Welcome to the Digital Scope.FAQ

Digital Storage Scope.FAQ

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Frequently Asked Questions

Dear Technologist(s):

About the Author:

John D. Seney,
LeCroy Sales Engineer,
All opinions are my own, including Digital Storage Scope.FAQ
LeCroy FAQ
WWW: http://www.lecroy.com/

(give a plug when plug is DUE!)

Thanks to the hundreds of respondees to the earlier versions of this FAQ!

Special thanks to David H. Whittum at Stanford University for this FAQ's first HTML/WWW site (http://beam.slac.stanford.edu/www/library/w3/dso.html) (dead link, don't bother - Ed).

This newest Digital Storage Scope.FAQ file contains many (but not all) of your answers to the more "Frequently Asked Questions" regarding Digital Storage Oscilloscopes (DSOs).

The answers and suggestions come from more than a decade of my experiences as a DSO sales engineer in the Boston, Massachusetts area.

This FAQ contains no links to other WWW sites although a few are mentioned.

The opinions are completely mine and represent no company or service - they are meant simply to be helpful, generic, and easy to understand.

Feel free to contact me anytime if you have additional questions or comments.

Digital Scope.FAQ Main Menu (in order of appearance)


THE VAST MAJORITY OF THE DSOS THAT ARE SOLD IN THE UNITED STATES are manufactured by US Corporations making delivery, service, calibrations, and support most convenient. UNITED STATES DSO MANUFACTURERS OFFER A NUMBER OF FREE SERVICES:

The primary US manufacturers of DSOs are:

The combination of Number of Channels, Sample Rate, Front End Bandwidth, and Memory Depth are the primary cost determinants of digital scopes. The current market suggests these sorts of performance/cost tiers.
Sample Rate    BW            Memory Depth           Average Cost
===========    =======       ============           ============    
100 MS/sec     100 MHz        10 K                  $ 3000 
200 MS/sec     100 MHz        20 K                  $ 3500
  1 GS/sec     100 MHz         1 K                  $ 4000
100 MS/sec     200 MHz        50 K                  $ 6000
2.5 GS/sec     300 MHz        .5 K                  $ 7000
100 MS/sec     400 MHz        50 K                  $ 7500
500 MS/sec     500 MHz        50 K                  $10000
  1 GS/sec     500 MHz       100 K                  $10000
  2 GS/sec     500 MHz       200 K                  $14500
  2 GS/sec       1 GHz       200 K                  $17500
  4 GS/sec       1 GHz        50 K                  $35000
  5 GS/sec       1 GHz        15 K                  $30000
  8 GS/sec       2 GHz        32 K                  $60000
 10 GS/sec     1.5 GHz         1 K                  $15000

DSO's go all the way to 50 GHz (the "sampling scope" variety) bandwidth.

MAINFRAME DSO POWER IS NOW IN THE NEWEST PORTABLES. DSOs now can include memory depths > 1M samples per channel and offer processing options such as HISTOGRAMMING or FFTs on up to 6M contiguous samples.

MOST US MAKERS OF ANALOG OSCILLOSCOPES are discontinuing their high BW models. Some manufacturers are offering hybrid analog and digital scopes.

DSOs ARE THE HIGHEST BW OSCILLOSCOPES AVAILABLE and are usually less expensive than their analog model equivalents. Several DSOs go well beyond 1 GHz.

DSO ACQUISITION MEMORY DEPTHS are expanding with 50 K (typical MINIMUMS) up to 8 Million samples (MAXIMUM).

SOME MODELS offer INTERLEAVING the CHANNELS so that, for example, in a 2 channel model, twice the sample rate is achieved when using just 1 channel compared with both channels being used.

SOME MODELS offer INTERLEAVING the MEMORIES so that, for example, in a 2 channel model, twice the memory depth is achieved when using just 1 channel (and twice the recording time) compared with both channels being used.


DSOs ARE THE PRIMARY DEBUGGING TOOLS FOR HIGH SPEED DIGITAL CIRCUITS since they can now sample so rapidly, have large acquisition memories, and can trigger on virtually all types of fault conditions involving multiple channels.

DSO TRIGGER CAPABILITIES ARE STRONGER THAN EVER. Emphasis is in minimizing dead time between triggers and triggering on the most elusive events.

