Oscilloscope Basics: A Beginner's Guide
As electronics engineers, we’re incredibly lucky compared to other engineering disciplines. Not only are electronics rapidly evolving and expanding in use and functionality, but our test equipment gives us the greatest capabilities to diagnose and investigate the devices we have built. While all disciplines of engineering have fantastic suites of simulation tools, being able to see how something is performing in the real world can provide a lot more insight.
We have many tools that can allow us to see what our circuits are doing, but as a beginner, you might not be sure where to start. The two most essential tools you will own for diagnosing any circuit is a digital multimeter and an oscilloscope. You might be asking, "What oscilloscope or other test equipment should I get?" which is a common question from students and makers. In this article, I'll go over some oscilloscope basics that every engineer should know, plus some tips and tricks for working with different oscilloscopes.
Digital Multimeter vs. Oscilloscope
A huge variety of electronic measurement tools and devices are available, the most popular of which is probably the multimeter. Multimeters can measure current, voltage, resistance and often other parameters, depending on the model. Some include a built-in temperature setting for RTD probes or an infrared sensors for temperature measurements. A multimeter is used to determine whether your power supply is working adequately, can help to find damaged parts, measure whether the voltage drop or resistance of the parts is correct, find the location of a short or open circuit, and so on.
A multimeter is helpful when it comes to electronics but quickly finds limitations as it’s frequency response is limited. The multimeter is perfect for seeing what an average voltage is, perhaps even counting the frequency of a circuit up to several hundred kilohertz. However, it does not provide any visualisation. When you need to look at a voltage over time in fine detail or visualise any aspect of a waveform, another measurement device is required – the oscilloscope.
Oscilloscopes help the engineer to measure various parameters, such as voltage, analog and digital signals, and noise. Modern oscilloscopes also have a huge number of additional functions which are useful for an electronic engineer.
Almost every oscilloscope you encounter for sale today will be a Digital Storage Oscilloscope (DSO) or a Mixed Signal Oscilloscope (MSO). A mixed signal oscilloscope is a digital storage oscilloscope with additional functionality that integrates logic analyser capabilities. Some models will also perform an FFT, giving measurements in the frequency domain.
Either style of an oscilloscope is a fantastic diagnostic tool when troubleshooting a circuit. You can see the exact waveform of your circuit with millivolt resolution, and with some oscilloscopes, picosecond resolution. This makes it possible to catch short transient spikes from sensors, encoders or circuits that a multimeter can’t catch reliably. It also allows you to view digital signals, inspect the quality of edge transitions and view ringing or other signal integrity issues.
Oscilloscopes have multiple channels. Therefore you can monitor the waveform going into a circuit, as well as the waveform coming out which makes it perfect for monitoring analog filters, amplifiers and other analog circuits. Suppose you’re primarily working with digital signals. In that case, oscilloscopes are fantastic tools for you too - you can one channel watching one signal, for example, a button, and then see a microcontroller’s response to that input - such as a transmission over SPI or I2C. With the precise timings of an oscilloscope, you can measure how long your code is taking to execute or react to an interrupt. Mixed Signal Oscilloscopes take this a step further, integrating a logic analyser that can give you many digital channels of input to monitor alongside the analog channels.
How to Measure EMI with an Oscilloscope
You can also use an oscilloscope as a crude near field electromagnetic interference detector, even if the scope does not have an FFT function. For example, in the image below, I’m trying to isolate the radiated noise source of a low-quality commercial LED driver. I’ve just connected the probe’s ground lead to the tip which gives me a big near field loop probe. The signal on the oscilloscope’s screen is purely radiated noise; the LED driver could still be in it’s housing.
We can see the LED driver switching and would be able to track down a potential noise source and look at the change in signal when adding filtering or damping components to the problem nets. While it’s no substitute for a spectrum analyser, an oscilloscope can still help you track down potential EMI issues that would cause you to fail a certification. If you need a more precise measurement, you can buy purpose-built near field probes for analysing your circuit board too.
