High-Speed PCBs and DDR5 Memory - Signal Integrity Issues Discussed with Stephen Slater
In the world of technology, a significant shift is underway as we move from DDR4 to DDR5 memory. This transition requires careful attention from signal integrity engineers, who must start with a good pre-layout design to ensure smooth operation.
One crucial aspect of this design process is managing capacitance and inductance to achieve the desired impedance for vias. Adjusting the antipad clearance size, number, and location of ground stitching vias can help balance these factors.
Keysight Technologies, a leading name in electronic measurement, has developed a library of PCI express-gen-5 reference channels for system simulation. This resource aids engineers in designing high-speed memory systems.
Signal integrity analysis is carried out using the Pathwave ADS SI pro, while power integrity analysis is handled by the PI pro. Keysight's High-Speed PCB Design Guide provides comprehensive information on understanding transmission lines and controlled impedance, as well as the selection process of high-speed PCB materials.
Crosstalk is a critical issue in the PCB layout for DDR5. To mitigate this, designers should consider using multiple PCB layers to route memory signal pathways, minimizing vias, and incorporating shielding zones between signals. ASUS OptiMem II technology, for example, maps memory signals across different layers and adds shielding zones to improve memory stability and reduce crosstalk in DDR5 motherboards.
Increasing the number of PCB layers, such as in DDR5 modules like G.SKILL T5 Neo, allows for better signal routing, separation, and isolation, enhancing signal integrity and reducing crosstalk at high frequencies.
Other best practices include length matching of differential pairs to minimize skew and carefully controlling trace geometry and spacing to reduce coupling noise. Simulating signal integrity and crosstalk with specialized tools helps verify and optimize these layouts before fabrication.
Stephen Slater, a product manager in the High-Speed Digital Simulation Technology at Keysight, specialises in high-speed SerDes channel simulations, DDR simulations, and electromagnetic simulations for PCB applications. He emphasises that designing high-speed boards can be complex due to signal integrity issues.
Keysight's Pathwave ADS via designer offers a three-dimensional view and is parameterized, allowing for easy adjustment of via width, spacing, and pad dimensions. A new conducted EMI analysis tool in Pathwave ADS allows for quick setup and analysis, helping engineers to fix potential problems before building prototypes.
Optimising vias can improve signal integrity at speeds of 16 Gbps and beyond in PCBs with multi-gigabit high-speed links. With many more DDR5 designs expected to start this year, these considerations will play a vital role in ensuring the success of these new memory modules.
[1] ASUS OptiMem II Technology: https://www.asus.com/motherboards/optimem/ [2] G.SKILL T5 Neo 16-layer PCB: https://www.gskill.com/product/f4-4800c36d-32gt5neo [3] Multi-gigabit high-speed links and DDR5: https://www.researchgate.net/publication/349444181_A_survey_on_high-speed_memory_technology_for_multi-gigabit_per_second_applications_DDR5_and_beyond
- In the manufacturing of high-speed memory systems, such as DDR5, financial investments in technology and real-estate are crucial for accommodating the intricate design processes and advanced tools required, like Keysight Technologies' Pathwave ADS SI pro and PI pro.
- Data-and-cloud-computing industries can benefit from the advancements in high-speed memory technology, such as DDR5, as the improved signal integrity and reduced crosstalk at high frequencies enable faster data processing and transmission.
- The business sector might find it advantageous to adopt DDR5 memory modules due to their enhanced signal integrity, which contributes to greater efficiency and reliability, leading to better performance and productivity.
- As the controlled impedance in high-speed PCB design plays a vital role in achieving the desired performance for memory systems, organizations in the manufacturing industry focusing on PCB production should implement Keysight's High-Speed PCB Design Guide and Pathwave ADS via designer for optimizing PCB layer structure, via design, and impedance control, thereby ensuring smooth operation and improving overall system performance.
