As electronic products achieve even higher performance, their increasing complexity makes it harder to design, verify and debug. During the extensive verification that is performed to pick up problems, the ability to simultaneously observe and analyse both the analogue as well as digital signal representations is bliss. This article analyses the recent advancements in mixed-signal oscilloscopes and tells you what you are missing
While today’s embedded design engineers are faced with the challenge of ever-increasing system complexity, there are engineers out there who have already started analysing and providing solutions to make sure that the engineers are not inhibited by this complexity.
“Debugging the hardware is a difficult and somewhat daunting task to the engineer who is armed with his favourite four-channel oscilloscope. Many engineers are comfortable with their oscilloscope, and in order to save time, may choose to buy three or four oscilloscopes so that they can probe multiple signals at once. Logic analysers provide the ability to probe multiple digital signals, but the complexity of the debug task may not merit the setup and learning curve required to use the logic analyser,” says Saivenkat Kumar, country marcomm (EMEA marketing), Tektronix.
Logic analysers and oscilloscopes have co-existed for decades, finally giving birth to mixed-signal oscilloscopes (MSOs). Once a niche product category pioneered by HP (now Agilent Technologies), MSOs are now offered by all major scope vendors.
“In old days test engineers were using two sets of instruments—basically an oscilloscope to check the analogue characteristics such as frequency, rise time and fall time of a signal, and logic analysers for digital characterisation. But now with more of mixed-signal designs and also for FPGAs and microcontrollers, MSO is the preferred choice. With two or four analogue channels and up to 16 digital channels, a user can do both analogue and digital characterisation from the same instrument. This saves the cost as well as the time to set up multiple instruments, and also makes it easy to use,” explains Sadaf Arif Siddiqui, marketing programme manager, Agilent Technologies.
High-resolution and larger displays
Mixed-signal oscilloscopes being visual tools, a larger and higher-resolution screen makes them better—unless there is a portability requirement. Utilising the latest display technologies available, vendors have packed better displays into their instruments. Thus with the ability to view more, engineers can spot jitters and infrequent events quicker than in a lower-resolution display.
“Designers are often interested to capture smallest pulse widths of their embedded designs. The smallest pulse widths that can be detected depend on the sampling rate and the detection architecture. Mixed-signal oscilloscopes can capture pulse width of minimum 200 ps due to a high resolution of 200 ps,” explains Srinivasa Appalla, area manager-product support & applications, test & measurement, at Rohde & Schwarz.
This is one of the most common trends seen amongst the latest instruments—Tektronix and Agilent MSOs also feature XGA resolution.
Targeting the education sector
The requirement of the education sector is different from the rest of the industry’s. The education sector requires equipment that are inexpensive and reliable, and cater to the changing requirements of students as the syllabus changes.
J.K. Baldua, director-technical at Scientech Indore, explains, “Change in the educational syllabus is an ongoing process, and because of this the university reframes the list of experiments. We have the instruments catering to these experiments.”
Apart from the instruments for lab work, universities and colleges have also started procuring instruments for field work by students. One example of such instruments is the Scientech 700 series, which is an extremely compact MSO that does not sacrifice much in terms of features.
“While the regular lab work requires benchtop instruments, field experiments conducted by the students and project testing require portable, compact and easy-to-handle instruments. All this, and an inexpensive price tag, attract the education sector,” adds Baldua.
Embedded design engineers commonly use serial protocols such as I2C and SPI to simplify communication between system blocks on a circuit board. While these serial protocols can reduce wiring complexity, debugging their implementation is cumbersome with traditional oscilloscopes.
“Designers are typically forced to decode the acquired serial data by hand or export the data from the oscilloscope for post-processing and decoding. Having the oscilloscope decode the serial data can save an embedded design engineer countless hours of debugging by allowing the engineer to see the effects of both the hardware and the software in real time,” explains Saivenkat.
2. Rate contract. A favourable rate contract is important, especially in the case of big contracts.
3. Compatibility. Compatibility with legacy instruments is a major factor for big companies as they have to ensure compatibility between the large number of equipment that they maintain. Moreover, radically new equipment might also require extensive re-training of staff handling the equipment.
4. Brand image and features. If a decision needs to be made between two products of the same price and features, consider also the brand image of the company and any proprietary features that they offer.
“The embedded engineers often require to monitor analogue and digital signals and some protocol analysis. Rohde & Schwarz MSO offer serial protocol analysis on digital channels, which enables viewing of analogue and digital signals and protocol analysis. What’s more, RTO’s intuitive user interface helps engineers to observe all these signals easily with drag-and-drop, gestures, etc,” adds Appalla.
In order to make sure that jitter, rare and infrequent events, and small signal details are visible to the engineer, a fast architecture is required that can keep up with the processing demand. This also ensures that the system gives almost immediate response.
“One way the potential of faster architecture is immediately realised, is the massive reduction in test time. With most of the processing offloaded to the onboard FPGA, and data transfers occurring over the high-throughput PCI Express bus, measurement times are faster than with traditional instruments. In either scenario, software-designed instruments that incorporate an FPGA, such as the vector signal transceiver, can result in cost and time savings,” says Shoebahmed Latif Shaikh, marcom specialist, NI India.
Appalla adds, “Application such as high-speed serial and digital RF increasingly require full system visibility to understand bus contention and other timing related issues. With Rohde & Schwarz RTC ASIC, it is now possible to view all-analogue, digital and spectrum view of signals with high responsiveness due to its hardware-accelerated processing power.”
Software-designed approach is an-other way in which things are being taken forward. Siddiqui points out, “The latest oscilloscopes give users working on mixed signals a couple of more advantages like DSO-to-MSO upgradability, wherein a mere software licence key is all that is required to go from a digital signal oscillo-scope to a mixed-signal oscilloscope. This makes it investment-friendly and saves time as well.”
“With a software-designed approach, engineers no longer have to ask “How do I make this box perform what the vendor intended?” Instead, they start asking “What do I need this instrument to do?” and easily make it happen,” adds Shoebahmed.
Instruments are being combined even further. While the MSO was initially conceived by combining the DSO and logic analyser, Agilent has further combined the function generator into some of its oscilloscopes so that an extra function generator is not required while testing. This serves to reduce the time spent on the test process.
“Many a times test engineers need to do some stress testing or check the response of the device under test by pumping some standard waveforms or arbitrary waveform signals. A function generator is normally required to perform these tasks. But with the latest Agilent InfiniiVision 2000 and 3000 X Series oscilloscopes, it gives users an optional in-built arbitrary waveform generator,” adds Siddiqui.
The author is a tech correspondent at EFY