Operational amplifier

Also called op amp. Integrated semiconductor circuits. Is a differential amplifier but usually only one input is used as a signal input. It can have a very large gain and output impedance. Most op amps are powered by dual voltages up to ca +/-15 Volts. It can work as an inverting or non-inverting amplifier. The simplest op amp circuit is a non-inverting buffer with unity gain and with no external components at all. There are many applications such as filter, integrator, comparator, mixer and many more.
The real breakthrough of op amps came in the mid 60s. For commercial use, the uA709 was introduced by Fairchild Semiconductors in 1965. It was easy to use and due to the following success, price was dropped from $70 later to just a few dollars. In 1967 National Semiconductors introduced the LM101 which had increased gain, simpler external capacitor frequency compensation and a short circuit protection.
In May 1968 the well known 741, known as uA741 or LM741 was introduced. It was a development of LM101, it had an on-chip capacitor for frequency compensation.
After that, more versions and models came. The first quad op amps came in 1974, the RC4558 and LM324. LM324 require little power and single voltage supply is possible. The beauty with this chip is that it handles levels all down to ground voltage, usually 0 Volt, with no margin like many other op amps. In 1975, RCA introduced the first FET op amp CA3130 with very low input currents required and also a single supply.