DSOs AREN'T JUST FOR SINGLE TRANSIENT CAPTURE. DSOs can now provide stand-alone measurements and tests that apply waveform analysis right in the instrument.

SOME MANUFACTURERS NOW OFFER APPLICATION SPECIFIC MEASUREMENTS. For instance, developers of disk drives can now have PW-50 and TAA measurements right in their scopes.

MOST DSO USERS ARE NOW PURCHASING 4 CHANNEL models as the cost difference is low and seeing what is happening on more than 2 channels is so beneficial.

DSOs ARE BECOMING EXTREMELY COMPUTATION INTENSIVE. Deeper memories, multiple channels, high resolution displays, and enhanced DSP routines tax the fastest CPUs and smartest firmware. Latest designs use multi-processor architectures.

FUNCTIONS ARE INCREASING SO THE USER INTERFACE IS GAINING INCREASING IMPORTANCE. There is virtually no standardization as to the method of giving a user control of a DSO. As you look, you'll see combinations of knobs, buttons, touch sensitive screens, mice, computer interfaces, and even programmable buttons on the probes. As a general rule of thumb, the more menus, the fewer the knobs.

DSOs WITH FLOPPY DISK DRIVES ARE THE RULE VS. THE EXCEPTION. Almost all new units offer them - either as options or as standard features. Most store front panel set-ups, screen shot graphics you can import into word processing, and waveform data archival.

SOME MANUFACTURERS ARE NOW OFFERING BUILT IN HARD DISKS that are removable and thus, transferable, (via PC Card interfaces) to laptops or PCs.

DSOS ARE BEING OPERATED BY MORE COMPUTERS as redundant tests and measurements are being automated. Most DSOs come with IEEE-488 and RS-232 interfaces and offer remote programmability and data transfer. Most DSOs have free or low cost device drivers for popular software packages. (WWW http://www.natinst.com for more information from National Instruments)

UPGRADE PATHS for firmware and hardware expansions are becoming common, but not all models can be upgraded.


DSOs are now available in 5 different form factors:

  1. PC CARD - A to D on a card that uses a PC's CPU and memory - PCB Style Interesting due to low cost. Look out for noise problems from some PC's backplanes.
  2. STAND ALONE CARD - DSO on a card for embedded systems - PCB Style Interesting due to low cost, small size, fewer noise issues - greater functionality.
  3. HANDHELD - Portable capabilities - Portable Style Battery operated for field measurements.
  4. PORTABLE - with some amount of upgrade capabilities - Portable Style Performance approaching mainframes and low cost due to high competition, high volume, and large scale integrations.
  5. MAINFRAME - typically with plug-ins that determine performance - Lab Style Highest cost but highest performance and greatest versatility.


The 5 Primary Functions of a DSO are to:

  1. CAPTURE.....the signal
  2. VIEW........the signal
  3. MEASURE.....the signal
  4. ANALYZE.....the signal
  5. DOCUMENT....the signal

CAPTURE = consider SAMPLE RATES, MEMORY DEPTH, BANDWIDTH, TRIGGER, NUMBER OF CHANNELS, DISPLAY UPDATE RATE and/or DEADTIME BETWEEN ACQUISITIONS and PROBES. (Here you should have a predetermined knowlege of the highest frequency signal you need to digitize, what its full scale amplitudes are, and whether or not you need to capture single shot or repetitive waveforms. If these issues are unclear to you, review them with your sales engineer.)

VIEW = consider ADC resolution, DISPLAY resolution, Display size, DSP results, and ZOOM EXPANSIONS.


ANALYZE = consider DSP, PASS/FAIL Testing, MASK Comparisons, and EYE Diagrams.



DSOs STILL VARY IN PERFORMANCE IN A VARIETY OF WAYS. Each manufacturer provides a certain degree of standard features, but their different design schemes produce unique performance strengths and weaknesses. Compare and evaluate.

SMART CHOOSERS typically let their S I G N A L S determine the primary specifications (Sample Rate, BW, Memory Depth, Trigger BW, etc.) and let their A P P L I C A T I O N determine secondary specifications (I/O, Measurement, DSP, etc.).

