Tektronix 4 Series vs Keysight InfiniiVision X-Series Oscilloscopes

It can be difficult to decipher which oscilloscope you need for your bench. With so many seemingly similar, high-quality oscilloscopes available, a side-by-side datasheet comparison can leave you in the same place you started – not sure which scope will really prove best for your bench. That’s why understanding specs beyond the datasheet is so valuable. Ultimately, the question you are trying to answer is, “Which scope will ensure I quickly and easily capture all anomalies and signal problems accurately and allow me to fully characterize my device?"

To help you answer this question, this blog will explore the differences between the Tektronix 4 Series and Keysight InfiniiVision oscilloscopes by comparing key specifications and looking beyond the datasheet to understand performance implications that could make a significant impact to your test time and results.

The Tektronix 4 series oscilloscope has bandwidth options from 200 MHz to 1.5 GHz. This overlaps with a few of Keysight’s InfiniiVision oscilloscopes including Keysight’s InfiniiVision 4000 X-Series oscilloscope which provides 200 MHz to 1.5 GHz and Keysight’s 6000 X-Series with bandwidth options from 1 GHz to 6 GHz. These oscilloscopes cover a wide range of applications and are primarily used for quick debug and signal characterization.

Waveform Update Rate and Zone Trigger

The main purpose of your oscilloscope is to quickly find problems in your signals. One of the best ways to do this is with a fast waveform update rate and zone trigger.

Waveform update rate has a direct impact on your ability to capture a random or infrequent event. It tells you the number of acquisitions per second. The time between these acquisitions is called “dead time” or “blind time” because no data is being acquired during this time. Therefore, the longer the time between acquisitions (aka slower waveform update rate), the more events will be missed. The faster a scope’s waveform update rate, the higher the probability of the scope capturing elusive events.

Figure 1 - Illustration of oscilloscope dead time and missed glitches

To learn more about Waveform update rate, read the Can Your Oscilloscope Capture Elusive Events whitepaper.

Keysight InfiniiVision scopes have the fastest waveform update rates in the industry with over 1,000,000 waveforms per second. Additionally, they are the only scopes in the industry that can maintain these fast update rates when you use logic channels or serial bus decoding. This means with InfiniiVision oscilloscopes, you have a higher probability of observing an infrequent glitch or signal anomaly in your system — even if it occurs just once every few million occurrences of the normal signal.

When you combine this fast update rate with zone trigger you have a very powerful debug tool on your bench. Zone trigger allows you to simply draw a box/zone on the touch screen of the scope in the area you see a glitch or think there may be a glitch occurring. The oscilloscope will then trigger on the waveforms that intersect with the zone you drew. It will update the glitch with a rate of 200,000 waveforms per second.

Therefore, using 1,000,000 waveforms per second update rate, you can observe if any anomalies are occurring, and then with zone trigger, you can capture and analyze the anomalies. This is only available on InfiniiVision oscilloscopes.

The Tektronix 4 Series has an update rate half the InfiniiVision scopes – assuming you use a special mode called FastAcq. This means you are twice as likely to miss an error in your design with the Tek 4 than with an InfiniiVision oscilloscope. To make matters worse, if you use their version of Zone Trigger, called Visual Trigger, to capture glitches, update rates drop to only 22 triggers per second, meaning you will only get 1 trigger for about every 10,000 zone triggers captured with an InfiniiVision scope. And this is just one of the many limitations of Tek 4’s FastAcq mode.

Figure 2 - InfiniiVision's Zone Trigger quickly isolates the infrequent glitch. Tek's Visual Trigger fails to capture it.

To learn more about Zone Trigger, read Triggering on Infrequent Anomalies and Complex Signals using Zone Trigger App Note.

Memory Depth

Looking at the key specifications, memory depth appears to be a significant advantage of the Tektronix 4 Series over Keysight InfiniiVision oscilloscopes. The Tektronix 4 Series oscilloscopes have significantly deeper acquisition memory with a standard 31.25 Mpts/channel and with the option to upgrade to 62.5 Mpts. InfiniiVision oscilloscopes provide 4 Mpts of memory. And while this may sound like a significant advantage in favor of the Tek 4 Series, it is misleading for many of your use-cases. To properly operate the Tek 4 Series for your measurements, you need to understand the tradeoffs between sample rate, memory depth, time base settings, and speed of test.

