Voltage-feedback op amps exhibit decreasing closed-loop bandwidth as the signal gain is increased. In theory, this relationship is described by the gain bandwidth product (GBP) shown in the Electrical Characteristics. Dividing GBP by the noninverting signal gain (also called the noise gain, or NG) predicts the closed-loop bandwidth. In practice, this calculation only holds true when the phase margin approaches 90°, similar to high-gain configurations. At low gains (increased feedback factors), most amplifiers exhibit a more complex response with lower phase margin. The OPA4830 is compensated to give a slightly peaked response in a noninverting gain of 2V/V (see Figure 8-3). This compensation results in a typical gain of +2V/V bandwidth of 110MHz, far exceeding that predicted by dividing the 110MHz GBP by 2V/V. Increasing the gain causes the phase margin to approach 90° and the bandwidth to more closely approach the predicted value of (GBP/NG). At a gain of +10V/V, the 11MHz bandwidth illustrated in the Electrical Characteristics agrees with that predicted using the simple formula and the typical GBP of 110MHz.

Frequency response in a gain of +2V/V can be modified to achieve exceptional flatness simply by increasing the noise gain to 3V/V. One way to do this, without affecting the +2V/V signal gain, is to add a 2.55kΩ resistor across the two inputs (see Figure 8-7). A similar technique can be used to reduce peaking in unity-gain (voltage follower) applications. For example, by using a 750Ω feedback resistor along with a 750Ω resistor across the two op amp inputs, the voltage follower response is similar to the gain of +2V/V response of Figure 8-2. Further reducing the value of the resistor across the op amp inputs further dampens the frequency response because of increased noise gain. The OPA4830 exhibits minimal bandwidth reduction going to single-supply (+5V) operation as compared with ±5V. This minimal reduction is because the internal bias control circuitry retains nearly constant quiescent current as the total supply voltage between the supply pins changes.