Mixed Domain Instrument Technology

By David Herres

The Tektronix MDO4000 is what is known as an integrated oscilloscope. This means it combines the functions of specific electronic test equipment with that of the basic scope. These instruments are not simply packaged in the same box as if to conserve bench space. They are actually wired together in such a way as to permit simultaneous viewing and analysis of different signals associated with a piece of problematic equipment in more than one domain.

By domain, we mean a parameter of a signal other than amplitude, that is generally displayed on the X axis. A traditional oscilloscope displays the signal amplitude on the Y axis and the time domain on the X axis. But the X axis doesn’t always display time. In a spectrum display, the X axis can be made to display frequency rather than time. In the spectrogram display, the X axis still represents frequency, but the Y axis represents time. Color is used to represent amplitude.

To get an idea of what an integrated instrument operating in multiple domains can look like, consider the Tektronix MDO4000. Fully loaded, it includes an integrated spectrum analyzer, an arbitrary function generator, logic analyzer, protocol analyzer and digital voltmeter with frequency counter.

It can be easier to debug a circuit problem when two domains are displayed together on a single screen, one above the other. This lets the engineer simultaneously examine two synchronized views of associated signals, the analog/digital trace in the time domain and the spectrum analyzer view in the frequency domain.

For some time, digital storage oscilloscopes from various vendors have included Fast Fourier Transform displays of the time-domain signal they acquire. Traditional instruments would create a relatively static portrait in the frequency domain of the signal over an extended period of time, based on the memory window of the particular oscilloscope. The mixed domain MDO4000, in contrast, draws a changing frequency domain graph at each moment. Thus the two displays are synchronized. They react together in close-to-real-time as there are moment-by-moment changes in the connected inputs.

An engineer can connect an analog channel, let us say, to an RF input and  to a transmitter output and view the two together so if unwanted anomalies arise, the actual evil doer can be identified.
In today’s increasingly wireless world, this capability is enormously beneficial in perfecting the right design for the right situation. Engineers have been doing this for years, but better equipment greatly accelerates this kind of work.