September 14, 2011 -- When integrating a radio chip or module into a typical embedded system, a common and often frustrating task designers face is tracking down and eliminating noise and spurious signals. Potential noise sources include switching power supplies, digital noise from other parts of the system, and external sources. Noise considerations also include any possible interference generated by the radio as well as the need to avoid interfering with other radios while meeting regulatory requirements.

The tool of choice for the embedded designer, the oscilloscope, is optimized for making time domain measurements only. An MSO (mixed-signal oscilloscope) can measure both analog and digital signals, but it remains difficult to effectively measure RF signals with an oscilloscope at the RF carrier. It is also quite difficult to adequately correlate events in the time and frequency domains — something critical for finding system-level problems.

While spectrum analyzers are available for making measurements in the frequency domain, these are not the tool of choice for most embedded designers. Using spectrum analyzers to make time correlated measurements with the rest of the system is virtually impossible.

In this article, we will explore tips and techniques for hunting noise sources using a new type of instrument called the mixed-domain oscilloscope, or MDO.

By Darren McCarthy. (McCarthy is the Worldwide RF Technical Marketing Manager for Tektronix, Inc.)