(SPECIFICATIONS TO COMPARE)            Model X         Model Y          Model Z
===========================            =======         =======          =======  
Max Transient Sample Rate                  
Max Repetitive Sample Rate
Analog BW
Timebase Range Max
Timebase Range Minimum
Volts/Div (Range)
Cust. Vertical Rescaling (Y/N)
Vertical Resolution (# of bits)

Number of Channels
Max Samples on each Channel
Max Samples on 1 Channel
Reference Memories       (# kbytes)
High Density DOS Disk    (Y/N)
Hard Disk                (Y/N)
Built-In Printer         (Y/N)
PC Card                  (Y/N)

PATTERN             (Y/N)
GLITCH              (Y/N)
INTERVAL            (Y/N)
DROPOUT             (Y/N)
EXCLUSION           (Y/N)
Video Trigger       (Y/N)
Maximum # of Triggers/second
Trigger Segments w/ Time Stamps         (Y/N)
Trigger Pass/Fail w/ Masks & Parameters (Y/N)
External Trigger Input                  (Y/N)
PEAK DETECT w/ Timing                   (Y/N)
Roll Mode Acquisitions                  (Y/N)
Display Update Rate
Display Size (Diagonal)        (# inches)
Display Pixel Resolution       (# pixels x # pixels)
Display Type                   (Color, Monochrome, etc.)
Multiple Zooms per Trace       (Y/N if Y, #?)
Multiple Grids for full 8 bits (Y/N)
Multiple Cursors per Screen    (Y/N if Y, #?)

CPU                       (Model and Clock Speed)
Math Co-Processer         (Y/N)
Max Record Size on Math   (Y/N)

Pulse Parameters          (#Total/#Viewable)
Statistics on Parameters  (Y/N)
Chained Math Operations   (Y/N if Y, #?)
Histogramming             (Y/N)
Advanced Mathematics      (Y/N)
FFT                       (Y/N)

Standard Warranty        (# of Years)
Free Firmware Upgrades   (Y/N if Y, #?)
Memory Upgrades          (Y/N)
Prices w/ all options    ($)


DUE TO EXPANDING FUNCTIONS AND CAPABILITIES, DSOs lend themselves to a wider variety of application areas. Like a computer, the more applications you can use an instrument, the greater value it has and the easier it is to justify. Here are a few for you to consider:

The most obvious one is to use a DSO as an OSCILLOSCOPE. Typical applications are electronic circuit design and debug and troubleshooting faulty or intermittent circuits.

Another common application is as the front end of a DATA ACQUISITION SYSTEM. DSO's cost per channel has become very competitive. Many people find that the triggering flexibility, deep memory, "live" view of waveforms, and fast transfer rates make the DSO a great candidate. If your experiment is short lived, it is nice to have a DSO when you are done vs. a black box that gets shelved and forgotten. Typical applications are research experiments, process monitoring, and flaw detections.

DSOs lend themselves to being fully integrated into ATE SYSTEMS. In this example, the DSO is under remote control from a host computer and conducts its business by computer command. Typical applications are incoming Quality Assurance of components, Manufacturing/Production Functional Test, Final Test, and System Test.

DSOs can be used (card level or portable rack mounted form factors) and can be embedded into systems that require Analog to Digital conversion and data analysis. Here the DSO is used as a SYSTEM COMPONENT and eliminates the need and time of engineering custom devices.

DSOs DISPLACE/REPLACE MANY DEDICATED INSTRUMENTS - i.e. DMMs, Spectrum Analyzers, Impedance Analyzers, Time Interval Analyzers, Frequency Counters, Pulse Counters, Power Meters, etc.

Some of the common DSO Application fields include:


ADCs - SPEED LOOK OUT for short record length DSOs that can only sample at maximum rates for short periods of time. Ideally, the sample rate value should be displayed on screen all the time. BE CERTAIN YOU CAN SAMPLE FAST ENOUGH IN REAL TIME (SINGLE SHOT) MODE ON ALL CHANNELS SO YOU CAN RECORD WITHOUT ALIASING.

