9.3.4 General Configurations

When receiving low-level signals, limiting the bandwidth of the incoming signals into the system is often required. To accomplish this, place an RC filter at the noninverting terminal (see Figure 35).

Figure 35. Single-Pole Low-Pass Filter

If even more attenuation is required, a multiple pole filter is required. The Sallen-key filter is used for this task. For best results, the amplifier must have a bandwidth that is eight to 10 times the filter frequency bandwidth. Failure to do this results in phase shift of the amplifier.

Figure 36. 2-Pole, Low-Pass, Sallen-Key Filter