3-25has been dropped by R2. In either case, the feedback signal (E_{fdbk}) is the ratio of R1 to the entire voltagedivider (R1 + R2) multiplied by the output signal (E_{out}).Mathematically, the relationship of the output signal, feedback signal, and voltage divider is:If you divide both sides of the equation by E_{out}:By inverting both sides of the equation:Separating the right-hand side:Remember:Therefore, by substitution:You can now see that the gain of the noninverting configuration is determined by the resistors. Theformula is different from the one used for the inverting configuration, but the gain is still determined bythe values of R1 and R2.BANDWIDTH LIMITATIONSAs with most amplifiers, the gain of an operational amplifier varies with frequency. Thespecification sheets for operational amplifiers will usually state the open-loop (no feedback) gain for d.c.(or 0 hertz). At higher frequencies, the gain is much lower. In fact, for an operational amplifier, the gaindecreases quite rapidly as frequency increases.Figure 3-17 shows the open-loop (no feedback) frequency-response curve for a typical operationalamplifier. As you should remember, bandwidth is measured to the half-power points of a frequency-response curve. The frequency-response curve shows that the bandwidth is only 10 hertz with this

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