8.5 Summary

Op amps are presently in wide use in just about every aspect of linear electronics. An op amp is a multi-stage amplifier treated as a single entity. The first stage usually utilizes a differential amplifier that can be made with either bipolar or FET devices. The following stage(s) create a large voltage gain. The final stage is a class B voltage follower. The resulting op amp typically has a high input impedance, a low output impedance, and voltage gains in excess of 10,000. The op amp operates from a bipolar power supply, usually around ±15 V. Externally, it has connections for the inverting and noninverting inputs, the single-ended output, and the power supplies. The op amp may be packaged in a variety of forms, including DIPs, SIPs, cans, flat packs and surface mount.

The general-purpose op amp is manufactured using a monolithic structure and a photolithographic process. Several chips are created from a single master wafer. Creation is a multi-step process involving the selective doping of specific areas on the chip through diffusion. The monolithic technique is relatively inexpensive and accurate. Because integration allows for very tight part matching and consistency, certain circuit design techniques are favored, including the use of current mirrors and active loads.

Finally, with very little supporting circuitry, simple op amps can make effective comparator circuits. A comparator is in essence, a bridge between the analog and digital worlds.