Page 196 - Op Amps Design, Applications, and Troubleshooting

Wien-Bridge Oscilbtor ! 79

Select the Op Amp. The two most significant considerations regarding op
amp selection are unity gain frequency (bandwidth) and slew rate. The minimum
required unity gain frequency can be estimated with the following equation;

In our particular example, the minimum required unity gain frequency is

The minimum required slew rate for our op amp can be estimated from the fol
lowing equation:

For our present application the minimum slew rate is estimated as

The required values for both unity gain frequency and slew rate are well within the
values offered by the 741 op amp, so we will choose the 741 for this application.
The final schematic of our Wien-bridge oscillator is shown in Figure 4.3. Its
performance is indicated by the oscilloscope plots presented in Figure 4.4. Also

FIGURE 4.3 A design example of a 10.5-kilohertz Wien-bridge oscillator.