Microchip Announces PCIe 5.0 And CXL Retimersby Billy Tallis on November 11, 2020 4:15 PM EST
Microchip is entering the market for PCIe retimer chips with a pair of new retimers supporting PCIe 5.0's 32GT/s link speed. The new XpressConnect RTM-C 8xG5 and 16xG5 chips extend the reach of PCIe signals while adding less than 10ns of latency.
As PCIe speeds have increased, the practical range of PCIe signals across a circuit board has decreased, requiring servers to start including PCIe signal repeaters. For PCIe gen3, mostly-analog redriver chips were often sufficient to amplify signals. With PCIe gen4 and especially gen5, the repeaters have to be retimers that operate in the digital domain, recovering the clock and data from the input signal with awareness of the PCIe protocol to re-transmit a clean copy of the original signal. Without retimers, PCIe gen5 signals only have a range of a few inches unless expensive low-loss PCB materials are used, so large rackmount servers with PCIe risers at the back and drive bays in the front are likely to need retimers in several places.
Microchip's new XpressConnect retimers add less than 10ns of latency, considerably better than the PCIe requirements of around 50–60ns. This also helps make the new XpressConnect retimers suitable for use with CXL 1.1 and 2.0, which use the same physical layer signaling as PCIe gen5 but target more latency-sensitive use cases. These retimers are the first Microchip products to support PCIe 5.0, but the rest of their PCIe product lineup including PCIe switches and NVMe SSD controllers will also be migrating to PCIe gen5.
The XpressConnect retimers come in 8-lane and 16-lane variants, both supporting bifurcation to smaller link widths, so that a single retimer can be used for multiple x1, x2 or x4 links. The retimers conform to Intel's specification for the BGA footprint and pinouts of PCIe retimers (13.4x8.5mm for 8 lanes, 22.8x8.9mm for 16 lanes), so these chips will eventually be competing against alternatives that could be used as drop-in replacements.
Common uses for PCIe retimers will be on drive bay backplanes, riser cards, and on large motherboards to extend PCIe 5.0 to the slots furthest from the CPU. Retimer chips will not necessarily be needed for every PCIe or CXL link in a server, but they are going to be an increasingly vital component of the PCIe ecosystem going forward. PCIe/CXL connections with a short distance from the CPU to the peripheral and few connectors will usually not need retimers, and riser or adapter cards that use PCIe switches to fan out PCIe connectivity to a larger number of lanes will already be re-transmitting signals and thus don't need extra retimers.
Microchip's XpressConnect PCIe 5.0 / CXL 2.0 retimers are currently sampling to customers, and are being incorporated into an Intel reference design for PCIe riser boards. Mass production will begin in 2021.