The Catch: The Tektronix 4 Series memory drops significantly in common modes of operation

Serial Bus Protocol Analysis

While the majority of applications don’t require deep memory, one use case in which it might come in handy is for capturing a long time-span of data. For example, when looking at a serial bus. In this case, Tek’s deep memory mode may seem like an advantage. And if your goal is purely around capturing long time spans, it is. However, capturing data without analyzing it is worthless. It can be extremely tedious to wade through huge time captures. A more efficient acquisition mode for serial analysis is Segmented Memory. This mode (available on Keysight InfiniiVision scopes) captures packetized serial data over long time-spans which allows you to quickly view and evaluate the data events you care about. You can set up segmented memory to capture all packets or only selective events that you want to see such as specific bit sequences or packets with errors. This is more efficient than digging through a continuous stream of serial packets captured with deep memory. Tektronix recognizes the benefit of segmented acquisition and offers a mode called FastFrame, attempting to achieve something similar. But like FastAcq, it has many limitations. These include:

Let’s look at an example. We tried symbolically decoding a CAN bus on both the Tektronix 4 Series oscilloscope and the Keysight InfiniiVision oscilloscopes starting with standard/default acquisition modes. Both scopes were set up to trigger on a specific frame ID that was cyclical and occurred every 10 ms. The Keysight InfiniiVision scope triggered and updated waveforms and decoding on every trigger event while observing a 2 ms window of time (200 µs/div), meaning nothing was missed. The Tek 4 Series updated just 2 times per second, which meant that for every event that the Tek scope triggered on, it missed 49 events failing to show many infrequent bus errors that were occurring.

If you were using the Tek 4 Series in this scenario, you might move ahead to production without knowing your end-product has a defect, leading to expensive recalls and redesigns. To double-check the results, you might apply the FastAcq mode on the Tektronix scope to speed up acquisitions and capture more of these missed errors. But this can lead you down another dangerous path. When you switch to Tek’s FastAcq mode, the scope’s memory depth will automatically drop to just 1 kpts of acquisition, which also forces the scope’s sample rate to drop to just 500 kSa/s to capture this 2 ms time-span of data. This could lead to under sampling.

During our CAN bus test, we tried using FastAcq mode to improve the CAN decode results. In this case, the Tektronix scope reported several false CAN errors. They were not actual errors in the CAN bus, but a decode error as a result of under sampling, and therefore, falsely displayed waveforms. If you didn’t know that this was a fault caused by the Tek 4 oscilloscope, you could waste hours tracking down a bug in your design that doesn’t exist.

Also, Keysight InfiniiVision scopes use hardware-based serial decoding while the Tektronix 4 Series use software-based decoding. Hardware-based decode is faster, while software-based decode takes additional time to process resulting in additional lag and missed events. Remember our previous discussion on dead-time? The longer it takes for the software to process the event, the more dead-time you will have, meaning more missed events.

It is much easier to analyze the results of the InfiniiVision decode because the InfiniiVision scopes automatically build a table of decoded results from all captured serial packets. Plus, you can use the scope’s Search and Navigation capabilities to quickly find specific criteria such as errors. If FastAcq is being used, the Tektronix scope does not produce a table and only displays the result of one frame at a time, requiring you to step through and read each segment’s decode results one at a time.

Figure 3 - Tektronix 4 Series oscilloscopes do not produce a table of decode results when FastAcq is turned on

If you revisit the ultimate question, “Which scope will ensure I quickly and easily capture all anomalies and signal problems accurately and allow me to fully characterize my device?” the answer, in this case, clearly points to the InfiniiVision scopes. The accuracy of InfiniiVision’s hardware-based serial decode plus the simplicity and efficiency of Segmented Acquisition with table and search capabilities should leave you confident in your device’s characterization.

Additional Debug Tools

There are more tools beyond zone trigger, serial decode, and segmented acquisition that can make analysis easier.

Figure 4 - Frequency response analysis of magnitude and phase on a Keysight InfiniiVision oscilloscope

Figure 5 - Mask limit testing performed on a Keysight InfiniiVision oscilloscope

Figure 6 - Spectrum analysis performed on a Keysight InfiniiVision oscilloscope

Figure 7 - Power analysis performed on a Keysight InfiniiVision oscilloscope

Budget

Finally, we all have bosses and budgets to please. If you find that it comes down to price as a major factor, keep in mind how quickly price can add up.

Keysight offers seven software packages that include a suite of measurement capabilities. For example, the embedded software package includes I2C, SPI, RS232/485/UART, I2S, USB-PD, mask test, Bode plots, and enhanced video test for $1955 on the 4000 X-Series scope. To get just 4 of these licenses, I2C, SPI, RS232/485/UART, and I2S, on the Tek 4 Series, you’d have to purchase four different options at $1910 each (that’s $7640 in total).

What about just the price of the unit, before adding software options? The InfiniiVision 6000 X-Series provides the highest bandwidths and sample rates at the lowest cost/GHz in the industry. You can purchase a 4-channel, 2.5 GHz bandwidth oscilloscope that samples up to 20 GSa/s from Keysight for $23,219 while the price of a 1.5 GHz bandwidth Tek 4 Series oscilloscope is $24,000. If these price points are out of your range, check the InfiniiVision 4000 X-Series which run, on average, about 27% less than the Tek 4 Series for equivalent bandwidth and channels. Plus, Keysight will have a promotion running from August 1, 2019, to March 31, 2020, which will further reduce the price.

Conclusion

All things considered, the InfiniiVision Series oscilloscopes provide the tools you need to efficiently and effectively debug your devices at the right price.

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Competitive comparisons were conducted with a Tektronix MSO46 with HW option vw4-1500 and a Keysight MSOX4154. Datasheet information was pulled from Tektronix 4 Series MSO datasheet, 48W-61558-1, published June 11, 2019.

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