Loebe Julie (December 10, 1920 - June 7, 2015) was an American engineer who has been credited with inventing the first operational amplifier circuit with differential inputs (1943), a topology which allowed much greater versatility in applications circuits and remains in wide use today.
After earning a BSEE from the City College of New York in 1941, Julie worked at the Army Signal Corps in Fort Monmouth, NJ, as a civilian engineer for two years.
In 1943, NDRC Division 7 contracted Columbia University's Division of War Research to improve and simplify the multi-stage vacuum tube-based amplifier circuits designed by Karl D. Swartzel Jr. for use in the Western Electric M9 gun director.
[1] Encouraged by George A. Philbrick, who was part of the Division 7 team,[2] Julie designed a circuit using two dual-triode vacuum tubes that not only had the novel feature of a differential input, but used fewer tubes, was much faster (100 kHz gain-bandwidth product) and more power efficient (2 × 300 V at 10 mA, plus tube heater) than the previous circuits.
In 1956, he founded the company Julie Research Laboratories to produce precision resistors, calibration standards and related products.