Next week at EE Live!, you'll see plenty of embedded systems that use MCUs and FPGAs. But like everything else, embedded systems need testing. Plus, designing FPGAs into test equipment enables you to add science to your measurements.
Oscilloscopes and logic analyzers give you insight into how a mixed-signal design performs. Mixed-signal oscilloscopes, which combine analog inputs (usually four) with logic inputs (usually 16) let you see, not only the analog characteristics in digital signals, but how the analog and digital sections of a design interact.
Arthur Pini, a former longtime engineer at Teledyne LeCroy, has written an article on using mixed-signal oscilloscopes, called "MSOs probe analog and digital":
Many microcontroller-based systems have both analog and digital signals. Even those that appear to be entirely digital aren't, because of analog effects such as ringing and crosstalk. Thus you often need both analog and digital views of your system's signals. That's where an MSO (mixed-signal oscilloscope) can help.
MSOs incorporate the functionality of both an oscilloscope and a subset of capabilities found in a logic analyzer. The most common MSO configuration has four analog channels and 16 digital channels. MSOs find their greatest applicability in troubleshooting embedded microprocessor boards.
Many test instruments use FPGAs to implement functions such as signal processing, triggering, and math, but most FPGAs are closed to the user. In the case of some modular instruments, you have access to their FPGAs, which lets you add functions that execute in hardware. That not only increases speed and flexibility, but it removes many tasks from a test system's host computer. To learn more about how FPGAs are used to create custom test functions, see "Open FPGAs add flexibility to test" by Ben James of National Instruments:
Most instruments today incorporate closed FPGAs (field programmable gate arrays) with fixed firmware to implement the capabilities of the instrument. If you've ever seen a teardown of an oscilloscope, you've probably seen the FPGAs inside. FPGAs add processing power to test instruments, and if you have access to an instrument's open FPGA, you can program your own test functions right into the instrument.
Instrument vendors have long seen the benefits of FPGAs and have taken advantage of their unique processing capabilities to implement instrument features, such as:
- The ability to do pre-trigger acquisition on an oscilloscope
- The signal processing to produce the I and Q data on a vector signal analyzer
- The pattern generation and vector comparisons of a high-speed digital instrument in real time
Reminder: You can still purchase an EE Live! 2014 All Access pass or register for a free Expo pass at the event’s official site. But don't wait! The last day to register online for the event is Thursday, March 27, 2014 -- today!
— Martin Rowe, Senior Technical Editor