So far, you have seen how to analyze and design op amp circuits for a variety of general-purpose applications. There are many applications in which the ease of op amp circuit design would be welcome, but in which the average op amp's performance is not suitable. Over the years, manufacturers have extended the performance of op amps outside of their original low-power, low-frequency realm. A variety of special-purpose op amps and op amp derivatives now exist for the designer's convenience. This chapter takes a look at a number of the areas where specialized op amps may now be used.
Perhaps the two most noticeable areas of extended device performance are in power handling and speed. At one time, op amps were considered to be suitable for use below 1 MHz. Today it is possible to find high-speed devices designed for applications such as video where bandwidths are measured in the tens of MHz. In the area of power, the general-purpose op amp typically operates from a \(\pm\)15 V supply and can produce output currents in the neighborhood of 25 milliamps. New devices can produce output currents measured in amperes, while other devices can produce signals in the hundreds of volts. This makes it possible to directly connect lowimpedance loads to the op amp, which is a very useful commodity.
There are a variety of other useful variations on the basic op amp theme. These include devices optimized for single-supply operation, dedicated voltage followers, devices that allow you to trade off speed for power consumption, and application-specific items like low-noise audio pre-amplifiers and voltage-controlled amplifiers. This chapter will introduce a selection of these devices and take a look at a few of their applications. Although these devices may not find as wide an appeal, as say, a 411 or 741, they allow you to extend your designs without “reinventing the wheel” each time.