Page 394 - Op Amps Design, Applications, and Troubleshooting

370 ARITHMETIC FUNCTION CIRCUITS

TABLE 9.2

Input Voltages Output Voltage
VA V B Design Goal Measured Value
+4.56 volts +2.1 volts +2.46 volts +2.42 volts
0 volts 0 volts 0 volts -0.05 volts
+1.6 volts +3.99 volts -2.39 volts -2.43 volts

2 of the oscilloscope are connected to the V A and V B inputs, respectively, and chan-
nel 4 shows the output of the op amp, which is the desired function (V o - V A - V B).
The response of the circuit to DC signals is listed in Table 9.2.

9.3 AVERAGING AMPLIFIER

The schematic diagram of an inverting averaging amplifier is shown in Figure 9.8.
Although this represents a separate mathematical operation, the configuration of
the circuit is similar to that of the inverting adder or inverting summing amplifier
discussed in Chapter 2.
Since its operation and design are nearly identical to that of the inverting
summing amplifier, only a brief analysis will be given here.
To understand the operation of the averaging amplifier, let us apply Ohm's
and Kirchhoff's Laws along with some basic equation manipulation. Since the
inverting input (-) is a virtual ground point, each of the input currents can be found
with Ohm's Law.

FIGURE 9.8 An N-inpui averaging
amplifier circuit.