Amplifiers, Comparators and Other Analog Circuits

In linear regime, operational amplifiers provide an output voltage that is proportional to differential input voltage as long as both inputs remain within a voltage range somewhat narrower than the range of bias voltages V+ and V-. Similar to all active components and resistors, operational amplifiers have sources of noise (voltages and currents of random instantaneous value), superimposed to the useful signal. In order to reduce this noise and also the input currents, operational amplifiers with field effect transistors are built. This chapter discusses various types of noise and their origin, and tabulates some examples of functions achieved by specialized analog integrated circuits. Comparators are operational amplifiers specifically optimized to perform the sign detector function. The most important characteristics are the differential static gain and the voltage offset, which determine the accuracy, and the slew rate or the switching time that conditions the output signal variation rate.