6.11: Summary

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In this chapter we have examined operational amplifiers that exhibit extended performance, and those that have been tailored to more specific applications. In the area of precision differential amplification comes the instrumentation amplifier. Instrumentation amplifiers may be formed from three separate op amps, or they may be purchased as single hybrid or monolithic ICs. Instrumentation amplifiers offer isolated high impedance inputs and excellent common-mode rejection characteristics.

Programmable op amps allow the designer to set desired performance characteristics. In this way, an optimum mix of parameters such \(f_{unity}\) and slew rate versus power consumption is achieved. Programmable op amps can also be set to a very low power consumption standby level. This is ideal for battery powered circuits. Generally, programming is performed by either a resistor for static applications, or via an external current or voltage for dynamic applications.

The output drive capabilities of the standard op amp have been pushed to high levels of current and voltage. Power op amps may be directly connected to low impedance loads such as servo motors or loudspeakers. Moderate power devices exist that have been designed for line drivers and audio applications. Due to the higher dissipation requirements these applications produce, power op amps are often packaged in TO-220 and TO-3 type cases.

Along with higher power devices, still other devices show increased bandwidth and slewing performance. These fast devices are particularly useful in video applications. Perhaps the fastest amplifiers are those that rely on current feedback and utilize a transimpedance output stage. These amplifiers are a significant departure from the ordinary op amp. They do not suffer from strict gain-bandwidth limitations, and can achieve very wide bandwidth with moderate gain.

Operational transconductance amplifiers, or OTAs, may be used as building blocks for larger circuits such as voltage-controlled amplifiers or filters. Norton amplifiers rely on a current mirror to perform a current-differencing operation. They are relatively inexpensive and operate directly from single-polarity power supplies with little support circuitry. Because they are current-sensing, input limiting resistors are required.