Another point of confusion! SAMPLE RATES specified for REPETITIVE vs. SINGLE SHOT acquisitions. REAL-TIME refers to SINGLE SHOT. RIS refers to Random Interleaved Sampling. RIS is sometimes called ET or EQUIVALENT TIME sample mode and can only be used with repetitive waveforms. Also referred to as "Random Repetitive Sampling".

The sample rate speed of the DSO's analog to digital converter is a very important specification. It is the minimum time between each sample. For instance, a 500 MS/sec. sample rate relates to 2 ns. per point resolution. Multiply the number of sample points * the sample period to determine a DSO's maximum recording time @ maximum sample rate.

Many people confuse the SAMPLE RATE speed with the BANDWIDTH. BANDWIDTH is simply the analog front end performance (preamplifier and sample and hold circuitry).


This refers to full scale resolution. An 8 bit digitizer will divide full scale input voltages by 255 counts. Thus the minimum discernible sampled value on a 1 volt full scale 8 bit DSO would be 1 / 256 or .00390 volts per step.

If you have repetitive waveforms, you can increase your vertical resolution with AVERAGING.

If you have transient waveforms, you can increase your vertical resolution by low-pass filtering each sweep for ENHANCED RESOLUTION.


Not all ADCs are created equally. The most common figure of merit is EFFECTIVE BITS that relate the number of correct bits of a given ADC's actual measurements vs.ideal.



BW is the amount your signal will be attenuated by the DSOs front end amplifier - specified at the -3dB point - as a function of input frequency. Remember that BW ratings are at the input to the amplifier and that your PROBES might also attenuate your signals. If you are looking at signals > 50 MHz, try a FET probe.

Remember that -3dB is down in amplitude by almost 30%. You probably DON'T want a 30% error in your amplitude measurements. Consider the higher BW DSOs so your measurements will be accurate.

CAUTION! Many DSOs have BW ratings that reflect their best performance but only in certain voltage ranges.

CAUTION! Some DSOs reduce sample rates by the number of channels activated. This could cause aliasing by changing the relationship of how fast the DSO is sampling vs. the BW of the signals you are digitizing.

Many DSOs have analog BW specifications far greater than their SINGLE-SHOT sample rate's Nyquist (.5 sample rate) frequency. This is so that when repetitive waveforms are viewed, the maximum BW signals can be seen.


If you can't TRIGGER on the waveforms you need to see, you have a real problem! This should be center stage for your demo if you are looking at a new DSO. There are various trigger capabilities and a combination of them that are easy to use that capture your waveforms is the most desirable.

Know how frequently you need to trigger. The maximum trigger rate is a key specification that isn't often published in manufacturer's specifications as there can be many variables. Evaluate and compare!

Some DSOs have a MEMORY SEGMENTATION feature that lets you trigger very rapidly and fill just a portion (1 segment out of #n segments) per trigger.

Most DSOs will let you trigger on the width of pulses , the INTERVALS between pulses, the LOGICAL or PATTERN conditions between inputs, after specific delays by events or time, drop out conditions, etc. Compare!

Look for TRIGGER ICONS that relate how the current trigger selection is working. This is very helpful if you are looking at a screen dump later and trying to reacquire with the same trigger conditions.

DSOs are valuable tools for looking at video signals but not all DSOs offer a video trigger as a standard feature. Compare!

DSOs can almost always capture single shot events but not always with the amount of pre or post trigger delay you might need. If your application requires capturing a lot of transient waveforms, look into the span of trigger delay as an important spec.



FLOPPY DISKS - They are nice - should be MS-DOS and should come with file formatter so you can convert to ASCII and back then back to binary.

HARD DISKS - They are becoming available and offer the same kind of convenience that is realized in PCs.

MEMORY CARDS - They are expensive but they are fast - up to 200 times faster than a floppy. Requires a reader at PC to use the data.

PRINTERS/PLOTTERS - They are the best way of showing the world your waveforms and your measurements. Plotters are great for elegant color - most impressive for overheads.


WAVEFORM FILES - Binary but with conversions to ASCII for import into other programs and from ASCII back to DSO's binary format.

SET UP FILES - Most DSOs have front panel setups that you can recall and store either in nonvolatile memory in DSO or to disk.

SCREEN SHOTS - "Print to disk" graphics files that are screen dump imports into your word processor.


