Welcome to "Oscilloscope FAQ"

Welcome to "Oscilloscope FAQ". Our goal is towards assisting everyone in leveraging more capabilities and useful troubleshooting functions from their Digital Storage Oscilloscopes (DSOs) - regardless of brand or model.

What different types of digital scopes are there?

There are three different types of DSOs:

• Real-Time Scopes (Single shot transient captures up to rated BW)
  
• Mixed Signal Scopes (MSOs) (Single shot transient captures up to rated BW)
  
• Sampling Scopes (ET Equivalent Time - repetitive waveforms only - very high rated BW)
  

What do real-time scopes do?

Real-time scopes digitize, capture, and display definitive, measured, evidence of live signal conditions. DSO trace displays can include:

• Multiple analog and digital channels with continuous live updates
  
• Static, single shot triggered, traces with variable pre-trigger data
  
• Zooms of specific portions of the main captured traces for higher resolution viewing
  
• Averaged traces to reduce random noise
  
• DSP enhanced traces such as FFTs, Histograms, Filters, Jitter Tracks
  
• Persistence envelopes or EYE plots with variable sized masks for margin testing

Scope traces can be measured with cursors or automatic measurements with statistics and DSP provide additional insights and analysis possibilities. Results are documented with easily saved and exported files for reports, presentations, or web.



DSOs are used in scientific, academic, military, and commercial engineering, research, and development projects. DSOs perform tests, automatic measurements, component/system performance verifications, enable debug with causal determining analysis, perform serial data compliance testing, and generate screen image files with traces and measurements used in technical reports. After projects are released, DSOs can be used for failure analysis, continuing engineering, maintenance, and repair. They may optionally sit on a network for full remote automated control and be viewed from anywhere.

Inputs can come from analog or digital electronics or optics using probes, sensors, cables, or antennas. Since real-time DSOs capture signals "live" and single shot, they are the best way to detect and analyze transient signal anomalies, jitter, noise, or any errant signal conditions. Their automated functions and DSP enable hundreds of different tests and troubleshooting methods and routinely calculate literally billions of measurements per hour.

How do you get just the signal data you need?

Often with conditional smart triggering and automated control, real-time scopes can capture just the data of interest and save only specific screen image (screen shots) and data files. Each screen shot file is date and time stamped and often includes measurements with statistics and scope settings at each trigger time. Screen shots document issues during electronic projects, help resolve component vendor disputes, show new specification proofs for marketing and sales, and illustrate solution proofs for customers. DSO screen shot files are small enough to include as email attachments and import easily into word processing, presentation, or page layout software. Waveform data files can often exceed 100 Mbytes per trace and may require large storage consideration and planning. They can be loaded back into the scope for comparisons or new measurements.

What are MSOs?

MSOs are "Mixed Signal Oscilloscopes" that mix a "real-time scope" with 4 analog channels + "logic analyzer" with up to 36 channels into one MSO scope system. MSOs are used for embedded system development and troubleshooting. Digital inputs can come from traditional parallel bus data, control, and address lines and from serial digital lines carrying I2C, SPI, or RS-232. Serial data can be part of the trigger description and get decoded right on the scope's display. The screen shot below is an example of a MSO.

Where do sampling scopes fit?

Sampling scopes require repetitive waveforms to function and thus will not capture single shots, transients, glitches, or randomly occurring events. They are best applied in higher BW applications (30 GHz or greater) such as TDR, S-parameters, signal integrity (SI), and serial data analysis for > 10 Gbit data rates.

What is an example of a real-time digital scope's capabilities?

A real-time scope example is the scope screen image above taken with a new LeCroy WavePro 760Zi. A 500 MHz clock signal was captured single shot at 20 GS/s with 20 M samples recorded. Even though the scope only triggered once, measurements with statistics reveal the scope made 2,995,347 total measurement calculations. More than 499,000 measurements were taken on each recurring parameter. That is a lot of processing over and above displaying the waveform. This new series uses a 64 bit OS and a Quad Core (2.5 GHz per stack) Duo processor interfaced to a pipelined streaming data architecture.

What happens if more than one trigger is taken?

Each new trigger adds to the measurement statistics providing greater certainty of the signal's true behaviors. Minimum and maximum values recorded over all total measurements reveal how close to actual target or goal specifications the signal is.

Note the 2.99 ps standard deviation of period jitter and the miniature histograms below each measurement. Histograms reveal the shapes of each measurement's statistical distribution and are giant clues as to what a signal is really doing. The quest is to find the root causes responsible for each measured variation (effects). Traditional cursors are applied in the rose colored zoomed trace to measure a local pulse amplitude. Individual sample points are displayed in bold eliminating concerns about having enough samples on each rising and falling edge.

How do you get scope screen images exported for reports?

Documenting what is seen and measured used to be time consuming and tedious. Now, for just screen shot images, its a single click or pushbutton to output variety of file formats (JPEG, Bitmap, etc.) with modern DSOs. You can then use a USB thumb drive or network connection to transfer the scope screen image file from the scope's hard drive.

How about saving waveform data and scope panel set-ups?

Its possible to save individual files. But if you want to save a lot of them, it can become tedious. There is a new alternative to save everything in a scope's LabNoteBook. Then waveform data, setup file, measurements, and lab notes are saved in a time stamped library in the scope. LabNoteBook entries can then be recalled to compare with live signals and allow additional tests or measurements on archived data.

How high do DSO's performance go today?

Digital scopes remain the best investigative tools for high BW electrical or optical signals. As signals have evolved from simple to complex, more analysis of information is often required to find fault causing conditions quickly. Leveraging developer's insights, scope displays can present mega-measurements that produce graphical predictions. An example is Iso-BER, the region inside of the serial data EYE that is predicting EYE openings as if billions of additional bits had been acquired.

The current industry leading banner specifications are:

• 100 GHz BW (sampling) with 10 MS/s sample rate
  
• 30 GHz BW (real-time) with 80 GS/s sample rate
  
• 500 MHz BW (MSO) with 2 GS/s sample rate
  

Fortunately scope designs have also evolved with new performance specifications driven way up. Once a signal is digitized modern DSO capabilities and functions transcend what most could have imagined "just a scope" could ever accomplish.

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