As memory technology evolves, there is an increasing move towards higher operating frequencies and the use of BGA (ball grid-array) chip packages. This is as true for the DDR/DDR2/DDR3 memory modules commonly found in desktop and laptop computers as it is for the low-power LPDDR/LPDDR2 memory used in mobile computing devices and embedded devices. Proper measurement instruments and detection tools are therefore essential for engineers to carry out signal testing, validation and error detection tasks for high-speed memory, so that detection and modifications can be quickly completed and the product can be brought to market as early as possible.
Tektronix technical support manager of T&M sales department David Yang, explained during the Digitimes Embedded Technology Forum held in February that design validation for memory systems must take into account how to work under specific conditions to accurately obtain circuit behavior models and boundary values, rapidly verify signal integrity and timing analyses to uncover problems; it must be able to work with different instruments, probes and jigs; and it must permit testing set ups for embedded systems that are simple and deliver test results quickly.
Challenges and industry solutions for DDR/DDR2/DDR3 measurement and validation
The challenges for memory testing lie in: 1) Signal access and detection: reliability and ease of use for connections, bandwidth and signal integrity, while remaining financially viable; 2) Can isolate the triggering or post-processing of read/write burst modes; 3) Complies with JEDEC standards for consistency of testing, such as for parameter timing, amplitude measurements, Vref/Vih/Vil voltage and derating measurements; 4) Ability to verify and compute statistics for test results; 5) Effective reporting and archiving; and 5) Advanced analytical capabilities required for circuit characteristics and troubleshooting.
Tektronix provides fast and precise solutions for DDR/DDR2/DDR3 measurement instruments. This includes DSA sampling oscilloscopes for verifying signal paths and characteristics; DPO/DSA real-time oscilloscopes and associated software for analog and electrical property troubleshooting; TLA logic analyzers for digital signal validation and troubleshooting; support for Nexus and FuturePlus memory chip jigs; and testing jigs, probes and clamping plates for DRAM memory chips.
Sampling oscilloscopes assist with the measurement of signal path characteristics and the validation of circuit boards
On the signal characteristic and circuit validation front, Yang pointed out that Tektronix's DSA8200 Sampling Oscilloscope can be used for measurement and validation in a broad range of applications including DDR 266/333/400MHz, DDR2 400/533/667/800/1066MHz, and DDR3 800/1066/1333/1600/1867MHz. For high-frequency DDR/DDR2/DDR3 memory that is placed on a DIMM module or soldered on to the motherboard, is can aid the calculation of S parameters for TDR (timeout detection and recovery) and frequency scattering interference, as well as the detection of signal pathway characteristics and signal loss during transmission.
Yang highlights Tektronix DSA8200 Sampling Oscilloscope
Another challenge is how to quantify signal integrity, for example in terms of impedance measurement, signal insertion, return loss and frequency domain crosstalk. In combination with TDR and S-parameter generation software, the DSA8200 Sampling Oscilloscope can measure and sample the frequencies up to 70GHz with minimal noise interference, allowing improvements in terms of the effects of impedance and making measurements more precise, as well as allowing the recording of signal information for one million high-frequency measurement points. The DSA8200 can also simulate channel effects under jitter timing or noise interference conditions, as well as automating the various steps of the measurement procedure to minimize errors and reduce testing time, shortening the time needed to complete the entire analysis to just a few minutes.
In terms of analog validation and debugging of DDR, Tektronix also offers detection and measurement software for the DSA70000 real-time oscilloscope, allowing measurement and validation of DDR/DDR2/DDR3. For example, accessing and detecting signals requires a reliable, yet easy to use type of physical connection, such that the various types of measurement point for memory measurement have frequency generation performance that demands the highest levels of signal integrity, as well as sufficiently quick response signals.
In terms of signal acquisition, it can automatically trigger and capture DQ and DQS signals for DDR, in order to isolate read/write signals; it also automatically sets up voltage levels and data transfer rates, allowing even signals captured over a sustained period to be presented in high resolution.
Software features for DDR analysis (DDRA) include automatic set up, read/write burst mode testing, and JEDEC-compliant pass/fail testing modes. It is also equipped with powerful DPOJET analytical tools for jitter, eye diagrams and timing. This makes it possible to perform tests including timing, amplitude, histogram plots, measurement plots, advancing timing jitter, eye diagrams and pass/fail tests; it also offers a wide range of display and graphical options, as well as a report generator.
Analog/digital and mixed signal measurement and validation
Higher data transfer rates have made signal access and measurement methods more complex in a variety of ways, including decreases in signal boundary values, higher signal fidelity requirements, smaller physical dimensions for components and distances between pins of less than 20mm; all these issues create measurement points that are difficult or even impossible to measure. There are already a number of different measurement methods for standard computer DIMMs, but the majority of embedded systems solder memory directly on to the PCB. As DDR2/DDR3 invariably uses BGA packages that are extremely difficult to tap and measure separately, the BGA socket can instead be soldered on the measurement IC, with a Nexus DDR intermediate board connected in between so that the signal can be tapped off and measured. It supports x4/x8 and x16 modes for DDR2/DDR3, and the onboard BGA socket can be directly installed on the memory IC to be tested.
