ABSTRACT
Rarely used "by itself," the op-amp is usually combined with passive elements, mainly resistors and capacitors. Figure 3-29a shows the coefficient multiplier. The function of this device is to accept a time-varying or constant input voltage e1 and produce an output voltage e0 which is Ke 1, where K is an adjustable constant of our choice. (The name coefficient multiplier comes from the analog computer application, where a signal representing, say, the velocity v of a mass, needed to be multiplied by a damper coefficient B, to simulate the damping force Bv in a differential equation being solved to find the motion of the mass.) In many, but not all, op-amp applications, the terminal where en is applied (called the positive input) is grounded, making this voltage exactly zero at all times. We also connect ordinary resistors R; (called the input resistor) and Rfb (called the feedback resistor) as shown.
