Overcoming analog passion

In recent a T&MW e-mail newsletter, I asked analog-scope users to explain why they hold their instruments so close to their hearts. In the next newsletter, I asked digital-scope users why they moved to digital scopes. While analog-scope users show more passion for their instruments, the digital scope users made some good points that the analog fans missed. On the analog side, Paul Rako of National Semiconductor said, "You can have my 400-MHz Tektronix analog scope when you pry it from my cold, dead hands." (I hope that won't happen for a long time.) Rako and colleague Bob Pease say that analog scopes are just easier to use than digital scopes. "You don't have to use any (expletive) menus just to get a simple job done," exclaims Pease.

These analog-scope fans also claim that digital scopes fool you because of aliasing and a lack of vertical resolution. Teradyne's Les Howell said, "I have seen engineers spend hours, days, and in one case several months because aliasing obscured the problem." Other analog-scope users commented that digital scopes don't have the intensity modulation that analog scopes provide.

The Tektronix 2467, a 350 MHz analog oscilloscope. Courtesy of Tektronix.

Digital-scope users say that scope manufacturers have responded to requests for analog-style knobs. Having first rejected digital scopes because of their unfriendly front-panel controls, Charles Thompson of Texas Instruments recently borrowed a new digital scope and later purchased one. He proclaims his new scope is user friendly and points out that he can store waveforms, perform calculations on waveforms, and operate his new scope under computer control—things he can't do with his analog scope.

Luc Hayden of Sparnex, NV, uses both types of scopes. He says that digital scopes work best on digital signals and analog scopes work best on analog signals. He laments, though, that while digital scopes now offer intensity modulation, you pay too much for what you can already get with any analog scope. He also argues that digital scopes lack the vertical resolution he needs to measure analog signals and that digital scopes are too noisy for some amplitude measurements.

Because test equipment often remains in use for 10 to 20 years, the perceptions created by the high price and the performance shortcomings of early digital scopes have taken a long time to fade. But the performance issues have been addressed, and prices have come down to the point where many engineers can now afford digital scopes.

Martin Rowe, Senior Technical Editor, m.rowe@tmworld.com