8.3 System Examples

When receiving low-level signals, limiting the bandwidth of the incoming signals into the system is often required. The simplest way to establish this limited bandwidth is to place an RC filter at the noninverting terminal of the amplifier, as shown in Figure 38.

Figure 38. Single-Pole Low-Pass Filter

If even more attenuation is needed, a multiple pole filter is required. The Sallen-Key filter may be used for this task, as shown in Figure 39. For best results, the amplifier must have a bandwidth that is 8 to 10 times the filter frequency bandwidth. Failure to follow this guideline may result in phase shift of the amplifier.

Figure 39. Two-Pole, Low-Pass, Sallen-Key Filter