Agilent Measurement Journal - Issue 5 - 2008 - (Page 28)

results because probing at these locations often causes signal reﬂections that produce non-monotonic edges. Rather than presenting true signal performance, the resulting measurements show a signal that has been affected by reﬂections from the components. This undesirable phenomenon can cause errors in slew-rate and setup/hold-time measurements since the nonmonotonic edge shifts the timing at a speciﬁc voltage threshold. This problem can be avoided by probing near the DRAM ballout. “Interposer probes” can be used for protocol validation by inserting the probe between the DIMM and connector.1 Signals then are routed through the probe to a logic analyzer. Because this memory design is most commonly used in computer systems, this method does not apply to embedded systems in which the DDR DRAM is attached directly to a circuit board (e.g., without a connector). In such cases, the circuit board may have probe points that can be accessed by a logic analyzer; however, these might not be sufﬁcient to enable probing of all signals simultaneously due to the high density — and wide buses — of clock, strobe, data, address, and control signals. One alternative is to lay out a probing footprint on the boards prior to placing components for protocol validation. While this approach will solve the issues described above, it probably will require more design effort and may increase the manufacturing cost of larger boards. BGA probe solution A DDR BGA probe adapter can address the probing problems described above. The adapter is a thin ﬁxture that can be attached between a DRAM chip and a circuit board because it has a compatible footprint on its top and bottom sides (Figure 1). The signals at the DRAM ballout are routed to the top side of the BGA probe adapter so they can be accessed by oscilloscope or logic-analyzer probes. This method provides a direct access point to the DRAM ballout for true physical and protocol validation versus the DDR speciﬁcation. DDR2 BGA probe adapter DDR2/3 BGA probe Probe here BGA probe DRAM DDR3 BGA probe adapter DDR3 BGA probe adapter Circuit board Embedded resistors Figure 1. DDR2 and DDR3 BGA probe adapters are compatible with scope and logic-analyzer probes. Embedded resistors ensure highly accurate results by minimizing probe loading on incoming signals. 1. Interposer probes provide an electrically and mechanically nonintrusive connection between a logic analyzer and the DIMM, enabling the capture and observation of data trafﬁc crossing the connector interface. 28 Agilent Measurement Journal

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 5 - 2008

Agilent Measurement Journal Issue 5 Finding a New Path when Assumptions Break Down Contents Testing MIPI D-PHY Protocols Oscilloscope Firmware Update DNA Replication Joining the LTE/SAE Trial Initiative Testing Proteins Praise for DC Power Analyzer Scripting Features for AMDS Testing Hybrid PCBA Systems Improving the Gene Expression System Workflow Turning a “Good Enough” Test Strategy into One That’s Reliable, Repeatable and Traceable Understanding the Effects of Limited-Bandwidth Channels on Digital Data Signals Introducing the 3GPP LTE Downlink Validating the 26 Validating the Physical and Protocol Layers in DDR Memory Interfaces Understanding Total Jitter Measurements of Low Probabilities Using Behavioral-Model Simulation to Accurately Predict First-Order PLL Performance Creating Synchronous High-Frequency Sampling across Multiple Digitizers Overcoming the Challenges of Testing FlexRay Networks Understanding Operating Life and Repeatability of Electromechanical Switches and their Effect on Total Cost of Ownership Implementing Micro and Nano LC/MS Techniques for High Sensitivity Lipidomics Analysis

Agilent Measurement Journal - Issue 5 - 2008

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