Page 318 - Op Amps Design, Applications, and Troubleshooting
P. 318

296    SIGNAL PROCESSING CIRCUITS








                Select the Op Amp. Two of the more important characteristics that must be
                considered when selecting the op amp are
                   1. Unity gain bandwidth
                   2. Slew rate
                The minimum unity gain bandwidth requirement can be estimated with Equation
                (2.16) by substituting our actual closed-loop gain for AOL:













                The minimum slew rate for the op amp is computed by applying Equation 2.11.
                The required slew rate for our present design is computed as








                     The bandwidth requirement is easy to satisfy with nearly any op amp. The
                 1.18-volts-per-microsecond slew rate, however, exceeds the capabilities of the
                 standard 741 op amp, but the MC1741SC op amp will work well for this applica-
                 tion. Let us choose the latter device.
                     Figure 7.5 shows the final schematic of our dual, half-wave rectifier circuit.
                 Its performance is indicated by the oscilloscope displays in Figure 7,6. Figures




















                    FIGURE 7.5 Final configuration of a dual half-wave rectifier circuit designed for 25
                    kilohertz operation.
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