Signetics 555 Timer: Happy 50th Birthday
Latest update time：2022-01-13
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Fifty years ago, in 1972, Signetics released the NE555 timer/oscillator IC. Billions of units of this simple 8-pin chip have been sold annually for the past 50 years, a perennial hobbyist favorite. Well-known authors such as Walter Jung wrote introductions to the 555 timer, and the 555 circuit has remained popular in new circuit designs since the 1970s. Engineering acceptance has been mixed. Some engineers routinely put 555 chips in their circuits. Others view the 555 timer IC as a somewhat sloppy way to create an oscillator or timer. However, the success of the 555 IC cannot be denied. They are everywhere. There are even spacecraft that have traveled through outer space carrying space-qualified 555 timer chips. The 555 timer is clearly one of the most successful linear or digital chip designs ever.
The 555 timer was designed in 1971 by Hans Camenzind, who personally selected and joined Signetics in 1968 because he specifically wanted to develop linear ICs, one of the company's main product lines. He chose Signetics after interviewing all the linear chip manufacturers including Fairchild, Motorola Semiconductor, Texas Instruments, Signetics, Sprague, Sylvania, and Westinghouse. I would say it was a pretty thorough search.
The idea for the 555 timer/oscillator chip came from Camenzind's early electronics experience. He grew up in Zurich, Switzerland, and learned to repair radios before going to college. He and his wife moved to the United States in 1960, and he earned a master's degree in electrical engineering from Northeastern University in Boston. He then joined P.R. Mallory and Company, which was primarily engaged in battery development and sales. Camenzind joined the company's physical science laboratory, so he was involved in basic research.
This position allowed Camenzind to explore any topic he liked. He decided to focus on shrinking the entire radio onto a single chip, and quickly focused on eliminating inductors from basic radio designs. He went looking for solutions:
“I went to the MIT library. I had access to this library, and under the round white dome, on the 6th and 7th floors, I spent almost a week going through old issues of the Proceedings of the IRE (Institute of Radio Engineers). There was no index, no computer search, so I had to go through volume after volume. I came across something called a phase-locked loop [PLL]. I had never heard of it before. I looked it up, and it was a very obscure concept, and it was used to lock onto some weak signals. I think NASA used it to lock onto the lunar landing signals coming back from the moon.”
However, PR Mallory was not interested in commercializing these ideas, which pushed Camenzind to Silicon Valley and Signetics. He lobbied Signetics to allow him to continue working on PLLs, and soon designed the NE565 and 566 PLLs.
Camenzind joined Signetics because he thought the company would compete head-on with Fairchild Semiconductor in the linear IC space. However, by 1970, he felt Signetics had lost its way, so he resigned from the company, thinking he would write a book. He became an independent consultant and IC designer, and Signetics became his first client. The 555 timer was his first consulting job at Signetics, and he designed the chip's circuitry and created its physical layout. Such was the Wild West days of Silicon Valley.
Here’s how Camenzind described the situation in an oral history with the Semiconductor Museum:
“They paid me $1,200 a month for a year and loaned me some equipment they didn’t need because they had just lost 50 percent of their engineers. So, it was an ideal situation.
"Looking back, I'm surprised I took the risk. I had a wife and four kids at home, $400 in the bank, and I had made $18,000 at Signetics, so it would have been $14,400. But I got two more contracts pretty quickly, so it worked out pretty well."
It took Camenzind about a year to design the 555 timer IC. In 1971, he had a working breadboard and laid out the chip using the 10-micron design rule. He cut the Rubylith mask by hand with a razor.
Signetics did not patent the device because it did not want to and could not afford to fight potential lawsuits. Companies like Fairchild had large patent portfolios and were not afraid to use them as a powerful weapon against troublesome competitors. Silicon Valley companies often copied successful designs of competitors at the time. This is how it was done. Because Signetics did not patent the design, knockoffs of the 555 timer chip appeared in less than a year.
Interestingly, Camenzind did not consider the 555 timer IC to be a very good design. As he stated in his oral history at the Semiconductor Museum:
"The problem is it wasn't a good design (the 555). I had a few years of experience, I would say about five years, but I had no teacher, I had to teach myself. You know that was really the beginning of [IC] design, so looking at it now, I say 'I wouldn't do that again.'"
Despite Camenzind’s complaints about his own design, the 555 timer chip easily outlived Signetics by decades. Philips Semiconductors (which spun off and renamed NXP in 2006) acquired Signetics in 1975 and eventually retired the brand. However, you can still buy 555 timer ICs from distributors like DigiKey for less than $1 a piece. The chip you buy today is just as useful as it was before; it just won’t be a Signetics 555. It’s one of its descendants. Dozens of major semiconductor suppliers still make 555 timers, including Texas Instruments, Intersil, Maxim, Avago, Exar, Fairchild, NXP, and STMicroelectronics.
In a digital world, it’s often hard to understand the persistence of analog design stalwarts like Camenzind. Today, we can’t ask him for explanations, as he passed away in 2012. But he explained his fascination with linear circuits in the preface to his book Designing Analog Chips:
“Everything is going digital. Cell phones, TVs, video disks, hearing aids, motor controllers, audio amplifiers, toys, printers, what have you. Analog design is obsolete, or will be soon. Or so most people think.
“The imminent death of analog has been predicted since the advent of the PC. But it’s still here; in fact, analog ICs are growing at almost the same rate as digital ICs. A digital video disk player has more analog content than an (analog) VCR.
“The explanation is simple: the world is essentially a simulation.
“Hearing is analog. Vision, taste, touch, smell, everything is analog. Lifting and walking are analog too. Generators, motors, speakers, microphones, solenoids, batteries, antennas, lights, LEDs, laser diodes, sensors are basically all analog components.
“The digital revolution was built on analog reality.”
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