P7500 Series TriMode Probes, 020-2954-xx extension socket cables, 4GHz TriMode copper micro coaxial measurement cables and P75TLRST measurement cables supporting up to 20GHz can be used for analog signals. Yang also cited a number of example implementations of BGA signal measurement.
For validation of mixed analog and digital signals, the P6780 automatic differential logic probe can be added, allowing 16-channel signal testing plus one clock channel with 2.5GHz bandwidth and low capacitive delays of just 0.5pf. The P6717 single-ended logic probe also supports 16-channel signal testing plus one clock channel with 350MHz bandwidth mixed analog/digital signals. Adding the iCapture probe and MSO70000 software makes analog/digital signal and mixed signal measurement possible with only a single analog measuring cable connected.
Digital design and validation
Yang noted that digital validation and debugging involves additional observation requirements, such as for data flow in/out of the memory, multiple channels, full-channel pulse and timing management, and data flow in/out of the processor and CPU. The hardware can also assist with determining bus-level or system-level errors, protocol sequencing and timing, startup memory initialization and system power source time counting, DRAM register settings, refresh operations, and time correlations for other system bus or oscilloscope waveforms. The Tektronix TLA7000 family of memory chip jigs and probes provides signal measurement solutions for DDR 266/333/400MHz, DDR2 400/533/667/800/1066MHz and DDR3 800/1066/1333/1600/1867MHz.
In terms of DDR2/DDR3 data access, the measurement instruments have ample performance to cope with all DDR signal measurement requirements, reserving frequency components and time segments, keeping signal reflection to a minimum, and achieving lower probe capacitive load than any competing company at just 0.5pF. The test jig for the Tektronix NEXVu DIMM probe for logic analyzers can also be used for enhanced-JEDEC design DIMMs and DIMM interposers, and can be paired with a BGA memory interposer, such that it can directly connect with and measure BGA signals underneath the memory chip. MagniVu logic analyzers also support clock signals at a minimum of just 20ps, equivalent to resolving power at 50GHz.
Tektronix's TLA7000 series logic analyzers support 64Mb full duplex signal measurement at 1.4Gb/s data and 1.4GHz clock, as well as full duplex 128Mb signal measurement recording at 2.8Gb/s data and 1.4GHz clock, with recording samples of up to 128K in length; includes triggers, 16 types of IF-THEN-ELSE trigger mechanism, 24-character set identification, 136-channel modules, and the use of P68xx and P69xx probes, as well as logic analyzers for measuring such as the TLA7016 and TLA7012. It also provides enhanced analytical software tools such as Sample Point Finder (SPF) and Protocol Violation Tool. Combined with the Nexus and FuturePlus memory measurement jigs, it constitutes the world's leading DDR3 measurement solution.
Putting together measurement solutions for mainstream, low-power and graphics memory
Yang listed a variety of measurement and validation solutions for different memory applications. For testing ordinary DDR, DDR3 and DDR3 DIMM memory modules, the TLA7102 Portable or TLA7016 Benchtop logic analyzer unit can be used; for DDR, this may be paired with the TLA7AA4 probe, while the TLA7BB4 probe can be used for DDR2/DDR3. On the test clamp/fixing jig front, the Nexus Technology NEXVu and the FuturePlus System DDR Support are recommended. In terms of probes, Tektronix midbus probes or Nexus & FuturePlus socket intermediate boards and DIMM test jigs can be used for DDR and DDR2, while the P6960HCD (>1500MT/s) or NEXPRB1XL(< 1500MT/s) should be used for DDR3.
When looking at oscilloscopes. DPO/DSA70404B, MSO70404 or higher models should be used for the measurement and validation of LP DDR/LPDDR2 and DDR chips; DPO/DSA70604B, MSO70604 or even higher end units should be used for DDR3; and DPO/DSA70804B, MSO70804 or even higher end models should be used for GDDR3 and DDR3. P7300 or P7500 differential probes may be used, while analytical software tools such as DDR Analysis (DDRA), Advanced Search & Mark (ASM), and DPOJET Jitter/Eye Analysis (DJA) can be selected. For bus command triggering or capturing with iCapture, an MSO70404 or even higher-end oscilloscope should be used for LPDDR/LPDDR2 or DDR, while a MSO70604 or even higher-end oscilloscope should be used for DDR2, and a MSO70804 or even higher-end unit should be used for DDR3 and GDDR3.
Yang summed up the world's best DDR validation and measurement solutions in the following terms. Tektronix provides comprehensive support for validation, signal characteristics and complete measurements with a range of tools for everything from DDR/DDR2/DDR3 and LP DDR/DDR2 to GDDR3; collaboration with partners like Nexus and FuturePlus enables Tektronix to offer complete protocol testing and probe support. In terms of measurement performance, Tektronix supports TriMode Probing, as well as automated set up testing and pass/fail determinations for JEDEC standards, providing complete services for the industry from analog signals to digital circuit validation.
Tektronix technical support manager of T&M sales department David Yang
Tektronix offers comprehensive measurement and validation solutions and services that have earned the interest and admiration of its customers