When receiving low-level signals, limiting the bandwidth of the incoming signals into the system is often required. Figure 7-2 shows how the simplest way to accomplish this limiting is to place an RC filter at the non-inverting pin of the amplifier.

If more attenuation at higher frequencies is required, a multiple-pole filter is required. Figure 7-3 shows a common implementation of a second-order filter called a Sallen-Key filter. When designing this type of filter, chose an amplifier who bandwidth is approximately an order of magnitude larger than the desired filter bandwidth. See Active Low-pass Filter Design for more detailed active-filter design information.

Assuming R₁ = R₂ = R and C₁ = C₂ = C, use Equation 2 to set the bandwidth of the filter.

The Q-factor of a filter controls the amount of peaking of the small-signal frequency response and the settling time of the pulse response. Set Q to 0.707 to provide a Butterworth response with a maximally flat pass-band. Chose the ratio of R_F and R_G to obtain the desired Q value as shown in Equation 3.