Faster data speeds generally require custom test fixtures
The demand for faster data centers and high-speed computing has increased over the past few years due to the emergence of artificial intelligence (AI) and many other data-hungry applications.
Processing capacity must increase, and challenges like power efficiency and signal integrity arise.
Leading technology companies are working to invent faster chips and PHY IP to push electrical and optical data standards forward.
These demands for progress push data signal speeds beyond what all but the highest-performance test equipment can measure. Developing PHY chips and transceivers with data rates over 100 Gb/s requires custom-built test fixtures to maintain acceptable and consistent signal integrity performance.
Fixed test points present debugging challenges
Validation measurements and compliance tests at these speeds must be made at fixed test points on prototype boards. Quality assurance and test engineers know that finding issues in the link, while only able to access specific test points, is a formidable challenge. Their best probes simply cannot handle the next-generation high speed PAM4 signals flowing through the channel without loading the circuit and causing inaccurate readings on their oscilloscopes.
Over time, new data standards codify their test points in the test procedures for compliance testing. Having only specific points in the data link accessible to developers is fine for testing conformance to the standards’ test specifications, but if anything goes wrong, it is more difficult to poke around and assess issues without a proper set of probes, especially for board-level development.
Ideally, a test engineer would have a tool that can measure high-frequency signals outside of the test points, maximizing flexibility and easing debugging. Otherwise, identifying compliance issues becomes a guessing game.
Until recently, probing technology has not caught up to modern data speeds to unlock debugging and quality assurance capabilities.
Introducing a flexible, high-bandwidth probe
InfiniiMax 4, a new RCRC probe amplifier series from Keysight, aims to advance probe technology so that test engineers can measure the fastest data signals anywhere in the link. The InfiniiMax 4 series is the first and only oscilloscope probe on the market to accurately measure signals over 50 GHz of bandwidth. That includes 52 GBd PAM4 signals, which means that even the fastest PCIe 6.0/7.0 and IEEE 802.3ck signals will be within reach (Figure 2).
Figure 2. Oscilloscope capture of an InfiniiMax 4 probe measuring a 53 GBd PAM4 signal
What determines a probe’s bandwidth?
Probing is a delicate science. All probes draw some current from the circuit, called “loading,” but too much probe loading can cause unwanted effects, making the measurements less accurate. Active RC probes have high impedance across a wide frequency range, making them great tools for many low-loading applications or applications that cover a broad spectrum of impedances, like DDR memory testing. However, RCRC probes have higher impedance at both low and high frequencies (Figure 4). For applications with consistently high-frequency measurements, such as those found in high-speed computing like PCIe and Ethernet, RCRC probes are the better choice. You can learn more about the difference between these probes in Demystifying RCRC and RC Probes.
Figure 3. Input impedance profile of two common probe architectures: RC and RCRC
Figure 4. Comparison of the filters across the InfiniiMax 4 series and their bandwidths
As of this writing, InfiniiMax 4 is the industry’s only probe that can analyze digital signals between 30 – 50+ GHz). This is partially due to the InfiniiMax 4 being an RCRC probe, which prioritizes performance at high bandwidths. InfiniiMax 4 comes in three amplifier models, each with exceptional high-frequency RCRC bandwidth: a 42 GHz brick wall filter model, a 52 GHz brick wall filter model, and a 40 GHz Bessel-Thomson model (Figure 3). Although the Bessel-Thomson filter’s bandwidth is only 40 GHz, it has a longer roll-off than the brick wall filters, so the probe can measure signals (with an attenuated frequency response) above 50 GHz. This puts 53 GBd PAM4 signals (106 Gb/s) of the IEEE 802.3ck Ethernet electrical standard well within measurement reach (Figure 4). Measuring a high-speed signal with an appropriate bandwidth probe makes a big difference in measurement accuracy when analyzing signals with low noise thresholds (Figure 5).
Figure 5. 64 GT/s NRZ signal measured with a 30 GHz bandwidth probe (top) vs a 42 GHz bandwidth probe (bottom)
The benefits of flexible, modular probing
Traditional testing methods with custom fixtures often introduce constraints and inefficiencies. Engineers are frequently bogged down by setup complexities, limiting their ability to swiftly identify and resolve issues within the intricate web of signals. The InfiniiMax 4 series is highly modular and flexible, maximizing the probe’s usability without sacrificing signal integrity performance.
Figure 6. InfiniiMax probe amplifier, connector, probe tip, and cradle on board-under-test
The three models of InfiniiMax 4 probe amplifiers are tailored for specific frequency ranges: 40 GHz, 50 GHz, and 40 GHz Bessel-Thomson. All three use AutoProbe 3 for interfacing with the oscilloscope, making the probes backward compatible with InfiniiMax III probe heads. Removable, flexible probe tips fit into connectors on the amplifier, with bendable probe tips with different bandwidth specifications. The connectors fit onto cradles that hold the amplifier and tips in place while you solder them to your test points and make your measurements (Figure 6). The modularity of these probes makes it possible to swap out tips or other components as more become available.
This modular probe system empowers engineers with flexibility and freedom in their testing processes. No longer constrained by rigid setups, engineers can now probe every signal anywhere in the link without the need for custom fixtures. This makes the InfiniiMax 4 probe the premier tool for comfortable probing for every test engineer working at the fastest speeds, like PCIe 6.0/7.0 and IEEE 802.3ck.
Where can I get one?
The InfiniiMax 4 probe family is designed specifically to work with UXR-Series oscilloscopes, the highest bandwidth, lowest ENOB oscilloscope ever designed.
Interested in trying InfiniiMax 4 probes? Visit the InfiniiMax High-Performance Probes page to get a quote and start your high-speed test journey today.
In addition to the InfiniiMax Series RC and RCRC high-bandwidth oscilloscope probes, Keysight has a large collection of passive, active, current, optical, high-voltage, and other probes. Find the right probes for your project.