As the landscape of computer technology continues to evolve and change, new standards emerge and device architectures need to be adjusted accordingly. This statement also applies to the generational change in standards from DDR3 to DDR4.
These advances in random access memory have also significantly improved overall performance. Therefore, to take advantage of the latest RAM, PCB designs need to change, just as they did when the USB standard evolved from USB 2.0 to USB 3.0. These types of changes are ongoing and necessary as market demand for more processing power, better performance, and more advanced features continue to drive the industry.
While most people will not notice or see the architectural changes required for PCB design, this does not diminish the importance of these key changes.
Double Data Rate 4 (DDR4), for short, comes in two different module types. One module type is the small dual inline memory module (260 pins), or So-DIMM, which is used in portable computing devices such as laptops. The other module type is the dual in-line memory module (288 pins), or DIMM for short, used in devices such as desktops and servers.
So, of course, the first change in architecture is due to the number of pins. The previous iteration (DDR3) of DIMMs used 240 pins, while So-DIMMs had 204 pins. The aforementioned DDR4 DIMMs use 288 pins. With more pins or contacts, DDR4 offers larger DIMM capacity, better data integrity, faster download speeds, and higher power efficiency.
Along with this overall performance improvement comes a curved design (bottom) that allows for better, more secure connections and improved stability and strength during installation. In addition, bench tests have proven that DDR4 enables a 50% performance improvement up to 3,200 MTs (megabits per second transfer rate).
And, these performance gains are achieved with reduced power consumption: each DIMM draws only 1.2 volts, instead of the 1.5 to 1.35 volts required by the previous generation standard. All of these changes mean that PCB designers must reevaluate their design approach to implement DDR4.
If we want electronic devices or components to operate at optimal levels, we need precise PCB designs that include DDR4 implementation. This is well understood. In addition to the need for design accuracy, it must also be compliant with today's memory.
PCB designers must also consider a variety of other factors, such as space allocation and critical connections. There is also a need to manage the initial design phase, as for a successful implementation, the design must meet the wiring topology and design specifications.
To effectively manage data, PCBs should follow cabling and best practices (PCBs), as failure to do so can lead to several problems, including susceptibility and radiated emissions. PCB designers should also utilize appropriate techniques to achieve massive fan-out and high edge rates to maintain low BER and a data range of 1.6 to 3.2 Gbps. Again, without proper design techniques, our PCBs will experience signal integrity issues and result in crosstalk and resulting (excessive) jitter.
Achieving the best routing path in a PCB design requires proper placement of DIMM connectors and proper use of memory chips. In general, DDR4 SDRAM requires shorter cabling and proper spacing to achieve peak timing and optimal signal integrity. PCB designers should also swap pins in the relevant signal groups. In addition, signal wiring at gaps, signal layer wiring adjacent to each other, and reference plane splitting should be avoided during implementation.
Also, if possible, we should also route the memory interface signals between the power supply layer or the appropriate ground (GND). In addition, you can help reduce or eliminate transfer speed differences by routing DQ (input/output data), DQS (data select), and DM (data mask) signals in the same byte channel group on the same layer. Clock signals have longer propagation delays than DQS signals, so the clock signal alignment lengths typically need to be longer than the longest DQS alignment in a two-row inline memory module.
Finally, we must keep in mind that each board stack is different and so are the spacing requirements. Therefore, a field solver (such as Cadence Clarity™ 3D Solver) must be used to establish crosstalk below -50dB between critical signals. Note: There is no length requirement from the clock to the DQS, but there is a length requirement from the clock to the command/control/address. The length requirement depends on the Dk (dielectric constant) of the material and the load on each SDRAM. 4.
DQS, DQ, and DM networks can be assigned to any available internal stripline layer in the stack. Instead, address/command/control and clock should be routed on layers closer to the SDRAM to minimize over-hole coupling.
Address/command/control SDRAM vias should have vias connected to ground (shaded vias) added at each SDRAM to reduce vias coupling.
In addition, the address and control reference power layer or ground depends on the controller. Note that DIMMs have address and control reference power layers, while on-board BGAs (ball grid arrays) rarely have address and control reference power layers.
DDR4, like the previous generation standard (DDR3), requires a new design approach in its implementation. Obviously, the design requirements have changed to accommodate the upgraded performance, which is a side effect of the innovation. However, following the right design and topology techniques can maximize performance by taking advantage of this new contemporary standard.
Whether you are implementing any form of DDR memory or working on a design with particularly demanding signal requirements, Cadence's suite of design and analysis tools can help you. designs faster than your expected "double data rate".
Zhejiang NeoDen Technology Co., LTD., founded in 2010, is a professional manufacturer specialized in SMT pick and place machine, reflow oven, stencil printing machine, SMT production line and other SMT Products. We have our own R & D team and own factory, taking advantage of our own rich experienced R&D, well trained production, won great reputation from the world wide customers.
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