Page 107 - Op Amps Design, Applications, and Troubleshooting

90 AMPLIFIERS

Using this equation, we can now compute values for R 12 and R^ as follows:

and

-2
= 18 kQ.

Compute the Value of R B. To minimize the effects of op amp bias currents,
we want to make the value of R B equal to the parallel combination of R f and all of
the input/source resistors.

We select the nearest standard value of 5.1 kilohms.

Determine the Required Power Supply Voltages. The DC power supply
voltages must be high enough to prevent saturation under the worst-case input
conditions. Generally, the condition to be considered is when all inputs are at the
maximum voltage at the same time. The worst-case output voltage, then, is com-
puted by adding the output voltages caused by each of the individual inputs, as in
Equation (2.1).