While oscilloscopes are fantastic diagnostic tools, they can also be utilised when planning a project too. When you are simulating a schematic with a simulation tool such as SPICE, for example, your component model may not be a perfect representation of the real-world component. By using an oscilloscope on a breadboard version of your schematic, you can interact with it in real-time and see the exact response of that component allowing you to determine if your simulation will be accurate or not. This process can also significantly improve component choices by trying samples of different parts in a test circuit rather than relying on a generic SPICE model for that component type.
In addition to component selection, you will often also find an oscilloscope used during the quality assurance testing of a production board. For analog circuits, such as amplifiers or power supplies, many oscilloscope models will allow you to configure a pass/fail mode that can tell you immediately if a circuit meets the criteria to continue on the production process.
An oscilloscope is a critical tool for any electronic engineer, hardware design, or firmware developer. They are also invaluable tools for makers, students and electronics hobbyists. There is a huge range of oscilloscope’s available on the market - so how do you choose one to meet your needs?
There is a vast range of oscilloscopes on the market, with a wide range of prices. A very cheap oscilloscope might cost you $100, but the sky’s the limit with some oscilloscopes costing over half a million dollars! Even some probes for high-end oscilloscopes cost more than a new family car.
Before we look at the specifications or models of oscilloscopes, let’s first briefly look at how an oscilloscope works.
A modern digital oscilloscope takes an analog input from the probe and converts it to a digital signal for display. It also works with an incredibly wide range of voltages; even a low-end oscilloscope can have a 1000 V(peak)/300 V(rms) maximum voltage and still be able to measure signals that are only a few millivolts in amplitude as well. The front end of the oscilloscope takes care of scaling this wide range of input voltages to something the oscilloscope can deal with. This conditioned signal is then used to trigger the oscilloscope as well as going into the sampling and ADC chain, which ultimately ends up as readings in memory. Those readings in memory, you can think of as a timestamped list of individual samples, which, when put together, will show your waveform on the screen.
The bandwidth is one of the most prominent methods of comparing different oscilloscopes. It represents the maximum signal frequency which can be measured without significant attention. The attenuation emanates from the inductive and capacitive reactance, which change as the frequency increases. This ultimately limits the bandwidth of the oscilloscope hardware. However, the probe itself also has bandwidth limitations. When you buy an oscilloscope, the included probes will typically have the same or greater bandwidth than the scope itself, however. The bandwidth advertised is the point at which the signal is attenuated by -3 dB or about 70.7% of the measured signal.
When buying an oscilloscope, it should have a higher bandwidth than the maximum frequency signal you want to measure. For many engineers, this is likely to be a clock/oscillator or a communications protocol.
Oscilloscope Sample Rate
The sample rate is how many points of data the oscilloscope can convert and store in memory per second. The more samples you can acquire, the more detailed the signal will be on display. The sample rate needs to be a minimum of two times the frequency of your signal, ideally at least four times greater than the signal frequency. Many quality oscilloscopes will provide 10 to 20 times their bandwidth as a maximum sample rate, which allows you to catch small transient spikes or dips in your signal.
With a low sample rate, you can completely miss small transients or jitters in the signal, as the chance of that transient landing between samples increases.
The memory depth of an oscilloscope is an easily overlooked specification which can be critical, especially with high sampling rates. The memory depth determines how many samples can be stored, and therefore how long your oscilloscope can capture data for. This influences how much you can scroll with a signal after the trigger, or how much you can zoom in to a specific area of a captured signal. In general, more memory depth is better; having more data is usually a good thing. Some lower-end scopes can struggle to process all the data in their memory if they have a substantial amount without the processing power to back it up. This can result in slow math or other operations, but in a general oscilloscope, manufacturers tend to keep a reasonable amount of memory relative to the processing capabilities.
More memory depth will also make it more likely that infrequent/glitchy signals are captured, making it easier to track down “weird behaviour” in your device under test.
We could discuss oscilloscope specifications for many pages, but those specifications are unlikely to be so critical as the options above for a first or second-time oscilloscope purchase. Unless you’re looking to push the limits of any oscilloscope you buy, most options on the market are going to be “good enough” for the average user.
What to Avoid?
