Page 428 - Op Amps Design, Applications, and Troubleshooting

CHAPTER ELEVEN

Specialized Devices

This chapter will provide an overview of specialized op amps and their applica-
tions. The focus will be on identifying the primary characteristics of the various
devices and on illustrating their potential applications.

11.1 PROGRAMMABLE OP AMPS

One class of specialized op amp is the micropower programmable op amp. Such
devices utilize an external resistor to establish the quiescent operating current for
the internal stages. That is, the internal stages are biased at a particular operating
current by the selection of an external resistor. Several characteristics of the ampli-
fier are altered by changes in the programming current (J P):

1. DC supply current
2. Open-loop voltage gain
3. Input bias current
4. Slew rate
5. Unity gain frequency
6. Input noise voltage

Typical values of DC supply current range from less than 1 microampere to
as high as 1 milliampere, and they are proportional to the value of programming
current. The ability to operate at very low currents makes these devices especially
attractive for battery-powered applications. Additionally, the DC voltage require-
ments are generally quite flexible, with ±1.2 to ±18 volte being a representative
range. Here again, the programmable op amp is well suited to battery-powered
applications. The DC supply current remains fairly constant with changes in sup-
ply voltage, provided the programming current is held constant.

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