CAUTION! Manufactures specify their largest numbers. Look out for some DSO's acquisition memory values that divide by the number of active channels.

CAUTION! Don't confuse ACQUISITION memory with REFERENCE memory specifications. Reference memory is used for copies of waveforms recorded earlier and made available for comparison either by viewing or by mathematics. Some DSOs have longer acquisition memories than reference memory. COMPARE!

Not all DSOs have the same number of reference memories. More are better. Make sure they have the width to contain your processed data. You can't store 12 bit averaged waveform data in 8 bit reference memory. Compare.

Not all DSOs have the same number of memories for front panel set-up/storage and recall. Compare.

Some manufacturers offer MEMORY CARDS for additional reference memory.

Some DSOs allow for MEMORY SEGMENTATION where you can acquire multiple trigger events in a single sweep display. A few models will also record the time of each trigger event that occurred.


NOT ALL DSOS ARE CREATED EQUALLY - ESPECIALLY THEIR DISPLAYS! IDEALLY the DSO will compact an entire sweep of acquisition memory onto a single screen with a min/max algorithm. The benefit is that you don't have to page thru screens to see the interesting details in your data. Min/max compaction makes faults obvious.

IDEALLY, THE SCREEN WILL BE LARGE enough so that you can see the WAVEFORMS and MEASUREMENTS clearly at the SAME TIME. Look out for small diagonal measurement displays that put measurements on top of the waveform data.

DSO displays are typically specified in terms of resolution and diagonal size. The higher the resolution, the easier it will be to see fine details and the better your publications that have imported DSO screens will appear. The larger the diagonal size, the greater the chance of being able to see critical information on screen all at the same time vs. pages of menus.

IDEALLY, YOU SHOULD HAVE ALL THE INFORMATION ON SCREEN THAT YOU WANT IN YOUR REPORT. Consider things like trigger parameters, ICONS, measurements, input and timebase settings for each trace, sample rate, cursors and their measurements for each trace, clock/calendar. That is a lot of information on screen. How does it look?

IDEALLY, YOU SHOULD HAVE THE ABILITY TO EXPAND OR ZOOM in on DIFFERENT PARTS of your waveforms to see details more clearly and to limit your measurements to within a given region of data. This means MULTIPLE EXPANSION WINDOWS are best.

Ideally, the graticule should be done in software and allow multiple traces to be displayed, each within their own grid. This preserves the full scale voltage input ranges for best accuracy.

Ideally, the DSO display should have a report of what the front panel status is so that the entire setup of the DSO can be observed, verified, replicated, and printed.


NO MORE FINGERPRINTS ON THE SCREEN FROM COUNTING GRID SQUARES! Modern DSOs display precise measurements of any waveform you capture.

Measurements are either made with CURSORS or automatically with PULSE PARAMETERS such as as RISE TIME, RMS, FREQUENCY, etc. seen right on the display.

Ideally, the PULSE PARAMETERS should include STATISTICS so you can see and measure HOW MUCH YOUR WAVEFORMS ARE CHANGING with every new trigger or acquisition.

Cursors should show:

Ideally, EACH TRACE should have its own set of cursors for SIMULTANEOUS measurements on all displayed traces.

You should be able to make measurements automatically on all displayed traces.



DSP is doing math on the waveforms so additional information can be obtained.

Some instruments really slow down when DSP is being performed. Ask for benchmark specifications on the key functions you need. Don't waste your time looking at DSOs that just aren't fast enough.

Another DSP concern is that some manufacturers don't process an ENTIRE waveform because of poor CPU power. Make sure the data you need processed is really being processed!

Another DSP concern is that you may wish to do a SERIES of functions. How many functions can be chained varies from model to model. Compare!

Consider these potential DSP functions:



BE IN TOUCH WITH YOUR BUSINESS NEEDS as they relate to your DSO needs. Are you going to faster designs soon that might impact the banner specifications you'll need in the near future?

WRITE DOWN EXACTLY WHAT YOU EXPECT THE NEW DSO TO DO. Make it your "Wish List". Try to find out what the most popular DSO is for your application.

GET A SENSE OF HOW SOLID YOUR BUDGET IS and how soon you can place an order once you make a decision. If it is more than 6 months away and your short term needs are critical, consider rental or lease.

