The next time you fire up your oscilloscope and look at a waveform, note how the waveform remains on screen for as long as you need it to. Depending on your scope’s specs, you’ll likely have little trouble inducing it to trigger on and capture random glitches and one-shot events of an extremely fleeting nature. The modern oscilloscope is the engineer’s Swiss Army knife, retaining graphic displays of such transient events for subsequent analysis.
Scope displays of this nature seem like a given to us today. Yet, old-timers will remember a day when the cathode-ray-tube (CRT) displays of oscilloscopes were not so capable. In fact, to capture an image of transient events, the only viable option was to employ an oscilloscope camera to take a photograph of that transient. Getting that image could be an arduous process, involving much wasted time and film.
All that was changed by a soft-spoken physicist named Robert H. “Bob” Anderson, who joined Tektronix in 1959 to work with a research group led by Dick Ropiequet. Some seven patents later, Bob left Tek in 1969, but not before he’d invented what Tektronix termed the direct-view bistable storage CRT, a device that would result in a new category of oscilloscope (the storage oscilloscope) and helped build Tektronix into a test-industry giant (see the figure).
The Road To Tek
Bob was born on March 27, 1925, in Jersey City, N.J., and grew up in nearby West Orange. His father, a civil engineer, helped design the foundation of New York’s Chrysler Building. By the time he was about 13 years old, Bob Anderson knew he wanted to be a “technical guy.” His older brother’s copy of Alfred Ghirardi’s Radio Physics Course Book firmed up his interest in technical topics.
Bob earned a degree in engineering physics from Lafayette College in Easton, Pa., which was one of only four schools in the United States offering that degree at the time. “It’s a physics degree where instead of taking humanities as electives, you take engineering courses,” says Anderson.
His first job out of school was at RCA Laboratories in Princeton, N.J., where he apprenticed in a tube assembly service group. Later, he worked on photomultiplier tubes with George Morton and Vladimir Zworykin, garnering two patents and inventing the first very small photomultipliers, which were intended to go down 1.125-in. inside-diameter oil well pipes.
“Now, what was interesting was before that, they used it in the first automatic headlight dimmers, which were in a little pod mounted on the dash,” says Bob. “I had the fun of seeing these cars go by with my invention in it.”
Anderson moved on to a job at Hughes Aircraft in Los Angeles at a time when many “technical guys” were heading west. At Hughes, Anderson had his first exposure to the primitive storage CRTs of the day. But when Hughes moved to Oceanside, Bob didn’t want to follow and landed a spot in Ropiequet’s research group at Tektronix.
The Storage Problem
“At Tektronix, I saw that bistable display tubes would be a natural for oscilloscopes because they didn’t need grey shades,” says Bob. “I thought I could come up with something simple. So I tried three different structures that came to mind, and the third one worked. The first two stored the trace but weren’t good enough.”
Designing a storage tube that combined a simple structure with good brightness, contrast, resolution, and uniformity was the challenge that Anderson assigned to himself. “The nature of the challenge was a structural problem,” says Anderson.
“I was after great simplicity. I knew that the basic physics that would make it work was secondary emissions. Then, there’s the problem of how to collect the secondary emissions. I was working on a tube in which I was using dot patterns,” he says.
“I knew the fundamental problem was that a stored trace would tend to spread or shrink on the tube’s surface. So you had to do something to stop that from happening. I was working with a polka-dot pattern so that the stored trace could not jump from one dot to another,” he says.
“Then, it was hard to make that dot pattern without having some scattered phosphor particles in between the dots,” he explains. “The phosphor particles were storing the trace, but they were too dim. I felt that by just making scattered particles without the dots, I would have at least a dim storage tube.”
With the addition of more phosphor, Anderson expected his CRT to fail when the particles touched each other and made a continuous layer. To his surprise, however, the tube worked and proved optimal when the phosphor layer was applied not in a dot pattern but in a scattered fashion in which the phosphor particles are irregular in shape and touch each other randomly.