8.3 System Examples

When receiving low-level signals, limiting the bandwidth of the incoming signals into the system is often required. To establish this minimum bandwidth, place an RC filter at the noninverting pin of the amplifier, as Figure 23 shows.

Figure 23. Single-Pole Low-Pass Filter

If even more attenuation is needed, a multiple pole filter is required. The Sallen-Key filter can be used for this task, as Figure 24 shows. For best results, the amplifier must have a bandwidth that is 8 to 10 times larger than the filter frequency bandwidth. Failure to follow this guideline can result in phase shift of the amplifier.

Figure 24. Two-Pole, Low-Pass, Sallen-Key Filter