How to ensure compliance with DDR4 standards using an oscilloscope

Figure 6. DDR BGA interposers come with a riser to elevate the interposer in areas with limited surface area.

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2. Choose an oscilloscope that can perform the appropriate application analysis

After determining the probing protocol, the next key consideration is the choice of test equipment. Although BER specifications for memory technologies are just beginning to be developed, this type of testing is already well established for high-speed designs and is supported by appropriate measurement tools such as oscilloscopes. It is important to use an oscilloscope with advanced measurement analysis capabilities, including de-embedding, real-time eye diagram measurements, mixed analog and digital signals; and cross-referencing simulated designs.

An MSO oscilloscope is an instrument that can display and analyze digital and analog signals simultaneously. One advantage of an MSO is the ability to separate read and write data. Users can connect the command bus, row address strobe (RAS), column address strobe (CAS), write enable (WE), chip select (CS), and clock signals to the digital channels, allowing the oscilloscope to trigger a read or write command based on any or a combination of these signals. It can separate the corresponding data and perform electrical and timing tests. An MSO also allows testers to view the flow of the command protocol and detect protocol violations.

When choosing an oscilloscope, it is important to understand how it integrates with other design and test tools. Keysight Technologies has leveraged its unique position as a world-renowned electronic measurement company to carefully build advanced EDA (software simulation) tools and oscilloscopes. When running traditional electronic and timing specifications in the final stages of DDR4 design, Keysight Technologies' tool suite provides a unique advantage, enabling the exact same consistency testing of simulated waveforms in candidate releases and waveform measurements of physical prototypes. In other words, simulated waveforms can be imported into the oscilloscope and compared to waveforms obtained from physical prototypes.

仿真过程可以显著减少设计的迭代次数和成本。每次执行探测时，都会给系统增加额外负载。仿真该负载可确保内插器不会破坏总线或产生任何未知负载。Keysight W2351 DDR4 一致性测试台可用于仿真负载效应并生成去嵌入文件，从而消除探测效应并使用示波器进行测量（关于去嵌入的详细信息，请参阅下一页的步骤 3），这样就可以真实地将您仿真的设计与原型进行比较。

Keysight Infiniium V-Series Oscilloscopes

Keysight Infiniium V-Series oscilloscopes are optimized for high-speed DDR memory measurements. The V-Series offers the industry's lowest noise and jitter measurement floors and a high effective number of bits (ENOB), making it an ideal tool for transmitter signal integrity measurements. Models are available from 8 GHz to 33 GHz, and their bandwidth can be upgraded to meet your future needs. It is used in conjunction with the InfiniiMax III and III+ probing systems to provide more accurate measurements to meet more demanding design margin requirements. In addition, it provides 16 digital channels with a time resolution of up to 50 ps. In addition, with Keysight's Advanced Design System (ADS) and DDR4 software, you can directly correlate simulation results with actual characteristics measured by the oscilloscope software.

Questions to ask your oscilloscope supplier:

• Can I cross-trigger and measure digital and analog channels?

• Does the oscilloscope have de-embedding capabilities?

• Does it have real-time eye diagram measurement capabilities?

• Can I cross reference this into my simulation design?

3. Use an automated compliance test application that complies with JEDEC standards

The final component of your test solution is oscilloscope software . With a DDR4 compliance test application, such as  the Keysight N6462A DDR4 Electrical Compliance Test Software , you can use the same oscilloscope you use for debugging on a daily basis to perform automated memory testing and margin analysis to the JEDEC specification. The application automatically configures the oscilloscope to provide valid results for each test. It also includes margin analysis, which indicates how close your device is to passing each specification.

The compliance application should also have some sort of “custom” mode that covers key measurements including eye diagram analysis, mask testing, and ringing. These measurements are critical to characterizing DDR4 devices.

The Keysight DDR4 compliance test application tests the clock, electrical, and timing parameters specified in the JEDEC SDRAM specification. The application helps you  test the compliance of all DDR4 and LPDDR4 (low power) devices using a Keysight Infiniium oscilloscope .

Keysight's application software also provides detailed reports, including worst-case values ​​with screenshots and pass/fail status of the measurement results according to the specification. It also calculates the margin from the specification pass line. Users can increase the number of runs to collect more data for statistical analysis. The statistical report will show the minimum, maximum and standard deviation of the test. This data is particularly useful when comparing test results from DRAM suppliers or different customers.

Keysight DDR4 electrical compliance test software reports include:
1. Worst case values ​​with screen shots
2. Pass/Fail status and margin from the standard
3. Multiple run results
4. Statistical report including minimum, maximum and standard deviation

Technology Insight: InfiniiSim

Keysight InfiniiSim waveform transformation toolkit provides a more flexible and accurate way to display waveforms anywhere in a digital serial data link. Highly configurable system modeling can easily and quickly help you eliminate the harmful effects of extraneous channel elements, simulate waveforms with channel models inserted, view waveforms at locations that cannot be physically probed, and compensate for the loading effects of probes and other circuit elements. The ultimate goal is to gain more margin when testing to specifications or performing characterization work.

Keysight DDR4 electrical compliance test software benefits:

1. Keysight Technologies actively participates in the work of JEDEC and makes key contributions to DDR4/LPDDR4 BER test methods

2. More test coverage than competitors

3. One-stop shop for DDR4 compliance test solutions (software + BGA interposer)

4. Cross-reference and simulate with W2351 Conformance Test Bench Software

5. Infiniisim Waveform Transformation Toolset

Summarize

DDR4 speeds require new ways to define and measure critical AC timing parameters (such as the timing and voltage of the data input valid window). The oscilloscope's probing analysis tools combined with automated compliance testing ensure repeatable and reliable test results.

If designers want to shorten the learning time and master the knowledge of the new generation of test and measurement protocols as soon as possible, it is best to consider working with test tool manufacturers who actively participate in the work of the JEDEC standards committee. Through close collaboration and communication, designers can find newer and better consistency test solutions. This is especially important for newly released technologies because their specifications and measurement methods are still under discussion.

Keysight's DDR4 eye profile test method is currently adopted by JEDEC for DDR4 standardization. Keysight is also a test and measurement company that provides hardware and software solutions at all stages of DDR chip development. From simulation to debugging, from verification to compliance testing, Keysight's solutions play an important role.

Anyone designing from DDR memory is under constant pressure to achieve faster access speeds and lower power consumption in ever-shrinking packages. Gaining insight into your design early in the product design phase allows for quick corrective action, ensuring your product meets quality, interoperability, and time-to-market goals. Successful design depends on efficiency and shortening design cycles to control design costs. Fortunately, there are many tools available today to help you achieve this goal.