The Birth of ADI

The emergence of a third Boston area op amp company took place in the mid 1960's. In January of 1965 Analog Devices Inc. (ADI) was founded by Matt Lorber and Ray Stata. Operating initially from Cambridge, MA, op amps were the first product of the new company. Many of the early op amps were modular designs (more on this below).

Dan Sheingold has suggested that the ADI founders may have intentionally left out the word "Research" as part of the ADI name (Reference 15: Dan Sheingold, "Analog Dialectic," Analog Dialogue, Vol. 30, No. 3, pp. 1.). This would be to differentiate the new company from all of the (then) three competitors, Burr-Brown, GAP/R, and Nexus Research Laboratories, and thus broaden market appeal for op amps.

And, it seemed to work for the new ADI venture, with sales taking off quite soon. One of the first "products" of the new ADI was application support for op amps (also noted by Sheingold, Reference 15, again). In the first year, Ray Stata authored a comprehensive guide to op amps (Reference 16: Ray Stata, "Operational Amplifiers, Parts I and II," Electromechanical Design, September and November, 1965 (The first ADI op amp application manual)). Examples of this application support were to continue through the early years and afterwards, echoing a successful business practice established by GAP/R.

The first few ADI years resulted in many new op amps, in mostly the modular package style, using both bipolar transistor and FET technologies. A complete list is much more broad than can be covered here, so just some highlights will be sampled.

Model 3xx Series Varactor Bridge Op Amps

To compete with GAP/R and their P2, ADI marketed a number of varactor bridge input op amps. The first varactor bridge op amps were the 301, 302, and 303 models, which were all similar, but differed in detail as to the input mode. They were differential (301), inverting (302), or non-inverting (303). The 301 had a max input current of 2pA, but the others got as low as 0.5pA. The 301 sold for $198, while the 302A and 303A were $110.

Lewis R. Smith designed these amplifiers, as well as their successors, models 310 and 311 (Reference 17: Data sheet for Model 310, 311 Ultra Low Bias Current Varactor Bridge Operational Amplifiers, Analog Devices, Inc., December 1969). These latter designs were able to achieve significantly improved input currents, which were ±10fA for the signal input of both amplifiers (just about 3 orders of magnitude below the GAP/R P2 series). An input current specification this low was then (and still is) a most impressive achievement. Interestingly, the 310 and 311 models were also sold for lower prices, which was $75 for the J grade.

Lewis Smith also described his varactor bridge designs in a patent (Reference 18: Lewis R. Smith, "Operational Amplifier with Varactor Bridge Input Circuit," US Patent 3,530,390, filed Dec. 28, 1966, issued Sept. 22, 1970 (A varactor bridge amplifier)). It is a high tribute to the model 310 and 311 designs that they are still being produced in 2002. The devices are available through Intronics (Reference 19: ADI Modular Products, http://www.intronics.com/products/analogproducts/).

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