Before we dive into looking at some options for popular oscilloscopes, I want first to offer a couple of warnings about very low-cost devices. I don’t usually like to say something is not worth buying, but if you look at the online marketplace, there are undoubtedly low-cost devices that call themselves oscilloscopes which are not worth wasting your time or money.
Generally speaking, these suggestions of items to avoid come down to bandwidth and sample rate. Suppose you’re looking for an oscilloscope to work with electronics. In that case, I’d suggest an absolute minimum bandwidth of 25MHz, with 50MHz as a minimum recommended bandwidth, and a sample rate commensurate with the bandwidth.
While there are portable oscilloscopes that are incredibly capable, the low-cost multimeter looking ones are not. These are designed for looking at an AC signal from something like a generator or your wall socket and are going to be of very little use for electronics design or testing purposes.
If you’re an electrician fixing a generator, I’m sure they’d be perfect, working with a microcontroller however the 20KHz bandwidth/200KSa/s is pretty pointless.
The Colour TFT Portable Mini Oscilloscopes
While these little units are cheap and look pretty neat, the reality is that they are just running on a low-cost ARM microcontroller if you’re lucky. With a typical bandwidth of just 1MHz and 10MSa/s, even low-speed SPI communication is well beyond the capabilities of this device. More expensive versions might go up to 15MHz or more bandwidth, with sample rates up to 100MSa/s, but again it’s just not enough to be of use in modern circuits.
The low-resolution screen and overall limited capabilities mean you do not get a lot of value for money, it's unlikely to be of much use for designing or testing electronics you might build.
While a kit is always fun to build, these are essentially a bare unhoused version of the option above and are just as limited.
While these are much cheaper than the above option, their usefulness is equally low.
9 Popular First Oscilloscopes
In comparison to the above devices, these oscilloscopes are very popular, and some are not much more expensive than those above. Generally, I prefer a 4-channel oscilloscope myself. I often find myself wanting to use 3-channels when experimenting with a circuit, or diagnosing a fault. Spending a little more on a 4-channel oscilloscope will give you room to grow if you can afford it. Oscilloscopes tend to retain their value exceptionally well, however, so if your budget is tight and you don’t see an immediate need for 3-4 channels, then a 2-channel option can offer some savings.
Many oscilloscopes offer a relatively cheap base model option with limited software features. You can upgrade these software features in the future by purchasing a license key which can be entered into the scope giving you an upgrade path without needing to buy a whole new piece of equipment. You might even find these upgrades bundled at a discounted price or for free during sale events.
The oscilloscopes in this list are offered in no particular order, and all are excellent choices for their target audience.
Despite being one of the cheapest entry-level oscilloscopes, the Rigol DS1052E is quite capable. It’s a 2-channel oscilloscope that is reasonably simple to use. The DS1052E is very popular with the maker/student/hobbyist communities because it offers excellent value for money. It’s also relatively compact, which is perfect for fitting on a small desk for hobbyists or students.
As this is a very entry-level scope, you can often find them used in good condition as people upgrade to more powerful oscilloscopes as their skill and experience grows. As mentioned earlier, oscilloscopes retain their value well, so don’t expect too much of a discount for a used model - however you may get one with unlocked options that give you more capabilities than a base level new scope.
While this is a very capable oscilloscope for the price, it is only 2-channels, and the screen is relatively small and low resolution.
I wouldn’t be surprised if the Rigol DS1054Z is one of the best selling oscilloscopes of all time. For the price, being only a bit more expensive than the DS1052E above, you get a tremendous amount of functionality very cheaply. I own a DS1054Z, it’s not my primary oscilloscope, but it’s compact and lightweight form factor makes it very convenient for working on high tech machinery when getting a bigger scope might be a bit of a hassle.
In addition to the extra 2-channels compared to the DS1052E, you also gain a much more substantial screen with high resolution, making it much easier to see what is happening. You also get more buttons around the screen, making it easier to access functions and generally just improving the user experience.
