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DDR Memory Design and Test Overview


Double Data Rate (DDR) Synchronous Dynamic Random Access Memory (SDRAM) is being implemented broadly in computing platforms and embedded applications. The overwhelming concern for developers of these products is interoperability. It starts with the physical layer where the data is transferred on both the rising and falling clock edges, to the functional test of read-to-write timing. Tools to validate the parametric and protocol aspects of these designs are required to understand if your design is in compliance, and how close design performance is to specification.

DDR technology is implemented in several forms today -- DDR (also called DDR1), DDR2, DDR3, DDR4, and low-power DDR (LPDDR1, LPDDR2, and LPDDR3) targeted for mobile devices. Specifications are defined by the Joint Electronic Devices Engineer­ing Council (JEDEC), but it’s up to designers to guarantee compliance.

Keysight Gets Involved, You Benefit

Keysight’s solutions for digital applications are driven and sup­ported by Keysight experts that are involved in the various international standard committees. We call it the Keysight Digital Test Standards Pro­gram. Our experts are active in the Joint Electronic Devices Engineering Council (JEDEC), PCI Special Interest Group (PCI-SIG®), Video Electronics Standards Association (VESA), Serial ATA International Organization (SATA-IO), USB-Implementers Forum (USB-IF), Mobile Industry Processor Interface (MIPI) Alliance, and many others. Our involvement in these standards groups and their related workshops, plugfests, and seminars enables Keysight to bring the right solutions to the market when our customers need them.

Key tasks

DDR design can be segmented into four areas: interconnect design, active signal validation, protocol validation, and functional test. While JEDEC defines the specifications, you are required to verify compliance. With no formal verification labs or test centers, you must decide the appropriate procedures, methods and equipment to perform these compli­ance tests. Keysight Technologies, Inc. offers solutions in each area for electrical physical layer, protocol layer, and functional test.

Physical Layer: Active Signal Validation

Validating DDR performance involves characterizing the clock and data signals. A big challenge is separating the read and write signals on the bidirectional bus. The ability to trigger properly will allow you to analyze the complex traffic on the DDR data bus.

Measure with confidence

Keysight’s Infiniium 90000 Series oscilloscopes provide the lowest noise floor, jitter noise floor, and trigger jitter in the industry, enabling more accurate characterization of your design. InfiniiScan provides zone triggering, enabling the oscilloscope to separate read and write cycles based on the distinctive pattern of the waveform.

Automate complex tasks

The Keysight DDR electrical perfor­mancecompliance software runs on the 90000 Series oscilloscopes, simplifying set up and performing compliance tests. With versions for DDR1, DDR2 and DDR3, the software provides busy engineers quick, accurate answers.

Physical Layer: Interconnect Design

As data rates increase, designers need to minimize signal integrity problems. To avoid signal attenu­ation, rise-time degradation, and jitter caused by long trace lengths, designers need tools like those used by high-frequency engineers.

Accurate impedance measurements

The Keysight 86100C Infiniium DCA-J with the 54754A differential TDR/TDT module makes quick work of interconnect analysis. It utilizes a unique calibration process to remove the effects of cabling, allowing you to isolate your device from the test system and view results in time or frequency mode.

Predict interconnect performance through simulation

The Keysight Advanced Design System (ADS) has several features optimized for high-speed digital design. Design guides provide a quick vehicle to start a DDR design. Analyze complete serial links by simulating at the circuit or system level. Make analyses quickly with oscilloscope-like displays.

Protocol Layer

You want to validate that your system is sending the correct DDR commands, that memory banks are addressed properly, and find any protocol violations. You will need to view read and write data signals at several levels of abstraction – from binary to protocol.

Decoding DDR signals

The Keysight U4154A logic analyzer allows the read and write data to be sampled at different times, and viewed separately. With the B4621A memory bus decoder, you can trigger on system attributes like burst length, CAS, and chip selects to decode key bus signals. The intuitive results display provides quick interpretation.

Automate complex tasks

The Keysight protocol compliance protocol compliance and analysis tool complements the 16900 Series logic analyzer by simplifying set-up and performing protocol decode and compliance tests. It runs on the logic analyzer, and produces quick, accurate answers.

Functional Test

Probing DDR Memory

Validating system performance requires properly triggering on the data bus or a specific memory address to ensure there are no timing, state or protocol violations. You need to analyze the DDR system behavior – are some commands being executed too often?

Validating system performance

The Keysight DDR protocol compli­ance and analysis tool automates deep DDR bus trace acquisition and analysis of the Keysight 16900 Series logic analyzer to quickly identify timing and protocol problems. It checks timing and state violations, then produces an HTML report and margin analysis to determine how close you are to the specification.

How robust is your design?

You meet all the timing and protocol specifications, but how does your design tolerate errors? The Keysight B4622A DDR2/3 protocol compliance and analysis tool provides a quick overview of DDR bus performance with statistic and histogram views for bus optimization.

When you characterize or validate your DDR design, are you measuring the right signal? The JEDEC stan­dards apply only at the BGA balls of the DRAMs, but in many cases these are difficult to access since many vias do not go through the board.

Probing specific signals

The Keysight InfiniiMax active probes are high-impedance, low capacitance probes that are minimally invasive to your signals. The solder-in probe head lets you easily solder to vias and quickly look at a signal.

Probing the data bus

To do a complete functional test, you need to measure the DDR bus. The Keysight Soft Touch logic analyzer probes can be used by just routing the traces in a specific manner. Their unique design makes solid contact with the traces without a connector.

Or use the Keysight DDR slot interposer, connecting directly to the standard DDR DIMM connector. The non-intrusive design lets you measure the full command, address, control and data bus signals.


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