Renesas has introduced the industry's first lineup of clock buffers and multiplexers that meet strict PCIe 6.0 specifications. The new devices will let companies build motherboards and other devices that should comply with PCIe 6.0 requirements when it comes to performance and signal integrity, but are also compatible with PCIe 5.0 applications.
Renesas is adding 11 new RC190xx clock buffers and four new RC192xx multiplexers that have an additive jitter of only 4fs RMS, which is virtually noiseless, a feature that's extremely important for PCIe Gen6 applications. Also, the new clock buffers feature a 1.4 ns in-out delay, 35ps out-out skew, and -80dB power supply rejection ratio (PSRR) at 100kHz. The new chips complement Renesas's low-jitter 9SQ440, 9FGV1002 and 9FGV1006 clock generators and enable the company to offer a complete PCIe 6.0 timing solution.
A 256 GBps bi-directional bandwidth over a 16-lane interface or a 64 GBps bi-directional bandwidth over a 4-lane interface will hardly be required by consumer graphics cards or solid-state drives any time soon. But in the data center, bandwidth is everything. Meanwhile, ultra-complex PCIe Gen 6 circuit design and tests will take time, so the earlier hardware developers start building new products, the better. This could enable developers of next-generation server platforms to start designing motherboards, accelerators, network cards and SSDs.
"By delivering the first discrete timing solution for PCIe Gen 6, Renesas is enabling customers to develop the next-generation of high-performance systems," said Rich Wawrzyniak, principal analyst for Semico Research in a statement from Renesas. "It will be interesting to see the innovative implementations that result from this new capability, especially when considering how solutions for the emerging chiplet market are starting to evolve, with the need for increasing speed and bandwidth as an underlying constant."
To boost a total bandwidth of a 16-lane PCIe slot to 256 GBps in both directions, the PCIe Gen 6 specification increases data transfer rate to 64 GTps and adopts pulse amplitude modulation with four levels (PAM-4) of signaling as well as forward error correction (FEC). A very high data transfer rate and a new signal encoding method not only require new logical enhancements to the specification (e.g., FEC further enhanced with CRC), but also increase requirements for quality of clock signals —clock jitter performance of a PCIe Gen 6 subsystem should be less than 100fs RMS. This is where the all-new clock buffers (also called clock drivers) and multiplexers come into play.
The operation of a circuit has to be synchronized, but sometimes the same-sourced clock signal arrives at different registers at different times due different path lengths between two clock paths, or because of gated or rippled clocks. This phenomenon is called clock skew, or timing skew, and can cause hold time violation errors. Clock buffers allow for distributing clocks synchronously and efficiently by preserving clock properties of the input signal, and minimization of the additive jitter noise is particularly important for PCIe 6.0 subsystems.
A multiplexer is essentially a multiple-input and single-output switch that is used for signal distribution. Since we are dealing with a 64 GTps data transfer rate, MUXes have to handle this signal rate and ensure clean signals, which is why brand-new multiplexers for PCIe Gen 6 applications are required.
"PCIe Gen6 timing will be at the heart of new equipment in data centers, high-speed networking and other applications, "said Zaher Baidas, Vice President of the Timing Products Division at Renesas. "As we have done for preceding generations, Renesas is providing customers with the first timing solution to enable these new, higher-performance systems. Our customers know that we have the technical expertise and market knowledge to ensure that their products will be able to meet future requirements as well."