PLAN SEVERAL DIFFERENT DEMOS WITH DIFFERENT MANUFACTURERS. Let them know it is a "competitive situation" and you want the best DSO you can get that meets your needs. You'll get a lot of attention and the best of services.

SCHEDULE THE DEMOS IN YOUR LAB INSTEAD OF YOUR CONFERENCE ROOM. You'll be closer to your signals and the real environment where the DSO will have to work.

YOU SHOULD PLAN TO SEE A DEMO OF THE EXACT MODEL DSO YOU ARE THINKING OF USING - with all the options you believe you'll need - conducted by a Sales Engineer that knows the instrument and what you need it to do extremely well.

THE DSO MANUFACTURER's SALES ENGINEER SHOULD BE A GREAT RESOURCE TO YOU. By reviewing your application and assisting you with a model selection that is technically correct, your demo will be much less likely to disappoint you or anyone else.

If you have never met the Sales Engineer, plan to start with a quick tour of your facility. Explain why you need the DSO showing them the area that it will be used in and what you expect it to do. The tour may let your Sales Engineer see things that will help you that you hadn't thought about.


A quick overview of the DSO's banner specifications and key features is a good place to start the demo. Focus quickly on how to drive the front panel and how to extract the various functions. If it looks complex, save front panels you'll need to recall. Ask questions.

You should see your signals on screen EARLY into the demo and plan to borrow the DSO for at least a few days to evaluate it if the demo goes well.

THE DEMO SHOULD PROVE THAT THE DSO MODEL BEING DEMOED CAN DO YOUR SPECIFIC APPLICATION(S). If the demo can't do that, you are probably wasting time by evaluating it further AFTER the demo. If the DSO has to do a specific task, see it happen at the demo and learn how to replicate the settings so you can do it after the Sales Engineer leaves.

PAY ATTENTION TO THE NUMBER OF BUTTONS that have to get pushed to go from one operation to the next. If the demo is really canned, force some hopping around so you see typical vs. streamlined operation.

Find out how long the DSO model you are looking at has been on the market. Ask for MTBF figures . Find out where the closest service center is and how long a typical repair or calibration turnaround might take.

If you are a LARGE company, find out who else in your company is using the same/similar DSO from the Sales Engineer. Chat with the other users.

If you are a SMALL company, find out who else in your industry within your area is using the same/similar DSO from the Sales Engineer. Chat with the other users.

Take as much time as you like. Don't rush it. Ask questions. Record answers. Enjoy the process.

Check the demo DSO that will be left for evaluation to make sure:



CALL THE FACTORY'S APPLICATION'S GROUP AND TEST THEM to see how well they answer your questions. Get application notes sent to you that address your areas of interest.

DON'T BELIEVE THERE IS ONE DSO THAT DOES EVERYTHING. Most labs have a variety of DSOs for various functions.

Try this experiment with the DSO you are considering. Connect a signal source up to the DSO where you can vary the amplitude of the signal by very small amounts. The waveform should have at least 3 or 4 complete cycles on screen and be 90% of full scale. Once you have a stable trigger, store a copy of the waveform into a reference memory. Then activate math so that all new waveforms are being subtracted from the waveform in reference memory. See how little you can change the amplitude level on the generator to see and measure the difference with the DSO. A large part of the utility of a DSO is verifying that things are exactly as they should be and seeing when they aren't.


IF THE DSO DIDN'T MEET YOUR EXPECTATIONS, MAKE SURE YOU KNOW WHY and include the new things you've discovered in your Wish List that you've learned.


Get a list of ALL OPTIONS available for the DSO so that you can order the exact configuration that really addresses your needs. Make sure you and your Sales Engineer determine issues that might include:

You should also explore the manufacturer's policies and costs regarding:

GET A WRITTEN QUOTATION that relates the model, specifications, options, all costs, delivery, and any discounts available. Most manufacturers offer Educational, GSA, Quantity, and/or Demo discounts if you qualify.

You might also consider rental or leasing options. Most rental companies offer equity rentals where rental/lease fees apply towards purchase. AT&T CAPITAL CORPORATION is an excellent source of information concerning this @ 800-874-7123.