As the final Rigol oscilloscope, we’ll look at the MSO5074. The MSO5074 is a mixed domain oscilloscope meaning it can also act as a protocol analyser with the additional digital inputs. With software options, it can act as an arbitrary function generator and spectrum analyser as well, making it incredibly diverse. The MSO5000 series oscilloscope is my current daily driver, as the value for money when I was rebuilding my home lab after moving countries was unbeatable.
In addition to a relatively huge screen, the touchscreen is surprisingly user friendly. When purchasing the scope, I thought the touchscreen was a bit of a gimmick. However, when I use my DS1054Z, I find myself touching the screen with no effect far too often - so it’s proven to be far more useful than I originally anticipated.
Another feature I’ve found surprisingly useful is that the scope has an HDMI output, which allows me to record the screen with an HDMI recorder, or put the output onto a large screen. With the amount of working from home, everyone is doing these days, and this is a pretty interesting option as it allows you to record an issue with the device under test, and send a video to another engineer. You could also use an HDMI capture card to stream your scope’s display directly into a conference call.
This is also an incredibly popular oscilloscope, and the price point is pretty fantastic for its capabilities. It’s so popular that the community has even made it so you can play classic Doom on the scope when you need a break from work at your electronics bench.
Tektronix is a very well regarded manufacturer of test equipment who has been in the industry for decades. The TBS1052B-EDU, being a 1000 series oscilloscope can be compared directly with the Rigol DS1052E and DS1054Z above. Features wise, the Rigol DS1054Z is more comparable. However, the TBS1202B-EDU is only dual channel. The oscilloscope is well suited as an entry-level oscilloscope. The DS1054Z is targeted towards students and educational institutions.
Tek also has several other models that are significantly lower priced in the same series, such as the TBS1052C which is a 50MHz oscilloscope the same as the Rigol options, at a similar price.
I like that the TBS1202B-EDU model has 200MHz bandwidth and comes with 2GSa/s sample rate, twice the other options in the TBS1000 series lineup. Unfortunately, the memory depth is somewhat limited at just 2500 points while alternatives in the same series have 20,000 points of record length.
Taking a step up to a 2000 series oscilloscope, the Tektronix TDS2024C has 4 channels. As with the TBS1202B we looked at above, it also has 200MHz of bandwidth, 2GSa/s sample rate and just 2500 points of record length. While it’s input specifications are pretty much the same, it is a more powerful scope with additional software functionality, more channels and dedicated hardware buttons for all the most commonly used features.
Unfortunately, the screen size is smaller than the 1000 series oscilloscopes above.
One of the main advantages to the 2000 series, in my opinion, is that it comes with limit testing capabilities making it great for quickly testing and approving devices before shipping.
Keysight, previously known as Agilent, has been a leader in test equipment for many decades. The DSOX1000 series is their entry-level oscilloscopes but by no means are they a basic scope. Their 1000 series scopes come in 70MHz, 100MHz and 200MHz variants. With 4 channels and a 2GSa/s sample rate plus 2 million points of memory depth, it’s a powerful and practical scope.
Keysight’s experience in test equipment shows in their user interface design for the display. The display is large and bright, with a fantastic layout that is very easy to use.
Keysight MSOX2004A Oscilloscope
Keysight’s 2000 series oscilloscopes come with variants that also feature an 8-channel logic/protocol analyser option. I’ve owned an MSOX2004A in the past, and they are very well designed scopes, with a simple yet powerful user interface. The MSOX2004A is the entry-level version of the mid-range 2000 series oscilloscopes, with a 70MHz bandwidth, 2 GSa/s sample rate and 1 million point memory depth as well as the 8-channel logic analyser.
In addition to the logic analyser/protocol analyser functionality, the scope also has options for an arbitrary function generator, and integrated digital voltmeter makes it a versatile oscilloscope.
Rohde and Schwarz RTB2004
Rohde and Schwarz are typically known for very high-end test equipment, especially in the RF engineering world. It should come as no surprise that their 2000 series oscilloscope, an entry-level model for them, is full of features and very high specification. The RTB2004 has a lot of optional features which can be purchased later, keeping the base price low.
The most innovative feature of this oscilloscope is that it has a 10 bit analog to digital converter. Typically oscilloscopes only have an 8 bit ADC. The extra resolution provides sufficient detail on waveforms and potentially allows more precise measurements.
