Chip Hall of Fame: Fairchild Semiconductor μA741 Op-Amp

This chip became the de facto standard for analog amplifier ICs. Still in production, it’s available everywhere there are electronics

Advertisement

Operational amplifiers are the sliced bread of analog design. You can slap them together with almost anything and get something satisfying. Designers use them to make audio and video preamplifiers, voltage comparators, precision rectifiers, and many other subsystems essential to everyday electronics.

In 1963, a 26-year-old engineer named Robert Widlar designed the first monolithic op-amp integrated circuit, the μA702, at Fairchild Semiconductor. It sold for US $300 a pop. Widlar followed up with an improved design, the μA709, cutting the cost to $70 and making the chip a huge commercial success. The story goes that the freewheeling Widlar then asked for a raise. When he didn’t get it, he quit. National Semiconductor (now part of Texas Instruments) was only too happy to scoop up a guy who was then helping establish the discipline of analog IC design. In 1967, Widlar created an even better op-amp for National, the LM101, a version of which is still in production.

While Fairchild managers fretted about the sudden Widlar-powered competition, over at Fairchild’s R&D lab a recent hire, David Fullagar, scrutinized the LM101. He realized that the chip, however brilliant, had a couple of drawbacks. The biggest of these was that the IC’s input stage, the so-called front end, was overly sensitive to noise in some chips, because of semiconductor quality variations.

“The front end looked kind of kludgy,” he says.

Fullagar embarked on his own design. The solution to the front end problem turned out to be profoundly simple—“it just came to me, I don’t know, driving to Tahoe”—and consisted of a couple of extra transistors. That additional circuitry made the amplification smoother and consistent from chip to chip.

Fullagar took his design to the head of R&D at Fairchild, a guy named Gordon Moore, who sent it to the company’s commercial division. The new chip, the μA741, would become the standard for op-amps. The IC—and variants created by Fairchild’s competitors—have sold in the hundreds of millions. Now, for $300—the price tag of that primordial 702 op-amp—you can get about 2,000 of today’s 741 chips.

Advertisement