A PCIe Retimer is a hardware component used to enhance the signal integrity of PCI Express (PCIe). Its primary function is to regenerate and recover PCIe signals, ensuring that signal quality and stability are maintained during long-distance transmissions or in complex topological structures.

Since the introduction of PCI Express 3.0 over a decade ago, Retimer and Redriver technologies have enabled longer physical channels in servers and storage systems. Today, PCIe 4.0 solutions are mature, PCIe 5.0 solutions are gradually rolling out, and the PCIe 6.0 specification was released in early 2022.

As communication rates steadily increase, signal attenuation becomes more severe, especially with each iteration of the PCIe standard. As application demands evolve, the PCIe standard continues to update, with transmission speeds doubling each generation. However, due to the physical size of servers being constrained by industrial standards, insertion loss across the entire link has become increasingly prominent. For example, it has risen from 22dB in the PCIe 3.0 era to 28dB in PCIe 4.0, and further to 36dB in PCIe 5.0.

Main Functions of a Retimer

Signal Regeneration:

A Retimer can receive signals from PCIe devices and regenerate them to eliminate signal quality issues caused by attenuation and distortion during transmission.

Clock Recovery:

A Retimer can also extract clock information from the received signal, ensuring synchronization of data transmission. This is especially critical for high-frequency PCIe signals.

Latency Compensation:

In complex systems, signals may experience varying delays. A Retimer can help compensate for these delays, ensuring synchronization between devices.

·Application Scenarios of Retimers

· Long-Distance Connections:

In applications requiring long-distance connections, such as between servers and storage devices, Retimers ensure signal quality.

Multi-Layer Circuit Boards:

In complex PCB designs where signals traverse multiple layers, Retimers help improve signal integrity.

High-Bandwidth Applications:

In applications demanding high bandwidth and low latency—such as data centers and high-performance computing—Retimers are critical components for ensuring performance.

In the figure, after receiving information, the RETIMER passes it through the CTLE (Continuous Time Linear Equalizer) and DFE (Decision Feedback Equalizer) for signal equalization, improving signal quality and data transmission reliability. CTLE and DFE are both important signal equalization technologies in high-speed digital communication systems. In practical applications, CTLE and DFE are often used together to achieve better equalization. The CDR (Clock and Data Recovery) circuit extracts the clock signal from the input serial data signal and uses this recovered clock signal to sample and recover the data.