The RTB2004 has four analog channels, 70MHz bandwidth (software upgradable), 2.5 GSa/s sample rate and 20 million sample memory depth. In addition to the typical oscilloscope features, the RTB2004 also can act as an arbitrary function generator, protocol analyser with 16 digital channels, and work as a spectrum analyser.
The PicoScope 2000 series are a bit different from everything else we’ve looked at being that they are PC based rather than fully integrated. You need a laptop or computer to be able to use one of these oscilloscopes, with the processing being offloaded to the more powerful computer using a USB connection.
Pico Tech are well known for their automotive instruments, and making low-cost PC connected oscilloscopes. While the lower bandwidth models are cheap, I wouldn’t recommend anything below the 50MHz model (2206B) as it would quickly find its limitations in embedded systems development.
The PicoScope 2206B has a 500 MSa/s sample rate giving it the lowest sample rate of any of the scopes we have looked at. The waveform rate is also similarly low compared to other options.
A previous employer had a PicoScope. However, I had to bring in my own oscilloscope for many tasks as the input voltage was only 20v peak maximum, with a 100V maximum limit. I was working on a 300V system, so if you’re working on anything higher than 20v, the PicoScope probably isn’t for you.
If space is limited, and you’re looking for a low-cost option, the PicoScope is an exciting option.
How to Select an Oscilloscope
When looking at buying your first oscilloscope, it’s good to consider what you want to use it for or what circuits you might have on something you design. Switched-mode power supply could be up to 2 MHz in frequency with some very short transient spikes as it switches. A microcontroller can quickly generate 50 MHz+ signals with it’s IO pins or communications like SPI. An encoder wheel can generate very short pulses which need a reasonable sample rate.
Microsecond long events are trivial for oscilloscopes, but consider if you need faster. What is the shortest event/transient/pulse that you need to be able to see with your oscilloscope? Calculate the bandwidth and/or sample rate requirements to witness these signals reliably.
Oscilloscopes with built-in logic/protocol analysers are incredibly powerful for firmware developers. The decoded digital channels can be used for triggers, allowing you to start recording the analog waveforms when a specific byte or byte sequence is detected on the communications channel.
There are a lot of great options for oscilloscopes on the market, even for those on a budget. Even budget oscilloscopes today are so powerful and capable compared to alternatives on the market 10 or 15 years ago that we are really spoilt for choice.
If you don’t get caught up in having a big name brand who have been building test equipment since the dawn of time, Rigol and Siglent offer some incredible value for money. About ten years ago, Rigol was building Agilent (now Keysight) low-end scopes for them as an OEM partner and have been around since the late 90s. In the last decade, Rigol has continued to innovate at a rapid pace.
I’ve owned Keysight and Rigol gear primarily over the past decade and have a lot of respect for both brands. Rigol is often seen more like a budget/hobbyist brand, but when you compare specifications especially on the higher end units, it’s a clear winner for me when you add the retail price into the mix. If you’re not planning to push your oscilloscope to the ragged limits most of the fine detail specifications can be practically considered equivalent between most of the major players in the market. My new home electronics lab is 80% Rigol, 20% Siglent after putting all the options head to head at suppliers showrooms - I try pretty hard not to let the logo on the equipment sway a decision.
I didn’t add Siglent to this list, as another low-cost Chinese vendor as the maker and hobbyist community ultimately tends to prefer Rigol. Certain pieces of equipment from Siglent are superior for a similar price to Rigol, but I feel Rigol still holds the edge on Oscilloscopes. Hantek (and all the other brands the equipment is sold under) and Owon didn’t make the cut either, as I feel they are not yet in the same league as Rigol and Siglent as far as quality or value - being marginally cheaper you might as well spend a little more money for the technically superior options with more community support.
Ultimately, your decision should depend on what you are going to use the equipment for, what your budget is, and what your future requirements might be. Out of this list, I feel Keysight has the easiest to use oscilloscopes, Rigol offers the best value for money, and R&S provides the most interesting option. All the oscilloscope basics shown here apply generally to the models presented above.
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