Figure 8-7 shows a noninverting amplifier that reduces peaking at low gains. The resistor RC compensates the OPA4830 to have higher noise gain (NG), which reduces the ac response peaking (typically 5dB at G = +1V/V without RC) without changing the dc gain. V_IN needs to be a low-impedance source, such as an op amp. The resistor values are low to reduce noise. Using both R_T and R_F helps minimize the impact of parasitic impedance.

Figure 8-7 Compensated Noninverting Amplifier

The noise gain can be calculated as shown in Equation 3, Equation 4, and Equation 5:

Equation 3.

Equation 4.

Equation 5.

A unity-gain buffer can be designed by selecting R_T = R_F = 20.0Ω and R_C = 40.2Ω (do not use R_G). This circuit gives a noise gain of 2V/V, so the response is similar to the characteristics plots with G = +2V/V. Decreasing R_C to 20.0Ω increases the noise gain to 3V/V, which typically gives a flat frequency response, but with less bandwidth.

The circuit in Figure 8-1 can be redesigned to have less peaking by increasing the noise gain to 3. This increase is accomplished by adding R_C = 2.55kΩ across the op amp inputs.