The μA741


In less than a year's time after the 101's introduction, Fairchild introduced their answer to it, which was the μA741 op amp. Designed by Dave Fullagar and introduced in 1968, the μA741 used a similar signal path to the LM101 (Reference 6: Dave Fullagar, "A New High Performance Monolithic Operational Amplifier," Fairchild Semiconductor Application Brief, May 1968 (The uA741 IC op amp)). A simplified schematic of the μA741 is shown above in Figure 17.

Although there are obvious biasing differences, the 741 signal path is essentially equivalent to the 101, and it provides similar features in terms of short-circuit and input over-voltage protection, and has a comparable bandwidth. Nevertheless, for the reason that the 741 had the 30pF compensation capacitor on the chip, it became the standard (George Erdi told an interesting story of the μA741's genesis while working at Fairchild and sharing an office with the designer, Dave Fullagar. It seems that shortly after the LM101 appeared, the two were discussing the reason why the required compensation cap was external. Fullagar's conclusion was that the National process in use at the time simply couldn't accommodate the internal capacitor. He said, "Well, we can do that!" and so, shortly afterwards, the internally compensated μA741 was born).

The moral here seems to be that ease-of-use is more valuable to users than is flexibility. The 101, with the user-added capacitor, was functionally equivalent to the 741. In fact, National Semiconductor had introduced the LH101, a hybrid package of an LM101 chip plus a 30pF capacitor, in early 1968. But nevertheless, the 741 became a greater standard.

The LM101A

Bob Widlar updated his basic LM101 design with the LM101A, which was introduced by National Semiconductor in late 1968. This was a more refined version of the 101 op amp architecture, featuring lower and more stable input bias current (Reference 7: Robert J. Widlar, "IC Op Amp with Improved Input-Current Characteristics," EEE, December 1968 (The LM101A IC op amp)).
At about the same time, they also introduced the LM107, which was an LM101A with the 30pF compensation capacitor on the same monolithic chip. The 107 and 741 could be said to be comparable for AC specifications, but the 107 had an edge for DC parameters.

The μA748

The μA748, an externally compensated derivative of the μA741, was introduced by Fairchild in 1969. It was Fairchild's answer to the National LM101/LM101A series. The 748 functioned just like the 101/101A types, with an external capacitor between pins 1-8.

Multiple 741 types, General Purpose Single-Supply Types

With the 741 being such a popular device, it lent itself readily to dual and quad versions. Space doesn't permit discussion of all, but among the more popular were the Motorola MC1558/1458, a pair of 741s in an 8-pin DIP pinout. Almost since the beginning dual versions have been the more popular for IC op amps. Quad 741 types also became available, such as the Motorola MC4741, and the National Semiconductor LM148.

In 1972, Russell and Frederiksen of National Semiconductor introduced an amplifier technique suitable for operation in a single-supply environment at low voltages (Reference 8: Ronald Russell, Thomas Frederiksen, "Automotive and Industrial Electronic Building Blocks," IEEE Journal of Solid-State Circuits, Vol. SC-7, December 1972, pp. 446-454, (The LM324 and other single-supply ICs)). This amplifier, which was to become the LM324, became the low cost industry standard general purpose quad op amp. It was followed by a similar dual, the LM358. One of the key concepts used in the paper was an input stage gm reduction method, credited to James Solomon (Reference 5, again).
Since this is a historical discussion of IC op amps, one would assume that all of the above general purpose IC op amps would have long since disappeared, being 30-odd years old. But such isn't the case— many of them are still available even now!

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