[360-degree view of the new generation of oscilloscopes]Series 4: Maximize memory usage and ensure waveform details
Debugging and validating complex systems presents many test technical challenges, including capturing and visualizing multiple infrequent or intermittent events such as serial data packets, laser pulses, and fault signals. To accurately measure and characterize these signals, they must be captured at high sampling rates over long periods of time.
The oscilloscope’s default acquisition mode forces a compromise between sample rate and capture time due to its limited record length. Using a higher sample rate fills the instrument’s memory faster, reducing the time window for data acquisition. Conversely, capturing long-duration data often comes at the expense of horizontal temporal resolution (sampling rate).
segmented storage architecture
FastFrameTM segmented storage allows memory to be split into multiple frames. The record length of each frame is the same as before FastFrame mode was enabled, and the maximum number of frames is the maximum record length of the instrument divided by the record length of one frame. Trigger the acquisition at the specified sample rate and fill each frame, capturing only the portion of the waveform of interest. The frames can be viewed individually in the order in which they were captured, or superimposed to show their similarities and differences, allowing you to easily review the waveform so you can focus on the signal of interest.
Figure 1. Using 5 Series MSO segmented memory to segment the memory to capture multiple pulses at high sample rates.
Figure 1 demonstrates this approach, capturing 100,000 frames. Pulses were captured at a sample rate of 3.125 GS/s using the FastFrame segmented memory in the 5-series MSO (same for 4-series, 6-series MSOs). The FastFrame acquisition mode can trigger at 5 million frames per second (acquisitions/sec), which is much faster than other oscilloscope trigger rates.
Figure 2. Overlaid Display of all acquired frames allows for quick visual comparison.
In Figure 2, the segmented memory frames are superimposed so all the pulses appear stacked on the screen. This allows for a quick visual comparison of all acquired frames. The selected frame is set to 100,000 and the waveform is displayed in blue on top of the overlay frame. The time difference (Delta) between the reference frame and the selected frame is displayed in the results panel on the right side of the display.
The advantages of the FastFrame segmented storage method include:
High FastFrame waveform capture rate increases probability of capturing infrequent events
Use of high sampling rate ensures waveform detail and minimizes dead time of captured pulses, ensuring efficient use of record length
Stored frames can be quickly and visually compared to determine if anomalies appear in the overlay display
Figure 3. 5 Series MSO segmented memory display showing average summary frame information.
FastFrame segmented storage supports standard sample acquisition modes, peak detection, and high-resolution modes. FastFrame can provide an extra “summary” frame at the end of the recording. For sampling and high-resolution acquisition modes, an averaged summary frame can be added to display the averaged waveform for all frames. For peak detect acquisition mode, an envelope summary can be added to display the maximum and minimum values of the waveform across all frames.
Figure 4. Displaying FastFrame timestamps, showing the time interval between frame 1 and frame 2 in the results panel to the right of the display. Showing the top pink time trend histogram, the time difference between all 100,000 pulses is very consistent.
The waveform of each frame reflects only part of the event. There is also important information in the absolute and relative timing of each frame. The timing of each trigger point is characterized by a timestamp. Trigger time interpolation provides very high timing resolution for each trigger timestamp, more precise than the sample interval, and timestamps are displayed at picosecond resolution. While this solution may not work with absolute timestamps for individual events, it becomes very powerful when measuring the time interval between events.
Test use case
Case 1: Describing Intermittent Events – Pulse Waveform Characteristics
Figure 5. Timing characteristics for segmented storage of intermittent pulses.
FastFrame segmented storage can provide digital design engineers with different types of functionality. For example, if your microprocessor system is interrupted occasionally, it can be difficult to collect timing information with an oscilloscope. If you don’t know when or how often events occur, you can’t set up the instrument in normal acquisition mode and make sure the information you need is captured.
FastFrame segmented memory is ideal for testing intermittent waveforms such as microprocessor interrupts. In the example in Figure 5, the narrow digital pulses are spaced in seconds, and with conventional acquisition methods, the temporal resolution of such pulse measurements would be low even with the full record length of the oscilloscope. FastFrame segmented storage captures a specified number of pulses to complete the analysis while eliminating the “dead time” between them. This saves memory while enabling you to capture each pulse in high resolution. The measurement results on the right in Figure 5 show that the pulse width measurement has an average value of 200.5 ns and a standard deviation of about 49 ps. The display at the top of the time trend graph shows that there are pulses 1 second apart.
Case 2: Measuring Sporadic Events
Figure 6. The FastFrame averaged frame summary provides a way to make high-resolution measurements of uncommon signals (in this case, noisy signals).
FastFrame averaging frames provide stable waveforms that can be used to measure unusual, noisy signals. As shown in Figure 6, 1000 noise pulses are captured, summed and averaged. The resulting waveform can be measured, providing very high time resolution pulse width measurements of noisy signals.
Case 3: Decoding a burst serial signal
Figure 7. Segmented memory captures analog/digital serial bus signals and decoded waveforms for each bus, capturing bus activity and ignoring dead time between packets.
Segmented memory allows more efficient use of the oscilloscope’s record length. As shown in Figure 7, the IC serial bus is inactive about half of the time. Using FastFrame effectively doubles the available record length. In this test setup, one bus was captured using an analog channel and the other was captured using a digital channel, and the bus waveforms decoded from both buses can be easily compared.
In addition to displaying the decoded bus waveform for the selected frame on the display, the time stamp data can also be displayed in the results table in tabular form. Further offline analysis and reporting is possible, and the entire acquired decoded bus information can be exported to a .csv file.
Case 4: Comparing Rare Events and “Standard” References
Figure 8. FastFrame can also be used to visually compare specific details between the acquired signal and a standard reference waveform.
The last example in Figure 8 shows a manual comparison between a stored FastFrame “standard” waveform reference and a FastFrame capture. The reference signal is taken from a known-good device and loaded into the reference waveform. Using the reference waveform controls, you can select a specific frame of interest and then capture a similar signal on another device under test using the same acquisition settings. The frame setting controls can be used to time-align the acquired frame to the reference frame for Compare.
Take advantage of the FastFrame segmented storage mode to increase memory usage and preserve waveform detail to meet the challenges of capturing infrequent signals The data.