Characterizing DDR2 memory devices requires the ability to isolate read and write access cycles. In LAB_WM776 LeCroy’s WaveScan was used to isolate DDR2 Read/Write operations by filtering waveform data using hold time. In read operations the data changes are synchronous with the strobe transition. During write operations the strobe transition precedes the data transition. Using parameter histograms it is possible to investigate the differences. Figure 1 shows a histogram of the hold time parameter for a 500 µs acquisition of the data and strobe lines of a DDR2 memory. The write operations have a hold time of approximately 750 ps. Read operations, which can have both inphase and out of phase timing show hold times below 500 ps and in the range of 1.2 to 2.4 ns. Based on this data it is possible to setup WaveScan to isolate the read and write operations.
Figure 2 shows the WaveScan setup for capturing the read operations where the strobe transition occurs within 600 ps of the data transition. Figure 3 shows the WaveScan setup for capturing read cycles with hold times in the range of 1.2 to 2.4 ns. This range must be set as a limit to exclude holds times that exceed 2.4 ns that can occur at the boundaries between read and write operations. These boundary conditions should be excluded.