes |
400GBASE-SR8 | MM | MPO-16/MPO-24 | 100m | 8× 50G PAM4 | |
400GBASE-DR4 | SM | MPO-12 | 500m | 4× 100G PAM4 | |
400GBASE-DR4+ | SM | MPO-12 | 2km | 4× 100G PAM4 | |
400GBASE-FR4 | SM | LC | 2km | 4× 100G PAM4 | |
400GBASE-LR4 | SM | LC | 10km | 4× 100G PAM4 | |
400GBASE-LR8 | SM | LC | 10km | 8× 50G PAM4 | |
400GBASE-ER8 | SM | LC | 40km | 8× 50G PAM4 |
Why Choose Starview 400G PAM4 Transceivers?
Starview sets the standard for reliability, performance, and support for transceiver modules. With our dedicated service, these transceivers are reprogrammable to work seamlessly with various networking equipment, eliminating error messages and alarms.
To learn more about Starview’s product lineup, explore our E-Catalog or contact us at sales@starviewtech.net. Embrace the power of long-haul data transmission with Starview.