Page 72 - Op Amps Design, Applications, and Troubleshooting

Inverting Amplifier 55

Determine the Required Unity Gain Frequency. The minimum unity gain
frequency for the op amp can be estimated by applying Equation (2.22). For the
present case, we have

Since this is well below the 1.0-megahertz unity gain frequency of the 741, we
should be able to use the 741 in this application (with regard to bandwidth),

Determine the Minimum Supply Voltages. The minimum supply voltages
are computed by simply ensuring that the maximum expected output voltage
swing is no greater than the ±V SAT values. The maximum output swing can be
found by using the basic equation, Equation (2.1), for voltage gain:

In our particular example, the maximum output voltage will be

Notice the multiplying factor 1.414 to convert our input voltage (given in
RMS) to a peak or worst-case value. The manufacturer's data sheet in Appendix 1
indicates that the 741 op amp will produce at least a ±12-volt output swing with a
±15-volt supply voltage as long as the load resistor is at least 10 kilohms. Thus, we
can infer that we have a worst-case internal voltage drop of 15 -12, or 3 volts. This
means that the minimum power supply voltage for our circuit must be higher
than the maximum output voltage by the amount of the internal voltage drop
(l/^.Thatis,