The new device is the first sixth-generation registered clock driver for DDR5 registered dual in-line memory modules.

Renesas has introduced its newest DDR5 registered clock driver (RCD). The company claims the RRG5006x is the industry’s first 6th-generation RCD. The new chip is designed to help close the gap between advanced processor performance scaling and RAM performance scaling.

Renesas' registered clock drivers. Image used courtesy of Renesas

As data center and AI processors have increased in speed and performance, their transfer demands have outpaced memory bandwidth. The Gen6 RRG5006x reportedly provides a 10% bandwidth increase over Renesas’ previous top-of-the-line RCD. This translates to 9,600 mega transfers per second (MT/s) to enable faster feeding of top-tier processing units.

The New RCD's Key Features

The RRG5006x Gen6 RCD targets the highest-demand applications, including next-generation server systems, AI data centers, and HPC applications.

The device achieves 9,600 MT/s compared to Renesas’ Gen5 RCD's 8,800 MT/s. It offers backward compatibility with Gen5 memory and processing platforms, enabling a faster and more efficient upgrade path with reduced development time. It also provides enhanced signal integrity and improved power efficiency to support demanding AI, HPC, and LLM workloads.

Its expanded decision feedback equalization architecture includes eight taps and 1.5-mV granularity to support precise margin tuning. The decision engine signal telemetry and margining (DESTM) system improves diagnostics by providing real-time signal quality indication, margin visibility, and feedback for higher transfer speeds.

The device supports I2C and I3C interfaces for configuration and control and is compatible with both 1-rank and 2-rank DIMM configurations. The RCD provides access to internal control words, allowing users to configure device features and adapt to various RDIMM system applications. It also includes loopback and pass-through modes for flexible testing and validation.

The Problem: CPU to Memory Signal Challenges

The path between high-performance CPU memory controllers and memory includes clock signals, command/address (CA) signals, and data signal lines. Every bit of incremental length differential between those signal lines, every PCB trace bend, and every solder joint and board-to-board connector offers opportunities for individual signal line voltage variations and timing delays. The result can be an unsynchronized clock, CA, and data in either or both directions between CPU and memory, as illustrated in the figure below.

Dramatization of signal cleanup and synchronization enabled by data registers and an RCD. 

This can cause the system to slow down and repeat transactions or lock up due to metastability. Registered dual inline memory modules (RDIMM) address this issue in data centers and HPC applications. RDIMMs are the highest-performing incarnation of DDR5. The “register” moniker indicates that the chip signals are buffered in a data register chip between the CPU memory controller and the RAM on a memory module. The clock, command, and address signals go into a separate RCD register chip. The data buffers accept data signals into registers.

The Solution: The RCD as Gatekeeper

Everything holds until the RCD output clock triggers and changes state. This ensures that, regardless of any drops or delays in the system prior to getting the memory, everything in the module is clocked at the same time and buffered to the same level.

As the gatekeeper, the RCD is the most critical component of the register circuitry. Delivering a 10% increase in RCD throughput, Renesas' Gen6 RRG5006x RCD improves the performance of the memory module as a whole. While the register circuitry and action take up an extra system clock cycle for synchronization within the RCD, the added reliability, along with careful design techniques such as interleaving, enable a net increase in transfer speed. This synchronization and buffering capability increases signal integrity and power efficiency.

Chip Availability

The new chip is backward compatible with Gen 5 platforms, streamlining a fast and easy upgrade path. The RRG5006x is currently sampling to key customers and is slated for full production in the first half of 2027.