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Operational Amplifiers

     What exactly is an OPerational AMPlifier? Let's define what that component is and look at the parameters of this amazing device. An operational amplifier IC is a solid-state integrated circuit that uses external feedback to control its functions. It is one of the most versatile devices in all of electronics.
The term 'op-amp' was originally used to describe a chain of high performance dc amplifiers that was used as a basis for the analog type computers of long ago. The very high gain op-amp IC's our days uses external feedback networks to control responses. The op-amp without any external devices is called 'open-loop' mode, refering actually to the so-called 'ideal' operational amplifier with infinite open-loop gain, input resistance, bandwidth and a zero output resistance. However, in practice no op-amp can meet these ideal characteristics. And as you will see, a little later on, there is no such thing as an ideal op-amp. Since the LM741/NE741/ľA741 Op-Amps are the most popular one, this tutorial is direct associated with this particular type. Nowadays the 741 is a frequency compensated device and although still widely used, the Bi-polar types are low-noise and replacing the old-style op-amps.

Let's go back in time a bit and see how this device was developed. The term "operational amplifier" goes all the way back to about 1943 where this name was mentioned in a paper written by John R. Ragazzinni with the title "Analysis of Problems in Dynamics" and also covered the work of technical aid George A. Philbrick. The paper, which was defined to the work of the U.S. National Defense Research Council (1940), was published by the IRE in May 1947 and is considered a classic in electronics. It was around 1947 that the Operational Amplifier concepts were originally advanced. The very first series of modular solid-state op-amps were introduced by Burr-Brown Research Corporation and G.A. Philbrick Researches Inc. in 1962. The op-amp has been a workhorse of linear systems ever since.

Tube Op-AmpAt the left you see a picture of a K2-W tubes general purpose computing Op-Amp from George A. Philbrick Researches. This type was first introduced in 1952, more than a decade before the first transistorized version. The op-amp is shown with and without its bakelite shell. What a beauty! The first solid-state monolithic op-amp, designed by Bob Widlar, offered to the public in 1963 was the ľA702 manufactured by Fairchild Semiconductors but it had very weird supply voltages such as +12 and -6 volts and had a tendency to burn out when it was temporarily shorted. Despite all these little shortcomings this device was the best in its day. It contained just nine transistors and sold for about $300.00 US which limited the sales to the Military and Aerospace consumers.
In 1965 the next major change was introduced in op-amp design by Bob Widlar with the ľA709 from Fairchild Semiconductor. It had higher gain, a larger bandwidth, lower input current, and a more user-friendly supply voltage requirement of approximately +/- 15 Volt DC. The tremendous success of the 709 was associated with high production demands causing rapid and steep price reductions. This particular op-amp, introduced at about $70, was the first to break the $10 barrier and again not much later the $5 barrier. By 1969, op-amps were selling for around $2.

The outrageous success of the ľA709 emboldened Bob Widlar to request a significant enhancement in his compensation. When his request was denied by his boss, Charles Sporck, Widlar left Fairchild in 1966 to join the young National Semiconductor. Ironically, one year later, Sporck became president of National Semiconductors and so again becoming Widlar's boss. However, this time Sporck had to accept Widlar's compensation package, which allowed Bob Widlar to retire in 1970 just before his 30th birthday. Widlar worked briefly in 1980 for Linear Technology and continued to produce designs for National Semiconductors on a consulting basis for the rest of his life.

Under the brilliant guidance and futuristic view again of Bob Widlar, National Semiconductor decided to jump on the bandwagen with the release of a more versatile op-amp version in the form of the LM101 in 1967. It had a an increased gain (up to 160K) and operation range. One of the nicest features of the LM101 was 'short-circuit' protection, and simplified frequency compensation. This was accomplished by placing an external capacitor across selected connection pins. The first op-amp to provide this internally was the hybrid LH101, which was basically a LM101 with a capacitor in a single package.
But Fairchild was not done yet. It introduced in May 1968 an internally compensated op-amp called the ľA741. However, the differences between their LM101 and the ľA741 were very slight. Frequency compensation is accomplished using an 'on-chip' capacitor. Offset null is accomplished by adjustment of currents in input stage emitters. On the LM101, Offset is achieved by adjusting current in input stage collectors.
In December 1968, an improved version of the LM101, the LM101A, was devised. This device provided better input control over the temperature and lower Offset currents.
National Semiconductor introduced the LM107, which had the frequency compensation capacitor built into the silicon chip. The LM107 came out at the same time as the LM101A.
In 1968, Fairchild Semiconductor issued the ľA748. The device had essentially the same performance characteristics as the ľA741. The difference was external frequency compensation.